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1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Budget Fair Queueing (BFQ) I/O scheduler.
4 *
5 * Based on ideas and code from CFQ:
6 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7 *
8 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
9 * Paolo Valente <paolo.valente@unimore.it>
10 *
11 * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
12 * Arianna Avanzini <avanzini@google.com>
13 *
14 * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
15 *
16 * BFQ is a proportional-share I/O scheduler, with some extra
17 * low-latency capabilities. BFQ also supports full hierarchical
18 * scheduling through cgroups. Next paragraphs provide an introduction
19 * on BFQ inner workings. Details on BFQ benefits, usage and
20 * limitations can be found in Documentation/block/bfq-iosched.rst.
21 *
22 * BFQ is a proportional-share storage-I/O scheduling algorithm based
23 * on the slice-by-slice service scheme of CFQ. But BFQ assigns
24 * budgets, measured in number of sectors, to processes instead of
25 * time slices. The device is not granted to the in-service process
26 * for a given time slice, but until it has exhausted its assigned
27 * budget. This change from the time to the service domain enables BFQ
28 * to distribute the device throughput among processes as desired,
29 * without any distortion due to throughput fluctuations, or to device
30 * internal queueing. BFQ uses an ad hoc internal scheduler, called
31 * B-WF2Q+, to schedule processes according to their budgets. More
32 * precisely, BFQ schedules queues associated with processes. Each
33 * process/queue is assigned a user-configurable weight, and B-WF2Q+
34 * guarantees that each queue receives a fraction of the throughput
35 * proportional to its weight. Thanks to the accurate policy of
36 * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
37 * processes issuing sequential requests (to boost the throughput),
38 * and yet guarantee a low latency to interactive and soft real-time
39 * applications.
40 *
41 * In particular, to provide these low-latency guarantees, BFQ
42 * explicitly privileges the I/O of two classes of time-sensitive
43 * applications: interactive and soft real-time. In more detail, BFQ
44 * behaves this way if the low_latency parameter is set (default
45 * configuration). This feature enables BFQ to provide applications in
46 * these classes with a very low latency.
47 *
48 * To implement this feature, BFQ constantly tries to detect whether
49 * the I/O requests in a bfq_queue come from an interactive or a soft
50 * real-time application. For brevity, in these cases, the queue is
51 * said to be interactive or soft real-time. In both cases, BFQ
52 * privileges the service of the queue, over that of non-interactive
53 * and non-soft-real-time queues. This privileging is performed,
54 * mainly, by raising the weight of the queue. So, for brevity, we
55 * call just weight-raising periods the time periods during which a
56 * queue is privileged, because deemed interactive or soft real-time.
57 *
58 * The detection of soft real-time queues/applications is described in
59 * detail in the comments on the function
60 * bfq_bfqq_softrt_next_start. On the other hand, the detection of an
61 * interactive queue works as follows: a queue is deemed interactive
62 * if it is constantly non empty only for a limited time interval,
63 * after which it does become empty. The queue may be deemed
64 * interactive again (for a limited time), if it restarts being
65 * constantly non empty, provided that this happens only after the
66 * queue has remained empty for a given minimum idle time.
67 *
68 * By default, BFQ computes automatically the above maximum time
69 * interval, i.e., the time interval after which a constantly
70 * non-empty queue stops being deemed interactive. Since a queue is
71 * weight-raised while it is deemed interactive, this maximum time
72 * interval happens to coincide with the (maximum) duration of the
73 * weight-raising for interactive queues.
74 *
75 * Finally, BFQ also features additional heuristics for
76 * preserving both a low latency and a high throughput on NCQ-capable,
77 * rotational or flash-based devices, and to get the job done quickly
78 * for applications consisting in many I/O-bound processes.
79 *
80 * NOTE: if the main or only goal, with a given device, is to achieve
81 * the maximum-possible throughput at all times, then do switch off
82 * all low-latency heuristics for that device, by setting low_latency
83 * to 0.
84 *
85 * BFQ is described in [1], where also a reference to the initial,
86 * more theoretical paper on BFQ can be found. The interested reader
87 * can find in the latter paper full details on the main algorithm, as
88 * well as formulas of the guarantees and formal proofs of all the
89 * properties. With respect to the version of BFQ presented in these
90 * papers, this implementation adds a few more heuristics, such as the
91 * ones that guarantee a low latency to interactive and soft real-time
92 * applications, and a hierarchical extension based on H-WF2Q+.
93 *
94 * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
95 * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
96 * with O(log N) complexity derives from the one introduced with EEVDF
97 * in [3].
98 *
99 * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
100 * Scheduler", Proceedings of the First Workshop on Mobile System
101 * Technologies (MST-2015), May 2015.
102 * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
103 *
104 * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
105 * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
106 * Oct 1997.
107 *
108 * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
109 *
110 * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
111 * First: A Flexible and Accurate Mechanism for Proportional Share
112 * Resource Allocation", technical report.
113 *
114 * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
115 */
116#include <linux/module.h>
117#include <linux/slab.h>
118#include <linux/blkdev.h>
119#include <linux/cgroup.h>
120#include <linux/ktime.h>
121#include <linux/rbtree.h>
122#include <linux/ioprio.h>
123#include <linux/sbitmap.h>
124#include <linux/delay.h>
125#include <linux/backing-dev.h>
126
127#include <trace/events/block.h>
128
129#include "elevator.h"
130#include "blk.h"
131#include "blk-mq.h"
132#include "blk-mq-tag.h"
133#include "blk-mq-sched.h"
134#include "bfq-iosched.h"
135#include "blk-wbt.h"
136
137#define BFQ_BFQQ_FNS(name) \
138void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
139{ \
140 __set_bit(BFQQF_##name, &(bfqq)->flags); \
141} \
142void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
143{ \
144 __clear_bit(BFQQF_##name, &(bfqq)->flags); \
145} \
146int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
147{ \
148 return test_bit(BFQQF_##name, &(bfqq)->flags); \
149}
150
151BFQ_BFQQ_FNS(just_created);
152BFQ_BFQQ_FNS(busy);
153BFQ_BFQQ_FNS(wait_request);
154BFQ_BFQQ_FNS(non_blocking_wait_rq);
155BFQ_BFQQ_FNS(fifo_expire);
156BFQ_BFQQ_FNS(has_short_ttime);
157BFQ_BFQQ_FNS(sync);
158BFQ_BFQQ_FNS(IO_bound);
159BFQ_BFQQ_FNS(in_large_burst);
160BFQ_BFQQ_FNS(coop);
161BFQ_BFQQ_FNS(split_coop);
162BFQ_BFQQ_FNS(softrt_update);
163#undef BFQ_BFQQ_FNS \
164
165/* Expiration time of async (0) and sync (1) requests, in ns. */
166static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
167
168/* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
169static const int bfq_back_max = 16 * 1024;
170
171/* Penalty of a backwards seek, in number of sectors. */
172static const int bfq_back_penalty = 2;
173
174/* Idling period duration, in ns. */
175static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
176
177/* Minimum number of assigned budgets for which stats are safe to compute. */
178static const int bfq_stats_min_budgets = 194;
179
180/* Default maximum budget values, in sectors and number of requests. */
181static const int bfq_default_max_budget = 16 * 1024;
182
183/*
184 * When a sync request is dispatched, the queue that contains that
185 * request, and all the ancestor entities of that queue, are charged
186 * with the number of sectors of the request. In contrast, if the
187 * request is async, then the queue and its ancestor entities are
188 * charged with the number of sectors of the request, multiplied by
189 * the factor below. This throttles the bandwidth for async I/O,
190 * w.r.t. to sync I/O, and it is done to counter the tendency of async
191 * writes to steal I/O throughput to reads.
192 *
193 * The current value of this parameter is the result of a tuning with
194 * several hardware and software configurations. We tried to find the
195 * lowest value for which writes do not cause noticeable problems to
196 * reads. In fact, the lower this parameter, the stabler I/O control,
197 * in the following respect. The lower this parameter is, the less
198 * the bandwidth enjoyed by a group decreases
199 * - when the group does writes, w.r.t. to when it does reads;
200 * - when other groups do reads, w.r.t. to when they do writes.
201 */
202static const int bfq_async_charge_factor = 3;
203
204/* Default timeout values, in jiffies, approximating CFQ defaults. */
205const int bfq_timeout = HZ / 8;
206
207/*
208 * Time limit for merging (see comments in bfq_setup_cooperator). Set
209 * to the slowest value that, in our tests, proved to be effective in
210 * removing false positives, while not causing true positives to miss
211 * queue merging.
212 *
213 * As can be deduced from the low time limit below, queue merging, if
214 * successful, happens at the very beginning of the I/O of the involved
215 * cooperating processes, as a consequence of the arrival of the very
216 * first requests from each cooperator. After that, there is very
217 * little chance to find cooperators.
218 */
219static const unsigned long bfq_merge_time_limit = HZ/10;
220
221static struct kmem_cache *bfq_pool;
222
223/* Below this threshold (in ns), we consider thinktime immediate. */
224#define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
225
226/* hw_tag detection: parallel requests threshold and min samples needed. */
227#define BFQ_HW_QUEUE_THRESHOLD 3
228#define BFQ_HW_QUEUE_SAMPLES 32
229
230#define BFQQ_SEEK_THR (sector_t)(8 * 100)
231#define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
232#define BFQ_RQ_SEEKY(bfqd, last_pos, rq) \
233 (get_sdist(last_pos, rq) > \
234 BFQQ_SEEK_THR && \
235 (!blk_queue_nonrot(bfqd->queue) || \
236 blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT))
237#define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
238#define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 19)
239/*
240 * Sync random I/O is likely to be confused with soft real-time I/O,
241 * because it is characterized by limited throughput and apparently
242 * isochronous arrival pattern. To avoid false positives, queues
243 * containing only random (seeky) I/O are prevented from being tagged
244 * as soft real-time.
245 */
246#define BFQQ_TOTALLY_SEEKY(bfqq) (bfqq->seek_history == -1)
247
248/* Min number of samples required to perform peak-rate update */
249#define BFQ_RATE_MIN_SAMPLES 32
250/* Min observation time interval required to perform a peak-rate update (ns) */
251#define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
252/* Target observation time interval for a peak-rate update (ns) */
253#define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
254
255/*
256 * Shift used for peak-rate fixed precision calculations.
257 * With
258 * - the current shift: 16 positions
259 * - the current type used to store rate: u32
260 * - the current unit of measure for rate: [sectors/usec], or, more precisely,
261 * [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
262 * the range of rates that can be stored is
263 * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
264 * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
265 * [15, 65G] sectors/sec
266 * Which, assuming a sector size of 512B, corresponds to a range of
267 * [7.5K, 33T] B/sec
268 */
269#define BFQ_RATE_SHIFT 16
270
271/*
272 * When configured for computing the duration of the weight-raising
273 * for interactive queues automatically (see the comments at the
274 * beginning of this file), BFQ does it using the following formula:
275 * duration = (ref_rate / r) * ref_wr_duration,
276 * where r is the peak rate of the device, and ref_rate and
277 * ref_wr_duration are two reference parameters. In particular,
278 * ref_rate is the peak rate of the reference storage device (see
279 * below), and ref_wr_duration is about the maximum time needed, with
280 * BFQ and while reading two files in parallel, to load typical large
281 * applications on the reference device (see the comments on
282 * max_service_from_wr below, for more details on how ref_wr_duration
283 * is obtained). In practice, the slower/faster the device at hand
284 * is, the more/less it takes to load applications with respect to the
285 * reference device. Accordingly, the longer/shorter BFQ grants
286 * weight raising to interactive applications.
287 *
288 * BFQ uses two different reference pairs (ref_rate, ref_wr_duration),
289 * depending on whether the device is rotational or non-rotational.
290 *
291 * In the following definitions, ref_rate[0] and ref_wr_duration[0]
292 * are the reference values for a rotational device, whereas
293 * ref_rate[1] and ref_wr_duration[1] are the reference values for a
294 * non-rotational device. The reference rates are not the actual peak
295 * rates of the devices used as a reference, but slightly lower
296 * values. The reason for using slightly lower values is that the
297 * peak-rate estimator tends to yield slightly lower values than the
298 * actual peak rate (it can yield the actual peak rate only if there
299 * is only one process doing I/O, and the process does sequential
300 * I/O).
301 *
302 * The reference peak rates are measured in sectors/usec, left-shifted
303 * by BFQ_RATE_SHIFT.
304 */
305static int ref_rate[2] = {14000, 33000};
306/*
307 * To improve readability, a conversion function is used to initialize
308 * the following array, which entails that the array can be
309 * initialized only in a function.
310 */
311static int ref_wr_duration[2];
312
313/*
314 * BFQ uses the above-detailed, time-based weight-raising mechanism to
315 * privilege interactive tasks. This mechanism is vulnerable to the
316 * following false positives: I/O-bound applications that will go on
317 * doing I/O for much longer than the duration of weight
318 * raising. These applications have basically no benefit from being
319 * weight-raised at the beginning of their I/O. On the opposite end,
320 * while being weight-raised, these applications
321 * a) unjustly steal throughput to applications that may actually need
322 * low latency;
323 * b) make BFQ uselessly perform device idling; device idling results
324 * in loss of device throughput with most flash-based storage, and may
325 * increase latencies when used purposelessly.
326 *
327 * BFQ tries to reduce these problems, by adopting the following
328 * countermeasure. To introduce this countermeasure, we need first to
329 * finish explaining how the duration of weight-raising for
330 * interactive tasks is computed.
331 *
332 * For a bfq_queue deemed as interactive, the duration of weight
333 * raising is dynamically adjusted, as a function of the estimated
334 * peak rate of the device, so as to be equal to the time needed to
335 * execute the 'largest' interactive task we benchmarked so far. By
336 * largest task, we mean the task for which each involved process has
337 * to do more I/O than for any of the other tasks we benchmarked. This
338 * reference interactive task is the start-up of LibreOffice Writer,
339 * and in this task each process/bfq_queue needs to have at most ~110K
340 * sectors transferred.
341 *
342 * This last piece of information enables BFQ to reduce the actual
343 * duration of weight-raising for at least one class of I/O-bound
344 * applications: those doing sequential or quasi-sequential I/O. An
345 * example is file copy. In fact, once started, the main I/O-bound
346 * processes of these applications usually consume the above 110K
347 * sectors in much less time than the processes of an application that
348 * is starting, because these I/O-bound processes will greedily devote
349 * almost all their CPU cycles only to their target,
350 * throughput-friendly I/O operations. This is even more true if BFQ
351 * happens to be underestimating the device peak rate, and thus
352 * overestimating the duration of weight raising. But, according to
353 * our measurements, once transferred 110K sectors, these processes
354 * have no right to be weight-raised any longer.
355 *
356 * Basing on the last consideration, BFQ ends weight-raising for a
357 * bfq_queue if the latter happens to have received an amount of
358 * service at least equal to the following constant. The constant is
359 * set to slightly more than 110K, to have a minimum safety margin.
360 *
361 * This early ending of weight-raising reduces the amount of time
362 * during which interactive false positives cause the two problems
363 * described at the beginning of these comments.
364 */
365static const unsigned long max_service_from_wr = 120000;
366
367/*
368 * Maximum time between the creation of two queues, for stable merge
369 * to be activated (in ms)
370 */
371static const unsigned long bfq_activation_stable_merging = 600;
372/*
373 * Minimum time to be waited before evaluating delayed stable merge (in ms)
374 */
375static const unsigned long bfq_late_stable_merging = 600;
376
377#define RQ_BIC(rq) ((struct bfq_io_cq *)((rq)->elv.priv[0]))
378#define RQ_BFQQ(rq) ((rq)->elv.priv[1])
379
380struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
381{
382 return bic->bfqq[is_sync];
383}
384
385static void bfq_put_stable_ref(struct bfq_queue *bfqq);
386
387void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
388{
389 struct bfq_queue *old_bfqq = bic->bfqq[is_sync];
390
391 /* Clear bic pointer if bfqq is detached from this bic */
392 if (old_bfqq && old_bfqq->bic == bic)
393 old_bfqq->bic = NULL;
394
395 /*
396 * If bfqq != NULL, then a non-stable queue merge between
397 * bic->bfqq and bfqq is happening here. This causes troubles
398 * in the following case: bic->bfqq has also been scheduled
399 * for a possible stable merge with bic->stable_merge_bfqq,
400 * and bic->stable_merge_bfqq == bfqq happens to
401 * hold. Troubles occur because bfqq may then undergo a split,
402 * thereby becoming eligible for a stable merge. Yet, if
403 * bic->stable_merge_bfqq points exactly to bfqq, then bfqq
404 * would be stably merged with itself. To avoid this anomaly,
405 * we cancel the stable merge if
406 * bic->stable_merge_bfqq == bfqq.
407 */
408 bic->bfqq[is_sync] = bfqq;
409
410 if (bfqq && bic->stable_merge_bfqq == bfqq) {
411 /*
412 * Actually, these same instructions are executed also
413 * in bfq_setup_cooperator, in case of abort or actual
414 * execution of a stable merge. We could avoid
415 * repeating these instructions there too, but if we
416 * did so, we would nest even more complexity in this
417 * function.
418 */
419 bfq_put_stable_ref(bic->stable_merge_bfqq);
420
421 bic->stable_merge_bfqq = NULL;
422 }
423}
424
425struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
426{
427 return bic->icq.q->elevator->elevator_data;
428}
429
430/**
431 * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
432 * @icq: the iocontext queue.
433 */
434static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
435{
436 /* bic->icq is the first member, %NULL will convert to %NULL */
437 return container_of(icq, struct bfq_io_cq, icq);
438}
439
440/**
441 * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
442 * @q: the request queue.
443 */
444static struct bfq_io_cq *bfq_bic_lookup(struct request_queue *q)
445{
446 struct bfq_io_cq *icq;
447 unsigned long flags;
448
449 if (!current->io_context)
450 return NULL;
451
452 spin_lock_irqsave(&q->queue_lock, flags);
453 icq = icq_to_bic(ioc_lookup_icq(q));
454 spin_unlock_irqrestore(&q->queue_lock, flags);
455
456 return icq;
457}
458
459/*
460 * Scheduler run of queue, if there are requests pending and no one in the
461 * driver that will restart queueing.
462 */
463void bfq_schedule_dispatch(struct bfq_data *bfqd)
464{
465 lockdep_assert_held(&bfqd->lock);
466
467 if (bfqd->queued != 0) {
468 bfq_log(bfqd, "schedule dispatch");
469 blk_mq_run_hw_queues(bfqd->queue, true);
470 }
471}
472
473#define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
474
475#define bfq_sample_valid(samples) ((samples) > 80)
476
477/*
478 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
479 * We choose the request that is closer to the head right now. Distance
480 * behind the head is penalized and only allowed to a certain extent.
481 */
482static struct request *bfq_choose_req(struct bfq_data *bfqd,
483 struct request *rq1,
484 struct request *rq2,
485 sector_t last)
486{
487 sector_t s1, s2, d1 = 0, d2 = 0;
488 unsigned long back_max;
489#define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
490#define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
491 unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
492
493 if (!rq1 || rq1 == rq2)
494 return rq2;
495 if (!rq2)
496 return rq1;
497
498 if (rq_is_sync(rq1) && !rq_is_sync(rq2))
499 return rq1;
500 else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
501 return rq2;
502 if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
503 return rq1;
504 else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
505 return rq2;
506
507 s1 = blk_rq_pos(rq1);
508 s2 = blk_rq_pos(rq2);
509
510 /*
511 * By definition, 1KiB is 2 sectors.
512 */
513 back_max = bfqd->bfq_back_max * 2;
514
515 /*
516 * Strict one way elevator _except_ in the case where we allow
517 * short backward seeks which are biased as twice the cost of a
518 * similar forward seek.
519 */
520 if (s1 >= last)
521 d1 = s1 - last;
522 else if (s1 + back_max >= last)
523 d1 = (last - s1) * bfqd->bfq_back_penalty;
524 else
525 wrap |= BFQ_RQ1_WRAP;
526
527 if (s2 >= last)
528 d2 = s2 - last;
529 else if (s2 + back_max >= last)
530 d2 = (last - s2) * bfqd->bfq_back_penalty;
531 else
532 wrap |= BFQ_RQ2_WRAP;
533
534 /* Found required data */
535
536 /*
537 * By doing switch() on the bit mask "wrap" we avoid having to
538 * check two variables for all permutations: --> faster!
539 */
540 switch (wrap) {
541 case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
542 if (d1 < d2)
543 return rq1;
544 else if (d2 < d1)
545 return rq2;
546
547 if (s1 >= s2)
548 return rq1;
549 else
550 return rq2;
551
552 case BFQ_RQ2_WRAP:
553 return rq1;
554 case BFQ_RQ1_WRAP:
555 return rq2;
556 case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
557 default:
558 /*
559 * Since both rqs are wrapped,
560 * start with the one that's further behind head
561 * (--> only *one* back seek required),
562 * since back seek takes more time than forward.
563 */
564 if (s1 <= s2)
565 return rq1;
566 else
567 return rq2;
568 }
569}
570
571#define BFQ_LIMIT_INLINE_DEPTH 16
572
573#ifdef CONFIG_BFQ_GROUP_IOSCHED
574static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
575{
576 struct bfq_data *bfqd = bfqq->bfqd;
577 struct bfq_entity *entity = &bfqq->entity;
578 struct bfq_entity *inline_entities[BFQ_LIMIT_INLINE_DEPTH];
579 struct bfq_entity **entities = inline_entities;
580 int depth, level, alloc_depth = BFQ_LIMIT_INLINE_DEPTH;
581 int class_idx = bfqq->ioprio_class - 1;
582 struct bfq_sched_data *sched_data;
583 unsigned long wsum;
584 bool ret = false;
585
586 if (!entity->on_st_or_in_serv)
587 return false;
588
589retry:
590 spin_lock_irq(&bfqd->lock);
591 /* +1 for bfqq entity, root cgroup not included */
592 depth = bfqg_to_blkg(bfqq_group(bfqq))->blkcg->css.cgroup->level + 1;
593 if (depth > alloc_depth) {
594 spin_unlock_irq(&bfqd->lock);
595 if (entities != inline_entities)
596 kfree(entities);
597 entities = kmalloc_array(depth, sizeof(*entities), GFP_NOIO);
598 if (!entities)
599 return false;
600 alloc_depth = depth;
601 goto retry;
602 }
603
604 sched_data = entity->sched_data;
605 /* Gather our ancestors as we need to traverse them in reverse order */
606 level = 0;
607 for_each_entity(entity) {
608 /*
609 * If at some level entity is not even active, allow request
610 * queueing so that BFQ knows there's work to do and activate
611 * entities.
612 */
613 if (!entity->on_st_or_in_serv)
614 goto out;
615 /* Uh, more parents than cgroup subsystem thinks? */
616 if (WARN_ON_ONCE(level >= depth))
617 break;
618 entities[level++] = entity;
619 }
620 WARN_ON_ONCE(level != depth);
621 for (level--; level >= 0; level--) {
622 entity = entities[level];
623 if (level > 0) {
624 wsum = bfq_entity_service_tree(entity)->wsum;
625 } else {
626 int i;
627 /*
628 * For bfqq itself we take into account service trees
629 * of all higher priority classes and multiply their
630 * weights so that low prio queue from higher class
631 * gets more requests than high prio queue from lower
632 * class.
633 */
634 wsum = 0;
635 for (i = 0; i <= class_idx; i++) {
636 wsum = wsum * IOPRIO_BE_NR +
637 sched_data->service_tree[i].wsum;
638 }
639 }
640 limit = DIV_ROUND_CLOSEST(limit * entity->weight, wsum);
641 if (entity->allocated >= limit) {
642 bfq_log_bfqq(bfqq->bfqd, bfqq,
643 "too many requests: allocated %d limit %d level %d",
644 entity->allocated, limit, level);
645 ret = true;
646 break;
647 }
648 }
649out:
650 spin_unlock_irq(&bfqd->lock);
651 if (entities != inline_entities)
652 kfree(entities);
653 return ret;
654}
655#else
656static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
657{
658 return false;
659}
660#endif
661
662/*
663 * Async I/O can easily starve sync I/O (both sync reads and sync
664 * writes), by consuming all tags. Similarly, storms of sync writes,
665 * such as those that sync(2) may trigger, can starve sync reads.
666 * Limit depths of async I/O and sync writes so as to counter both
667 * problems.
668 *
669 * Also if a bfq queue or its parent cgroup consume more tags than would be
670 * appropriate for their weight, we trim the available tag depth to 1. This
671 * avoids a situation where one cgroup can starve another cgroup from tags and
672 * thus block service differentiation among cgroups. Note that because the
673 * queue / cgroup already has many requests allocated and queued, this does not
674 * significantly affect service guarantees coming from the BFQ scheduling
675 * algorithm.
676 */
677static void bfq_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
678{
679 struct bfq_data *bfqd = data->q->elevator->elevator_data;
680 struct bfq_io_cq *bic = bfq_bic_lookup(data->q);
681 struct bfq_queue *bfqq = bic ? bic_to_bfqq(bic, op_is_sync(opf)) : NULL;
682 int depth;
683 unsigned limit = data->q->nr_requests;
684
685 /* Sync reads have full depth available */
686 if (op_is_sync(opf) && !op_is_write(opf)) {
687 depth = 0;
688 } else {
689 depth = bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(opf)];
690 limit = (limit * depth) >> bfqd->full_depth_shift;
691 }
692
693 /*
694 * Does queue (or any parent entity) exceed number of requests that
695 * should be available to it? Heavily limit depth so that it cannot
696 * consume more available requests and thus starve other entities.
697 */
698 if (bfqq && bfqq_request_over_limit(bfqq, limit))
699 depth = 1;
700
701 bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
702 __func__, bfqd->wr_busy_queues, op_is_sync(opf), depth);
703 if (depth)
704 data->shallow_depth = depth;
705}
706
707static struct bfq_queue *
708bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
709 sector_t sector, struct rb_node **ret_parent,
710 struct rb_node ***rb_link)
711{
712 struct rb_node **p, *parent;
713 struct bfq_queue *bfqq = NULL;
714
715 parent = NULL;
716 p = &root->rb_node;
717 while (*p) {
718 struct rb_node **n;
719
720 parent = *p;
721 bfqq = rb_entry(parent, struct bfq_queue, pos_node);
722
723 /*
724 * Sort strictly based on sector. Smallest to the left,
725 * largest to the right.
726 */
727 if (sector > blk_rq_pos(bfqq->next_rq))
728 n = &(*p)->rb_right;
729 else if (sector < blk_rq_pos(bfqq->next_rq))
730 n = &(*p)->rb_left;
731 else
732 break;
733 p = n;
734 bfqq = NULL;
735 }
736
737 *ret_parent = parent;
738 if (rb_link)
739 *rb_link = p;
740
741 bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
742 (unsigned long long)sector,
743 bfqq ? bfqq->pid : 0);
744
745 return bfqq;
746}
747
748static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
749{
750 return bfqq->service_from_backlogged > 0 &&
751 time_is_before_jiffies(bfqq->first_IO_time +
752 bfq_merge_time_limit);
753}
754
755/*
756 * The following function is not marked as __cold because it is
757 * actually cold, but for the same performance goal described in the
758 * comments on the likely() at the beginning of
759 * bfq_setup_cooperator(). Unexpectedly, to reach an even lower
760 * execution time for the case where this function is not invoked, we
761 * had to add an unlikely() in each involved if().
762 */
763void __cold
764bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
765{
766 struct rb_node **p, *parent;
767 struct bfq_queue *__bfqq;
768
769 if (bfqq->pos_root) {
770 rb_erase(&bfqq->pos_node, bfqq->pos_root);
771 bfqq->pos_root = NULL;
772 }
773
774 /* oom_bfqq does not participate in queue merging */
775 if (bfqq == &bfqd->oom_bfqq)
776 return;
777
778 /*
779 * bfqq cannot be merged any longer (see comments in
780 * bfq_setup_cooperator): no point in adding bfqq into the
781 * position tree.
782 */
783 if (bfq_too_late_for_merging(bfqq))
784 return;
785
786 if (bfq_class_idle(bfqq))
787 return;
788 if (!bfqq->next_rq)
789 return;
790
791 bfqq->pos_root = &bfqq_group(bfqq)->rq_pos_tree;
792 __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
793 blk_rq_pos(bfqq->next_rq), &parent, &p);
794 if (!__bfqq) {
795 rb_link_node(&bfqq->pos_node, parent, p);
796 rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
797 } else
798 bfqq->pos_root = NULL;
799}
800
801/*
802 * The following function returns false either if every active queue
803 * must receive the same share of the throughput (symmetric scenario),
804 * or, as a special case, if bfqq must receive a share of the
805 * throughput lower than or equal to the share that every other active
806 * queue must receive. If bfqq does sync I/O, then these are the only
807 * two cases where bfqq happens to be guaranteed its share of the
808 * throughput even if I/O dispatching is not plugged when bfqq remains
809 * temporarily empty (for more details, see the comments in the
810 * function bfq_better_to_idle()). For this reason, the return value
811 * of this function is used to check whether I/O-dispatch plugging can
812 * be avoided.
813 *
814 * The above first case (symmetric scenario) occurs when:
815 * 1) all active queues have the same weight,
816 * 2) all active queues belong to the same I/O-priority class,
817 * 3) all active groups at the same level in the groups tree have the same
818 * weight,
819 * 4) all active groups at the same level in the groups tree have the same
820 * number of children.
821 *
822 * Unfortunately, keeping the necessary state for evaluating exactly
823 * the last two symmetry sub-conditions above would be quite complex
824 * and time consuming. Therefore this function evaluates, instead,
825 * only the following stronger three sub-conditions, for which it is
826 * much easier to maintain the needed state:
827 * 1) all active queues have the same weight,
828 * 2) all active queues belong to the same I/O-priority class,
829 * 3) there is at most one active group.
830 * In particular, the last condition is always true if hierarchical
831 * support or the cgroups interface are not enabled, thus no state
832 * needs to be maintained in this case.
833 */
834static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
835 struct bfq_queue *bfqq)
836{
837 bool smallest_weight = bfqq &&
838 bfqq->weight_counter &&
839 bfqq->weight_counter ==
840 container_of(
841 rb_first_cached(&bfqd->queue_weights_tree),
842 struct bfq_weight_counter,
843 weights_node);
844
845 /*
846 * For queue weights to differ, queue_weights_tree must contain
847 * at least two nodes.
848 */
849 bool varied_queue_weights = !smallest_weight &&
850 !RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) &&
851 (bfqd->queue_weights_tree.rb_root.rb_node->rb_left ||
852 bfqd->queue_weights_tree.rb_root.rb_node->rb_right);
853
854 bool multiple_classes_busy =
855 (bfqd->busy_queues[0] && bfqd->busy_queues[1]) ||
856 (bfqd->busy_queues[0] && bfqd->busy_queues[2]) ||
857 (bfqd->busy_queues[1] && bfqd->busy_queues[2]);
858
859 return varied_queue_weights || multiple_classes_busy
860#ifdef CONFIG_BFQ_GROUP_IOSCHED
861 || bfqd->num_groups_with_pending_reqs > 1
862#endif
863 ;
864}
865
866/*
867 * If the weight-counter tree passed as input contains no counter for
868 * the weight of the input queue, then add that counter; otherwise just
869 * increment the existing counter.
870 *
871 * Note that weight-counter trees contain few nodes in mostly symmetric
872 * scenarios. For example, if all queues have the same weight, then the
873 * weight-counter tree for the queues may contain at most one node.
874 * This holds even if low_latency is on, because weight-raised queues
875 * are not inserted in the tree.
876 * In most scenarios, the rate at which nodes are created/destroyed
877 * should be low too.
878 */
879void bfq_weights_tree_add(struct bfq_queue *bfqq)
880{
881 struct rb_root_cached *root = &bfqq->bfqd->queue_weights_tree;
882 struct bfq_entity *entity = &bfqq->entity;
883 struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL;
884 bool leftmost = true;
885
886 /*
887 * Do not insert if the queue is already associated with a
888 * counter, which happens if:
889 * 1) a request arrival has caused the queue to become both
890 * non-weight-raised, and hence change its weight, and
891 * backlogged; in this respect, each of the two events
892 * causes an invocation of this function,
893 * 2) this is the invocation of this function caused by the
894 * second event. This second invocation is actually useless,
895 * and we handle this fact by exiting immediately. More
896 * efficient or clearer solutions might possibly be adopted.
897 */
898 if (bfqq->weight_counter)
899 return;
900
901 while (*new) {
902 struct bfq_weight_counter *__counter = container_of(*new,
903 struct bfq_weight_counter,
904 weights_node);
905 parent = *new;
906
907 if (entity->weight == __counter->weight) {
908 bfqq->weight_counter = __counter;
909 goto inc_counter;
910 }
911 if (entity->weight < __counter->weight)
912 new = &((*new)->rb_left);
913 else {
914 new = &((*new)->rb_right);
915 leftmost = false;
916 }
917 }
918
919 bfqq->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
920 GFP_ATOMIC);
921
922 /*
923 * In the unlucky event of an allocation failure, we just
924 * exit. This will cause the weight of queue to not be
925 * considered in bfq_asymmetric_scenario, which, in its turn,
926 * causes the scenario to be deemed wrongly symmetric in case
927 * bfqq's weight would have been the only weight making the
928 * scenario asymmetric. On the bright side, no unbalance will
929 * however occur when bfqq becomes inactive again (the
930 * invocation of this function is triggered by an activation
931 * of queue). In fact, bfq_weights_tree_remove does nothing
932 * if !bfqq->weight_counter.
933 */
934 if (unlikely(!bfqq->weight_counter))
935 return;
936
937 bfqq->weight_counter->weight = entity->weight;
938 rb_link_node(&bfqq->weight_counter->weights_node, parent, new);
939 rb_insert_color_cached(&bfqq->weight_counter->weights_node, root,
940 leftmost);
941
942inc_counter:
943 bfqq->weight_counter->num_active++;
944 bfqq->ref++;
945}
946
947/*
948 * Decrement the weight counter associated with the queue, and, if the
949 * counter reaches 0, remove the counter from the tree.
950 * See the comments to the function bfq_weights_tree_add() for considerations
951 * about overhead.
952 */
953void bfq_weights_tree_remove(struct bfq_queue *bfqq)
954{
955 struct rb_root_cached *root;
956
957 if (!bfqq->weight_counter)
958 return;
959
960 root = &bfqq->bfqd->queue_weights_tree;
961 bfqq->weight_counter->num_active--;
962 if (bfqq->weight_counter->num_active > 0)
963 goto reset_entity_pointer;
964
965 rb_erase_cached(&bfqq->weight_counter->weights_node, root);
966 kfree(bfqq->weight_counter);
967
968reset_entity_pointer:
969 bfqq->weight_counter = NULL;
970 bfq_put_queue(bfqq);
971}
972
973/*
974 * Return expired entry, or NULL to just start from scratch in rbtree.
975 */
976static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
977 struct request *last)
978{
979 struct request *rq;
980
981 if (bfq_bfqq_fifo_expire(bfqq))
982 return NULL;
983
984 bfq_mark_bfqq_fifo_expire(bfqq);
985
986 rq = rq_entry_fifo(bfqq->fifo.next);
987
988 if (rq == last || ktime_get_ns() < rq->fifo_time)
989 return NULL;
990
991 bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
992 return rq;
993}
994
995static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
996 struct bfq_queue *bfqq,
997 struct request *last)
998{
999 struct rb_node *rbnext = rb_next(&last->rb_node);
1000 struct rb_node *rbprev = rb_prev(&last->rb_node);
1001 struct request *next, *prev = NULL;
1002
1003 /* Follow expired path, else get first next available. */
1004 next = bfq_check_fifo(bfqq, last);
1005 if (next)
1006 return next;
1007
1008 if (rbprev)
1009 prev = rb_entry_rq(rbprev);
1010
1011 if (rbnext)
1012 next = rb_entry_rq(rbnext);
1013 else {
1014 rbnext = rb_first(&bfqq->sort_list);
1015 if (rbnext && rbnext != &last->rb_node)
1016 next = rb_entry_rq(rbnext);
1017 }
1018
1019 return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
1020}
1021
1022/* see the definition of bfq_async_charge_factor for details */
1023static unsigned long bfq_serv_to_charge(struct request *rq,
1024 struct bfq_queue *bfqq)
1025{
1026 if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1 ||
1027 bfq_asymmetric_scenario(bfqq->bfqd, bfqq))
1028 return blk_rq_sectors(rq);
1029
1030 return blk_rq_sectors(rq) * bfq_async_charge_factor;
1031}
1032
1033/**
1034 * bfq_updated_next_req - update the queue after a new next_rq selection.
1035 * @bfqd: the device data the queue belongs to.
1036 * @bfqq: the queue to update.
1037 *
1038 * If the first request of a queue changes we make sure that the queue
1039 * has enough budget to serve at least its first request (if the
1040 * request has grown). We do this because if the queue has not enough
1041 * budget for its first request, it has to go through two dispatch
1042 * rounds to actually get it dispatched.
1043 */
1044static void bfq_updated_next_req(struct bfq_data *bfqd,
1045 struct bfq_queue *bfqq)
1046{
1047 struct bfq_entity *entity = &bfqq->entity;
1048 struct request *next_rq = bfqq->next_rq;
1049 unsigned long new_budget;
1050
1051 if (!next_rq)
1052 return;
1053
1054 if (bfqq == bfqd->in_service_queue)
1055 /*
1056 * In order not to break guarantees, budgets cannot be
1057 * changed after an entity has been selected.
1058 */
1059 return;
1060
1061 new_budget = max_t(unsigned long,
1062 max_t(unsigned long, bfqq->max_budget,
1063 bfq_serv_to_charge(next_rq, bfqq)),
1064 entity->service);
1065 if (entity->budget != new_budget) {
1066 entity->budget = new_budget;
1067 bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
1068 new_budget);
1069 bfq_requeue_bfqq(bfqd, bfqq, false);
1070 }
1071}
1072
1073static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
1074{
1075 u64 dur;
1076
1077 if (bfqd->bfq_wr_max_time > 0)
1078 return bfqd->bfq_wr_max_time;
1079
1080 dur = bfqd->rate_dur_prod;
1081 do_div(dur, bfqd->peak_rate);
1082
1083 /*
1084 * Limit duration between 3 and 25 seconds. The upper limit
1085 * has been conservatively set after the following worst case:
1086 * on a QEMU/KVM virtual machine
1087 * - running in a slow PC
1088 * - with a virtual disk stacked on a slow low-end 5400rpm HDD
1089 * - serving a heavy I/O workload, such as the sequential reading
1090 * of several files
1091 * mplayer took 23 seconds to start, if constantly weight-raised.
1092 *
1093 * As for higher values than that accommodating the above bad
1094 * scenario, tests show that higher values would often yield
1095 * the opposite of the desired result, i.e., would worsen
1096 * responsiveness by allowing non-interactive applications to
1097 * preserve weight raising for too long.
1098 *
1099 * On the other end, lower values than 3 seconds make it
1100 * difficult for most interactive tasks to complete their jobs
1101 * before weight-raising finishes.
1102 */
1103 return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000));
1104}
1105
1106/* switch back from soft real-time to interactive weight raising */
1107static void switch_back_to_interactive_wr(struct bfq_queue *bfqq,
1108 struct bfq_data *bfqd)
1109{
1110 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1111 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1112 bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt;
1113}
1114
1115static void
1116bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
1117 struct bfq_io_cq *bic, bool bfq_already_existing)
1118{
1119 unsigned int old_wr_coeff = 1;
1120 bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
1121
1122 if (bic->saved_has_short_ttime)
1123 bfq_mark_bfqq_has_short_ttime(bfqq);
1124 else
1125 bfq_clear_bfqq_has_short_ttime(bfqq);
1126
1127 if (bic->saved_IO_bound)
1128 bfq_mark_bfqq_IO_bound(bfqq);
1129 else
1130 bfq_clear_bfqq_IO_bound(bfqq);
1131
1132 bfqq->last_serv_time_ns = bic->saved_last_serv_time_ns;
1133 bfqq->inject_limit = bic->saved_inject_limit;
1134 bfqq->decrease_time_jif = bic->saved_decrease_time_jif;
1135
1136 bfqq->entity.new_weight = bic->saved_weight;
1137 bfqq->ttime = bic->saved_ttime;
1138 bfqq->io_start_time = bic->saved_io_start_time;
1139 bfqq->tot_idle_time = bic->saved_tot_idle_time;
1140 /*
1141 * Restore weight coefficient only if low_latency is on
1142 */
1143 if (bfqd->low_latency) {
1144 old_wr_coeff = bfqq->wr_coeff;
1145 bfqq->wr_coeff = bic->saved_wr_coeff;
1146 }
1147 bfqq->service_from_wr = bic->saved_service_from_wr;
1148 bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
1149 bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
1150 bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
1151
1152 if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
1153 time_is_before_jiffies(bfqq->last_wr_start_finish +
1154 bfqq->wr_cur_max_time))) {
1155 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
1156 !bfq_bfqq_in_large_burst(bfqq) &&
1157 time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt +
1158 bfq_wr_duration(bfqd))) {
1159 switch_back_to_interactive_wr(bfqq, bfqd);
1160 } else {
1161 bfqq->wr_coeff = 1;
1162 bfq_log_bfqq(bfqq->bfqd, bfqq,
1163 "resume state: switching off wr");
1164 }
1165 }
1166
1167 /* make sure weight will be updated, however we got here */
1168 bfqq->entity.prio_changed = 1;
1169
1170 if (likely(!busy))
1171 return;
1172
1173 if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
1174 bfqd->wr_busy_queues++;
1175 else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
1176 bfqd->wr_busy_queues--;
1177}
1178
1179static int bfqq_process_refs(struct bfq_queue *bfqq)
1180{
1181 return bfqq->ref - bfqq->entity.allocated -
1182 bfqq->entity.on_st_or_in_serv -
1183 (bfqq->weight_counter != NULL) - bfqq->stable_ref;
1184}
1185
1186/* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
1187static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1188{
1189 struct bfq_queue *item;
1190 struct hlist_node *n;
1191
1192 hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
1193 hlist_del_init(&item->burst_list_node);
1194
1195 /*
1196 * Start the creation of a new burst list only if there is no
1197 * active queue. See comments on the conditional invocation of
1198 * bfq_handle_burst().
1199 */
1200 if (bfq_tot_busy_queues(bfqd) == 0) {
1201 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1202 bfqd->burst_size = 1;
1203 } else
1204 bfqd->burst_size = 0;
1205
1206 bfqd->burst_parent_entity = bfqq->entity.parent;
1207}
1208
1209/* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
1210static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1211{
1212 /* Increment burst size to take into account also bfqq */
1213 bfqd->burst_size++;
1214
1215 if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
1216 struct bfq_queue *pos, *bfqq_item;
1217 struct hlist_node *n;
1218
1219 /*
1220 * Enough queues have been activated shortly after each
1221 * other to consider this burst as large.
1222 */
1223 bfqd->large_burst = true;
1224
1225 /*
1226 * We can now mark all queues in the burst list as
1227 * belonging to a large burst.
1228 */
1229 hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
1230 burst_list_node)
1231 bfq_mark_bfqq_in_large_burst(bfqq_item);
1232 bfq_mark_bfqq_in_large_burst(bfqq);
1233
1234 /*
1235 * From now on, and until the current burst finishes, any
1236 * new queue being activated shortly after the last queue
1237 * was inserted in the burst can be immediately marked as
1238 * belonging to a large burst. So the burst list is not
1239 * needed any more. Remove it.
1240 */
1241 hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
1242 burst_list_node)
1243 hlist_del_init(&pos->burst_list_node);
1244 } else /*
1245 * Burst not yet large: add bfqq to the burst list. Do
1246 * not increment the ref counter for bfqq, because bfqq
1247 * is removed from the burst list before freeing bfqq
1248 * in put_queue.
1249 */
1250 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1251}
1252
1253/*
1254 * If many queues belonging to the same group happen to be created
1255 * shortly after each other, then the processes associated with these
1256 * queues have typically a common goal. In particular, bursts of queue
1257 * creations are usually caused by services or applications that spawn
1258 * many parallel threads/processes. Examples are systemd during boot,
1259 * or git grep. To help these processes get their job done as soon as
1260 * possible, it is usually better to not grant either weight-raising
1261 * or device idling to their queues, unless these queues must be
1262 * protected from the I/O flowing through other active queues.
1263 *
1264 * In this comment we describe, firstly, the reasons why this fact
1265 * holds, and, secondly, the next function, which implements the main
1266 * steps needed to properly mark these queues so that they can then be
1267 * treated in a different way.
1268 *
1269 * The above services or applications benefit mostly from a high
1270 * throughput: the quicker the requests of the activated queues are
1271 * cumulatively served, the sooner the target job of these queues gets
1272 * completed. As a consequence, weight-raising any of these queues,
1273 * which also implies idling the device for it, is almost always
1274 * counterproductive, unless there are other active queues to isolate
1275 * these new queues from. If there no other active queues, then
1276 * weight-raising these new queues just lowers throughput in most
1277 * cases.
1278 *
1279 * On the other hand, a burst of queue creations may be caused also by
1280 * the start of an application that does not consist of a lot of
1281 * parallel I/O-bound threads. In fact, with a complex application,
1282 * several short processes may need to be executed to start-up the
1283 * application. In this respect, to start an application as quickly as
1284 * possible, the best thing to do is in any case to privilege the I/O
1285 * related to the application with respect to all other
1286 * I/O. Therefore, the best strategy to start as quickly as possible
1287 * an application that causes a burst of queue creations is to
1288 * weight-raise all the queues created during the burst. This is the
1289 * exact opposite of the best strategy for the other type of bursts.
1290 *
1291 * In the end, to take the best action for each of the two cases, the
1292 * two types of bursts need to be distinguished. Fortunately, this
1293 * seems relatively easy, by looking at the sizes of the bursts. In
1294 * particular, we found a threshold such that only bursts with a
1295 * larger size than that threshold are apparently caused by
1296 * services or commands such as systemd or git grep. For brevity,
1297 * hereafter we call just 'large' these bursts. BFQ *does not*
1298 * weight-raise queues whose creation occurs in a large burst. In
1299 * addition, for each of these queues BFQ performs or does not perform
1300 * idling depending on which choice boosts the throughput more. The
1301 * exact choice depends on the device and request pattern at
1302 * hand.
1303 *
1304 * Unfortunately, false positives may occur while an interactive task
1305 * is starting (e.g., an application is being started). The
1306 * consequence is that the queues associated with the task do not
1307 * enjoy weight raising as expected. Fortunately these false positives
1308 * are very rare. They typically occur if some service happens to
1309 * start doing I/O exactly when the interactive task starts.
1310 *
1311 * Turning back to the next function, it is invoked only if there are
1312 * no active queues (apart from active queues that would belong to the
1313 * same, possible burst bfqq would belong to), and it implements all
1314 * the steps needed to detect the occurrence of a large burst and to
1315 * properly mark all the queues belonging to it (so that they can then
1316 * be treated in a different way). This goal is achieved by
1317 * maintaining a "burst list" that holds, temporarily, the queues that
1318 * belong to the burst in progress. The list is then used to mark
1319 * these queues as belonging to a large burst if the burst does become
1320 * large. The main steps are the following.
1321 *
1322 * . when the very first queue is created, the queue is inserted into the
1323 * list (as it could be the first queue in a possible burst)
1324 *
1325 * . if the current burst has not yet become large, and a queue Q that does
1326 * not yet belong to the burst is activated shortly after the last time
1327 * at which a new queue entered the burst list, then the function appends
1328 * Q to the burst list
1329 *
1330 * . if, as a consequence of the previous step, the burst size reaches
1331 * the large-burst threshold, then
1332 *
1333 * . all the queues in the burst list are marked as belonging to a
1334 * large burst
1335 *
1336 * . the burst list is deleted; in fact, the burst list already served
1337 * its purpose (keeping temporarily track of the queues in a burst,
1338 * so as to be able to mark them as belonging to a large burst in the
1339 * previous sub-step), and now is not needed any more
1340 *
1341 * . the device enters a large-burst mode
1342 *
1343 * . if a queue Q that does not belong to the burst is created while
1344 * the device is in large-burst mode and shortly after the last time
1345 * at which a queue either entered the burst list or was marked as
1346 * belonging to the current large burst, then Q is immediately marked
1347 * as belonging to a large burst.
1348 *
1349 * . if a queue Q that does not belong to the burst is created a while
1350 * later, i.e., not shortly after, than the last time at which a queue
1351 * either entered the burst list or was marked as belonging to the
1352 * current large burst, then the current burst is deemed as finished and:
1353 *
1354 * . the large-burst mode is reset if set
1355 *
1356 * . the burst list is emptied
1357 *
1358 * . Q is inserted in the burst list, as Q may be the first queue
1359 * in a possible new burst (then the burst list contains just Q
1360 * after this step).
1361 */
1362static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1363{
1364 /*
1365 * If bfqq is already in the burst list or is part of a large
1366 * burst, or finally has just been split, then there is
1367 * nothing else to do.
1368 */
1369 if (!hlist_unhashed(&bfqq->burst_list_node) ||
1370 bfq_bfqq_in_large_burst(bfqq) ||
1371 time_is_after_eq_jiffies(bfqq->split_time +
1372 msecs_to_jiffies(10)))
1373 return;
1374
1375 /*
1376 * If bfqq's creation happens late enough, or bfqq belongs to
1377 * a different group than the burst group, then the current
1378 * burst is finished, and related data structures must be
1379 * reset.
1380 *
1381 * In this respect, consider the special case where bfqq is
1382 * the very first queue created after BFQ is selected for this
1383 * device. In this case, last_ins_in_burst and
1384 * burst_parent_entity are not yet significant when we get
1385 * here. But it is easy to verify that, whether or not the
1386 * following condition is true, bfqq will end up being
1387 * inserted into the burst list. In particular the list will
1388 * happen to contain only bfqq. And this is exactly what has
1389 * to happen, as bfqq may be the first queue of the first
1390 * burst.
1391 */
1392 if (time_is_before_jiffies(bfqd->last_ins_in_burst +
1393 bfqd->bfq_burst_interval) ||
1394 bfqq->entity.parent != bfqd->burst_parent_entity) {
1395 bfqd->large_burst = false;
1396 bfq_reset_burst_list(bfqd, bfqq);
1397 goto end;
1398 }
1399
1400 /*
1401 * If we get here, then bfqq is being activated shortly after the
1402 * last queue. So, if the current burst is also large, we can mark
1403 * bfqq as belonging to this large burst immediately.
1404 */
1405 if (bfqd->large_burst) {
1406 bfq_mark_bfqq_in_large_burst(bfqq);
1407 goto end;
1408 }
1409
1410 /*
1411 * If we get here, then a large-burst state has not yet been
1412 * reached, but bfqq is being activated shortly after the last
1413 * queue. Then we add bfqq to the burst.
1414 */
1415 bfq_add_to_burst(bfqd, bfqq);
1416end:
1417 /*
1418 * At this point, bfqq either has been added to the current
1419 * burst or has caused the current burst to terminate and a
1420 * possible new burst to start. In particular, in the second
1421 * case, bfqq has become the first queue in the possible new
1422 * burst. In both cases last_ins_in_burst needs to be moved
1423 * forward.
1424 */
1425 bfqd->last_ins_in_burst = jiffies;
1426}
1427
1428static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1429{
1430 struct bfq_entity *entity = &bfqq->entity;
1431
1432 return entity->budget - entity->service;
1433}
1434
1435/*
1436 * If enough samples have been computed, return the current max budget
1437 * stored in bfqd, which is dynamically updated according to the
1438 * estimated disk peak rate; otherwise return the default max budget
1439 */
1440static int bfq_max_budget(struct bfq_data *bfqd)
1441{
1442 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1443 return bfq_default_max_budget;
1444 else
1445 return bfqd->bfq_max_budget;
1446}
1447
1448/*
1449 * Return min budget, which is a fraction of the current or default
1450 * max budget (trying with 1/32)
1451 */
1452static int bfq_min_budget(struct bfq_data *bfqd)
1453{
1454 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1455 return bfq_default_max_budget / 32;
1456 else
1457 return bfqd->bfq_max_budget / 32;
1458}
1459
1460/*
1461 * The next function, invoked after the input queue bfqq switches from
1462 * idle to busy, updates the budget of bfqq. The function also tells
1463 * whether the in-service queue should be expired, by returning
1464 * true. The purpose of expiring the in-service queue is to give bfqq
1465 * the chance to possibly preempt the in-service queue, and the reason
1466 * for preempting the in-service queue is to achieve one of the two
1467 * goals below.
1468 *
1469 * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1470 * expired because it has remained idle. In particular, bfqq may have
1471 * expired for one of the following two reasons:
1472 *
1473 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1474 * and did not make it to issue a new request before its last
1475 * request was served;
1476 *
1477 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1478 * a new request before the expiration of the idling-time.
1479 *
1480 * Even if bfqq has expired for one of the above reasons, the process
1481 * associated with the queue may be however issuing requests greedily,
1482 * and thus be sensitive to the bandwidth it receives (bfqq may have
1483 * remained idle for other reasons: CPU high load, bfqq not enjoying
1484 * idling, I/O throttling somewhere in the path from the process to
1485 * the I/O scheduler, ...). But if, after every expiration for one of
1486 * the above two reasons, bfqq has to wait for the service of at least
1487 * one full budget of another queue before being served again, then
1488 * bfqq is likely to get a much lower bandwidth or resource time than
1489 * its reserved ones. To address this issue, two countermeasures need
1490 * to be taken.
1491 *
1492 * First, the budget and the timestamps of bfqq need to be updated in
1493 * a special way on bfqq reactivation: they need to be updated as if
1494 * bfqq did not remain idle and did not expire. In fact, if they are
1495 * computed as if bfqq expired and remained idle until reactivation,
1496 * then the process associated with bfqq is treated as if, instead of
1497 * being greedy, it stopped issuing requests when bfqq remained idle,
1498 * and restarts issuing requests only on this reactivation. In other
1499 * words, the scheduler does not help the process recover the "service
1500 * hole" between bfqq expiration and reactivation. As a consequence,
1501 * the process receives a lower bandwidth than its reserved one. In
1502 * contrast, to recover this hole, the budget must be updated as if
1503 * bfqq was not expired at all before this reactivation, i.e., it must
1504 * be set to the value of the remaining budget when bfqq was
1505 * expired. Along the same line, timestamps need to be assigned the
1506 * value they had the last time bfqq was selected for service, i.e.,
1507 * before last expiration. Thus timestamps need to be back-shifted
1508 * with respect to their normal computation (see [1] for more details
1509 * on this tricky aspect).
1510 *
1511 * Secondly, to allow the process to recover the hole, the in-service
1512 * queue must be expired too, to give bfqq the chance to preempt it
1513 * immediately. In fact, if bfqq has to wait for a full budget of the
1514 * in-service queue to be completed, then it may become impossible to
1515 * let the process recover the hole, even if the back-shifted
1516 * timestamps of bfqq are lower than those of the in-service queue. If
1517 * this happens for most or all of the holes, then the process may not
1518 * receive its reserved bandwidth. In this respect, it is worth noting
1519 * that, being the service of outstanding requests unpreemptible, a
1520 * little fraction of the holes may however be unrecoverable, thereby
1521 * causing a little loss of bandwidth.
1522 *
1523 * The last important point is detecting whether bfqq does need this
1524 * bandwidth recovery. In this respect, the next function deems the
1525 * process associated with bfqq greedy, and thus allows it to recover
1526 * the hole, if: 1) the process is waiting for the arrival of a new
1527 * request (which implies that bfqq expired for one of the above two
1528 * reasons), and 2) such a request has arrived soon. The first
1529 * condition is controlled through the flag non_blocking_wait_rq,
1530 * while the second through the flag arrived_in_time. If both
1531 * conditions hold, then the function computes the budget in the
1532 * above-described special way, and signals that the in-service queue
1533 * should be expired. Timestamp back-shifting is done later in
1534 * __bfq_activate_entity.
1535 *
1536 * 2. Reduce latency. Even if timestamps are not backshifted to let
1537 * the process associated with bfqq recover a service hole, bfqq may
1538 * however happen to have, after being (re)activated, a lower finish
1539 * timestamp than the in-service queue. That is, the next budget of
1540 * bfqq may have to be completed before the one of the in-service
1541 * queue. If this is the case, then preempting the in-service queue
1542 * allows this goal to be achieved, apart from the unpreemptible,
1543 * outstanding requests mentioned above.
1544 *
1545 * Unfortunately, regardless of which of the above two goals one wants
1546 * to achieve, service trees need first to be updated to know whether
1547 * the in-service queue must be preempted. To have service trees
1548 * correctly updated, the in-service queue must be expired and
1549 * rescheduled, and bfqq must be scheduled too. This is one of the
1550 * most costly operations (in future versions, the scheduling
1551 * mechanism may be re-designed in such a way to make it possible to
1552 * know whether preemption is needed without needing to update service
1553 * trees). In addition, queue preemptions almost always cause random
1554 * I/O, which may in turn cause loss of throughput. Finally, there may
1555 * even be no in-service queue when the next function is invoked (so,
1556 * no queue to compare timestamps with). Because of these facts, the
1557 * next function adopts the following simple scheme to avoid costly
1558 * operations, too frequent preemptions and too many dependencies on
1559 * the state of the scheduler: it requests the expiration of the
1560 * in-service queue (unconditionally) only for queues that need to
1561 * recover a hole. Then it delegates to other parts of the code the
1562 * responsibility of handling the above case 2.
1563 */
1564static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1565 struct bfq_queue *bfqq,
1566 bool arrived_in_time)
1567{
1568 struct bfq_entity *entity = &bfqq->entity;
1569
1570 /*
1571 * In the next compound condition, we check also whether there
1572 * is some budget left, because otherwise there is no point in
1573 * trying to go on serving bfqq with this same budget: bfqq
1574 * would be expired immediately after being selected for
1575 * service. This would only cause useless overhead.
1576 */
1577 if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
1578 bfq_bfqq_budget_left(bfqq) > 0) {
1579 /*
1580 * We do not clear the flag non_blocking_wait_rq here, as
1581 * the latter is used in bfq_activate_bfqq to signal
1582 * that timestamps need to be back-shifted (and is
1583 * cleared right after).
1584 */
1585
1586 /*
1587 * In next assignment we rely on that either
1588 * entity->service or entity->budget are not updated
1589 * on expiration if bfqq is empty (see
1590 * __bfq_bfqq_recalc_budget). Thus both quantities
1591 * remain unchanged after such an expiration, and the
1592 * following statement therefore assigns to
1593 * entity->budget the remaining budget on such an
1594 * expiration.
1595 */
1596 entity->budget = min_t(unsigned long,
1597 bfq_bfqq_budget_left(bfqq),
1598 bfqq->max_budget);
1599
1600 /*
1601 * At this point, we have used entity->service to get
1602 * the budget left (needed for updating
1603 * entity->budget). Thus we finally can, and have to,
1604 * reset entity->service. The latter must be reset
1605 * because bfqq would otherwise be charged again for
1606 * the service it has received during its previous
1607 * service slot(s).
1608 */
1609 entity->service = 0;
1610
1611 return true;
1612 }
1613
1614 /*
1615 * We can finally complete expiration, by setting service to 0.
1616 */
1617 entity->service = 0;
1618 entity->budget = max_t(unsigned long, bfqq->max_budget,
1619 bfq_serv_to_charge(bfqq->next_rq, bfqq));
1620 bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1621 return false;
1622}
1623
1624/*
1625 * Return the farthest past time instant according to jiffies
1626 * macros.
1627 */
1628static unsigned long bfq_smallest_from_now(void)
1629{
1630 return jiffies - MAX_JIFFY_OFFSET;
1631}
1632
1633static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1634 struct bfq_queue *bfqq,
1635 unsigned int old_wr_coeff,
1636 bool wr_or_deserves_wr,
1637 bool interactive,
1638 bool in_burst,
1639 bool soft_rt)
1640{
1641 if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1642 /* start a weight-raising period */
1643 if (interactive) {
1644 bfqq->service_from_wr = 0;
1645 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1646 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1647 } else {
1648 /*
1649 * No interactive weight raising in progress
1650 * here: assign minus infinity to
1651 * wr_start_at_switch_to_srt, to make sure
1652 * that, at the end of the soft-real-time
1653 * weight raising periods that is starting
1654 * now, no interactive weight-raising period
1655 * may be wrongly considered as still in
1656 * progress (and thus actually started by
1657 * mistake).
1658 */
1659 bfqq->wr_start_at_switch_to_srt =
1660 bfq_smallest_from_now();
1661 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1662 BFQ_SOFTRT_WEIGHT_FACTOR;
1663 bfqq->wr_cur_max_time =
1664 bfqd->bfq_wr_rt_max_time;
1665 }
1666
1667 /*
1668 * If needed, further reduce budget to make sure it is
1669 * close to bfqq's backlog, so as to reduce the
1670 * scheduling-error component due to a too large
1671 * budget. Do not care about throughput consequences,
1672 * but only about latency. Finally, do not assign a
1673 * too small budget either, to avoid increasing
1674 * latency by causing too frequent expirations.
1675 */
1676 bfqq->entity.budget = min_t(unsigned long,
1677 bfqq->entity.budget,
1678 2 * bfq_min_budget(bfqd));
1679 } else if (old_wr_coeff > 1) {
1680 if (interactive) { /* update wr coeff and duration */
1681 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1682 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1683 } else if (in_burst)
1684 bfqq->wr_coeff = 1;
1685 else if (soft_rt) {
1686 /*
1687 * The application is now or still meeting the
1688 * requirements for being deemed soft rt. We
1689 * can then correctly and safely (re)charge
1690 * the weight-raising duration for the
1691 * application with the weight-raising
1692 * duration for soft rt applications.
1693 *
1694 * In particular, doing this recharge now, i.e.,
1695 * before the weight-raising period for the
1696 * application finishes, reduces the probability
1697 * of the following negative scenario:
1698 * 1) the weight of a soft rt application is
1699 * raised at startup (as for any newly
1700 * created application),
1701 * 2) since the application is not interactive,
1702 * at a certain time weight-raising is
1703 * stopped for the application,
1704 * 3) at that time the application happens to
1705 * still have pending requests, and hence
1706 * is destined to not have a chance to be
1707 * deemed soft rt before these requests are
1708 * completed (see the comments to the
1709 * function bfq_bfqq_softrt_next_start()
1710 * for details on soft rt detection),
1711 * 4) these pending requests experience a high
1712 * latency because the application is not
1713 * weight-raised while they are pending.
1714 */
1715 if (bfqq->wr_cur_max_time !=
1716 bfqd->bfq_wr_rt_max_time) {
1717 bfqq->wr_start_at_switch_to_srt =
1718 bfqq->last_wr_start_finish;
1719
1720 bfqq->wr_cur_max_time =
1721 bfqd->bfq_wr_rt_max_time;
1722 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1723 BFQ_SOFTRT_WEIGHT_FACTOR;
1724 }
1725 bfqq->last_wr_start_finish = jiffies;
1726 }
1727 }
1728}
1729
1730static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1731 struct bfq_queue *bfqq)
1732{
1733 return bfqq->dispatched == 0 &&
1734 time_is_before_jiffies(
1735 bfqq->budget_timeout +
1736 bfqd->bfq_wr_min_idle_time);
1737}
1738
1739
1740/*
1741 * Return true if bfqq is in a higher priority class, or has a higher
1742 * weight than the in-service queue.
1743 */
1744static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
1745 struct bfq_queue *in_serv_bfqq)
1746{
1747 int bfqq_weight, in_serv_weight;
1748
1749 if (bfqq->ioprio_class < in_serv_bfqq->ioprio_class)
1750 return true;
1751
1752 if (in_serv_bfqq->entity.parent == bfqq->entity.parent) {
1753 bfqq_weight = bfqq->entity.weight;
1754 in_serv_weight = in_serv_bfqq->entity.weight;
1755 } else {
1756 if (bfqq->entity.parent)
1757 bfqq_weight = bfqq->entity.parent->weight;
1758 else
1759 bfqq_weight = bfqq->entity.weight;
1760 if (in_serv_bfqq->entity.parent)
1761 in_serv_weight = in_serv_bfqq->entity.parent->weight;
1762 else
1763 in_serv_weight = in_serv_bfqq->entity.weight;
1764 }
1765
1766 return bfqq_weight > in_serv_weight;
1767}
1768
1769static bool bfq_better_to_idle(struct bfq_queue *bfqq);
1770
1771static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1772 struct bfq_queue *bfqq,
1773 int old_wr_coeff,
1774 struct request *rq,
1775 bool *interactive)
1776{
1777 bool soft_rt, in_burst, wr_or_deserves_wr,
1778 bfqq_wants_to_preempt,
1779 idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1780 /*
1781 * See the comments on
1782 * bfq_bfqq_update_budg_for_activation for
1783 * details on the usage of the next variable.
1784 */
1785 arrived_in_time = ktime_get_ns() <=
1786 bfqq->ttime.last_end_request +
1787 bfqd->bfq_slice_idle * 3;
1788
1789
1790 /*
1791 * bfqq deserves to be weight-raised if:
1792 * - it is sync,
1793 * - it does not belong to a large burst,
1794 * - it has been idle for enough time or is soft real-time,
1795 * - is linked to a bfq_io_cq (it is not shared in any sense),
1796 * - has a default weight (otherwise we assume the user wanted
1797 * to control its weight explicitly)
1798 */
1799 in_burst = bfq_bfqq_in_large_burst(bfqq);
1800 soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1801 !BFQQ_TOTALLY_SEEKY(bfqq) &&
1802 !in_burst &&
1803 time_is_before_jiffies(bfqq->soft_rt_next_start) &&
1804 bfqq->dispatched == 0 &&
1805 bfqq->entity.new_weight == 40;
1806 *interactive = !in_burst && idle_for_long_time &&
1807 bfqq->entity.new_weight == 40;
1808 /*
1809 * Merged bfq_queues are kept out of weight-raising
1810 * (low-latency) mechanisms. The reason is that these queues
1811 * are usually created for non-interactive and
1812 * non-soft-real-time tasks. Yet this is not the case for
1813 * stably-merged queues. These queues are merged just because
1814 * they are created shortly after each other. So they may
1815 * easily serve the I/O of an interactive or soft-real time
1816 * application, if the application happens to spawn multiple
1817 * processes. So let also stably-merged queued enjoy weight
1818 * raising.
1819 */
1820 wr_or_deserves_wr = bfqd->low_latency &&
1821 (bfqq->wr_coeff > 1 ||
1822 (bfq_bfqq_sync(bfqq) &&
1823 (bfqq->bic || RQ_BIC(rq)->stably_merged) &&
1824 (*interactive || soft_rt)));
1825
1826 /*
1827 * Using the last flag, update budget and check whether bfqq
1828 * may want to preempt the in-service queue.
1829 */
1830 bfqq_wants_to_preempt =
1831 bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1832 arrived_in_time);
1833
1834 /*
1835 * If bfqq happened to be activated in a burst, but has been
1836 * idle for much more than an interactive queue, then we
1837 * assume that, in the overall I/O initiated in the burst, the
1838 * I/O associated with bfqq is finished. So bfqq does not need
1839 * to be treated as a queue belonging to a burst
1840 * anymore. Accordingly, we reset bfqq's in_large_burst flag
1841 * if set, and remove bfqq from the burst list if it's
1842 * there. We do not decrement burst_size, because the fact
1843 * that bfqq does not need to belong to the burst list any
1844 * more does not invalidate the fact that bfqq was created in
1845 * a burst.
1846 */
1847 if (likely(!bfq_bfqq_just_created(bfqq)) &&
1848 idle_for_long_time &&
1849 time_is_before_jiffies(
1850 bfqq->budget_timeout +
1851 msecs_to_jiffies(10000))) {
1852 hlist_del_init(&bfqq->burst_list_node);
1853 bfq_clear_bfqq_in_large_burst(bfqq);
1854 }
1855
1856 bfq_clear_bfqq_just_created(bfqq);
1857
1858 if (bfqd->low_latency) {
1859 if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1860 /* wraparound */
1861 bfqq->split_time =
1862 jiffies - bfqd->bfq_wr_min_idle_time - 1;
1863
1864 if (time_is_before_jiffies(bfqq->split_time +
1865 bfqd->bfq_wr_min_idle_time)) {
1866 bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1867 old_wr_coeff,
1868 wr_or_deserves_wr,
1869 *interactive,
1870 in_burst,
1871 soft_rt);
1872
1873 if (old_wr_coeff != bfqq->wr_coeff)
1874 bfqq->entity.prio_changed = 1;
1875 }
1876 }
1877
1878 bfqq->last_idle_bklogged = jiffies;
1879 bfqq->service_from_backlogged = 0;
1880 bfq_clear_bfqq_softrt_update(bfqq);
1881
1882 bfq_add_bfqq_busy(bfqq);
1883
1884 /*
1885 * Expire in-service queue if preemption may be needed for
1886 * guarantees or throughput. As for guarantees, we care
1887 * explicitly about two cases. The first is that bfqq has to
1888 * recover a service hole, as explained in the comments on
1889 * bfq_bfqq_update_budg_for_activation(), i.e., that
1890 * bfqq_wants_to_preempt is true. However, if bfqq does not
1891 * carry time-critical I/O, then bfqq's bandwidth is less
1892 * important than that of queues that carry time-critical I/O.
1893 * So, as a further constraint, we consider this case only if
1894 * bfqq is at least as weight-raised, i.e., at least as time
1895 * critical, as the in-service queue.
1896 *
1897 * The second case is that bfqq is in a higher priority class,
1898 * or has a higher weight than the in-service queue. If this
1899 * condition does not hold, we don't care because, even if
1900 * bfqq does not start to be served immediately, the resulting
1901 * delay for bfqq's I/O is however lower or much lower than
1902 * the ideal completion time to be guaranteed to bfqq's I/O.
1903 *
1904 * In both cases, preemption is needed only if, according to
1905 * the timestamps of both bfqq and of the in-service queue,
1906 * bfqq actually is the next queue to serve. So, to reduce
1907 * useless preemptions, the return value of
1908 * next_queue_may_preempt() is considered in the next compound
1909 * condition too. Yet next_queue_may_preempt() just checks a
1910 * simple, necessary condition for bfqq to be the next queue
1911 * to serve. In fact, to evaluate a sufficient condition, the
1912 * timestamps of the in-service queue would need to be
1913 * updated, and this operation is quite costly (see the
1914 * comments on bfq_bfqq_update_budg_for_activation()).
1915 *
1916 * As for throughput, we ask bfq_better_to_idle() whether we
1917 * still need to plug I/O dispatching. If bfq_better_to_idle()
1918 * says no, then plugging is not needed any longer, either to
1919 * boost throughput or to perserve service guarantees. Then
1920 * the best option is to stop plugging I/O, as not doing so
1921 * would certainly lower throughput. We may end up in this
1922 * case if: (1) upon a dispatch attempt, we detected that it
1923 * was better to plug I/O dispatch, and to wait for a new
1924 * request to arrive for the currently in-service queue, but
1925 * (2) this switch of bfqq to busy changes the scenario.
1926 */
1927 if (bfqd->in_service_queue &&
1928 ((bfqq_wants_to_preempt &&
1929 bfqq->wr_coeff >= bfqd->in_service_queue->wr_coeff) ||
1930 bfq_bfqq_higher_class_or_weight(bfqq, bfqd->in_service_queue) ||
1931 !bfq_better_to_idle(bfqd->in_service_queue)) &&
1932 next_queue_may_preempt(bfqd))
1933 bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
1934 false, BFQQE_PREEMPTED);
1935}
1936
1937static void bfq_reset_inject_limit(struct bfq_data *bfqd,
1938 struct bfq_queue *bfqq)
1939{
1940 /* invalidate baseline total service time */
1941 bfqq->last_serv_time_ns = 0;
1942
1943 /*
1944 * Reset pointer in case we are waiting for
1945 * some request completion.
1946 */
1947 bfqd->waited_rq = NULL;
1948
1949 /*
1950 * If bfqq has a short think time, then start by setting the
1951 * inject limit to 0 prudentially, because the service time of
1952 * an injected I/O request may be higher than the think time
1953 * of bfqq, and therefore, if one request was injected when
1954 * bfqq remains empty, this injected request might delay the
1955 * service of the next I/O request for bfqq significantly. In
1956 * case bfqq can actually tolerate some injection, then the
1957 * adaptive update will however raise the limit soon. This
1958 * lucky circumstance holds exactly because bfqq has a short
1959 * think time, and thus, after remaining empty, is likely to
1960 * get new I/O enqueued---and then completed---before being
1961 * expired. This is the very pattern that gives the
1962 * limit-update algorithm the chance to measure the effect of
1963 * injection on request service times, and then to update the
1964 * limit accordingly.
1965 *
1966 * However, in the following special case, the inject limit is
1967 * left to 1 even if the think time is short: bfqq's I/O is
1968 * synchronized with that of some other queue, i.e., bfqq may
1969 * receive new I/O only after the I/O of the other queue is
1970 * completed. Keeping the inject limit to 1 allows the
1971 * blocking I/O to be served while bfqq is in service. And
1972 * this is very convenient both for bfqq and for overall
1973 * throughput, as explained in detail in the comments in
1974 * bfq_update_has_short_ttime().
1975 *
1976 * On the opposite end, if bfqq has a long think time, then
1977 * start directly by 1, because:
1978 * a) on the bright side, keeping at most one request in
1979 * service in the drive is unlikely to cause any harm to the
1980 * latency of bfqq's requests, as the service time of a single
1981 * request is likely to be lower than the think time of bfqq;
1982 * b) on the downside, after becoming empty, bfqq is likely to
1983 * expire before getting its next request. With this request
1984 * arrival pattern, it is very hard to sample total service
1985 * times and update the inject limit accordingly (see comments
1986 * on bfq_update_inject_limit()). So the limit is likely to be
1987 * never, or at least seldom, updated. As a consequence, by
1988 * setting the limit to 1, we avoid that no injection ever
1989 * occurs with bfqq. On the downside, this proactive step
1990 * further reduces chances to actually compute the baseline
1991 * total service time. Thus it reduces chances to execute the
1992 * limit-update algorithm and possibly raise the limit to more
1993 * than 1.
1994 */
1995 if (bfq_bfqq_has_short_ttime(bfqq))
1996 bfqq->inject_limit = 0;
1997 else
1998 bfqq->inject_limit = 1;
1999
2000 bfqq->decrease_time_jif = jiffies;
2001}
2002
2003static void bfq_update_io_intensity(struct bfq_queue *bfqq, u64 now_ns)
2004{
2005 u64 tot_io_time = now_ns - bfqq->io_start_time;
2006
2007 if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfqq->dispatched == 0)
2008 bfqq->tot_idle_time +=
2009 now_ns - bfqq->ttime.last_end_request;
2010
2011 if (unlikely(bfq_bfqq_just_created(bfqq)))
2012 return;
2013
2014 /*
2015 * Must be busy for at least about 80% of the time to be
2016 * considered I/O bound.
2017 */
2018 if (bfqq->tot_idle_time * 5 > tot_io_time)
2019 bfq_clear_bfqq_IO_bound(bfqq);
2020 else
2021 bfq_mark_bfqq_IO_bound(bfqq);
2022
2023 /*
2024 * Keep an observation window of at most 200 ms in the past
2025 * from now.
2026 */
2027 if (tot_io_time > 200 * NSEC_PER_MSEC) {
2028 bfqq->io_start_time = now_ns - (tot_io_time>>1);
2029 bfqq->tot_idle_time >>= 1;
2030 }
2031}
2032
2033/*
2034 * Detect whether bfqq's I/O seems synchronized with that of some
2035 * other queue, i.e., whether bfqq, after remaining empty, happens to
2036 * receive new I/O only right after some I/O request of the other
2037 * queue has been completed. We call waker queue the other queue, and
2038 * we assume, for simplicity, that bfqq may have at most one waker
2039 * queue.
2040 *
2041 * A remarkable throughput boost can be reached by unconditionally
2042 * injecting the I/O of the waker queue, every time a new
2043 * bfq_dispatch_request happens to be invoked while I/O is being
2044 * plugged for bfqq. In addition to boosting throughput, this
2045 * unblocks bfqq's I/O, thereby improving bandwidth and latency for
2046 * bfqq. Note that these same results may be achieved with the general
2047 * injection mechanism, but less effectively. For details on this
2048 * aspect, see the comments on the choice of the queue for injection
2049 * in bfq_select_queue().
2050 *
2051 * Turning back to the detection of a waker queue, a queue Q is deemed as a
2052 * waker queue for bfqq if, for three consecutive times, bfqq happens to become
2053 * non empty right after a request of Q has been completed within given
2054 * timeout. In this respect, even if bfqq is empty, we do not check for a waker
2055 * if it still has some in-flight I/O. In fact, in this case bfqq is actually
2056 * still being served by the drive, and may receive new I/O on the completion
2057 * of some of the in-flight requests. In particular, on the first time, Q is
2058 * tentatively set as a candidate waker queue, while on the third consecutive
2059 * time that Q is detected, the field waker_bfqq is set to Q, to confirm that Q
2060 * is a waker queue for bfqq. These detection steps are performed only if bfqq
2061 * has a long think time, so as to make it more likely that bfqq's I/O is
2062 * actually being blocked by a synchronization. This last filter, plus the
2063 * above three-times requirement and time limit for detection, make false
2064 * positives less likely.
2065 *
2066 * NOTE
2067 *
2068 * The sooner a waker queue is detected, the sooner throughput can be
2069 * boosted by injecting I/O from the waker queue. Fortunately,
2070 * detection is likely to be actually fast, for the following
2071 * reasons. While blocked by synchronization, bfqq has a long think
2072 * time. This implies that bfqq's inject limit is at least equal to 1
2073 * (see the comments in bfq_update_inject_limit()). So, thanks to
2074 * injection, the waker queue is likely to be served during the very
2075 * first I/O-plugging time interval for bfqq. This triggers the first
2076 * step of the detection mechanism. Thanks again to injection, the
2077 * candidate waker queue is then likely to be confirmed no later than
2078 * during the next I/O-plugging interval for bfqq.
2079 *
2080 * ISSUE
2081 *
2082 * On queue merging all waker information is lost.
2083 */
2084static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2085 u64 now_ns)
2086{
2087 char waker_name[MAX_BFQQ_NAME_LENGTH];
2088
2089 if (!bfqd->last_completed_rq_bfqq ||
2090 bfqd->last_completed_rq_bfqq == bfqq ||
2091 bfq_bfqq_has_short_ttime(bfqq) ||
2092 now_ns - bfqd->last_completion >= 4 * NSEC_PER_MSEC ||
2093 bfqd->last_completed_rq_bfqq == &bfqd->oom_bfqq ||
2094 bfqq == &bfqd->oom_bfqq)
2095 return;
2096
2097 /*
2098 * We reset waker detection logic also if too much time has passed
2099 * since the first detection. If wakeups are rare, pointless idling
2100 * doesn't hurt throughput that much. The condition below makes sure
2101 * we do not uselessly idle blocking waker in more than 1/64 cases.
2102 */
2103 if (bfqd->last_completed_rq_bfqq !=
2104 bfqq->tentative_waker_bfqq ||
2105 now_ns > bfqq->waker_detection_started +
2106 128 * (u64)bfqd->bfq_slice_idle) {
2107 /*
2108 * First synchronization detected with a
2109 * candidate waker queue, or with a different
2110 * candidate waker queue from the current one.
2111 */
2112 bfqq->tentative_waker_bfqq =
2113 bfqd->last_completed_rq_bfqq;
2114 bfqq->num_waker_detections = 1;
2115 bfqq->waker_detection_started = now_ns;
2116 bfq_bfqq_name(bfqq->tentative_waker_bfqq, waker_name,
2117 MAX_BFQQ_NAME_LENGTH);
2118 bfq_log_bfqq(bfqd, bfqq, "set tentative waker %s", waker_name);
2119 } else /* Same tentative waker queue detected again */
2120 bfqq->num_waker_detections++;
2121
2122 if (bfqq->num_waker_detections == 3) {
2123 bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq;
2124 bfqq->tentative_waker_bfqq = NULL;
2125 bfq_bfqq_name(bfqq->waker_bfqq, waker_name,
2126 MAX_BFQQ_NAME_LENGTH);
2127 bfq_log_bfqq(bfqd, bfqq, "set waker %s", waker_name);
2128
2129 /*
2130 * If the waker queue disappears, then
2131 * bfqq->waker_bfqq must be reset. To
2132 * this goal, we maintain in each
2133 * waker queue a list, woken_list, of
2134 * all the queues that reference the
2135 * waker queue through their
2136 * waker_bfqq pointer. When the waker
2137 * queue exits, the waker_bfqq pointer
2138 * of all the queues in the woken_list
2139 * is reset.
2140 *
2141 * In addition, if bfqq is already in
2142 * the woken_list of a waker queue,
2143 * then, before being inserted into
2144 * the woken_list of a new waker
2145 * queue, bfqq must be removed from
2146 * the woken_list of the old waker
2147 * queue.
2148 */
2149 if (!hlist_unhashed(&bfqq->woken_list_node))
2150 hlist_del_init(&bfqq->woken_list_node);
2151 hlist_add_head(&bfqq->woken_list_node,
2152 &bfqd->last_completed_rq_bfqq->woken_list);
2153 }
2154}
2155
2156static void bfq_add_request(struct request *rq)
2157{
2158 struct bfq_queue *bfqq = RQ_BFQQ(rq);
2159 struct bfq_data *bfqd = bfqq->bfqd;
2160 struct request *next_rq, *prev;
2161 unsigned int old_wr_coeff = bfqq->wr_coeff;
2162 bool interactive = false;
2163 u64 now_ns = ktime_get_ns();
2164
2165 bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
2166 bfqq->queued[rq_is_sync(rq)]++;
2167 /*
2168 * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2169 * may be read without holding the lock in bfq_has_work().
2170 */
2171 WRITE_ONCE(bfqd->queued, bfqd->queued + 1);
2172
2173 if (bfq_bfqq_sync(bfqq) && RQ_BIC(rq)->requests <= 1) {
2174 bfq_check_waker(bfqd, bfqq, now_ns);
2175
2176 /*
2177 * Periodically reset inject limit, to make sure that
2178 * the latter eventually drops in case workload
2179 * changes, see step (3) in the comments on
2180 * bfq_update_inject_limit().
2181 */
2182 if (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2183 msecs_to_jiffies(1000)))
2184 bfq_reset_inject_limit(bfqd, bfqq);
2185
2186 /*
2187 * The following conditions must hold to setup a new
2188 * sampling of total service time, and then a new
2189 * update of the inject limit:
2190 * - bfqq is in service, because the total service
2191 * time is evaluated only for the I/O requests of
2192 * the queues in service;
2193 * - this is the right occasion to compute or to
2194 * lower the baseline total service time, because
2195 * there are actually no requests in the drive,
2196 * or
2197 * the baseline total service time is available, and
2198 * this is the right occasion to compute the other
2199 * quantity needed to update the inject limit, i.e.,
2200 * the total service time caused by the amount of
2201 * injection allowed by the current value of the
2202 * limit. It is the right occasion because injection
2203 * has actually been performed during the service
2204 * hole, and there are still in-flight requests,
2205 * which are very likely to be exactly the injected
2206 * requests, or part of them;
2207 * - the minimum interval for sampling the total
2208 * service time and updating the inject limit has
2209 * elapsed.
2210 */
2211 if (bfqq == bfqd->in_service_queue &&
2212 (bfqd->rq_in_driver == 0 ||
2213 (bfqq->last_serv_time_ns > 0 &&
2214 bfqd->rqs_injected && bfqd->rq_in_driver > 0)) &&
2215 time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2216 msecs_to_jiffies(10))) {
2217 bfqd->last_empty_occupied_ns = ktime_get_ns();
2218 /*
2219 * Start the state machine for measuring the
2220 * total service time of rq: setting
2221 * wait_dispatch will cause bfqd->waited_rq to
2222 * be set when rq will be dispatched.
2223 */
2224 bfqd->wait_dispatch = true;
2225 /*
2226 * If there is no I/O in service in the drive,
2227 * then possible injection occurred before the
2228 * arrival of rq will not affect the total
2229 * service time of rq. So the injection limit
2230 * must not be updated as a function of such
2231 * total service time, unless new injection
2232 * occurs before rq is completed. To have the
2233 * injection limit updated only in the latter
2234 * case, reset rqs_injected here (rqs_injected
2235 * will be set in case injection is performed
2236 * on bfqq before rq is completed).
2237 */
2238 if (bfqd->rq_in_driver == 0)
2239 bfqd->rqs_injected = false;
2240 }
2241 }
2242
2243 if (bfq_bfqq_sync(bfqq))
2244 bfq_update_io_intensity(bfqq, now_ns);
2245
2246 elv_rb_add(&bfqq->sort_list, rq);
2247
2248 /*
2249 * Check if this request is a better next-serve candidate.
2250 */
2251 prev = bfqq->next_rq;
2252 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
2253 bfqq->next_rq = next_rq;
2254
2255 /*
2256 * Adjust priority tree position, if next_rq changes.
2257 * See comments on bfq_pos_tree_add_move() for the unlikely().
2258 */
2259 if (unlikely(!bfqd->nonrot_with_queueing && prev != bfqq->next_rq))
2260 bfq_pos_tree_add_move(bfqd, bfqq);
2261
2262 if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
2263 bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
2264 rq, &interactive);
2265 else {
2266 if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
2267 time_is_before_jiffies(
2268 bfqq->last_wr_start_finish +
2269 bfqd->bfq_wr_min_inter_arr_async)) {
2270 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
2271 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
2272
2273 bfqd->wr_busy_queues++;
2274 bfqq->entity.prio_changed = 1;
2275 }
2276 if (prev != bfqq->next_rq)
2277 bfq_updated_next_req(bfqd, bfqq);
2278 }
2279
2280 /*
2281 * Assign jiffies to last_wr_start_finish in the following
2282 * cases:
2283 *
2284 * . if bfqq is not going to be weight-raised, because, for
2285 * non weight-raised queues, last_wr_start_finish stores the
2286 * arrival time of the last request; as of now, this piece
2287 * of information is used only for deciding whether to
2288 * weight-raise async queues
2289 *
2290 * . if bfqq is not weight-raised, because, if bfqq is now
2291 * switching to weight-raised, then last_wr_start_finish
2292 * stores the time when weight-raising starts
2293 *
2294 * . if bfqq is interactive, because, regardless of whether
2295 * bfqq is currently weight-raised, the weight-raising
2296 * period must start or restart (this case is considered
2297 * separately because it is not detected by the above
2298 * conditions, if bfqq is already weight-raised)
2299 *
2300 * last_wr_start_finish has to be updated also if bfqq is soft
2301 * real-time, because the weight-raising period is constantly
2302 * restarted on idle-to-busy transitions for these queues, but
2303 * this is already done in bfq_bfqq_handle_idle_busy_switch if
2304 * needed.
2305 */
2306 if (bfqd->low_latency &&
2307 (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
2308 bfqq->last_wr_start_finish = jiffies;
2309}
2310
2311static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
2312 struct bio *bio,
2313 struct request_queue *q)
2314{
2315 struct bfq_queue *bfqq = bfqd->bio_bfqq;
2316
2317
2318 if (bfqq)
2319 return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
2320
2321 return NULL;
2322}
2323
2324static sector_t get_sdist(sector_t last_pos, struct request *rq)
2325{
2326 if (last_pos)
2327 return abs(blk_rq_pos(rq) - last_pos);
2328
2329 return 0;
2330}
2331
2332static void bfq_remove_request(struct request_queue *q,
2333 struct request *rq)
2334{
2335 struct bfq_queue *bfqq = RQ_BFQQ(rq);
2336 struct bfq_data *bfqd = bfqq->bfqd;
2337 const int sync = rq_is_sync(rq);
2338
2339 if (bfqq->next_rq == rq) {
2340 bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
2341 bfq_updated_next_req(bfqd, bfqq);
2342 }
2343
2344 if (rq->queuelist.prev != &rq->queuelist)
2345 list_del_init(&rq->queuelist);
2346 bfqq->queued[sync]--;
2347 /*
2348 * Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2349 * may be read without holding the lock in bfq_has_work().
2350 */
2351 WRITE_ONCE(bfqd->queued, bfqd->queued - 1);
2352 elv_rb_del(&bfqq->sort_list, rq);
2353
2354 elv_rqhash_del(q, rq);
2355 if (q->last_merge == rq)
2356 q->last_merge = NULL;
2357
2358 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2359 bfqq->next_rq = NULL;
2360
2361 if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
2362 bfq_del_bfqq_busy(bfqq, false);
2363 /*
2364 * bfqq emptied. In normal operation, when
2365 * bfqq is empty, bfqq->entity.service and
2366 * bfqq->entity.budget must contain,
2367 * respectively, the service received and the
2368 * budget used last time bfqq emptied. These
2369 * facts do not hold in this case, as at least
2370 * this last removal occurred while bfqq is
2371 * not in service. To avoid inconsistencies,
2372 * reset both bfqq->entity.service and
2373 * bfqq->entity.budget, if bfqq has still a
2374 * process that may issue I/O requests to it.
2375 */
2376 bfqq->entity.budget = bfqq->entity.service = 0;
2377 }
2378
2379 /*
2380 * Remove queue from request-position tree as it is empty.
2381 */
2382 if (bfqq->pos_root) {
2383 rb_erase(&bfqq->pos_node, bfqq->pos_root);
2384 bfqq->pos_root = NULL;
2385 }
2386 } else {
2387 /* see comments on bfq_pos_tree_add_move() for the unlikely() */
2388 if (unlikely(!bfqd->nonrot_with_queueing))
2389 bfq_pos_tree_add_move(bfqd, bfqq);
2390 }
2391
2392 if (rq->cmd_flags & REQ_META)
2393 bfqq->meta_pending--;
2394
2395}
2396
2397static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
2398 unsigned int nr_segs)
2399{
2400 struct bfq_data *bfqd = q->elevator->elevator_data;
2401 struct request *free = NULL;
2402 /*
2403 * bfq_bic_lookup grabs the queue_lock: invoke it now and
2404 * store its return value for later use, to avoid nesting
2405 * queue_lock inside the bfqd->lock. We assume that the bic
2406 * returned by bfq_bic_lookup does not go away before
2407 * bfqd->lock is taken.
2408 */
2409 struct bfq_io_cq *bic = bfq_bic_lookup(q);
2410 bool ret;
2411
2412 spin_lock_irq(&bfqd->lock);
2413
2414 if (bic) {
2415 /*
2416 * Make sure cgroup info is uptodate for current process before
2417 * considering the merge.
2418 */
2419 bfq_bic_update_cgroup(bic, bio);
2420
2421 bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
2422 } else {
2423 bfqd->bio_bfqq = NULL;
2424 }
2425 bfqd->bio_bic = bic;
2426
2427 ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);
2428
2429 spin_unlock_irq(&bfqd->lock);
2430 if (free)
2431 blk_mq_free_request(free);
2432
2433 return ret;
2434}
2435
2436static int bfq_request_merge(struct request_queue *q, struct request **req,
2437 struct bio *bio)
2438{
2439 struct bfq_data *bfqd = q->elevator->elevator_data;
2440 struct request *__rq;
2441
2442 __rq = bfq_find_rq_fmerge(bfqd, bio, q);
2443 if (__rq && elv_bio_merge_ok(__rq, bio)) {
2444 *req = __rq;
2445
2446 if (blk_discard_mergable(__rq))
2447 return ELEVATOR_DISCARD_MERGE;
2448 return ELEVATOR_FRONT_MERGE;
2449 }
2450
2451 return ELEVATOR_NO_MERGE;
2452}
2453
2454static void bfq_request_merged(struct request_queue *q, struct request *req,
2455 enum elv_merge type)
2456{
2457 if (type == ELEVATOR_FRONT_MERGE &&
2458 rb_prev(&req->rb_node) &&
2459 blk_rq_pos(req) <
2460 blk_rq_pos(container_of(rb_prev(&req->rb_node),
2461 struct request, rb_node))) {
2462 struct bfq_queue *bfqq = RQ_BFQQ(req);
2463 struct bfq_data *bfqd;
2464 struct request *prev, *next_rq;
2465
2466 if (!bfqq)
2467 return;
2468
2469 bfqd = bfqq->bfqd;
2470
2471 /* Reposition request in its sort_list */
2472 elv_rb_del(&bfqq->sort_list, req);
2473 elv_rb_add(&bfqq->sort_list, req);
2474
2475 /* Choose next request to be served for bfqq */
2476 prev = bfqq->next_rq;
2477 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
2478 bfqd->last_position);
2479 bfqq->next_rq = next_rq;
2480 /*
2481 * If next_rq changes, update both the queue's budget to
2482 * fit the new request and the queue's position in its
2483 * rq_pos_tree.
2484 */
2485 if (prev != bfqq->next_rq) {
2486 bfq_updated_next_req(bfqd, bfqq);
2487 /*
2488 * See comments on bfq_pos_tree_add_move() for
2489 * the unlikely().
2490 */
2491 if (unlikely(!bfqd->nonrot_with_queueing))
2492 bfq_pos_tree_add_move(bfqd, bfqq);
2493 }
2494 }
2495}
2496
2497/*
2498 * This function is called to notify the scheduler that the requests
2499 * rq and 'next' have been merged, with 'next' going away. BFQ
2500 * exploits this hook to address the following issue: if 'next' has a
2501 * fifo_time lower that rq, then the fifo_time of rq must be set to
2502 * the value of 'next', to not forget the greater age of 'next'.
2503 *
2504 * NOTE: in this function we assume that rq is in a bfq_queue, basing
2505 * on that rq is picked from the hash table q->elevator->hash, which,
2506 * in its turn, is filled only with I/O requests present in
2507 * bfq_queues, while BFQ is in use for the request queue q. In fact,
2508 * the function that fills this hash table (elv_rqhash_add) is called
2509 * only by bfq_insert_request.
2510 */
2511static void bfq_requests_merged(struct request_queue *q, struct request *rq,
2512 struct request *next)
2513{
2514 struct bfq_queue *bfqq = RQ_BFQQ(rq),
2515 *next_bfqq = RQ_BFQQ(next);
2516
2517 if (!bfqq)
2518 goto remove;
2519
2520 /*
2521 * If next and rq belong to the same bfq_queue and next is older
2522 * than rq, then reposition rq in the fifo (by substituting next
2523 * with rq). Otherwise, if next and rq belong to different
2524 * bfq_queues, never reposition rq: in fact, we would have to
2525 * reposition it with respect to next's position in its own fifo,
2526 * which would most certainly be too expensive with respect to
2527 * the benefits.
2528 */
2529 if (bfqq == next_bfqq &&
2530 !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
2531 next->fifo_time < rq->fifo_time) {
2532 list_del_init(&rq->queuelist);
2533 list_replace_init(&next->queuelist, &rq->queuelist);
2534 rq->fifo_time = next->fifo_time;
2535 }
2536
2537 if (bfqq->next_rq == next)
2538 bfqq->next_rq = rq;
2539
2540 bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
2541remove:
2542 /* Merged request may be in the IO scheduler. Remove it. */
2543 if (!RB_EMPTY_NODE(&next->rb_node)) {
2544 bfq_remove_request(next->q, next);
2545 if (next_bfqq)
2546 bfqg_stats_update_io_remove(bfqq_group(next_bfqq),
2547 next->cmd_flags);
2548 }
2549}
2550
2551/* Must be called with bfqq != NULL */
2552static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
2553{
2554 /*
2555 * If bfqq has been enjoying interactive weight-raising, then
2556 * reset soft_rt_next_start. We do it for the following
2557 * reason. bfqq may have been conveying the I/O needed to load
2558 * a soft real-time application. Such an application actually
2559 * exhibits a soft real-time I/O pattern after it finishes
2560 * loading, and finally starts doing its job. But, if bfqq has
2561 * been receiving a lot of bandwidth so far (likely to happen
2562 * on a fast device), then soft_rt_next_start now contains a
2563 * high value that. So, without this reset, bfqq would be
2564 * prevented from being possibly considered as soft_rt for a
2565 * very long time.
2566 */
2567
2568 if (bfqq->wr_cur_max_time !=
2569 bfqq->bfqd->bfq_wr_rt_max_time)
2570 bfqq->soft_rt_next_start = jiffies;
2571
2572 if (bfq_bfqq_busy(bfqq))
2573 bfqq->bfqd->wr_busy_queues--;
2574 bfqq->wr_coeff = 1;
2575 bfqq->wr_cur_max_time = 0;
2576 bfqq->last_wr_start_finish = jiffies;
2577 /*
2578 * Trigger a weight change on the next invocation of
2579 * __bfq_entity_update_weight_prio.
2580 */
2581 bfqq->entity.prio_changed = 1;
2582}
2583
2584void bfq_end_wr_async_queues(struct bfq_data *bfqd,
2585 struct bfq_group *bfqg)
2586{
2587 int i, j;
2588
2589 for (i = 0; i < 2; i++)
2590 for (j = 0; j < IOPRIO_NR_LEVELS; j++)
2591 if (bfqg->async_bfqq[i][j])
2592 bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
2593 if (bfqg->async_idle_bfqq)
2594 bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
2595}
2596
2597static void bfq_end_wr(struct bfq_data *bfqd)
2598{
2599 struct bfq_queue *bfqq;
2600
2601 spin_lock_irq(&bfqd->lock);
2602
2603 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
2604 bfq_bfqq_end_wr(bfqq);
2605 list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
2606 bfq_bfqq_end_wr(bfqq);
2607 bfq_end_wr_async(bfqd);
2608
2609 spin_unlock_irq(&bfqd->lock);
2610}
2611
2612static sector_t bfq_io_struct_pos(void *io_struct, bool request)
2613{
2614 if (request)
2615 return blk_rq_pos(io_struct);
2616 else
2617 return ((struct bio *)io_struct)->bi_iter.bi_sector;
2618}
2619
2620static int bfq_rq_close_to_sector(void *io_struct, bool request,
2621 sector_t sector)
2622{
2623 return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
2624 BFQQ_CLOSE_THR;
2625}
2626
2627static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
2628 struct bfq_queue *bfqq,
2629 sector_t sector)
2630{
2631 struct rb_root *root = &bfqq_group(bfqq)->rq_pos_tree;
2632 struct rb_node *parent, *node;
2633 struct bfq_queue *__bfqq;
2634
2635 if (RB_EMPTY_ROOT(root))
2636 return NULL;
2637
2638 /*
2639 * First, if we find a request starting at the end of the last
2640 * request, choose it.
2641 */
2642 __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
2643 if (__bfqq)
2644 return __bfqq;
2645
2646 /*
2647 * If the exact sector wasn't found, the parent of the NULL leaf
2648 * will contain the closest sector (rq_pos_tree sorted by
2649 * next_request position).
2650 */
2651 __bfqq = rb_entry(parent, struct bfq_queue, pos_node);
2652 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2653 return __bfqq;
2654
2655 if (blk_rq_pos(__bfqq->next_rq) < sector)
2656 node = rb_next(&__bfqq->pos_node);
2657 else
2658 node = rb_prev(&__bfqq->pos_node);
2659 if (!node)
2660 return NULL;
2661
2662 __bfqq = rb_entry(node, struct bfq_queue, pos_node);
2663 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2664 return __bfqq;
2665
2666 return NULL;
2667}
2668
2669static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
2670 struct bfq_queue *cur_bfqq,
2671 sector_t sector)
2672{
2673 struct bfq_queue *bfqq;
2674
2675 /*
2676 * We shall notice if some of the queues are cooperating,
2677 * e.g., working closely on the same area of the device. In
2678 * that case, we can group them together and: 1) don't waste
2679 * time idling, and 2) serve the union of their requests in
2680 * the best possible order for throughput.
2681 */
2682 bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
2683 if (!bfqq || bfqq == cur_bfqq)
2684 return NULL;
2685
2686 return bfqq;
2687}
2688
2689static struct bfq_queue *
2690bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2691{
2692 int process_refs, new_process_refs;
2693 struct bfq_queue *__bfqq;
2694
2695 /*
2696 * If there are no process references on the new_bfqq, then it is
2697 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
2698 * may have dropped their last reference (not just their last process
2699 * reference).
2700 */
2701 if (!bfqq_process_refs(new_bfqq))
2702 return NULL;
2703
2704 /* Avoid a circular list and skip interim queue merges. */
2705 while ((__bfqq = new_bfqq->new_bfqq)) {
2706 if (__bfqq == bfqq)
2707 return NULL;
2708 new_bfqq = __bfqq;
2709 }
2710
2711 process_refs = bfqq_process_refs(bfqq);
2712 new_process_refs = bfqq_process_refs(new_bfqq);
2713 /*
2714 * If the process for the bfqq has gone away, there is no
2715 * sense in merging the queues.
2716 */
2717 if (process_refs == 0 || new_process_refs == 0)
2718 return NULL;
2719
2720 /*
2721 * Make sure merged queues belong to the same parent. Parents could
2722 * have changed since the time we decided the two queues are suitable
2723 * for merging.
2724 */
2725 if (new_bfqq->entity.parent != bfqq->entity.parent)
2726 return NULL;
2727
2728 bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
2729 new_bfqq->pid);
2730
2731 /*
2732 * Merging is just a redirection: the requests of the process
2733 * owning one of the two queues are redirected to the other queue.
2734 * The latter queue, in its turn, is set as shared if this is the
2735 * first time that the requests of some process are redirected to
2736 * it.
2737 *
2738 * We redirect bfqq to new_bfqq and not the opposite, because
2739 * we are in the context of the process owning bfqq, thus we
2740 * have the io_cq of this process. So we can immediately
2741 * configure this io_cq to redirect the requests of the
2742 * process to new_bfqq. In contrast, the io_cq of new_bfqq is
2743 * not available any more (new_bfqq->bic == NULL).
2744 *
2745 * Anyway, even in case new_bfqq coincides with the in-service
2746 * queue, redirecting requests the in-service queue is the
2747 * best option, as we feed the in-service queue with new
2748 * requests close to the last request served and, by doing so,
2749 * are likely to increase the throughput.
2750 */
2751 bfqq->new_bfqq = new_bfqq;
2752 /*
2753 * The above assignment schedules the following redirections:
2754 * each time some I/O for bfqq arrives, the process that
2755 * generated that I/O is disassociated from bfqq and
2756 * associated with new_bfqq. Here we increases new_bfqq->ref
2757 * in advance, adding the number of processes that are
2758 * expected to be associated with new_bfqq as they happen to
2759 * issue I/O.
2760 */
2761 new_bfqq->ref += process_refs;
2762 return new_bfqq;
2763}
2764
2765static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
2766 struct bfq_queue *new_bfqq)
2767{
2768 if (bfq_too_late_for_merging(new_bfqq))
2769 return false;
2770
2771 if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
2772 (bfqq->ioprio_class != new_bfqq->ioprio_class))
2773 return false;
2774
2775 /*
2776 * If either of the queues has already been detected as seeky,
2777 * then merging it with the other queue is unlikely to lead to
2778 * sequential I/O.
2779 */
2780 if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
2781 return false;
2782
2783 /*
2784 * Interleaved I/O is known to be done by (some) applications
2785 * only for reads, so it does not make sense to merge async
2786 * queues.
2787 */
2788 if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
2789 return false;
2790
2791 return true;
2792}
2793
2794static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
2795 struct bfq_queue *bfqq);
2796
2797/*
2798 * Attempt to schedule a merge of bfqq with the currently in-service
2799 * queue or with a close queue among the scheduled queues. Return
2800 * NULL if no merge was scheduled, a pointer to the shared bfq_queue
2801 * structure otherwise.
2802 *
2803 * The OOM queue is not allowed to participate to cooperation: in fact, since
2804 * the requests temporarily redirected to the OOM queue could be redirected
2805 * again to dedicated queues at any time, the state needed to correctly
2806 * handle merging with the OOM queue would be quite complex and expensive
2807 * to maintain. Besides, in such a critical condition as an out of memory,
2808 * the benefits of queue merging may be little relevant, or even negligible.
2809 *
2810 * WARNING: queue merging may impair fairness among non-weight raised
2811 * queues, for at least two reasons: 1) the original weight of a
2812 * merged queue may change during the merged state, 2) even being the
2813 * weight the same, a merged queue may be bloated with many more
2814 * requests than the ones produced by its originally-associated
2815 * process.
2816 */
2817static struct bfq_queue *
2818bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2819 void *io_struct, bool request, struct bfq_io_cq *bic)
2820{
2821 struct bfq_queue *in_service_bfqq, *new_bfqq;
2822
2823 /* if a merge has already been setup, then proceed with that first */
2824 if (bfqq->new_bfqq)
2825 return bfqq->new_bfqq;
2826
2827 /*
2828 * Check delayed stable merge for rotational or non-queueing
2829 * devs. For this branch to be executed, bfqq must not be
2830 * currently merged with some other queue (i.e., bfqq->bic
2831 * must be non null). If we considered also merged queues,
2832 * then we should also check whether bfqq has already been
2833 * merged with bic->stable_merge_bfqq. But this would be
2834 * costly and complicated.
2835 */
2836 if (unlikely(!bfqd->nonrot_with_queueing)) {
2837 /*
2838 * Make sure also that bfqq is sync, because
2839 * bic->stable_merge_bfqq may point to some queue (for
2840 * stable merging) also if bic is associated with a
2841 * sync queue, but this bfqq is async
2842 */
2843 if (bfq_bfqq_sync(bfqq) && bic->stable_merge_bfqq &&
2844 !bfq_bfqq_just_created(bfqq) &&
2845 time_is_before_jiffies(bfqq->split_time +
2846 msecs_to_jiffies(bfq_late_stable_merging)) &&
2847 time_is_before_jiffies(bfqq->creation_time +
2848 msecs_to_jiffies(bfq_late_stable_merging))) {
2849 struct bfq_queue *stable_merge_bfqq =
2850 bic->stable_merge_bfqq;
2851 int proc_ref = min(bfqq_process_refs(bfqq),
2852 bfqq_process_refs(stable_merge_bfqq));
2853
2854 /* deschedule stable merge, because done or aborted here */
2855 bfq_put_stable_ref(stable_merge_bfqq);
2856
2857 bic->stable_merge_bfqq = NULL;
2858
2859 if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
2860 proc_ref > 0) {
2861 /* next function will take at least one ref */
2862 struct bfq_queue *new_bfqq =
2863 bfq_setup_merge(bfqq, stable_merge_bfqq);
2864
2865 if (new_bfqq) {
2866 bic->stably_merged = true;
2867 if (new_bfqq->bic)
2868 new_bfqq->bic->stably_merged =
2869 true;
2870 }
2871 return new_bfqq;
2872 } else
2873 return NULL;
2874 }
2875 }
2876
2877 /*
2878 * Do not perform queue merging if the device is non
2879 * rotational and performs internal queueing. In fact, such a
2880 * device reaches a high speed through internal parallelism
2881 * and pipelining. This means that, to reach a high
2882 * throughput, it must have many requests enqueued at the same
2883 * time. But, in this configuration, the internal scheduling
2884 * algorithm of the device does exactly the job of queue
2885 * merging: it reorders requests so as to obtain as much as
2886 * possible a sequential I/O pattern. As a consequence, with
2887 * the workload generated by processes doing interleaved I/O,
2888 * the throughput reached by the device is likely to be the
2889 * same, with and without queue merging.
2890 *
2891 * Disabling merging also provides a remarkable benefit in
2892 * terms of throughput. Merging tends to make many workloads
2893 * artificially more uneven, because of shared queues
2894 * remaining non empty for incomparably more time than
2895 * non-merged queues. This may accentuate workload
2896 * asymmetries. For example, if one of the queues in a set of
2897 * merged queues has a higher weight than a normal queue, then
2898 * the shared queue may inherit such a high weight and, by
2899 * staying almost always active, may force BFQ to perform I/O
2900 * plugging most of the time. This evidently makes it harder
2901 * for BFQ to let the device reach a high throughput.
2902 *
2903 * Finally, the likely() macro below is not used because one
2904 * of the two branches is more likely than the other, but to
2905 * have the code path after the following if() executed as
2906 * fast as possible for the case of a non rotational device
2907 * with queueing. We want it because this is the fastest kind
2908 * of device. On the opposite end, the likely() may lengthen
2909 * the execution time of BFQ for the case of slower devices
2910 * (rotational or at least without queueing). But in this case
2911 * the execution time of BFQ matters very little, if not at
2912 * all.
2913 */
2914 if (likely(bfqd->nonrot_with_queueing))
2915 return NULL;
2916
2917 /*
2918 * Prevent bfqq from being merged if it has been created too
2919 * long ago. The idea is that true cooperating processes, and
2920 * thus their associated bfq_queues, are supposed to be
2921 * created shortly after each other. This is the case, e.g.,
2922 * for KVM/QEMU and dump I/O threads. Basing on this
2923 * assumption, the following filtering greatly reduces the
2924 * probability that two non-cooperating processes, which just
2925 * happen to do close I/O for some short time interval, have
2926 * their queues merged by mistake.
2927 */
2928 if (bfq_too_late_for_merging(bfqq))
2929 return NULL;
2930
2931 if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
2932 return NULL;
2933
2934 /* If there is only one backlogged queue, don't search. */
2935 if (bfq_tot_busy_queues(bfqd) == 1)
2936 return NULL;
2937
2938 in_service_bfqq = bfqd->in_service_queue;
2939
2940 if (in_service_bfqq && in_service_bfqq != bfqq &&
2941 likely(in_service_bfqq != &bfqd->oom_bfqq) &&
2942 bfq_rq_close_to_sector(io_struct, request,
2943 bfqd->in_serv_last_pos) &&
2944 bfqq->entity.parent == in_service_bfqq->entity.parent &&
2945 bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
2946 new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
2947 if (new_bfqq)
2948 return new_bfqq;
2949 }
2950 /*
2951 * Check whether there is a cooperator among currently scheduled
2952 * queues. The only thing we need is that the bio/request is not
2953 * NULL, as we need it to establish whether a cooperator exists.
2954 */
2955 new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
2956 bfq_io_struct_pos(io_struct, request));
2957
2958 if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
2959 bfq_may_be_close_cooperator(bfqq, new_bfqq))
2960 return bfq_setup_merge(bfqq, new_bfqq);
2961
2962 return NULL;
2963}
2964
2965static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
2966{
2967 struct bfq_io_cq *bic = bfqq->bic;
2968
2969 /*
2970 * If !bfqq->bic, the queue is already shared or its requests
2971 * have already been redirected to a shared queue; both idle window
2972 * and weight raising state have already been saved. Do nothing.
2973 */
2974 if (!bic)
2975 return;
2976
2977 bic->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
2978 bic->saved_inject_limit = bfqq->inject_limit;
2979 bic->saved_decrease_time_jif = bfqq->decrease_time_jif;
2980
2981 bic->saved_weight = bfqq->entity.orig_weight;
2982 bic->saved_ttime = bfqq->ttime;
2983 bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
2984 bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
2985 bic->saved_io_start_time = bfqq->io_start_time;
2986 bic->saved_tot_idle_time = bfqq->tot_idle_time;
2987 bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
2988 bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
2989 if (unlikely(bfq_bfqq_just_created(bfqq) &&
2990 !bfq_bfqq_in_large_burst(bfqq) &&
2991 bfqq->bfqd->low_latency)) {
2992 /*
2993 * bfqq being merged right after being created: bfqq
2994 * would have deserved interactive weight raising, but
2995 * did not make it to be set in a weight-raised state,
2996 * because of this early merge. Store directly the
2997 * weight-raising state that would have been assigned
2998 * to bfqq, so that to avoid that bfqq unjustly fails
2999 * to enjoy weight raising if split soon.
3000 */
3001 bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
3002 bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
3003 bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
3004 bic->saved_last_wr_start_finish = jiffies;
3005 } else {
3006 bic->saved_wr_coeff = bfqq->wr_coeff;
3007 bic->saved_wr_start_at_switch_to_srt =
3008 bfqq->wr_start_at_switch_to_srt;
3009 bic->saved_service_from_wr = bfqq->service_from_wr;
3010 bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
3011 bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
3012 }
3013}
3014
3015
3016static void
3017bfq_reassign_last_bfqq(struct bfq_queue *cur_bfqq, struct bfq_queue *new_bfqq)
3018{
3019 if (cur_bfqq->entity.parent &&
3020 cur_bfqq->entity.parent->last_bfqq_created == cur_bfqq)
3021 cur_bfqq->entity.parent->last_bfqq_created = new_bfqq;
3022 else if (cur_bfqq->bfqd && cur_bfqq->bfqd->last_bfqq_created == cur_bfqq)
3023 cur_bfqq->bfqd->last_bfqq_created = new_bfqq;
3024}
3025
3026void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq)
3027{
3028 /*
3029 * To prevent bfqq's service guarantees from being violated,
3030 * bfqq may be left busy, i.e., queued for service, even if
3031 * empty (see comments in __bfq_bfqq_expire() for
3032 * details). But, if no process will send requests to bfqq any
3033 * longer, then there is no point in keeping bfqq queued for
3034 * service. In addition, keeping bfqq queued for service, but
3035 * with no process ref any longer, may have caused bfqq to be
3036 * freed when dequeued from service. But this is assumed to
3037 * never happen.
3038 */
3039 if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) &&
3040 bfqq != bfqd->in_service_queue)
3041 bfq_del_bfqq_busy(bfqq, false);
3042
3043 bfq_reassign_last_bfqq(bfqq, NULL);
3044
3045 bfq_put_queue(bfqq);
3046}
3047
3048static void
3049bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
3050 struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
3051{
3052 bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
3053 (unsigned long)new_bfqq->pid);
3054 /* Save weight raising and idle window of the merged queues */
3055 bfq_bfqq_save_state(bfqq);
3056 bfq_bfqq_save_state(new_bfqq);
3057 if (bfq_bfqq_IO_bound(bfqq))
3058 bfq_mark_bfqq_IO_bound(new_bfqq);
3059 bfq_clear_bfqq_IO_bound(bfqq);
3060
3061 /*
3062 * The processes associated with bfqq are cooperators of the
3063 * processes associated with new_bfqq. So, if bfqq has a
3064 * waker, then assume that all these processes will be happy
3065 * to let bfqq's waker freely inject I/O when they have no
3066 * I/O.
3067 */
3068 if (bfqq->waker_bfqq && !new_bfqq->waker_bfqq &&
3069 bfqq->waker_bfqq != new_bfqq) {
3070 new_bfqq->waker_bfqq = bfqq->waker_bfqq;
3071 new_bfqq->tentative_waker_bfqq = NULL;
3072
3073 /*
3074 * If the waker queue disappears, then
3075 * new_bfqq->waker_bfqq must be reset. So insert
3076 * new_bfqq into the woken_list of the waker. See
3077 * bfq_check_waker for details.
3078 */
3079 hlist_add_head(&new_bfqq->woken_list_node,
3080 &new_bfqq->waker_bfqq->woken_list);
3081
3082 }
3083
3084 /*
3085 * If bfqq is weight-raised, then let new_bfqq inherit
3086 * weight-raising. To reduce false positives, neglect the case
3087 * where bfqq has just been created, but has not yet made it
3088 * to be weight-raised (which may happen because EQM may merge
3089 * bfqq even before bfq_add_request is executed for the first
3090 * time for bfqq). Handling this case would however be very
3091 * easy, thanks to the flag just_created.
3092 */
3093 if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
3094 new_bfqq->wr_coeff = bfqq->wr_coeff;
3095 new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
3096 new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
3097 new_bfqq->wr_start_at_switch_to_srt =
3098 bfqq->wr_start_at_switch_to_srt;
3099 if (bfq_bfqq_busy(new_bfqq))
3100 bfqd->wr_busy_queues++;
3101 new_bfqq->entity.prio_changed = 1;
3102 }
3103
3104 if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
3105 bfqq->wr_coeff = 1;
3106 bfqq->entity.prio_changed = 1;
3107 if (bfq_bfqq_busy(bfqq))
3108 bfqd->wr_busy_queues--;
3109 }
3110
3111 bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
3112 bfqd->wr_busy_queues);
3113
3114 /*
3115 * Merge queues (that is, let bic redirect its requests to new_bfqq)
3116 */
3117 bic_set_bfqq(bic, new_bfqq, true);
3118 bfq_mark_bfqq_coop(new_bfqq);
3119 /*
3120 * new_bfqq now belongs to at least two bics (it is a shared queue):
3121 * set new_bfqq->bic to NULL. bfqq either:
3122 * - does not belong to any bic any more, and hence bfqq->bic must
3123 * be set to NULL, or
3124 * - is a queue whose owning bics have already been redirected to a
3125 * different queue, hence the queue is destined to not belong to
3126 * any bic soon and bfqq->bic is already NULL (therefore the next
3127 * assignment causes no harm).
3128 */
3129 new_bfqq->bic = NULL;
3130 /*
3131 * If the queue is shared, the pid is the pid of one of the associated
3132 * processes. Which pid depends on the exact sequence of merge events
3133 * the queue underwent. So printing such a pid is useless and confusing
3134 * because it reports a random pid between those of the associated
3135 * processes.
3136 * We mark such a queue with a pid -1, and then print SHARED instead of
3137 * a pid in logging messages.
3138 */
3139 new_bfqq->pid = -1;
3140 bfqq->bic = NULL;
3141
3142 bfq_reassign_last_bfqq(bfqq, new_bfqq);
3143
3144 bfq_release_process_ref(bfqd, bfqq);
3145}
3146
3147static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
3148 struct bio *bio)
3149{
3150 struct bfq_data *bfqd = q->elevator->elevator_data;
3151 bool is_sync = op_is_sync(bio->bi_opf);
3152 struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
3153
3154 /*
3155 * Disallow merge of a sync bio into an async request.
3156 */
3157 if (is_sync && !rq_is_sync(rq))
3158 return false;
3159
3160 /*
3161 * Lookup the bfqq that this bio will be queued with. Allow
3162 * merge only if rq is queued there.
3163 */
3164 if (!bfqq)
3165 return false;
3166
3167 /*
3168 * We take advantage of this function to perform an early merge
3169 * of the queues of possible cooperating processes.
3170 */
3171 new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false, bfqd->bio_bic);
3172 if (new_bfqq) {
3173 /*
3174 * bic still points to bfqq, then it has not yet been
3175 * redirected to some other bfq_queue, and a queue
3176 * merge between bfqq and new_bfqq can be safely
3177 * fulfilled, i.e., bic can be redirected to new_bfqq
3178 * and bfqq can be put.
3179 */
3180 bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
3181 new_bfqq);
3182 /*
3183 * If we get here, bio will be queued into new_queue,
3184 * so use new_bfqq to decide whether bio and rq can be
3185 * merged.
3186 */
3187 bfqq = new_bfqq;
3188
3189 /*
3190 * Change also bqfd->bio_bfqq, as
3191 * bfqd->bio_bic now points to new_bfqq, and
3192 * this function may be invoked again (and then may
3193 * use again bqfd->bio_bfqq).
3194 */
3195 bfqd->bio_bfqq = bfqq;
3196 }
3197
3198 return bfqq == RQ_BFQQ(rq);
3199}
3200
3201/*
3202 * Set the maximum time for the in-service queue to consume its
3203 * budget. This prevents seeky processes from lowering the throughput.
3204 * In practice, a time-slice service scheme is used with seeky
3205 * processes.
3206 */
3207static void bfq_set_budget_timeout(struct bfq_data *bfqd,
3208 struct bfq_queue *bfqq)
3209{
3210 unsigned int timeout_coeff;
3211
3212 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
3213 timeout_coeff = 1;
3214 else
3215 timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
3216
3217 bfqd->last_budget_start = ktime_get();
3218
3219 bfqq->budget_timeout = jiffies +
3220 bfqd->bfq_timeout * timeout_coeff;
3221}
3222
3223static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
3224 struct bfq_queue *bfqq)
3225{
3226 if (bfqq) {
3227 bfq_clear_bfqq_fifo_expire(bfqq);
3228
3229 bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
3230
3231 if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
3232 bfqq->wr_coeff > 1 &&
3233 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
3234 time_is_before_jiffies(bfqq->budget_timeout)) {
3235 /*
3236 * For soft real-time queues, move the start
3237 * of the weight-raising period forward by the
3238 * time the queue has not received any
3239 * service. Otherwise, a relatively long
3240 * service delay is likely to cause the
3241 * weight-raising period of the queue to end,
3242 * because of the short duration of the
3243 * weight-raising period of a soft real-time
3244 * queue. It is worth noting that this move
3245 * is not so dangerous for the other queues,
3246 * because soft real-time queues are not
3247 * greedy.
3248 *
3249 * To not add a further variable, we use the
3250 * overloaded field budget_timeout to
3251 * determine for how long the queue has not
3252 * received service, i.e., how much time has
3253 * elapsed since the queue expired. However,
3254 * this is a little imprecise, because
3255 * budget_timeout is set to jiffies if bfqq
3256 * not only expires, but also remains with no
3257 * request.
3258 */
3259 if (time_after(bfqq->budget_timeout,
3260 bfqq->last_wr_start_finish))
3261 bfqq->last_wr_start_finish +=
3262 jiffies - bfqq->budget_timeout;
3263 else
3264 bfqq->last_wr_start_finish = jiffies;
3265 }
3266
3267 bfq_set_budget_timeout(bfqd, bfqq);
3268 bfq_log_bfqq(bfqd, bfqq,
3269 "set_in_service_queue, cur-budget = %d",
3270 bfqq->entity.budget);
3271 }
3272
3273 bfqd->in_service_queue = bfqq;
3274 bfqd->in_serv_last_pos = 0;
3275}
3276
3277/*
3278 * Get and set a new queue for service.
3279 */
3280static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
3281{
3282 struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
3283
3284 __bfq_set_in_service_queue(bfqd, bfqq);
3285 return bfqq;
3286}
3287
3288static void bfq_arm_slice_timer(struct bfq_data *bfqd)
3289{
3290 struct bfq_queue *bfqq = bfqd->in_service_queue;
3291 u32 sl;
3292
3293 bfq_mark_bfqq_wait_request(bfqq);
3294
3295 /*
3296 * We don't want to idle for seeks, but we do want to allow
3297 * fair distribution of slice time for a process doing back-to-back
3298 * seeks. So allow a little bit of time for him to submit a new rq.
3299 */
3300 sl = bfqd->bfq_slice_idle;
3301 /*
3302 * Unless the queue is being weight-raised or the scenario is
3303 * asymmetric, grant only minimum idle time if the queue
3304 * is seeky. A long idling is preserved for a weight-raised
3305 * queue, or, more in general, in an asymmetric scenario,
3306 * because a long idling is needed for guaranteeing to a queue
3307 * its reserved share of the throughput (in particular, it is
3308 * needed if the queue has a higher weight than some other
3309 * queue).
3310 */
3311 if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
3312 !bfq_asymmetric_scenario(bfqd, bfqq))
3313 sl = min_t(u64, sl, BFQ_MIN_TT);
3314 else if (bfqq->wr_coeff > 1)
3315 sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC);
3316
3317 bfqd->last_idling_start = ktime_get();
3318 bfqd->last_idling_start_jiffies = jiffies;
3319
3320 hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
3321 HRTIMER_MODE_REL);
3322 bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
3323}
3324
3325/*
3326 * In autotuning mode, max_budget is dynamically recomputed as the
3327 * amount of sectors transferred in timeout at the estimated peak
3328 * rate. This enables BFQ to utilize a full timeslice with a full
3329 * budget, even if the in-service queue is served at peak rate. And
3330 * this maximises throughput with sequential workloads.
3331 */
3332static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
3333{
3334 return (u64)bfqd->peak_rate * USEC_PER_MSEC *
3335 jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
3336}
3337
3338/*
3339 * Update parameters related to throughput and responsiveness, as a
3340 * function of the estimated peak rate. See comments on
3341 * bfq_calc_max_budget(), and on the ref_wr_duration array.
3342 */
3343static void update_thr_responsiveness_params(struct bfq_data *bfqd)
3344{
3345 if (bfqd->bfq_user_max_budget == 0) {
3346 bfqd->bfq_max_budget =
3347 bfq_calc_max_budget(bfqd);
3348 bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget);
3349 }
3350}
3351
3352static void bfq_reset_rate_computation(struct bfq_data *bfqd,
3353 struct request *rq)
3354{
3355 if (rq != NULL) { /* new rq dispatch now, reset accordingly */
3356 bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
3357 bfqd->peak_rate_samples = 1;
3358 bfqd->sequential_samples = 0;
3359 bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
3360 blk_rq_sectors(rq);
3361 } else /* no new rq dispatched, just reset the number of samples */
3362 bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
3363
3364 bfq_log(bfqd,
3365 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
3366 bfqd->peak_rate_samples, bfqd->sequential_samples,
3367 bfqd->tot_sectors_dispatched);
3368}
3369
3370static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
3371{
3372 u32 rate, weight, divisor;
3373
3374 /*
3375 * For the convergence property to hold (see comments on
3376 * bfq_update_peak_rate()) and for the assessment to be
3377 * reliable, a minimum number of samples must be present, and
3378 * a minimum amount of time must have elapsed. If not so, do
3379 * not compute new rate. Just reset parameters, to get ready
3380 * for a new evaluation attempt.
3381 */
3382 if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
3383 bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
3384 goto reset_computation;
3385
3386 /*
3387 * If a new request completion has occurred after last
3388 * dispatch, then, to approximate the rate at which requests
3389 * have been served by the device, it is more precise to
3390 * extend the observation interval to the last completion.
3391 */
3392 bfqd->delta_from_first =
3393 max_t(u64, bfqd->delta_from_first,
3394 bfqd->last_completion - bfqd->first_dispatch);
3395
3396 /*
3397 * Rate computed in sects/usec, and not sects/nsec, for
3398 * precision issues.
3399 */
3400 rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
3401 div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
3402
3403 /*
3404 * Peak rate not updated if:
3405 * - the percentage of sequential dispatches is below 3/4 of the
3406 * total, and rate is below the current estimated peak rate
3407 * - rate is unreasonably high (> 20M sectors/sec)
3408 */
3409 if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
3410 rate <= bfqd->peak_rate) ||
3411 rate > 20<<BFQ_RATE_SHIFT)
3412 goto reset_computation;
3413
3414 /*
3415 * We have to update the peak rate, at last! To this purpose,
3416 * we use a low-pass filter. We compute the smoothing constant
3417 * of the filter as a function of the 'weight' of the new
3418 * measured rate.
3419 *
3420 * As can be seen in next formulas, we define this weight as a
3421 * quantity proportional to how sequential the workload is,
3422 * and to how long the observation time interval is.
3423 *
3424 * The weight runs from 0 to 8. The maximum value of the
3425 * weight, 8, yields the minimum value for the smoothing
3426 * constant. At this minimum value for the smoothing constant,
3427 * the measured rate contributes for half of the next value of
3428 * the estimated peak rate.
3429 *
3430 * So, the first step is to compute the weight as a function
3431 * of how sequential the workload is. Note that the weight
3432 * cannot reach 9, because bfqd->sequential_samples cannot
3433 * become equal to bfqd->peak_rate_samples, which, in its
3434 * turn, holds true because bfqd->sequential_samples is not
3435 * incremented for the first sample.
3436 */
3437 weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
3438
3439 /*
3440 * Second step: further refine the weight as a function of the
3441 * duration of the observation interval.
3442 */
3443 weight = min_t(u32, 8,
3444 div_u64(weight * bfqd->delta_from_first,
3445 BFQ_RATE_REF_INTERVAL));
3446
3447 /*
3448 * Divisor ranging from 10, for minimum weight, to 2, for
3449 * maximum weight.
3450 */
3451 divisor = 10 - weight;
3452
3453 /*
3454 * Finally, update peak rate:
3455 *
3456 * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
3457 */
3458 bfqd->peak_rate *= divisor-1;
3459 bfqd->peak_rate /= divisor;
3460 rate /= divisor; /* smoothing constant alpha = 1/divisor */
3461
3462 bfqd->peak_rate += rate;
3463
3464 /*
3465 * For a very slow device, bfqd->peak_rate can reach 0 (see
3466 * the minimum representable values reported in the comments
3467 * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
3468 * divisions by zero where bfqd->peak_rate is used as a
3469 * divisor.
3470 */
3471 bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
3472
3473 update_thr_responsiveness_params(bfqd);
3474
3475reset_computation:
3476 bfq_reset_rate_computation(bfqd, rq);
3477}
3478
3479/*
3480 * Update the read/write peak rate (the main quantity used for
3481 * auto-tuning, see update_thr_responsiveness_params()).
3482 *
3483 * It is not trivial to estimate the peak rate (correctly): because of
3484 * the presence of sw and hw queues between the scheduler and the
3485 * device components that finally serve I/O requests, it is hard to
3486 * say exactly when a given dispatched request is served inside the
3487 * device, and for how long. As a consequence, it is hard to know
3488 * precisely at what rate a given set of requests is actually served
3489 * by the device.
3490 *
3491 * On the opposite end, the dispatch time of any request is trivially
3492 * available, and, from this piece of information, the "dispatch rate"
3493 * of requests can be immediately computed. So, the idea in the next
3494 * function is to use what is known, namely request dispatch times
3495 * (plus, when useful, request completion times), to estimate what is
3496 * unknown, namely in-device request service rate.
3497 *
3498 * The main issue is that, because of the above facts, the rate at
3499 * which a certain set of requests is dispatched over a certain time
3500 * interval can vary greatly with respect to the rate at which the
3501 * same requests are then served. But, since the size of any
3502 * intermediate queue is limited, and the service scheme is lossless
3503 * (no request is silently dropped), the following obvious convergence
3504 * property holds: the number of requests dispatched MUST become
3505 * closer and closer to the number of requests completed as the
3506 * observation interval grows. This is the key property used in
3507 * the next function to estimate the peak service rate as a function
3508 * of the observed dispatch rate. The function assumes to be invoked
3509 * on every request dispatch.
3510 */
3511static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
3512{
3513 u64 now_ns = ktime_get_ns();
3514
3515 if (bfqd->peak_rate_samples == 0) { /* first dispatch */
3516 bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
3517 bfqd->peak_rate_samples);
3518 bfq_reset_rate_computation(bfqd, rq);
3519 goto update_last_values; /* will add one sample */
3520 }
3521
3522 /*
3523 * Device idle for very long: the observation interval lasting
3524 * up to this dispatch cannot be a valid observation interval
3525 * for computing a new peak rate (similarly to the late-
3526 * completion event in bfq_completed_request()). Go to
3527 * update_rate_and_reset to have the following three steps
3528 * taken:
3529 * - close the observation interval at the last (previous)
3530 * request dispatch or completion
3531 * - compute rate, if possible, for that observation interval
3532 * - start a new observation interval with this dispatch
3533 */
3534 if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
3535 bfqd->rq_in_driver == 0)
3536 goto update_rate_and_reset;
3537
3538 /* Update sampling information */
3539 bfqd->peak_rate_samples++;
3540
3541 if ((bfqd->rq_in_driver > 0 ||
3542 now_ns - bfqd->last_completion < BFQ_MIN_TT)
3543 && !BFQ_RQ_SEEKY(bfqd, bfqd->last_position, rq))
3544 bfqd->sequential_samples++;
3545
3546 bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
3547
3548 /* Reset max observed rq size every 32 dispatches */
3549 if (likely(bfqd->peak_rate_samples % 32))
3550 bfqd->last_rq_max_size =
3551 max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
3552 else
3553 bfqd->last_rq_max_size = blk_rq_sectors(rq);
3554
3555 bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
3556
3557 /* Target observation interval not yet reached, go on sampling */
3558 if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
3559 goto update_last_values;
3560
3561update_rate_and_reset:
3562 bfq_update_rate_reset(bfqd, rq);
3563update_last_values:
3564 bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
3565 if (RQ_BFQQ(rq) == bfqd->in_service_queue)
3566 bfqd->in_serv_last_pos = bfqd->last_position;
3567 bfqd->last_dispatch = now_ns;
3568}
3569
3570/*
3571 * Remove request from internal lists.
3572 */
3573static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
3574{
3575 struct bfq_queue *bfqq = RQ_BFQQ(rq);
3576
3577 /*
3578 * For consistency, the next instruction should have been
3579 * executed after removing the request from the queue and
3580 * dispatching it. We execute instead this instruction before
3581 * bfq_remove_request() (and hence introduce a temporary
3582 * inconsistency), for efficiency. In fact, should this
3583 * dispatch occur for a non in-service bfqq, this anticipated
3584 * increment prevents two counters related to bfqq->dispatched
3585 * from risking to be, first, uselessly decremented, and then
3586 * incremented again when the (new) value of bfqq->dispatched
3587 * happens to be taken into account.
3588 */
3589 bfqq->dispatched++;
3590 bfq_update_peak_rate(q->elevator->elevator_data, rq);
3591
3592 bfq_remove_request(q, rq);
3593}
3594
3595/*
3596 * There is a case where idling does not have to be performed for
3597 * throughput concerns, but to preserve the throughput share of
3598 * the process associated with bfqq.
3599 *
3600 * To introduce this case, we can note that allowing the drive
3601 * to enqueue more than one request at a time, and hence
3602 * delegating de facto final scheduling decisions to the
3603 * drive's internal scheduler, entails loss of control on the
3604 * actual request service order. In particular, the critical
3605 * situation is when requests from different processes happen
3606 * to be present, at the same time, in the internal queue(s)
3607 * of the drive. In such a situation, the drive, by deciding
3608 * the service order of the internally-queued requests, does
3609 * determine also the actual throughput distribution among
3610 * these processes. But the drive typically has no notion or
3611 * concern about per-process throughput distribution, and
3612 * makes its decisions only on a per-request basis. Therefore,
3613 * the service distribution enforced by the drive's internal
3614 * scheduler is likely to coincide with the desired throughput
3615 * distribution only in a completely symmetric, or favorably
3616 * skewed scenario where:
3617 * (i-a) each of these processes must get the same throughput as
3618 * the others,
3619 * (i-b) in case (i-a) does not hold, it holds that the process
3620 * associated with bfqq must receive a lower or equal
3621 * throughput than any of the other processes;
3622 * (ii) the I/O of each process has the same properties, in
3623 * terms of locality (sequential or random), direction
3624 * (reads or writes), request sizes, greediness
3625 * (from I/O-bound to sporadic), and so on;
3626
3627 * In fact, in such a scenario, the drive tends to treat the requests
3628 * of each process in about the same way as the requests of the
3629 * others, and thus to provide each of these processes with about the
3630 * same throughput. This is exactly the desired throughput
3631 * distribution if (i-a) holds, or, if (i-b) holds instead, this is an
3632 * even more convenient distribution for (the process associated with)
3633 * bfqq.
3634 *
3635 * In contrast, in any asymmetric or unfavorable scenario, device
3636 * idling (I/O-dispatch plugging) is certainly needed to guarantee
3637 * that bfqq receives its assigned fraction of the device throughput
3638 * (see [1] for details).
3639 *
3640 * The problem is that idling may significantly reduce throughput with
3641 * certain combinations of types of I/O and devices. An important
3642 * example is sync random I/O on flash storage with command
3643 * queueing. So, unless bfqq falls in cases where idling also boosts
3644 * throughput, it is important to check conditions (i-a), i(-b) and
3645 * (ii) accurately, so as to avoid idling when not strictly needed for
3646 * service guarantees.
3647 *
3648 * Unfortunately, it is extremely difficult to thoroughly check
3649 * condition (ii). And, in case there are active groups, it becomes
3650 * very difficult to check conditions (i-a) and (i-b) too. In fact,
3651 * if there are active groups, then, for conditions (i-a) or (i-b) to
3652 * become false 'indirectly', it is enough that an active group
3653 * contains more active processes or sub-groups than some other active
3654 * group. More precisely, for conditions (i-a) or (i-b) to become
3655 * false because of such a group, it is not even necessary that the
3656 * group is (still) active: it is sufficient that, even if the group
3657 * has become inactive, some of its descendant processes still have
3658 * some request already dispatched but still waiting for
3659 * completion. In fact, requests have still to be guaranteed their
3660 * share of the throughput even after being dispatched. In this
3661 * respect, it is easy to show that, if a group frequently becomes
3662 * inactive while still having in-flight requests, and if, when this
3663 * happens, the group is not considered in the calculation of whether
3664 * the scenario is asymmetric, then the group may fail to be
3665 * guaranteed its fair share of the throughput (basically because
3666 * idling may not be performed for the descendant processes of the
3667 * group, but it had to be). We address this issue with the following
3668 * bi-modal behavior, implemented in the function
3669 * bfq_asymmetric_scenario().
3670 *
3671 * If there are groups with requests waiting for completion
3672 * (as commented above, some of these groups may even be
3673 * already inactive), then the scenario is tagged as
3674 * asymmetric, conservatively, without checking any of the
3675 * conditions (i-a), (i-b) or (ii). So the device is idled for bfqq.
3676 * This behavior matches also the fact that groups are created
3677 * exactly if controlling I/O is a primary concern (to
3678 * preserve bandwidth and latency guarantees).
3679 *
3680 * On the opposite end, if there are no groups with requests waiting
3681 * for completion, then only conditions (i-a) and (i-b) are actually
3682 * controlled, i.e., provided that conditions (i-a) or (i-b) holds,
3683 * idling is not performed, regardless of whether condition (ii)
3684 * holds. In other words, only if conditions (i-a) and (i-b) do not
3685 * hold, then idling is allowed, and the device tends to be prevented
3686 * from queueing many requests, possibly of several processes. Since
3687 * there are no groups with requests waiting for completion, then, to
3688 * control conditions (i-a) and (i-b) it is enough to check just
3689 * whether all the queues with requests waiting for completion also
3690 * have the same weight.
3691 *
3692 * Not checking condition (ii) evidently exposes bfqq to the
3693 * risk of getting less throughput than its fair share.
3694 * However, for queues with the same weight, a further
3695 * mechanism, preemption, mitigates or even eliminates this
3696 * problem. And it does so without consequences on overall
3697 * throughput. This mechanism and its benefits are explained
3698 * in the next three paragraphs.
3699 *
3700 * Even if a queue, say Q, is expired when it remains idle, Q
3701 * can still preempt the new in-service queue if the next
3702 * request of Q arrives soon (see the comments on
3703 * bfq_bfqq_update_budg_for_activation). If all queues and
3704 * groups have the same weight, this form of preemption,
3705 * combined with the hole-recovery heuristic described in the
3706 * comments on function bfq_bfqq_update_budg_for_activation,
3707 * are enough to preserve a correct bandwidth distribution in
3708 * the mid term, even without idling. In fact, even if not
3709 * idling allows the internal queues of the device to contain
3710 * many requests, and thus to reorder requests, we can rather
3711 * safely assume that the internal scheduler still preserves a
3712 * minimum of mid-term fairness.
3713 *
3714 * More precisely, this preemption-based, idleless approach
3715 * provides fairness in terms of IOPS, and not sectors per
3716 * second. This can be seen with a simple example. Suppose
3717 * that there are two queues with the same weight, but that
3718 * the first queue receives requests of 8 sectors, while the
3719 * second queue receives requests of 1024 sectors. In
3720 * addition, suppose that each of the two queues contains at
3721 * most one request at a time, which implies that each queue
3722 * always remains idle after it is served. Finally, after
3723 * remaining idle, each queue receives very quickly a new
3724 * request. It follows that the two queues are served
3725 * alternatively, preempting each other if needed. This
3726 * implies that, although both queues have the same weight,
3727 * the queue with large requests receives a service that is
3728 * 1024/8 times as high as the service received by the other
3729 * queue.
3730 *
3731 * The motivation for using preemption instead of idling (for
3732 * queues with the same weight) is that, by not idling,
3733 * service guarantees are preserved (completely or at least in
3734 * part) without minimally sacrificing throughput. And, if
3735 * there is no active group, then the primary expectation for
3736 * this device is probably a high throughput.
3737 *
3738 * We are now left only with explaining the two sub-conditions in the
3739 * additional compound condition that is checked below for deciding
3740 * whether the scenario is asymmetric. To explain the first
3741 * sub-condition, we need to add that the function
3742 * bfq_asymmetric_scenario checks the weights of only
3743 * non-weight-raised queues, for efficiency reasons (see comments on
3744 * bfq_weights_tree_add()). Then the fact that bfqq is weight-raised
3745 * is checked explicitly here. More precisely, the compound condition
3746 * below takes into account also the fact that, even if bfqq is being
3747 * weight-raised, the scenario is still symmetric if all queues with
3748 * requests waiting for completion happen to be
3749 * weight-raised. Actually, we should be even more precise here, and
3750 * differentiate between interactive weight raising and soft real-time
3751 * weight raising.
3752 *
3753 * The second sub-condition checked in the compound condition is
3754 * whether there is a fair amount of already in-flight I/O not
3755 * belonging to bfqq. If so, I/O dispatching is to be plugged, for the
3756 * following reason. The drive may decide to serve in-flight
3757 * non-bfqq's I/O requests before bfqq's ones, thereby delaying the
3758 * arrival of new I/O requests for bfqq (recall that bfqq is sync). If
3759 * I/O-dispatching is not plugged, then, while bfqq remains empty, a
3760 * basically uncontrolled amount of I/O from other queues may be
3761 * dispatched too, possibly causing the service of bfqq's I/O to be
3762 * delayed even longer in the drive. This problem gets more and more
3763 * serious as the speed and the queue depth of the drive grow,
3764 * because, as these two quantities grow, the probability to find no
3765 * queue busy but many requests in flight grows too. By contrast,
3766 * plugging I/O dispatching minimizes the delay induced by already
3767 * in-flight I/O, and enables bfqq to recover the bandwidth it may
3768 * lose because of this delay.
3769 *
3770 * As a side note, it is worth considering that the above
3771 * device-idling countermeasures may however fail in the following
3772 * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled
3773 * in a time period during which all symmetry sub-conditions hold, and
3774 * therefore the device is allowed to enqueue many requests, but at
3775 * some later point in time some sub-condition stops to hold, then it
3776 * may become impossible to make requests be served in the desired
3777 * order until all the requests already queued in the device have been
3778 * served. The last sub-condition commented above somewhat mitigates
3779 * this problem for weight-raised queues.
3780 *
3781 * However, as an additional mitigation for this problem, we preserve
3782 * plugging for a special symmetric case that may suddenly turn into
3783 * asymmetric: the case where only bfqq is busy. In this case, not
3784 * expiring bfqq does not cause any harm to any other queues in terms
3785 * of service guarantees. In contrast, it avoids the following unlucky
3786 * sequence of events: (1) bfqq is expired, (2) a new queue with a
3787 * lower weight than bfqq becomes busy (or more queues), (3) the new
3788 * queue is served until a new request arrives for bfqq, (4) when bfqq
3789 * is finally served, there are so many requests of the new queue in
3790 * the drive that the pending requests for bfqq take a lot of time to
3791 * be served. In particular, event (2) may case even already
3792 * dispatched requests of bfqq to be delayed, inside the drive. So, to
3793 * avoid this series of events, the scenario is preventively declared
3794 * as asymmetric also if bfqq is the only busy queues
3795 */
3796static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
3797 struct bfq_queue *bfqq)
3798{
3799 int tot_busy_queues = bfq_tot_busy_queues(bfqd);
3800
3801 /* No point in idling for bfqq if it won't get requests any longer */
3802 if (unlikely(!bfqq_process_refs(bfqq)))
3803 return false;
3804
3805 return (bfqq->wr_coeff > 1 &&
3806 (bfqd->wr_busy_queues <
3807 tot_busy_queues ||
3808 bfqd->rq_in_driver >=
3809 bfqq->dispatched + 4)) ||
3810 bfq_asymmetric_scenario(bfqd, bfqq) ||
3811 tot_busy_queues == 1;
3812}
3813
3814static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3815 enum bfqq_expiration reason)
3816{
3817 /*
3818 * If this bfqq is shared between multiple processes, check
3819 * to make sure that those processes are still issuing I/Os
3820 * within the mean seek distance. If not, it may be time to
3821 * break the queues apart again.
3822 */
3823 if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
3824 bfq_mark_bfqq_split_coop(bfqq);
3825
3826 /*
3827 * Consider queues with a higher finish virtual time than
3828 * bfqq. If idling_needed_for_service_guarantees(bfqq) returns
3829 * true, then bfqq's bandwidth would be violated if an
3830 * uncontrolled amount of I/O from these queues were
3831 * dispatched while bfqq is waiting for its new I/O to
3832 * arrive. This is exactly what may happen if this is a forced
3833 * expiration caused by a preemption attempt, and if bfqq is
3834 * not re-scheduled. To prevent this from happening, re-queue
3835 * bfqq if it needs I/O-dispatch plugging, even if it is
3836 * empty. By doing so, bfqq is granted to be served before the
3837 * above queues (provided that bfqq is of course eligible).
3838 */
3839 if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
3840 !(reason == BFQQE_PREEMPTED &&
3841 idling_needed_for_service_guarantees(bfqd, bfqq))) {
3842 if (bfqq->dispatched == 0)
3843 /*
3844 * Overloading budget_timeout field to store
3845 * the time at which the queue remains with no
3846 * backlog and no outstanding request; used by
3847 * the weight-raising mechanism.
3848 */
3849 bfqq->budget_timeout = jiffies;
3850
3851 bfq_del_bfqq_busy(bfqq, true);
3852 } else {
3853 bfq_requeue_bfqq(bfqd, bfqq, true);
3854 /*
3855 * Resort priority tree of potential close cooperators.
3856 * See comments on bfq_pos_tree_add_move() for the unlikely().
3857 */
3858 if (unlikely(!bfqd->nonrot_with_queueing &&
3859 !RB_EMPTY_ROOT(&bfqq->sort_list)))
3860 bfq_pos_tree_add_move(bfqd, bfqq);
3861 }
3862
3863 /*
3864 * All in-service entities must have been properly deactivated
3865 * or requeued before executing the next function, which
3866 * resets all in-service entities as no more in service. This
3867 * may cause bfqq to be freed. If this happens, the next
3868 * function returns true.
3869 */
3870 return __bfq_bfqd_reset_in_service(bfqd);
3871}
3872
3873/**
3874 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
3875 * @bfqd: device data.
3876 * @bfqq: queue to update.
3877 * @reason: reason for expiration.
3878 *
3879 * Handle the feedback on @bfqq budget at queue expiration.
3880 * See the body for detailed comments.
3881 */
3882static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
3883 struct bfq_queue *bfqq,
3884 enum bfqq_expiration reason)
3885{
3886 struct request *next_rq;
3887 int budget, min_budget;
3888
3889 min_budget = bfq_min_budget(bfqd);
3890
3891 if (bfqq->wr_coeff == 1)
3892 budget = bfqq->max_budget;
3893 else /*
3894 * Use a constant, low budget for weight-raised queues,
3895 * to help achieve a low latency. Keep it slightly higher
3896 * than the minimum possible budget, to cause a little
3897 * bit fewer expirations.
3898 */
3899 budget = 2 * min_budget;
3900
3901 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
3902 bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
3903 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
3904 budget, bfq_min_budget(bfqd));
3905 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
3906 bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
3907
3908 if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
3909 switch (reason) {
3910 /*
3911 * Caveat: in all the following cases we trade latency
3912 * for throughput.
3913 */
3914 case BFQQE_TOO_IDLE:
3915 /*
3916 * This is the only case where we may reduce
3917 * the budget: if there is no request of the
3918 * process still waiting for completion, then
3919 * we assume (tentatively) that the timer has
3920 * expired because the batch of requests of
3921 * the process could have been served with a
3922 * smaller budget. Hence, betting that
3923 * process will behave in the same way when it
3924 * becomes backlogged again, we reduce its
3925 * next budget. As long as we guess right,
3926 * this budget cut reduces the latency
3927 * experienced by the process.
3928 *
3929 * However, if there are still outstanding
3930 * requests, then the process may have not yet
3931 * issued its next request just because it is
3932 * still waiting for the completion of some of
3933 * the still outstanding ones. So in this
3934 * subcase we do not reduce its budget, on the
3935 * contrary we increase it to possibly boost
3936 * the throughput, as discussed in the
3937 * comments to the BUDGET_TIMEOUT case.
3938 */
3939 if (bfqq->dispatched > 0) /* still outstanding reqs */
3940 budget = min(budget * 2, bfqd->bfq_max_budget);
3941 else {
3942 if (budget > 5 * min_budget)
3943 budget -= 4 * min_budget;
3944 else
3945 budget = min_budget;
3946 }
3947 break;
3948 case BFQQE_BUDGET_TIMEOUT:
3949 /*
3950 * We double the budget here because it gives
3951 * the chance to boost the throughput if this
3952 * is not a seeky process (and has bumped into
3953 * this timeout because of, e.g., ZBR).
3954 */
3955 budget = min(budget * 2, bfqd->bfq_max_budget);
3956 break;
3957 case BFQQE_BUDGET_EXHAUSTED:
3958 /*
3959 * The process still has backlog, and did not
3960 * let either the budget timeout or the disk
3961 * idling timeout expire. Hence it is not
3962 * seeky, has a short thinktime and may be
3963 * happy with a higher budget too. So
3964 * definitely increase the budget of this good
3965 * candidate to boost the disk throughput.
3966 */
3967 budget = min(budget * 4, bfqd->bfq_max_budget);
3968 break;
3969 case BFQQE_NO_MORE_REQUESTS:
3970 /*
3971 * For queues that expire for this reason, it
3972 * is particularly important to keep the
3973 * budget close to the actual service they
3974 * need. Doing so reduces the timestamp
3975 * misalignment problem described in the
3976 * comments in the body of
3977 * __bfq_activate_entity. In fact, suppose
3978 * that a queue systematically expires for
3979 * BFQQE_NO_MORE_REQUESTS and presents a
3980 * new request in time to enjoy timestamp
3981 * back-shifting. The larger the budget of the
3982 * queue is with respect to the service the
3983 * queue actually requests in each service
3984 * slot, the more times the queue can be
3985 * reactivated with the same virtual finish
3986 * time. It follows that, even if this finish
3987 * time is pushed to the system virtual time
3988 * to reduce the consequent timestamp
3989 * misalignment, the queue unjustly enjoys for
3990 * many re-activations a lower finish time
3991 * than all newly activated queues.
3992 *
3993 * The service needed by bfqq is measured
3994 * quite precisely by bfqq->entity.service.
3995 * Since bfqq does not enjoy device idling,
3996 * bfqq->entity.service is equal to the number
3997 * of sectors that the process associated with
3998 * bfqq requested to read/write before waiting
3999 * for request completions, or blocking for
4000 * other reasons.
4001 */
4002 budget = max_t(int, bfqq->entity.service, min_budget);
4003 break;
4004 default:
4005 return;
4006 }
4007 } else if (!bfq_bfqq_sync(bfqq)) {
4008 /*
4009 * Async queues get always the maximum possible
4010 * budget, as for them we do not care about latency
4011 * (in addition, their ability to dispatch is limited
4012 * by the charging factor).
4013 */
4014 budget = bfqd->bfq_max_budget;
4015 }
4016
4017 bfqq->max_budget = budget;
4018
4019 if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
4020 !bfqd->bfq_user_max_budget)
4021 bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
4022
4023 /*
4024 * If there is still backlog, then assign a new budget, making
4025 * sure that it is large enough for the next request. Since
4026 * the finish time of bfqq must be kept in sync with the
4027 * budget, be sure to call __bfq_bfqq_expire() *after* this
4028 * update.
4029 *
4030 * If there is no backlog, then no need to update the budget;
4031 * it will be updated on the arrival of a new request.
4032 */
4033 next_rq = bfqq->next_rq;
4034 if (next_rq)
4035 bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
4036 bfq_serv_to_charge(next_rq, bfqq));
4037
4038 bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
4039 next_rq ? blk_rq_sectors(next_rq) : 0,
4040 bfqq->entity.budget);
4041}
4042
4043/*
4044 * Return true if the process associated with bfqq is "slow". The slow
4045 * flag is used, in addition to the budget timeout, to reduce the
4046 * amount of service provided to seeky processes, and thus reduce
4047 * their chances to lower the throughput. More details in the comments
4048 * on the function bfq_bfqq_expire().
4049 *
4050 * An important observation is in order: as discussed in the comments
4051 * on the function bfq_update_peak_rate(), with devices with internal
4052 * queues, it is hard if ever possible to know when and for how long
4053 * an I/O request is processed by the device (apart from the trivial
4054 * I/O pattern where a new request is dispatched only after the
4055 * previous one has been completed). This makes it hard to evaluate
4056 * the real rate at which the I/O requests of each bfq_queue are
4057 * served. In fact, for an I/O scheduler like BFQ, serving a
4058 * bfq_queue means just dispatching its requests during its service
4059 * slot (i.e., until the budget of the queue is exhausted, or the
4060 * queue remains idle, or, finally, a timeout fires). But, during the
4061 * service slot of a bfq_queue, around 100 ms at most, the device may
4062 * be even still processing requests of bfq_queues served in previous
4063 * service slots. On the opposite end, the requests of the in-service
4064 * bfq_queue may be completed after the service slot of the queue
4065 * finishes.
4066 *
4067 * Anyway, unless more sophisticated solutions are used
4068 * (where possible), the sum of the sizes of the requests dispatched
4069 * during the service slot of a bfq_queue is probably the only
4070 * approximation available for the service received by the bfq_queue
4071 * during its service slot. And this sum is the quantity used in this
4072 * function to evaluate the I/O speed of a process.
4073 */
4074static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4075 bool compensate, enum bfqq_expiration reason,
4076 unsigned long *delta_ms)
4077{
4078 ktime_t delta_ktime;
4079 u32 delta_usecs;
4080 bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
4081
4082 if (!bfq_bfqq_sync(bfqq))
4083 return false;
4084
4085 if (compensate)
4086 delta_ktime = bfqd->last_idling_start;
4087 else
4088 delta_ktime = ktime_get();
4089 delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
4090 delta_usecs = ktime_to_us(delta_ktime);
4091
4092 /* don't use too short time intervals */
4093 if (delta_usecs < 1000) {
4094 if (blk_queue_nonrot(bfqd->queue))
4095 /*
4096 * give same worst-case guarantees as idling
4097 * for seeky
4098 */
4099 *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
4100 else /* charge at least one seek */
4101 *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
4102
4103 return slow;
4104 }
4105
4106 *delta_ms = delta_usecs / USEC_PER_MSEC;
4107
4108 /*
4109 * Use only long (> 20ms) intervals to filter out excessive
4110 * spikes in service rate estimation.
4111 */
4112 if (delta_usecs > 20000) {
4113 /*
4114 * Caveat for rotational devices: processes doing I/O
4115 * in the slower disk zones tend to be slow(er) even
4116 * if not seeky. In this respect, the estimated peak
4117 * rate is likely to be an average over the disk
4118 * surface. Accordingly, to not be too harsh with
4119 * unlucky processes, a process is deemed slow only if
4120 * its rate has been lower than half of the estimated
4121 * peak rate.
4122 */
4123 slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
4124 }
4125
4126 bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
4127
4128 return slow;
4129}
4130
4131/*
4132 * To be deemed as soft real-time, an application must meet two
4133 * requirements. First, the application must not require an average
4134 * bandwidth higher than the approximate bandwidth required to playback or
4135 * record a compressed high-definition video.
4136 * The next function is invoked on the completion of the last request of a
4137 * batch, to compute the next-start time instant, soft_rt_next_start, such
4138 * that, if the next request of the application does not arrive before
4139 * soft_rt_next_start, then the above requirement on the bandwidth is met.
4140 *
4141 * The second requirement is that the request pattern of the application is
4142 * isochronous, i.e., that, after issuing a request or a batch of requests,
4143 * the application stops issuing new requests until all its pending requests
4144 * have been completed. After that, the application may issue a new batch,
4145 * and so on.
4146 * For this reason the next function is invoked to compute
4147 * soft_rt_next_start only for applications that meet this requirement,
4148 * whereas soft_rt_next_start is set to infinity for applications that do
4149 * not.
4150 *
4151 * Unfortunately, even a greedy (i.e., I/O-bound) application may
4152 * happen to meet, occasionally or systematically, both the above
4153 * bandwidth and isochrony requirements. This may happen at least in
4154 * the following circumstances. First, if the CPU load is high. The
4155 * application may stop issuing requests while the CPUs are busy
4156 * serving other processes, then restart, then stop again for a while,
4157 * and so on. The other circumstances are related to the storage
4158 * device: the storage device is highly loaded or reaches a low-enough
4159 * throughput with the I/O of the application (e.g., because the I/O
4160 * is random and/or the device is slow). In all these cases, the
4161 * I/O of the application may be simply slowed down enough to meet
4162 * the bandwidth and isochrony requirements. To reduce the probability
4163 * that greedy applications are deemed as soft real-time in these
4164 * corner cases, a further rule is used in the computation of
4165 * soft_rt_next_start: the return value of this function is forced to
4166 * be higher than the maximum between the following two quantities.
4167 *
4168 * (a) Current time plus: (1) the maximum time for which the arrival
4169 * of a request is waited for when a sync queue becomes idle,
4170 * namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We
4171 * postpone for a moment the reason for adding a few extra
4172 * jiffies; we get back to it after next item (b). Lower-bounding
4173 * the return value of this function with the current time plus
4174 * bfqd->bfq_slice_idle tends to filter out greedy applications,
4175 * because the latter issue their next request as soon as possible
4176 * after the last one has been completed. In contrast, a soft
4177 * real-time application spends some time processing data, after a
4178 * batch of its requests has been completed.
4179 *
4180 * (b) Current value of bfqq->soft_rt_next_start. As pointed out
4181 * above, greedy applications may happen to meet both the
4182 * bandwidth and isochrony requirements under heavy CPU or
4183 * storage-device load. In more detail, in these scenarios, these
4184 * applications happen, only for limited time periods, to do I/O
4185 * slowly enough to meet all the requirements described so far,
4186 * including the filtering in above item (a). These slow-speed
4187 * time intervals are usually interspersed between other time
4188 * intervals during which these applications do I/O at a very high
4189 * speed. Fortunately, exactly because of the high speed of the
4190 * I/O in the high-speed intervals, the values returned by this
4191 * function happen to be so high, near the end of any such
4192 * high-speed interval, to be likely to fall *after* the end of
4193 * the low-speed time interval that follows. These high values are
4194 * stored in bfqq->soft_rt_next_start after each invocation of
4195 * this function. As a consequence, if the last value of
4196 * bfqq->soft_rt_next_start is constantly used to lower-bound the
4197 * next value that this function may return, then, from the very
4198 * beginning of a low-speed interval, bfqq->soft_rt_next_start is
4199 * likely to be constantly kept so high that any I/O request
4200 * issued during the low-speed interval is considered as arriving
4201 * to soon for the application to be deemed as soft
4202 * real-time. Then, in the high-speed interval that follows, the
4203 * application will not be deemed as soft real-time, just because
4204 * it will do I/O at a high speed. And so on.
4205 *
4206 * Getting back to the filtering in item (a), in the following two
4207 * cases this filtering might be easily passed by a greedy
4208 * application, if the reference quantity was just
4209 * bfqd->bfq_slice_idle:
4210 * 1) HZ is so low that the duration of a jiffy is comparable to or
4211 * higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
4212 * devices with HZ=100. The time granularity may be so coarse
4213 * that the approximation, in jiffies, of bfqd->bfq_slice_idle
4214 * is rather lower than the exact value.
4215 * 2) jiffies, instead of increasing at a constant rate, may stop increasing
4216 * for a while, then suddenly 'jump' by several units to recover the lost
4217 * increments. This seems to happen, e.g., inside virtual machines.
4218 * To address this issue, in the filtering in (a) we do not use as a
4219 * reference time interval just bfqd->bfq_slice_idle, but
4220 * bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the
4221 * minimum number of jiffies for which the filter seems to be quite
4222 * precise also in embedded systems and KVM/QEMU virtual machines.
4223 */
4224static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
4225 struct bfq_queue *bfqq)
4226{
4227 return max3(bfqq->soft_rt_next_start,
4228 bfqq->last_idle_bklogged +
4229 HZ * bfqq->service_from_backlogged /
4230 bfqd->bfq_wr_max_softrt_rate,
4231 jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
4232}
4233
4234/**
4235 * bfq_bfqq_expire - expire a queue.
4236 * @bfqd: device owning the queue.
4237 * @bfqq: the queue to expire.
4238 * @compensate: if true, compensate for the time spent idling.
4239 * @reason: the reason causing the expiration.
4240 *
4241 * If the process associated with bfqq does slow I/O (e.g., because it
4242 * issues random requests), we charge bfqq with the time it has been
4243 * in service instead of the service it has received (see
4244 * bfq_bfqq_charge_time for details on how this goal is achieved). As
4245 * a consequence, bfqq will typically get higher timestamps upon
4246 * reactivation, and hence it will be rescheduled as if it had
4247 * received more service than what it has actually received. In the
4248 * end, bfqq receives less service in proportion to how slowly its
4249 * associated process consumes its budgets (and hence how seriously it
4250 * tends to lower the throughput). In addition, this time-charging
4251 * strategy guarantees time fairness among slow processes. In
4252 * contrast, if the process associated with bfqq is not slow, we
4253 * charge bfqq exactly with the service it has received.
4254 *
4255 * Charging time to the first type of queues and the exact service to
4256 * the other has the effect of using the WF2Q+ policy to schedule the
4257 * former on a timeslice basis, without violating service domain
4258 * guarantees among the latter.
4259 */
4260void bfq_bfqq_expire(struct bfq_data *bfqd,
4261 struct bfq_queue *bfqq,
4262 bool compensate,
4263 enum bfqq_expiration reason)
4264{
4265 bool slow;
4266 unsigned long delta = 0;
4267 struct bfq_entity *entity = &bfqq->entity;
4268
4269 /*
4270 * Check whether the process is slow (see bfq_bfqq_is_slow).
4271 */
4272 slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
4273
4274 /*
4275 * As above explained, charge slow (typically seeky) and
4276 * timed-out queues with the time and not the service
4277 * received, to favor sequential workloads.
4278 *
4279 * Processes doing I/O in the slower disk zones will tend to
4280 * be slow(er) even if not seeky. Therefore, since the
4281 * estimated peak rate is actually an average over the disk
4282 * surface, these processes may timeout just for bad luck. To
4283 * avoid punishing them, do not charge time to processes that
4284 * succeeded in consuming at least 2/3 of their budget. This
4285 * allows BFQ to preserve enough elasticity to still perform
4286 * bandwidth, and not time, distribution with little unlucky
4287 * or quasi-sequential processes.
4288 */
4289 if (bfqq->wr_coeff == 1 &&
4290 (slow ||
4291 (reason == BFQQE_BUDGET_TIMEOUT &&
4292 bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
4293 bfq_bfqq_charge_time(bfqd, bfqq, delta);
4294
4295 if (bfqd->low_latency && bfqq->wr_coeff == 1)
4296 bfqq->last_wr_start_finish = jiffies;
4297
4298 if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
4299 RB_EMPTY_ROOT(&bfqq->sort_list)) {
4300 /*
4301 * If we get here, and there are no outstanding
4302 * requests, then the request pattern is isochronous
4303 * (see the comments on the function
4304 * bfq_bfqq_softrt_next_start()). Therefore we can
4305 * compute soft_rt_next_start.
4306 *
4307 * If, instead, the queue still has outstanding
4308 * requests, then we have to wait for the completion
4309 * of all the outstanding requests to discover whether
4310 * the request pattern is actually isochronous.
4311 */
4312 if (bfqq->dispatched == 0)
4313 bfqq->soft_rt_next_start =
4314 bfq_bfqq_softrt_next_start(bfqd, bfqq);
4315 else if (bfqq->dispatched > 0) {
4316 /*
4317 * Schedule an update of soft_rt_next_start to when
4318 * the task may be discovered to be isochronous.
4319 */
4320 bfq_mark_bfqq_softrt_update(bfqq);
4321 }
4322 }
4323
4324 bfq_log_bfqq(bfqd, bfqq,
4325 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
4326 slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
4327
4328 /*
4329 * bfqq expired, so no total service time needs to be computed
4330 * any longer: reset state machine for measuring total service
4331 * times.
4332 */
4333 bfqd->rqs_injected = bfqd->wait_dispatch = false;
4334 bfqd->waited_rq = NULL;
4335
4336 /*
4337 * Increase, decrease or leave budget unchanged according to
4338 * reason.
4339 */
4340 __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
4341 if (__bfq_bfqq_expire(bfqd, bfqq, reason))
4342 /* bfqq is gone, no more actions on it */
4343 return;
4344
4345 /* mark bfqq as waiting a request only if a bic still points to it */
4346 if (!bfq_bfqq_busy(bfqq) &&
4347 reason != BFQQE_BUDGET_TIMEOUT &&
4348 reason != BFQQE_BUDGET_EXHAUSTED) {
4349 bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
4350 /*
4351 * Not setting service to 0, because, if the next rq
4352 * arrives in time, the queue will go on receiving
4353 * service with this same budget (as if it never expired)
4354 */
4355 } else
4356 entity->service = 0;
4357
4358 /*
4359 * Reset the received-service counter for every parent entity.
4360 * Differently from what happens with bfqq->entity.service,
4361 * the resetting of this counter never needs to be postponed
4362 * for parent entities. In fact, in case bfqq may have a
4363 * chance to go on being served using the last, partially
4364 * consumed budget, bfqq->entity.service needs to be kept,
4365 * because if bfqq then actually goes on being served using
4366 * the same budget, the last value of bfqq->entity.service is
4367 * needed to properly decrement bfqq->entity.budget by the
4368 * portion already consumed. In contrast, it is not necessary
4369 * to keep entity->service for parent entities too, because
4370 * the bubble up of the new value of bfqq->entity.budget will
4371 * make sure that the budgets of parent entities are correct,
4372 * even in case bfqq and thus parent entities go on receiving
4373 * service with the same budget.
4374 */
4375 entity = entity->parent;
4376 for_each_entity(entity)
4377 entity->service = 0;
4378}
4379
4380/*
4381 * Budget timeout is not implemented through a dedicated timer, but
4382 * just checked on request arrivals and completions, as well as on
4383 * idle timer expirations.
4384 */
4385static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
4386{
4387 return time_is_before_eq_jiffies(bfqq->budget_timeout);
4388}
4389
4390/*
4391 * If we expire a queue that is actively waiting (i.e., with the
4392 * device idled) for the arrival of a new request, then we may incur
4393 * the timestamp misalignment problem described in the body of the
4394 * function __bfq_activate_entity. Hence we return true only if this
4395 * condition does not hold, or if the queue is slow enough to deserve
4396 * only to be kicked off for preserving a high throughput.
4397 */
4398static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
4399{
4400 bfq_log_bfqq(bfqq->bfqd, bfqq,
4401 "may_budget_timeout: wait_request %d left %d timeout %d",
4402 bfq_bfqq_wait_request(bfqq),
4403 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3,
4404 bfq_bfqq_budget_timeout(bfqq));
4405
4406 return (!bfq_bfqq_wait_request(bfqq) ||
4407 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3)
4408 &&
4409 bfq_bfqq_budget_timeout(bfqq);
4410}
4411
4412static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
4413 struct bfq_queue *bfqq)
4414{
4415 bool rot_without_queueing =
4416 !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
4417 bfqq_sequential_and_IO_bound,
4418 idling_boosts_thr;
4419
4420 /* No point in idling for bfqq if it won't get requests any longer */
4421 if (unlikely(!bfqq_process_refs(bfqq)))
4422 return false;
4423
4424 bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
4425 bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
4426
4427 /*
4428 * The next variable takes into account the cases where idling
4429 * boosts the throughput.
4430 *
4431 * The value of the variable is computed considering, first, that
4432 * idling is virtually always beneficial for the throughput if:
4433 * (a) the device is not NCQ-capable and rotational, or
4434 * (b) regardless of the presence of NCQ, the device is rotational and
4435 * the request pattern for bfqq is I/O-bound and sequential, or
4436 * (c) regardless of whether it is rotational, the device is
4437 * not NCQ-capable and the request pattern for bfqq is
4438 * I/O-bound and sequential.
4439 *
4440 * Secondly, and in contrast to the above item (b), idling an
4441 * NCQ-capable flash-based device would not boost the
4442 * throughput even with sequential I/O; rather it would lower
4443 * the throughput in proportion to how fast the device
4444 * is. Accordingly, the next variable is true if any of the
4445 * above conditions (a), (b) or (c) is true, and, in
4446 * particular, happens to be false if bfqd is an NCQ-capable
4447 * flash-based device.
4448 */
4449 idling_boosts_thr = rot_without_queueing ||
4450 ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
4451 bfqq_sequential_and_IO_bound);
4452
4453 /*
4454 * The return value of this function is equal to that of
4455 * idling_boosts_thr, unless a special case holds. In this
4456 * special case, described below, idling may cause problems to
4457 * weight-raised queues.
4458 *
4459 * When the request pool is saturated (e.g., in the presence
4460 * of write hogs), if the processes associated with
4461 * non-weight-raised queues ask for requests at a lower rate,
4462 * then processes associated with weight-raised queues have a
4463 * higher probability to get a request from the pool
4464 * immediately (or at least soon) when they need one. Thus
4465 * they have a higher probability to actually get a fraction
4466 * of the device throughput proportional to their high
4467 * weight. This is especially true with NCQ-capable drives,
4468 * which enqueue several requests in advance, and further
4469 * reorder internally-queued requests.
4470 *
4471 * For this reason, we force to false the return value if
4472 * there are weight-raised busy queues. In this case, and if
4473 * bfqq is not weight-raised, this guarantees that the device
4474 * is not idled for bfqq (if, instead, bfqq is weight-raised,
4475 * then idling will be guaranteed by another variable, see
4476 * below). Combined with the timestamping rules of BFQ (see
4477 * [1] for details), this behavior causes bfqq, and hence any
4478 * sync non-weight-raised queue, to get a lower number of
4479 * requests served, and thus to ask for a lower number of
4480 * requests from the request pool, before the busy
4481 * weight-raised queues get served again. This often mitigates
4482 * starvation problems in the presence of heavy write
4483 * workloads and NCQ, thereby guaranteeing a higher
4484 * application and system responsiveness in these hostile
4485 * scenarios.
4486 */
4487 return idling_boosts_thr &&
4488 bfqd->wr_busy_queues == 0;
4489}
4490
4491/*
4492 * For a queue that becomes empty, device idling is allowed only if
4493 * this function returns true for that queue. As a consequence, since
4494 * device idling plays a critical role for both throughput boosting
4495 * and service guarantees, the return value of this function plays a
4496 * critical role as well.
4497 *
4498 * In a nutshell, this function returns true only if idling is
4499 * beneficial for throughput or, even if detrimental for throughput,
4500 * idling is however necessary to preserve service guarantees (low
4501 * latency, desired throughput distribution, ...). In particular, on
4502 * NCQ-capable devices, this function tries to return false, so as to
4503 * help keep the drives' internal queues full, whenever this helps the
4504 * device boost the throughput without causing any service-guarantee
4505 * issue.
4506 *
4507 * Most of the issues taken into account to get the return value of
4508 * this function are not trivial. We discuss these issues in the two
4509 * functions providing the main pieces of information needed by this
4510 * function.
4511 */
4512static bool bfq_better_to_idle(struct bfq_queue *bfqq)
4513{
4514 struct bfq_data *bfqd = bfqq->bfqd;
4515 bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar;
4516
4517 /* No point in idling for bfqq if it won't get requests any longer */
4518 if (unlikely(!bfqq_process_refs(bfqq)))
4519 return false;
4520
4521 if (unlikely(bfqd->strict_guarantees))
4522 return true;
4523
4524 /*
4525 * Idling is performed only if slice_idle > 0. In addition, we
4526 * do not idle if
4527 * (a) bfqq is async
4528 * (b) bfqq is in the idle io prio class: in this case we do
4529 * not idle because we want to minimize the bandwidth that
4530 * queues in this class can steal to higher-priority queues
4531 */
4532 if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
4533 bfq_class_idle(bfqq))
4534 return false;
4535
4536 idling_boosts_thr_with_no_issue =
4537 idling_boosts_thr_without_issues(bfqd, bfqq);
4538
4539 idling_needed_for_service_guar =
4540 idling_needed_for_service_guarantees(bfqd, bfqq);
4541
4542 /*
4543 * We have now the two components we need to compute the
4544 * return value of the function, which is true only if idling
4545 * either boosts the throughput (without issues), or is
4546 * necessary to preserve service guarantees.
4547 */
4548 return idling_boosts_thr_with_no_issue ||
4549 idling_needed_for_service_guar;
4550}
4551
4552/*
4553 * If the in-service queue is empty but the function bfq_better_to_idle
4554 * returns true, then:
4555 * 1) the queue must remain in service and cannot be expired, and
4556 * 2) the device must be idled to wait for the possible arrival of a new
4557 * request for the queue.
4558 * See the comments on the function bfq_better_to_idle for the reasons
4559 * why performing device idling is the best choice to boost the throughput
4560 * and preserve service guarantees when bfq_better_to_idle itself
4561 * returns true.
4562 */
4563static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
4564{
4565 return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq);
4566}
4567
4568/*
4569 * This function chooses the queue from which to pick the next extra
4570 * I/O request to inject, if it finds a compatible queue. See the
4571 * comments on bfq_update_inject_limit() for details on the injection
4572 * mechanism, and for the definitions of the quantities mentioned
4573 * below.
4574 */
4575static struct bfq_queue *
4576bfq_choose_bfqq_for_injection(struct bfq_data *bfqd)
4577{
4578 struct bfq_queue *bfqq, *in_serv_bfqq = bfqd->in_service_queue;
4579 unsigned int limit = in_serv_bfqq->inject_limit;
4580 /*
4581 * If
4582 * - bfqq is not weight-raised and therefore does not carry
4583 * time-critical I/O,
4584 * or
4585 * - regardless of whether bfqq is weight-raised, bfqq has
4586 * however a long think time, during which it can absorb the
4587 * effect of an appropriate number of extra I/O requests
4588 * from other queues (see bfq_update_inject_limit for
4589 * details on the computation of this number);
4590 * then injection can be performed without restrictions.
4591 */
4592 bool in_serv_always_inject = in_serv_bfqq->wr_coeff == 1 ||
4593 !bfq_bfqq_has_short_ttime(in_serv_bfqq);
4594
4595 /*
4596 * If
4597 * - the baseline total service time could not be sampled yet,
4598 * so the inject limit happens to be still 0, and
4599 * - a lot of time has elapsed since the plugging of I/O
4600 * dispatching started, so drive speed is being wasted
4601 * significantly;
4602 * then temporarily raise inject limit to one request.
4603 */
4604 if (limit == 0 && in_serv_bfqq->last_serv_time_ns == 0 &&
4605 bfq_bfqq_wait_request(in_serv_bfqq) &&
4606 time_is_before_eq_jiffies(bfqd->last_idling_start_jiffies +
4607 bfqd->bfq_slice_idle)
4608 )
4609 limit = 1;
4610
4611 if (bfqd->rq_in_driver >= limit)
4612 return NULL;
4613
4614 /*
4615 * Linear search of the source queue for injection; but, with
4616 * a high probability, very few steps are needed to find a
4617 * candidate queue, i.e., a queue with enough budget left for
4618 * its next request. In fact:
4619 * - BFQ dynamically updates the budget of every queue so as
4620 * to accommodate the expected backlog of the queue;
4621 * - if a queue gets all its requests dispatched as injected
4622 * service, then the queue is removed from the active list
4623 * (and re-added only if it gets new requests, but then it
4624 * is assigned again enough budget for its new backlog).
4625 */
4626 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
4627 if (!RB_EMPTY_ROOT(&bfqq->sort_list) &&
4628 (in_serv_always_inject || bfqq->wr_coeff > 1) &&
4629 bfq_serv_to_charge(bfqq->next_rq, bfqq) <=
4630 bfq_bfqq_budget_left(bfqq)) {
4631 /*
4632 * Allow for only one large in-flight request
4633 * on non-rotational devices, for the
4634 * following reason. On non-rotationl drives,
4635 * large requests take much longer than
4636 * smaller requests to be served. In addition,
4637 * the drive prefers to serve large requests
4638 * w.r.t. to small ones, if it can choose. So,
4639 * having more than one large requests queued
4640 * in the drive may easily make the next first
4641 * request of the in-service queue wait for so
4642 * long to break bfqq's service guarantees. On
4643 * the bright side, large requests let the
4644 * drive reach a very high throughput, even if
4645 * there is only one in-flight large request
4646 * at a time.
4647 */
4648 if (blk_queue_nonrot(bfqd->queue) &&
4649 blk_rq_sectors(bfqq->next_rq) >=
4650 BFQQ_SECT_THR_NONROT)
4651 limit = min_t(unsigned int, 1, limit);
4652 else
4653 limit = in_serv_bfqq->inject_limit;
4654
4655 if (bfqd->rq_in_driver < limit) {
4656 bfqd->rqs_injected = true;
4657 return bfqq;
4658 }
4659 }
4660
4661 return NULL;
4662}
4663
4664/*
4665 * Select a queue for service. If we have a current queue in service,
4666 * check whether to continue servicing it, or retrieve and set a new one.
4667 */
4668static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
4669{
4670 struct bfq_queue *bfqq;
4671 struct request *next_rq;
4672 enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
4673
4674 bfqq = bfqd->in_service_queue;
4675 if (!bfqq)
4676 goto new_queue;
4677
4678 bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
4679
4680 /*
4681 * Do not expire bfqq for budget timeout if bfqq may be about
4682 * to enjoy device idling. The reason why, in this case, we
4683 * prevent bfqq from expiring is the same as in the comments
4684 * on the case where bfq_bfqq_must_idle() returns true, in
4685 * bfq_completed_request().
4686 */
4687 if (bfq_may_expire_for_budg_timeout(bfqq) &&
4688 !bfq_bfqq_must_idle(bfqq))
4689 goto expire;
4690
4691check_queue:
4692 /*
4693 * This loop is rarely executed more than once. Even when it
4694 * happens, it is much more convenient to re-execute this loop
4695 * than to return NULL and trigger a new dispatch to get a
4696 * request served.
4697 */
4698 next_rq = bfqq->next_rq;
4699 /*
4700 * If bfqq has requests queued and it has enough budget left to
4701 * serve them, keep the queue, otherwise expire it.
4702 */
4703 if (next_rq) {
4704 if (bfq_serv_to_charge(next_rq, bfqq) >
4705 bfq_bfqq_budget_left(bfqq)) {
4706 /*
4707 * Expire the queue for budget exhaustion,
4708 * which makes sure that the next budget is
4709 * enough to serve the next request, even if
4710 * it comes from the fifo expired path.
4711 */
4712 reason = BFQQE_BUDGET_EXHAUSTED;
4713 goto expire;
4714 } else {
4715 /*
4716 * The idle timer may be pending because we may
4717 * not disable disk idling even when a new request
4718 * arrives.
4719 */
4720 if (bfq_bfqq_wait_request(bfqq)) {
4721 /*
4722 * If we get here: 1) at least a new request
4723 * has arrived but we have not disabled the
4724 * timer because the request was too small,
4725 * 2) then the block layer has unplugged
4726 * the device, causing the dispatch to be
4727 * invoked.
4728 *
4729 * Since the device is unplugged, now the
4730 * requests are probably large enough to
4731 * provide a reasonable throughput.
4732 * So we disable idling.
4733 */
4734 bfq_clear_bfqq_wait_request(bfqq);
4735 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
4736 }
4737 goto keep_queue;
4738 }
4739 }
4740
4741 /*
4742 * No requests pending. However, if the in-service queue is idling
4743 * for a new request, or has requests waiting for a completion and
4744 * may idle after their completion, then keep it anyway.
4745 *
4746 * Yet, inject service from other queues if it boosts
4747 * throughput and is possible.
4748 */
4749 if (bfq_bfqq_wait_request(bfqq) ||
4750 (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) {
4751 struct bfq_queue *async_bfqq =
4752 bfqq->bic && bfqq->bic->bfqq[0] &&
4753 bfq_bfqq_busy(bfqq->bic->bfqq[0]) &&
4754 bfqq->bic->bfqq[0]->next_rq ?
4755 bfqq->bic->bfqq[0] : NULL;
4756 struct bfq_queue *blocked_bfqq =
4757 !hlist_empty(&bfqq->woken_list) ?
4758 container_of(bfqq->woken_list.first,
4759 struct bfq_queue,
4760 woken_list_node)
4761 : NULL;
4762
4763 /*
4764 * The next four mutually-exclusive ifs decide
4765 * whether to try injection, and choose the queue to
4766 * pick an I/O request from.
4767 *
4768 * The first if checks whether the process associated
4769 * with bfqq has also async I/O pending. If so, it
4770 * injects such I/O unconditionally. Injecting async
4771 * I/O from the same process can cause no harm to the
4772 * process. On the contrary, it can only increase
4773 * bandwidth and reduce latency for the process.
4774 *
4775 * The second if checks whether there happens to be a
4776 * non-empty waker queue for bfqq, i.e., a queue whose
4777 * I/O needs to be completed for bfqq to receive new
4778 * I/O. This happens, e.g., if bfqq is associated with
4779 * a process that does some sync. A sync generates
4780 * extra blocking I/O, which must be completed before
4781 * the process associated with bfqq can go on with its
4782 * I/O. If the I/O of the waker queue is not served,
4783 * then bfqq remains empty, and no I/O is dispatched,
4784 * until the idle timeout fires for bfqq. This is
4785 * likely to result in lower bandwidth and higher
4786 * latencies for bfqq, and in a severe loss of total
4787 * throughput. The best action to take is therefore to
4788 * serve the waker queue as soon as possible. So do it
4789 * (without relying on the third alternative below for
4790 * eventually serving waker_bfqq's I/O; see the last
4791 * paragraph for further details). This systematic
4792 * injection of I/O from the waker queue does not
4793 * cause any delay to bfqq's I/O. On the contrary,
4794 * next bfqq's I/O is brought forward dramatically,
4795 * for it is not blocked for milliseconds.
4796 *
4797 * The third if checks whether there is a queue woken
4798 * by bfqq, and currently with pending I/O. Such a
4799 * woken queue does not steal bandwidth from bfqq,
4800 * because it remains soon without I/O if bfqq is not
4801 * served. So there is virtually no risk of loss of
4802 * bandwidth for bfqq if this woken queue has I/O
4803 * dispatched while bfqq is waiting for new I/O.
4804 *
4805 * The fourth if checks whether bfqq is a queue for
4806 * which it is better to avoid injection. It is so if
4807 * bfqq delivers more throughput when served without
4808 * any further I/O from other queues in the middle, or
4809 * if the service times of bfqq's I/O requests both
4810 * count more than overall throughput, and may be
4811 * easily increased by injection (this happens if bfqq
4812 * has a short think time). If none of these
4813 * conditions holds, then a candidate queue for
4814 * injection is looked for through
4815 * bfq_choose_bfqq_for_injection(). Note that the
4816 * latter may return NULL (for example if the inject
4817 * limit for bfqq is currently 0).
4818 *
4819 * NOTE: motivation for the second alternative
4820 *
4821 * Thanks to the way the inject limit is updated in
4822 * bfq_update_has_short_ttime(), it is rather likely
4823 * that, if I/O is being plugged for bfqq and the
4824 * waker queue has pending I/O requests that are
4825 * blocking bfqq's I/O, then the fourth alternative
4826 * above lets the waker queue get served before the
4827 * I/O-plugging timeout fires. So one may deem the
4828 * second alternative superfluous. It is not, because
4829 * the fourth alternative may be way less effective in
4830 * case of a synchronization. For two main
4831 * reasons. First, throughput may be low because the
4832 * inject limit may be too low to guarantee the same
4833 * amount of injected I/O, from the waker queue or
4834 * other queues, that the second alternative
4835 * guarantees (the second alternative unconditionally
4836 * injects a pending I/O request of the waker queue
4837 * for each bfq_dispatch_request()). Second, with the
4838 * fourth alternative, the duration of the plugging,
4839 * i.e., the time before bfqq finally receives new I/O,
4840 * may not be minimized, because the waker queue may
4841 * happen to be served only after other queues.
4842 */
4843 if (async_bfqq &&
4844 icq_to_bic(async_bfqq->next_rq->elv.icq) == bfqq->bic &&
4845 bfq_serv_to_charge(async_bfqq->next_rq, async_bfqq) <=
4846 bfq_bfqq_budget_left(async_bfqq))
4847 bfqq = bfqq->bic->bfqq[0];
4848 else if (bfqq->waker_bfqq &&
4849 bfq_bfqq_busy(bfqq->waker_bfqq) &&
4850 bfqq->waker_bfqq->next_rq &&
4851 bfq_serv_to_charge(bfqq->waker_bfqq->next_rq,
4852 bfqq->waker_bfqq) <=
4853 bfq_bfqq_budget_left(bfqq->waker_bfqq)
4854 )
4855 bfqq = bfqq->waker_bfqq;
4856 else if (blocked_bfqq &&
4857 bfq_bfqq_busy(blocked_bfqq) &&
4858 blocked_bfqq->next_rq &&
4859 bfq_serv_to_charge(blocked_bfqq->next_rq,
4860 blocked_bfqq) <=
4861 bfq_bfqq_budget_left(blocked_bfqq)
4862 )
4863 bfqq = blocked_bfqq;
4864 else if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
4865 (bfqq->wr_coeff == 1 || bfqd->wr_busy_queues > 1 ||
4866 !bfq_bfqq_has_short_ttime(bfqq)))
4867 bfqq = bfq_choose_bfqq_for_injection(bfqd);
4868 else
4869 bfqq = NULL;
4870
4871 goto keep_queue;
4872 }
4873
4874 reason = BFQQE_NO_MORE_REQUESTS;
4875expire:
4876 bfq_bfqq_expire(bfqd, bfqq, false, reason);
4877new_queue:
4878 bfqq = bfq_set_in_service_queue(bfqd);
4879 if (bfqq) {
4880 bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
4881 goto check_queue;
4882 }
4883keep_queue:
4884 if (bfqq)
4885 bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
4886 else
4887 bfq_log(bfqd, "select_queue: no queue returned");
4888
4889 return bfqq;
4890}
4891
4892static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4893{
4894 struct bfq_entity *entity = &bfqq->entity;
4895
4896 if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
4897 bfq_log_bfqq(bfqd, bfqq,
4898 "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
4899 jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
4900 jiffies_to_msecs(bfqq->wr_cur_max_time),
4901 bfqq->wr_coeff,
4902 bfqq->entity.weight, bfqq->entity.orig_weight);
4903
4904 if (entity->prio_changed)
4905 bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
4906
4907 /*
4908 * If the queue was activated in a burst, or too much
4909 * time has elapsed from the beginning of this
4910 * weight-raising period, then end weight raising.
4911 */
4912 if (bfq_bfqq_in_large_burst(bfqq))
4913 bfq_bfqq_end_wr(bfqq);
4914 else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
4915 bfqq->wr_cur_max_time)) {
4916 if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
4917 time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
4918 bfq_wr_duration(bfqd))) {
4919 /*
4920 * Either in interactive weight
4921 * raising, or in soft_rt weight
4922 * raising with the
4923 * interactive-weight-raising period
4924 * elapsed (so no switch back to
4925 * interactive weight raising).
4926 */
4927 bfq_bfqq_end_wr(bfqq);
4928 } else { /*
4929 * soft_rt finishing while still in
4930 * interactive period, switch back to
4931 * interactive weight raising
4932 */
4933 switch_back_to_interactive_wr(bfqq, bfqd);
4934 bfqq->entity.prio_changed = 1;
4935 }
4936 }
4937 if (bfqq->wr_coeff > 1 &&
4938 bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time &&
4939 bfqq->service_from_wr > max_service_from_wr) {
4940 /* see comments on max_service_from_wr */
4941 bfq_bfqq_end_wr(bfqq);
4942 }
4943 }
4944 /*
4945 * To improve latency (for this or other queues), immediately
4946 * update weight both if it must be raised and if it must be
4947 * lowered. Since, entity may be on some active tree here, and
4948 * might have a pending change of its ioprio class, invoke
4949 * next function with the last parameter unset (see the
4950 * comments on the function).
4951 */
4952 if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
4953 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
4954 entity, false);
4955}
4956
4957/*
4958 * Dispatch next request from bfqq.
4959 */
4960static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
4961 struct bfq_queue *bfqq)
4962{
4963 struct request *rq = bfqq->next_rq;
4964 unsigned long service_to_charge;
4965
4966 service_to_charge = bfq_serv_to_charge(rq, bfqq);
4967
4968 bfq_bfqq_served(bfqq, service_to_charge);
4969
4970 if (bfqq == bfqd->in_service_queue && bfqd->wait_dispatch) {
4971 bfqd->wait_dispatch = false;
4972 bfqd->waited_rq = rq;
4973 }
4974
4975 bfq_dispatch_remove(bfqd->queue, rq);
4976
4977 if (bfqq != bfqd->in_service_queue)
4978 goto return_rq;
4979
4980 /*
4981 * If weight raising has to terminate for bfqq, then next
4982 * function causes an immediate update of bfqq's weight,
4983 * without waiting for next activation. As a consequence, on
4984 * expiration, bfqq will be timestamped as if has never been
4985 * weight-raised during this service slot, even if it has
4986 * received part or even most of the service as a
4987 * weight-raised queue. This inflates bfqq's timestamps, which
4988 * is beneficial, as bfqq is then more willing to leave the
4989 * device immediately to possible other weight-raised queues.
4990 */
4991 bfq_update_wr_data(bfqd, bfqq);
4992
4993 /*
4994 * Expire bfqq, pretending that its budget expired, if bfqq
4995 * belongs to CLASS_IDLE and other queues are waiting for
4996 * service.
4997 */
4998 if (!(bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq)))
4999 goto return_rq;
5000
5001 bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
5002
5003return_rq:
5004 return rq;
5005}
5006
5007static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
5008{
5009 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5010
5011 /*
5012 * Avoiding lock: a race on bfqd->queued should cause at
5013 * most a call to dispatch for nothing
5014 */
5015 return !list_empty_careful(&bfqd->dispatch) ||
5016 READ_ONCE(bfqd->queued);
5017}
5018
5019static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5020{
5021 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5022 struct request *rq = NULL;
5023 struct bfq_queue *bfqq = NULL;
5024
5025 if (!list_empty(&bfqd->dispatch)) {
5026 rq = list_first_entry(&bfqd->dispatch, struct request,
5027 queuelist);
5028 list_del_init(&rq->queuelist);
5029
5030 bfqq = RQ_BFQQ(rq);
5031
5032 if (bfqq) {
5033 /*
5034 * Increment counters here, because this
5035 * dispatch does not follow the standard
5036 * dispatch flow (where counters are
5037 * incremented)
5038 */
5039 bfqq->dispatched++;
5040
5041 goto inc_in_driver_start_rq;
5042 }
5043
5044 /*
5045 * We exploit the bfq_finish_requeue_request hook to
5046 * decrement rq_in_driver, but
5047 * bfq_finish_requeue_request will not be invoked on
5048 * this request. So, to avoid unbalance, just start
5049 * this request, without incrementing rq_in_driver. As
5050 * a negative consequence, rq_in_driver is deceptively
5051 * lower than it should be while this request is in
5052 * service. This may cause bfq_schedule_dispatch to be
5053 * invoked uselessly.
5054 *
5055 * As for implementing an exact solution, the
5056 * bfq_finish_requeue_request hook, if defined, is
5057 * probably invoked also on this request. So, by
5058 * exploiting this hook, we could 1) increment
5059 * rq_in_driver here, and 2) decrement it in
5060 * bfq_finish_requeue_request. Such a solution would
5061 * let the value of the counter be always accurate,
5062 * but it would entail using an extra interface
5063 * function. This cost seems higher than the benefit,
5064 * being the frequency of non-elevator-private
5065 * requests very low.
5066 */
5067 goto start_rq;
5068 }
5069
5070 bfq_log(bfqd, "dispatch requests: %d busy queues",
5071 bfq_tot_busy_queues(bfqd));
5072
5073 if (bfq_tot_busy_queues(bfqd) == 0)
5074 goto exit;
5075
5076 /*
5077 * Force device to serve one request at a time if
5078 * strict_guarantees is true. Forcing this service scheme is
5079 * currently the ONLY way to guarantee that the request
5080 * service order enforced by the scheduler is respected by a
5081 * queueing device. Otherwise the device is free even to make
5082 * some unlucky request wait for as long as the device
5083 * wishes.
5084 *
5085 * Of course, serving one request at a time may cause loss of
5086 * throughput.
5087 */
5088 if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
5089 goto exit;
5090
5091 bfqq = bfq_select_queue(bfqd);
5092 if (!bfqq)
5093 goto exit;
5094
5095 rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
5096
5097 if (rq) {
5098inc_in_driver_start_rq:
5099 bfqd->rq_in_driver++;
5100start_rq:
5101 rq->rq_flags |= RQF_STARTED;
5102 }
5103exit:
5104 return rq;
5105}
5106
5107#ifdef CONFIG_BFQ_CGROUP_DEBUG
5108static void bfq_update_dispatch_stats(struct request_queue *q,
5109 struct request *rq,
5110 struct bfq_queue *in_serv_queue,
5111 bool idle_timer_disabled)
5112{
5113 struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
5114
5115 if (!idle_timer_disabled && !bfqq)
5116 return;
5117
5118 /*
5119 * rq and bfqq are guaranteed to exist until this function
5120 * ends, for the following reasons. First, rq can be
5121 * dispatched to the device, and then can be completed and
5122 * freed, only after this function ends. Second, rq cannot be
5123 * merged (and thus freed because of a merge) any longer,
5124 * because it has already started. Thus rq cannot be freed
5125 * before this function ends, and, since rq has a reference to
5126 * bfqq, the same guarantee holds for bfqq too.
5127 *
5128 * In addition, the following queue lock guarantees that
5129 * bfqq_group(bfqq) exists as well.
5130 */
5131 spin_lock_irq(&q->queue_lock);
5132 if (idle_timer_disabled)
5133 /*
5134 * Since the idle timer has been disabled,
5135 * in_serv_queue contained some request when
5136 * __bfq_dispatch_request was invoked above, which
5137 * implies that rq was picked exactly from
5138 * in_serv_queue. Thus in_serv_queue == bfqq, and is
5139 * therefore guaranteed to exist because of the above
5140 * arguments.
5141 */
5142 bfqg_stats_update_idle_time(bfqq_group(in_serv_queue));
5143 if (bfqq) {
5144 struct bfq_group *bfqg = bfqq_group(bfqq);
5145
5146 bfqg_stats_update_avg_queue_size(bfqg);
5147 bfqg_stats_set_start_empty_time(bfqg);
5148 bfqg_stats_update_io_remove(bfqg, rq->cmd_flags);
5149 }
5150 spin_unlock_irq(&q->queue_lock);
5151}
5152#else
5153static inline void bfq_update_dispatch_stats(struct request_queue *q,
5154 struct request *rq,
5155 struct bfq_queue *in_serv_queue,
5156 bool idle_timer_disabled) {}
5157#endif /* CONFIG_BFQ_CGROUP_DEBUG */
5158
5159static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5160{
5161 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5162 struct request *rq;
5163 struct bfq_queue *in_serv_queue;
5164 bool waiting_rq, idle_timer_disabled = false;
5165
5166 spin_lock_irq(&bfqd->lock);
5167
5168 in_serv_queue = bfqd->in_service_queue;
5169 waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
5170
5171 rq = __bfq_dispatch_request(hctx);
5172 if (in_serv_queue == bfqd->in_service_queue) {
5173 idle_timer_disabled =
5174 waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
5175 }
5176
5177 spin_unlock_irq(&bfqd->lock);
5178 bfq_update_dispatch_stats(hctx->queue, rq,
5179 idle_timer_disabled ? in_serv_queue : NULL,
5180 idle_timer_disabled);
5181
5182 return rq;
5183}
5184
5185/*
5186 * Task holds one reference to the queue, dropped when task exits. Each rq
5187 * in-flight on this queue also holds a reference, dropped when rq is freed.
5188 *
5189 * Scheduler lock must be held here. Recall not to use bfqq after calling
5190 * this function on it.
5191 */
5192void bfq_put_queue(struct bfq_queue *bfqq)
5193{
5194 struct bfq_queue *item;
5195 struct hlist_node *n;
5196 struct bfq_group *bfqg = bfqq_group(bfqq);
5197
5198 bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", bfqq, bfqq->ref);
5199
5200 bfqq->ref--;
5201 if (bfqq->ref)
5202 return;
5203
5204 if (!hlist_unhashed(&bfqq->burst_list_node)) {
5205 hlist_del_init(&bfqq->burst_list_node);
5206 /*
5207 * Decrement also burst size after the removal, if the
5208 * process associated with bfqq is exiting, and thus
5209 * does not contribute to the burst any longer. This
5210 * decrement helps filter out false positives of large
5211 * bursts, when some short-lived process (often due to
5212 * the execution of commands by some service) happens
5213 * to start and exit while a complex application is
5214 * starting, and thus spawning several processes that
5215 * do I/O (and that *must not* be treated as a large
5216 * burst, see comments on bfq_handle_burst).
5217 *
5218 * In particular, the decrement is performed only if:
5219 * 1) bfqq is not a merged queue, because, if it is,
5220 * then this free of bfqq is not triggered by the exit
5221 * of the process bfqq is associated with, but exactly
5222 * by the fact that bfqq has just been merged.
5223 * 2) burst_size is greater than 0, to handle
5224 * unbalanced decrements. Unbalanced decrements may
5225 * happen in te following case: bfqq is inserted into
5226 * the current burst list--without incrementing
5227 * bust_size--because of a split, but the current
5228 * burst list is not the burst list bfqq belonged to
5229 * (see comments on the case of a split in
5230 * bfq_set_request).
5231 */
5232 if (bfqq->bic && bfqq->bfqd->burst_size > 0)
5233 bfqq->bfqd->burst_size--;
5234 }
5235
5236 /*
5237 * bfqq does not exist any longer, so it cannot be woken by
5238 * any other queue, and cannot wake any other queue. Then bfqq
5239 * must be removed from the woken list of its possible waker
5240 * queue, and all queues in the woken list of bfqq must stop
5241 * having a waker queue. Strictly speaking, these updates
5242 * should be performed when bfqq remains with no I/O source
5243 * attached to it, which happens before bfqq gets freed. In
5244 * particular, this happens when the last process associated
5245 * with bfqq exits or gets associated with a different
5246 * queue. However, both events lead to bfqq being freed soon,
5247 * and dangling references would come out only after bfqq gets
5248 * freed. So these updates are done here, as a simple and safe
5249 * way to handle all cases.
5250 */
5251 /* remove bfqq from woken list */
5252 if (!hlist_unhashed(&bfqq->woken_list_node))
5253 hlist_del_init(&bfqq->woken_list_node);
5254
5255 /* reset waker for all queues in woken list */
5256 hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
5257 woken_list_node) {
5258 item->waker_bfqq = NULL;
5259 hlist_del_init(&item->woken_list_node);
5260 }
5261
5262 if (bfqq->bfqd->last_completed_rq_bfqq == bfqq)
5263 bfqq->bfqd->last_completed_rq_bfqq = NULL;
5264
5265 kmem_cache_free(bfq_pool, bfqq);
5266 bfqg_and_blkg_put(bfqg);
5267}
5268
5269static void bfq_put_stable_ref(struct bfq_queue *bfqq)
5270{
5271 bfqq->stable_ref--;
5272 bfq_put_queue(bfqq);
5273}
5274
5275void bfq_put_cooperator(struct bfq_queue *bfqq)
5276{
5277 struct bfq_queue *__bfqq, *next;
5278
5279 /*
5280 * If this queue was scheduled to merge with another queue, be
5281 * sure to drop the reference taken on that queue (and others in
5282 * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
5283 */
5284 __bfqq = bfqq->new_bfqq;
5285 while (__bfqq) {
5286 if (__bfqq == bfqq)
5287 break;
5288 next = __bfqq->new_bfqq;
5289 bfq_put_queue(__bfqq);
5290 __bfqq = next;
5291 }
5292}
5293
5294static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
5295{
5296 if (bfqq == bfqd->in_service_queue) {
5297 __bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);
5298 bfq_schedule_dispatch(bfqd);
5299 }
5300
5301 bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
5302
5303 bfq_put_cooperator(bfqq);
5304
5305 bfq_release_process_ref(bfqd, bfqq);
5306}
5307
5308static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
5309{
5310 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
5311 struct bfq_data *bfqd;
5312
5313 if (bfqq)
5314 bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
5315
5316 if (bfqq && bfqd) {
5317 unsigned long flags;
5318
5319 spin_lock_irqsave(&bfqd->lock, flags);
5320 bic_set_bfqq(bic, NULL, is_sync);
5321 bfq_exit_bfqq(bfqd, bfqq);
5322 spin_unlock_irqrestore(&bfqd->lock, flags);
5323 }
5324}
5325
5326static void bfq_exit_icq(struct io_cq *icq)
5327{
5328 struct bfq_io_cq *bic = icq_to_bic(icq);
5329
5330 if (bic->stable_merge_bfqq) {
5331 struct bfq_data *bfqd = bic->stable_merge_bfqq->bfqd;
5332
5333 /*
5334 * bfqd is NULL if scheduler already exited, and in
5335 * that case this is the last time bfqq is accessed.
5336 */
5337 if (bfqd) {
5338 unsigned long flags;
5339
5340 spin_lock_irqsave(&bfqd->lock, flags);
5341 bfq_put_stable_ref(bic->stable_merge_bfqq);
5342 spin_unlock_irqrestore(&bfqd->lock, flags);
5343 } else {
5344 bfq_put_stable_ref(bic->stable_merge_bfqq);
5345 }
5346 }
5347
5348 bfq_exit_icq_bfqq(bic, true);
5349 bfq_exit_icq_bfqq(bic, false);
5350}
5351
5352/*
5353 * Update the entity prio values; note that the new values will not
5354 * be used until the next (re)activation.
5355 */
5356static void
5357bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
5358{
5359 struct task_struct *tsk = current;
5360 int ioprio_class;
5361 struct bfq_data *bfqd = bfqq->bfqd;
5362
5363 if (!bfqd)
5364 return;
5365
5366 ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5367 switch (ioprio_class) {
5368 default:
5369 pr_err("bdi %s: bfq: bad prio class %d\n",
5370 bdi_dev_name(bfqq->bfqd->queue->disk->bdi),
5371 ioprio_class);
5372 fallthrough;
5373 case IOPRIO_CLASS_NONE:
5374 /*
5375 * No prio set, inherit CPU scheduling settings.
5376 */
5377 bfqq->new_ioprio = task_nice_ioprio(tsk);
5378 bfqq->new_ioprio_class = task_nice_ioclass(tsk);
5379 break;
5380 case IOPRIO_CLASS_RT:
5381 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5382 bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
5383 break;
5384 case IOPRIO_CLASS_BE:
5385 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5386 bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
5387 break;
5388 case IOPRIO_CLASS_IDLE:
5389 bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
5390 bfqq->new_ioprio = 7;
5391 break;
5392 }
5393
5394 if (bfqq->new_ioprio >= IOPRIO_NR_LEVELS) {
5395 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
5396 bfqq->new_ioprio);
5397 bfqq->new_ioprio = IOPRIO_NR_LEVELS - 1;
5398 }
5399
5400 bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
5401 bfq_log_bfqq(bfqd, bfqq, "new_ioprio %d new_weight %d",
5402 bfqq->new_ioprio, bfqq->entity.new_weight);
5403 bfqq->entity.prio_changed = 1;
5404}
5405
5406static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5407 struct bio *bio, bool is_sync,
5408 struct bfq_io_cq *bic,
5409 bool respawn);
5410
5411static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
5412{
5413 struct bfq_data *bfqd = bic_to_bfqd(bic);
5414 struct bfq_queue *bfqq;
5415 int ioprio = bic->icq.ioc->ioprio;
5416
5417 /*
5418 * This condition may trigger on a newly created bic, be sure to
5419 * drop the lock before returning.
5420 */
5421 if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
5422 return;
5423
5424 bic->ioprio = ioprio;
5425
5426 bfqq = bic_to_bfqq(bic, false);
5427 if (bfqq) {
5428 struct bfq_queue *old_bfqq = bfqq;
5429
5430 bfqq = bfq_get_queue(bfqd, bio, false, bic, true);
5431 bic_set_bfqq(bic, bfqq, false);
5432 bfq_release_process_ref(bfqd, old_bfqq);
5433 }
5434
5435 bfqq = bic_to_bfqq(bic, true);
5436 if (bfqq)
5437 bfq_set_next_ioprio_data(bfqq, bic);
5438}
5439
5440static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5441 struct bfq_io_cq *bic, pid_t pid, int is_sync)
5442{
5443 u64 now_ns = ktime_get_ns();
5444
5445 RB_CLEAR_NODE(&bfqq->entity.rb_node);
5446 INIT_LIST_HEAD(&bfqq->fifo);
5447 INIT_HLIST_NODE(&bfqq->burst_list_node);
5448 INIT_HLIST_NODE(&bfqq->woken_list_node);
5449 INIT_HLIST_HEAD(&bfqq->woken_list);
5450
5451 bfqq->ref = 0;
5452 bfqq->bfqd = bfqd;
5453
5454 if (bic)
5455 bfq_set_next_ioprio_data(bfqq, bic);
5456
5457 if (is_sync) {
5458 /*
5459 * No need to mark as has_short_ttime if in
5460 * idle_class, because no device idling is performed
5461 * for queues in idle class
5462 */
5463 if (!bfq_class_idle(bfqq))
5464 /* tentatively mark as has_short_ttime */
5465 bfq_mark_bfqq_has_short_ttime(bfqq);
5466 bfq_mark_bfqq_sync(bfqq);
5467 bfq_mark_bfqq_just_created(bfqq);
5468 } else
5469 bfq_clear_bfqq_sync(bfqq);
5470
5471 /* set end request to minus infinity from now */
5472 bfqq->ttime.last_end_request = now_ns + 1;
5473
5474 bfqq->creation_time = jiffies;
5475
5476 bfqq->io_start_time = now_ns;
5477
5478 bfq_mark_bfqq_IO_bound(bfqq);
5479
5480 bfqq->pid = pid;
5481
5482 /* Tentative initial value to trade off between thr and lat */
5483 bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
5484 bfqq->budget_timeout = bfq_smallest_from_now();
5485
5486 bfqq->wr_coeff = 1;
5487 bfqq->last_wr_start_finish = jiffies;
5488 bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
5489 bfqq->split_time = bfq_smallest_from_now();
5490
5491 /*
5492 * To not forget the possibly high bandwidth consumed by a
5493 * process/queue in the recent past,
5494 * bfq_bfqq_softrt_next_start() returns a value at least equal
5495 * to the current value of bfqq->soft_rt_next_start (see
5496 * comments on bfq_bfqq_softrt_next_start). Set
5497 * soft_rt_next_start to now, to mean that bfqq has consumed
5498 * no bandwidth so far.
5499 */
5500 bfqq->soft_rt_next_start = jiffies;
5501
5502 /* first request is almost certainly seeky */
5503 bfqq->seek_history = 1;
5504}
5505
5506static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
5507 struct bfq_group *bfqg,
5508 int ioprio_class, int ioprio)
5509{
5510 switch (ioprio_class) {
5511 case IOPRIO_CLASS_RT:
5512 return &bfqg->async_bfqq[0][ioprio];
5513 case IOPRIO_CLASS_NONE:
5514 ioprio = IOPRIO_BE_NORM;
5515 fallthrough;
5516 case IOPRIO_CLASS_BE:
5517 return &bfqg->async_bfqq[1][ioprio];
5518 case IOPRIO_CLASS_IDLE:
5519 return &bfqg->async_idle_bfqq;
5520 default:
5521 return NULL;
5522 }
5523}
5524
5525static struct bfq_queue *
5526bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5527 struct bfq_io_cq *bic,
5528 struct bfq_queue *last_bfqq_created)
5529{
5530 struct bfq_queue *new_bfqq =
5531 bfq_setup_merge(bfqq, last_bfqq_created);
5532
5533 if (!new_bfqq)
5534 return bfqq;
5535
5536 if (new_bfqq->bic)
5537 new_bfqq->bic->stably_merged = true;
5538 bic->stably_merged = true;
5539
5540 /*
5541 * Reusing merge functions. This implies that
5542 * bfqq->bic must be set too, for
5543 * bfq_merge_bfqqs to correctly save bfqq's
5544 * state before killing it.
5545 */
5546 bfqq->bic = bic;
5547 bfq_merge_bfqqs(bfqd, bic, bfqq, new_bfqq);
5548
5549 return new_bfqq;
5550}
5551
5552/*
5553 * Many throughput-sensitive workloads are made of several parallel
5554 * I/O flows, with all flows generated by the same application, or
5555 * more generically by the same task (e.g., system boot). The most
5556 * counterproductive action with these workloads is plugging I/O
5557 * dispatch when one of the bfq_queues associated with these flows
5558 * remains temporarily empty.
5559 *
5560 * To avoid this plugging, BFQ has been using a burst-handling
5561 * mechanism for years now. This mechanism has proven effective for
5562 * throughput, and not detrimental for service guarantees. The
5563 * following function pushes this mechanism a little bit further,
5564 * basing on the following two facts.
5565 *
5566 * First, all the I/O flows of a the same application or task
5567 * contribute to the execution/completion of that common application
5568 * or task. So the performance figures that matter are total
5569 * throughput of the flows and task-wide I/O latency. In particular,
5570 * these flows do not need to be protected from each other, in terms
5571 * of individual bandwidth or latency.
5572 *
5573 * Second, the above fact holds regardless of the number of flows.
5574 *
5575 * Putting these two facts together, this commits merges stably the
5576 * bfq_queues associated with these I/O flows, i.e., with the
5577 * processes that generate these IO/ flows, regardless of how many the
5578 * involved processes are.
5579 *
5580 * To decide whether a set of bfq_queues is actually associated with
5581 * the I/O flows of a common application or task, and to merge these
5582 * queues stably, this function operates as follows: given a bfq_queue,
5583 * say Q2, currently being created, and the last bfq_queue, say Q1,
5584 * created before Q2, Q2 is merged stably with Q1 if
5585 * - very little time has elapsed since when Q1 was created
5586 * - Q2 has the same ioprio as Q1
5587 * - Q2 belongs to the same group as Q1
5588 *
5589 * Merging bfq_queues also reduces scheduling overhead. A fio test
5590 * with ten random readers on /dev/nullb shows a throughput boost of
5591 * 40%, with a quadcore. Since BFQ's execution time amounts to ~50% of
5592 * the total per-request processing time, the above throughput boost
5593 * implies that BFQ's overhead is reduced by more than 50%.
5594 *
5595 * This new mechanism most certainly obsoletes the current
5596 * burst-handling heuristics. We keep those heuristics for the moment.
5597 */
5598static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
5599 struct bfq_queue *bfqq,
5600 struct bfq_io_cq *bic)
5601{
5602 struct bfq_queue **source_bfqq = bfqq->entity.parent ?
5603 &bfqq->entity.parent->last_bfqq_created :
5604 &bfqd->last_bfqq_created;
5605
5606 struct bfq_queue *last_bfqq_created = *source_bfqq;
5607
5608 /*
5609 * If last_bfqq_created has not been set yet, then init it. If
5610 * it has been set already, but too long ago, then move it
5611 * forward to bfqq. Finally, move also if bfqq belongs to a
5612 * different group than last_bfqq_created, or if bfqq has a
5613 * different ioprio or ioprio_class. If none of these
5614 * conditions holds true, then try an early stable merge or
5615 * schedule a delayed stable merge.
5616 *
5617 * A delayed merge is scheduled (instead of performing an
5618 * early merge), in case bfqq might soon prove to be more
5619 * throughput-beneficial if not merged. Currently this is
5620 * possible only if bfqd is rotational with no queueing. For
5621 * such a drive, not merging bfqq is better for throughput if
5622 * bfqq happens to contain sequential I/O. So, we wait a
5623 * little bit for enough I/O to flow through bfqq. After that,
5624 * if such an I/O is sequential, then the merge is
5625 * canceled. Otherwise the merge is finally performed.
5626 */
5627 if (!last_bfqq_created ||
5628 time_before(last_bfqq_created->creation_time +
5629 msecs_to_jiffies(bfq_activation_stable_merging),
5630 bfqq->creation_time) ||
5631 bfqq->entity.parent != last_bfqq_created->entity.parent ||
5632 bfqq->ioprio != last_bfqq_created->ioprio ||
5633 bfqq->ioprio_class != last_bfqq_created->ioprio_class)
5634 *source_bfqq = bfqq;
5635 else if (time_after_eq(last_bfqq_created->creation_time +
5636 bfqd->bfq_burst_interval,
5637 bfqq->creation_time)) {
5638 if (likely(bfqd->nonrot_with_queueing))
5639 /*
5640 * With this type of drive, leaving
5641 * bfqq alone may provide no
5642 * throughput benefits compared with
5643 * merging bfqq. So merge bfqq now.
5644 */
5645 bfqq = bfq_do_early_stable_merge(bfqd, bfqq,
5646 bic,
5647 last_bfqq_created);
5648 else { /* schedule tentative stable merge */
5649 /*
5650 * get reference on last_bfqq_created,
5651 * to prevent it from being freed,
5652 * until we decide whether to merge
5653 */
5654 last_bfqq_created->ref++;
5655 /*
5656 * need to keep track of stable refs, to
5657 * compute process refs correctly
5658 */
5659 last_bfqq_created->stable_ref++;
5660 /*
5661 * Record the bfqq to merge to.
5662 */
5663 bic->stable_merge_bfqq = last_bfqq_created;
5664 }
5665 }
5666
5667 return bfqq;
5668}
5669
5670
5671static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5672 struct bio *bio, bool is_sync,
5673 struct bfq_io_cq *bic,
5674 bool respawn)
5675{
5676 const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5677 const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5678 struct bfq_queue **async_bfqq = NULL;
5679 struct bfq_queue *bfqq;
5680 struct bfq_group *bfqg;
5681
5682 bfqg = bfq_bio_bfqg(bfqd, bio);
5683 if (!is_sync) {
5684 async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
5685 ioprio);
5686 bfqq = *async_bfqq;
5687 if (bfqq)
5688 goto out;
5689 }
5690
5691 bfqq = kmem_cache_alloc_node(bfq_pool,
5692 GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
5693 bfqd->queue->node);
5694
5695 if (bfqq) {
5696 bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
5697 is_sync);
5698 bfq_init_entity(&bfqq->entity, bfqg);
5699 bfq_log_bfqq(bfqd, bfqq, "allocated");
5700 } else {
5701 bfqq = &bfqd->oom_bfqq;
5702 bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
5703 goto out;
5704 }
5705
5706 /*
5707 * Pin the queue now that it's allocated, scheduler exit will
5708 * prune it.
5709 */
5710 if (async_bfqq) {
5711 bfqq->ref++; /*
5712 * Extra group reference, w.r.t. sync
5713 * queue. This extra reference is removed
5714 * only if bfqq->bfqg disappears, to
5715 * guarantee that this queue is not freed
5716 * until its group goes away.
5717 */
5718 bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
5719 bfqq, bfqq->ref);
5720 *async_bfqq = bfqq;
5721 }
5722
5723out:
5724 bfqq->ref++; /* get a process reference to this queue */
5725
5726 if (bfqq != &bfqd->oom_bfqq && is_sync && !respawn)
5727 bfqq = bfq_do_or_sched_stable_merge(bfqd, bfqq, bic);
5728 return bfqq;
5729}
5730
5731static void bfq_update_io_thinktime(struct bfq_data *bfqd,
5732 struct bfq_queue *bfqq)
5733{
5734 struct bfq_ttime *ttime = &bfqq->ttime;
5735 u64 elapsed;
5736
5737 /*
5738 * We are really interested in how long it takes for the queue to
5739 * become busy when there is no outstanding IO for this queue. So
5740 * ignore cases when the bfq queue has already IO queued.
5741 */
5742 if (bfqq->dispatched || bfq_bfqq_busy(bfqq))
5743 return;
5744 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
5745 elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
5746
5747 ttime->ttime_samples = (7*ttime->ttime_samples + 256) / 8;
5748 ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8);
5749 ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
5750 ttime->ttime_samples);
5751}
5752
5753static void
5754bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5755 struct request *rq)
5756{
5757 bfqq->seek_history <<= 1;
5758 bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq);
5759
5760 if (bfqq->wr_coeff > 1 &&
5761 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
5762 BFQQ_TOTALLY_SEEKY(bfqq)) {
5763 if (time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
5764 bfq_wr_duration(bfqd))) {
5765 /*
5766 * In soft_rt weight raising with the
5767 * interactive-weight-raising period
5768 * elapsed (so no switch back to
5769 * interactive weight raising).
5770 */
5771 bfq_bfqq_end_wr(bfqq);
5772 } else { /*
5773 * stopping soft_rt weight raising
5774 * while still in interactive period,
5775 * switch back to interactive weight
5776 * raising
5777 */
5778 switch_back_to_interactive_wr(bfqq, bfqd);
5779 bfqq->entity.prio_changed = 1;
5780 }
5781 }
5782}
5783
5784static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
5785 struct bfq_queue *bfqq,
5786 struct bfq_io_cq *bic)
5787{
5788 bool has_short_ttime = true, state_changed;
5789
5790 /*
5791 * No need to update has_short_ttime if bfqq is async or in
5792 * idle io prio class, or if bfq_slice_idle is zero, because
5793 * no device idling is performed for bfqq in this case.
5794 */
5795 if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
5796 bfqd->bfq_slice_idle == 0)
5797 return;
5798
5799 /* Idle window just restored, statistics are meaningless. */
5800 if (time_is_after_eq_jiffies(bfqq->split_time +
5801 bfqd->bfq_wr_min_idle_time))
5802 return;
5803
5804 /* Think time is infinite if no process is linked to
5805 * bfqq. Otherwise check average think time to decide whether
5806 * to mark as has_short_ttime. To this goal, compare average
5807 * think time with half the I/O-plugging timeout.
5808 */
5809 if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
5810 (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
5811 bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle>>1))
5812 has_short_ttime = false;
5813
5814 state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq);
5815
5816 if (has_short_ttime)
5817 bfq_mark_bfqq_has_short_ttime(bfqq);
5818 else
5819 bfq_clear_bfqq_has_short_ttime(bfqq);
5820
5821 /*
5822 * Until the base value for the total service time gets
5823 * finally computed for bfqq, the inject limit does depend on
5824 * the think-time state (short|long). In particular, the limit
5825 * is 0 or 1 if the think time is deemed, respectively, as
5826 * short or long (details in the comments in
5827 * bfq_update_inject_limit()). Accordingly, the next
5828 * instructions reset the inject limit if the think-time state
5829 * has changed and the above base value is still to be
5830 * computed.
5831 *
5832 * However, the reset is performed only if more than 100 ms
5833 * have elapsed since the last update of the inject limit, or
5834 * (inclusive) if the change is from short to long think
5835 * time. The reason for this waiting is as follows.
5836 *
5837 * bfqq may have a long think time because of a
5838 * synchronization with some other queue, i.e., because the
5839 * I/O of some other queue may need to be completed for bfqq
5840 * to receive new I/O. Details in the comments on the choice
5841 * of the queue for injection in bfq_select_queue().
5842 *
5843 * As stressed in those comments, if such a synchronization is
5844 * actually in place, then, without injection on bfqq, the
5845 * blocking I/O cannot happen to served while bfqq is in
5846 * service. As a consequence, if bfqq is granted
5847 * I/O-dispatch-plugging, then bfqq remains empty, and no I/O
5848 * is dispatched, until the idle timeout fires. This is likely
5849 * to result in lower bandwidth and higher latencies for bfqq,
5850 * and in a severe loss of total throughput.
5851 *
5852 * On the opposite end, a non-zero inject limit may allow the
5853 * I/O that blocks bfqq to be executed soon, and therefore
5854 * bfqq to receive new I/O soon.
5855 *
5856 * But, if the blocking gets actually eliminated, then the
5857 * next think-time sample for bfqq may be very low. This in
5858 * turn may cause bfqq's think time to be deemed
5859 * short. Without the 100 ms barrier, this new state change
5860 * would cause the body of the next if to be executed
5861 * immediately. But this would set to 0 the inject
5862 * limit. Without injection, the blocking I/O would cause the
5863 * think time of bfqq to become long again, and therefore the
5864 * inject limit to be raised again, and so on. The only effect
5865 * of such a steady oscillation between the two think-time
5866 * states would be to prevent effective injection on bfqq.
5867 *
5868 * In contrast, if the inject limit is not reset during such a
5869 * long time interval as 100 ms, then the number of short
5870 * think time samples can grow significantly before the reset
5871 * is performed. As a consequence, the think time state can
5872 * become stable before the reset. Therefore there will be no
5873 * state change when the 100 ms elapse, and no reset of the
5874 * inject limit. The inject limit remains steadily equal to 1
5875 * both during and after the 100 ms. So injection can be
5876 * performed at all times, and throughput gets boosted.
5877 *
5878 * An inject limit equal to 1 is however in conflict, in
5879 * general, with the fact that the think time of bfqq is
5880 * short, because injection may be likely to delay bfqq's I/O
5881 * (as explained in the comments in
5882 * bfq_update_inject_limit()). But this does not happen in
5883 * this special case, because bfqq's low think time is due to
5884 * an effective handling of a synchronization, through
5885 * injection. In this special case, bfqq's I/O does not get
5886 * delayed by injection; on the contrary, bfqq's I/O is
5887 * brought forward, because it is not blocked for
5888 * milliseconds.
5889 *
5890 * In addition, serving the blocking I/O much sooner, and much
5891 * more frequently than once per I/O-plugging timeout, makes
5892 * it much quicker to detect a waker queue (the concept of
5893 * waker queue is defined in the comments in
5894 * bfq_add_request()). This makes it possible to start sooner
5895 * to boost throughput more effectively, by injecting the I/O
5896 * of the waker queue unconditionally on every
5897 * bfq_dispatch_request().
5898 *
5899 * One last, important benefit of not resetting the inject
5900 * limit before 100 ms is that, during this time interval, the
5901 * base value for the total service time is likely to get
5902 * finally computed for bfqq, freeing the inject limit from
5903 * its relation with the think time.
5904 */
5905 if (state_changed && bfqq->last_serv_time_ns == 0 &&
5906 (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
5907 msecs_to_jiffies(100)) ||
5908 !has_short_ttime))
5909 bfq_reset_inject_limit(bfqd, bfqq);
5910}
5911
5912/*
5913 * Called when a new fs request (rq) is added to bfqq. Check if there's
5914 * something we should do about it.
5915 */
5916static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5917 struct request *rq)
5918{
5919 if (rq->cmd_flags & REQ_META)
5920 bfqq->meta_pending++;
5921
5922 bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
5923
5924 if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
5925 bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
5926 blk_rq_sectors(rq) < 32;
5927 bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
5928
5929 /*
5930 * There is just this request queued: if
5931 * - the request is small, and
5932 * - we are idling to boost throughput, and
5933 * - the queue is not to be expired,
5934 * then just exit.
5935 *
5936 * In this way, if the device is being idled to wait
5937 * for a new request from the in-service queue, we
5938 * avoid unplugging the device and committing the
5939 * device to serve just a small request. In contrast
5940 * we wait for the block layer to decide when to
5941 * unplug the device: hopefully, new requests will be
5942 * merged to this one quickly, then the device will be
5943 * unplugged and larger requests will be dispatched.
5944 */
5945 if (small_req && idling_boosts_thr_without_issues(bfqd, bfqq) &&
5946 !budget_timeout)
5947 return;
5948
5949 /*
5950 * A large enough request arrived, or idling is being
5951 * performed to preserve service guarantees, or
5952 * finally the queue is to be expired: in all these
5953 * cases disk idling is to be stopped, so clear
5954 * wait_request flag and reset timer.
5955 */
5956 bfq_clear_bfqq_wait_request(bfqq);
5957 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
5958
5959 /*
5960 * The queue is not empty, because a new request just
5961 * arrived. Hence we can safely expire the queue, in
5962 * case of budget timeout, without risking that the
5963 * timestamps of the queue are not updated correctly.
5964 * See [1] for more details.
5965 */
5966 if (budget_timeout)
5967 bfq_bfqq_expire(bfqd, bfqq, false,
5968 BFQQE_BUDGET_TIMEOUT);
5969 }
5970}
5971
5972static void bfqq_request_allocated(struct bfq_queue *bfqq)
5973{
5974 struct bfq_entity *entity = &bfqq->entity;
5975
5976 for_each_entity(entity)
5977 entity->allocated++;
5978}
5979
5980static void bfqq_request_freed(struct bfq_queue *bfqq)
5981{
5982 struct bfq_entity *entity = &bfqq->entity;
5983
5984 for_each_entity(entity)
5985 entity->allocated--;
5986}
5987
5988/* returns true if it causes the idle timer to be disabled */
5989static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
5990{
5991 struct bfq_queue *bfqq = RQ_BFQQ(rq),
5992 *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true,
5993 RQ_BIC(rq));
5994 bool waiting, idle_timer_disabled = false;
5995
5996 if (new_bfqq) {
5997 /*
5998 * Release the request's reference to the old bfqq
5999 * and make sure one is taken to the shared queue.
6000 */
6001 bfqq_request_allocated(new_bfqq);
6002 bfqq_request_freed(bfqq);
6003 new_bfqq->ref++;
6004 /*
6005 * If the bic associated with the process
6006 * issuing this request still points to bfqq
6007 * (and thus has not been already redirected
6008 * to new_bfqq or even some other bfq_queue),
6009 * then complete the merge and redirect it to
6010 * new_bfqq.
6011 */
6012 if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
6013 bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
6014 bfqq, new_bfqq);
6015
6016 bfq_clear_bfqq_just_created(bfqq);
6017 /*
6018 * rq is about to be enqueued into new_bfqq,
6019 * release rq reference on bfqq
6020 */
6021 bfq_put_queue(bfqq);
6022 rq->elv.priv[1] = new_bfqq;
6023 bfqq = new_bfqq;
6024 }
6025
6026 bfq_update_io_thinktime(bfqd, bfqq);
6027 bfq_update_has_short_ttime(bfqd, bfqq, RQ_BIC(rq));
6028 bfq_update_io_seektime(bfqd, bfqq, rq);
6029
6030 waiting = bfqq && bfq_bfqq_wait_request(bfqq);
6031 bfq_add_request(rq);
6032 idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq);
6033
6034 rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
6035 list_add_tail(&rq->queuelist, &bfqq->fifo);
6036
6037 bfq_rq_enqueued(bfqd, bfqq, rq);
6038
6039 return idle_timer_disabled;
6040}
6041
6042#ifdef CONFIG_BFQ_CGROUP_DEBUG
6043static void bfq_update_insert_stats(struct request_queue *q,
6044 struct bfq_queue *bfqq,
6045 bool idle_timer_disabled,
6046 blk_opf_t cmd_flags)
6047{
6048 if (!bfqq)
6049 return;
6050
6051 /*
6052 * bfqq still exists, because it can disappear only after
6053 * either it is merged with another queue, or the process it
6054 * is associated with exits. But both actions must be taken by
6055 * the same process currently executing this flow of
6056 * instructions.
6057 *
6058 * In addition, the following queue lock guarantees that
6059 * bfqq_group(bfqq) exists as well.
6060 */
6061 spin_lock_irq(&q->queue_lock);
6062 bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags);
6063 if (idle_timer_disabled)
6064 bfqg_stats_update_idle_time(bfqq_group(bfqq));
6065 spin_unlock_irq(&q->queue_lock);
6066}
6067#else
6068static inline void bfq_update_insert_stats(struct request_queue *q,
6069 struct bfq_queue *bfqq,
6070 bool idle_timer_disabled,
6071 blk_opf_t cmd_flags) {}
6072#endif /* CONFIG_BFQ_CGROUP_DEBUG */
6073
6074static struct bfq_queue *bfq_init_rq(struct request *rq);
6075
6076static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
6077 bool at_head)
6078{
6079 struct request_queue *q = hctx->queue;
6080 struct bfq_data *bfqd = q->elevator->elevator_data;
6081 struct bfq_queue *bfqq;
6082 bool idle_timer_disabled = false;
6083 blk_opf_t cmd_flags;
6084 LIST_HEAD(free);
6085
6086#ifdef CONFIG_BFQ_GROUP_IOSCHED
6087 if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio)
6088 bfqg_stats_update_legacy_io(q, rq);
6089#endif
6090 spin_lock_irq(&bfqd->lock);
6091 bfqq = bfq_init_rq(rq);
6092 if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
6093 spin_unlock_irq(&bfqd->lock);
6094 blk_mq_free_requests(&free);
6095 return;
6096 }
6097
6098 trace_block_rq_insert(rq);
6099
6100 if (!bfqq || at_head) {
6101 if (at_head)
6102 list_add(&rq->queuelist, &bfqd->dispatch);
6103 else
6104 list_add_tail(&rq->queuelist, &bfqd->dispatch);
6105 } else {
6106 idle_timer_disabled = __bfq_insert_request(bfqd, rq);
6107 /*
6108 * Update bfqq, because, if a queue merge has occurred
6109 * in __bfq_insert_request, then rq has been
6110 * redirected into a new queue.
6111 */
6112 bfqq = RQ_BFQQ(rq);
6113
6114 if (rq_mergeable(rq)) {
6115 elv_rqhash_add(q, rq);
6116 if (!q->last_merge)
6117 q->last_merge = rq;
6118 }
6119 }
6120
6121 /*
6122 * Cache cmd_flags before releasing scheduler lock, because rq
6123 * may disappear afterwards (for example, because of a request
6124 * merge).
6125 */
6126 cmd_flags = rq->cmd_flags;
6127 spin_unlock_irq(&bfqd->lock);
6128
6129 bfq_update_insert_stats(q, bfqq, idle_timer_disabled,
6130 cmd_flags);
6131}
6132
6133static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
6134 struct list_head *list, bool at_head)
6135{
6136 while (!list_empty(list)) {
6137 struct request *rq;
6138
6139 rq = list_first_entry(list, struct request, queuelist);
6140 list_del_init(&rq->queuelist);
6141 bfq_insert_request(hctx, rq, at_head);
6142 }
6143}
6144
6145static void bfq_update_hw_tag(struct bfq_data *bfqd)
6146{
6147 struct bfq_queue *bfqq = bfqd->in_service_queue;
6148
6149 bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
6150 bfqd->rq_in_driver);
6151
6152 if (bfqd->hw_tag == 1)
6153 return;
6154
6155 /*
6156 * This sample is valid if the number of outstanding requests
6157 * is large enough to allow a queueing behavior. Note that the
6158 * sum is not exact, as it's not taking into account deactivated
6159 * requests.
6160 */
6161 if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
6162 return;
6163
6164 /*
6165 * If active queue hasn't enough requests and can idle, bfq might not
6166 * dispatch sufficient requests to hardware. Don't zero hw_tag in this
6167 * case
6168 */
6169 if (bfqq && bfq_bfqq_has_short_ttime(bfqq) &&
6170 bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] <
6171 BFQ_HW_QUEUE_THRESHOLD &&
6172 bfqd->rq_in_driver < BFQ_HW_QUEUE_THRESHOLD)
6173 return;
6174
6175 if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
6176 return;
6177
6178 bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
6179 bfqd->max_rq_in_driver = 0;
6180 bfqd->hw_tag_samples = 0;
6181
6182 bfqd->nonrot_with_queueing =
6183 blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag;
6184}
6185
6186static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
6187{
6188 u64 now_ns;
6189 u32 delta_us;
6190
6191 bfq_update_hw_tag(bfqd);
6192
6193 bfqd->rq_in_driver--;
6194 bfqq->dispatched--;
6195
6196 if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
6197 /*
6198 * Set budget_timeout (which we overload to store the
6199 * time at which the queue remains with no backlog and
6200 * no outstanding request; used by the weight-raising
6201 * mechanism).
6202 */
6203 bfqq->budget_timeout = jiffies;
6204
6205 bfq_del_bfqq_in_groups_with_pending_reqs(bfqq);
6206 bfq_weights_tree_remove(bfqq);
6207 }
6208
6209 now_ns = ktime_get_ns();
6210
6211 bfqq->ttime.last_end_request = now_ns;
6212
6213 /*
6214 * Using us instead of ns, to get a reasonable precision in
6215 * computing rate in next check.
6216 */
6217 delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
6218
6219 /*
6220 * If the request took rather long to complete, and, according
6221 * to the maximum request size recorded, this completion latency
6222 * implies that the request was certainly served at a very low
6223 * rate (less than 1M sectors/sec), then the whole observation
6224 * interval that lasts up to this time instant cannot be a
6225 * valid time interval for computing a new peak rate. Invoke
6226 * bfq_update_rate_reset to have the following three steps
6227 * taken:
6228 * - close the observation interval at the last (previous)
6229 * request dispatch or completion
6230 * - compute rate, if possible, for that observation interval
6231 * - reset to zero samples, which will trigger a proper
6232 * re-initialization of the observation interval on next
6233 * dispatch
6234 */
6235 if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
6236 (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
6237 1UL<<(BFQ_RATE_SHIFT - 10))
6238 bfq_update_rate_reset(bfqd, NULL);
6239 bfqd->last_completion = now_ns;
6240 /*
6241 * Shared queues are likely to receive I/O at a high
6242 * rate. This may deceptively let them be considered as wakers
6243 * of other queues. But a false waker will unjustly steal
6244 * bandwidth to its supposedly woken queue. So considering
6245 * also shared queues in the waking mechanism may cause more
6246 * control troubles than throughput benefits. Then reset
6247 * last_completed_rq_bfqq if bfqq is a shared queue.
6248 */
6249 if (!bfq_bfqq_coop(bfqq))
6250 bfqd->last_completed_rq_bfqq = bfqq;
6251 else
6252 bfqd->last_completed_rq_bfqq = NULL;
6253
6254 /*
6255 * If we are waiting to discover whether the request pattern
6256 * of the task associated with the queue is actually
6257 * isochronous, and both requisites for this condition to hold
6258 * are now satisfied, then compute soft_rt_next_start (see the
6259 * comments on the function bfq_bfqq_softrt_next_start()). We
6260 * do not compute soft_rt_next_start if bfqq is in interactive
6261 * weight raising (see the comments in bfq_bfqq_expire() for
6262 * an explanation). We schedule this delayed update when bfqq
6263 * expires, if it still has in-flight requests.
6264 */
6265 if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
6266 RB_EMPTY_ROOT(&bfqq->sort_list) &&
6267 bfqq->wr_coeff != bfqd->bfq_wr_coeff)
6268 bfqq->soft_rt_next_start =
6269 bfq_bfqq_softrt_next_start(bfqd, bfqq);
6270
6271 /*
6272 * If this is the in-service queue, check if it needs to be expired,
6273 * or if we want to idle in case it has no pending requests.
6274 */
6275 if (bfqd->in_service_queue == bfqq) {
6276 if (bfq_bfqq_must_idle(bfqq)) {
6277 if (bfqq->dispatched == 0)
6278 bfq_arm_slice_timer(bfqd);
6279 /*
6280 * If we get here, we do not expire bfqq, even
6281 * if bfqq was in budget timeout or had no
6282 * more requests (as controlled in the next
6283 * conditional instructions). The reason for
6284 * not expiring bfqq is as follows.
6285 *
6286 * Here bfqq->dispatched > 0 holds, but
6287 * bfq_bfqq_must_idle() returned true. This
6288 * implies that, even if no request arrives
6289 * for bfqq before bfqq->dispatched reaches 0,
6290 * bfqq will, however, not be expired on the
6291 * completion event that causes bfqq->dispatch
6292 * to reach zero. In contrast, on this event,
6293 * bfqq will start enjoying device idling
6294 * (I/O-dispatch plugging).
6295 *
6296 * But, if we expired bfqq here, bfqq would
6297 * not have the chance to enjoy device idling
6298 * when bfqq->dispatched finally reaches
6299 * zero. This would expose bfqq to violation
6300 * of its reserved service guarantees.
6301 */
6302 return;
6303 } else if (bfq_may_expire_for_budg_timeout(bfqq))
6304 bfq_bfqq_expire(bfqd, bfqq, false,
6305 BFQQE_BUDGET_TIMEOUT);
6306 else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
6307 (bfqq->dispatched == 0 ||
6308 !bfq_better_to_idle(bfqq)))
6309 bfq_bfqq_expire(bfqd, bfqq, false,
6310 BFQQE_NO_MORE_REQUESTS);
6311 }
6312
6313 if (!bfqd->rq_in_driver)
6314 bfq_schedule_dispatch(bfqd);
6315}
6316
6317/*
6318 * The processes associated with bfqq may happen to generate their
6319 * cumulative I/O at a lower rate than the rate at which the device
6320 * could serve the same I/O. This is rather probable, e.g., if only
6321 * one process is associated with bfqq and the device is an SSD. It
6322 * results in bfqq becoming often empty while in service. In this
6323 * respect, if BFQ is allowed to switch to another queue when bfqq
6324 * remains empty, then the device goes on being fed with I/O requests,
6325 * and the throughput is not affected. In contrast, if BFQ is not
6326 * allowed to switch to another queue---because bfqq is sync and
6327 * I/O-dispatch needs to be plugged while bfqq is temporarily
6328 * empty---then, during the service of bfqq, there will be frequent
6329 * "service holes", i.e., time intervals during which bfqq gets empty
6330 * and the device can only consume the I/O already queued in its
6331 * hardware queues. During service holes, the device may even get to
6332 * remaining idle. In the end, during the service of bfqq, the device
6333 * is driven at a lower speed than the one it can reach with the kind
6334 * of I/O flowing through bfqq.
6335 *
6336 * To counter this loss of throughput, BFQ implements a "request
6337 * injection mechanism", which tries to fill the above service holes
6338 * with I/O requests taken from other queues. The hard part in this
6339 * mechanism is finding the right amount of I/O to inject, so as to
6340 * both boost throughput and not break bfqq's bandwidth and latency
6341 * guarantees. In this respect, the mechanism maintains a per-queue
6342 * inject limit, computed as below. While bfqq is empty, the injection
6343 * mechanism dispatches extra I/O requests only until the total number
6344 * of I/O requests in flight---i.e., already dispatched but not yet
6345 * completed---remains lower than this limit.
6346 *
6347 * A first definition comes in handy to introduce the algorithm by
6348 * which the inject limit is computed. We define as first request for
6349 * bfqq, an I/O request for bfqq that arrives while bfqq is in
6350 * service, and causes bfqq to switch from empty to non-empty. The
6351 * algorithm updates the limit as a function of the effect of
6352 * injection on the service times of only the first requests of
6353 * bfqq. The reason for this restriction is that these are the
6354 * requests whose service time is affected most, because they are the
6355 * first to arrive after injection possibly occurred.
6356 *
6357 * To evaluate the effect of injection, the algorithm measures the
6358 * "total service time" of first requests. We define as total service
6359 * time of an I/O request, the time that elapses since when the
6360 * request is enqueued into bfqq, to when it is completed. This
6361 * quantity allows the whole effect of injection to be measured. It is
6362 * easy to see why. Suppose that some requests of other queues are
6363 * actually injected while bfqq is empty, and that a new request R
6364 * then arrives for bfqq. If the device does start to serve all or
6365 * part of the injected requests during the service hole, then,
6366 * because of this extra service, it may delay the next invocation of
6367 * the dispatch hook of BFQ. Then, even after R gets eventually
6368 * dispatched, the device may delay the actual service of R if it is
6369 * still busy serving the extra requests, or if it decides to serve,
6370 * before R, some extra request still present in its queues. As a
6371 * conclusion, the cumulative extra delay caused by injection can be
6372 * easily evaluated by just comparing the total service time of first
6373 * requests with and without injection.
6374 *
6375 * The limit-update algorithm works as follows. On the arrival of a
6376 * first request of bfqq, the algorithm measures the total time of the
6377 * request only if one of the three cases below holds, and, for each
6378 * case, it updates the limit as described below:
6379 *
6380 * (1) If there is no in-flight request. This gives a baseline for the
6381 * total service time of the requests of bfqq. If the baseline has
6382 * not been computed yet, then, after computing it, the limit is
6383 * set to 1, to start boosting throughput, and to prepare the
6384 * ground for the next case. If the baseline has already been
6385 * computed, then it is updated, in case it results to be lower
6386 * than the previous value.
6387 *
6388 * (2) If the limit is higher than 0 and there are in-flight
6389 * requests. By comparing the total service time in this case with
6390 * the above baseline, it is possible to know at which extent the
6391 * current value of the limit is inflating the total service
6392 * time. If the inflation is below a certain threshold, then bfqq
6393 * is assumed to be suffering from no perceivable loss of its
6394 * service guarantees, and the limit is even tentatively
6395 * increased. If the inflation is above the threshold, then the
6396 * limit is decreased. Due to the lack of any hysteresis, this
6397 * logic makes the limit oscillate even in steady workload
6398 * conditions. Yet we opted for it, because it is fast in reaching
6399 * the best value for the limit, as a function of the current I/O
6400 * workload. To reduce oscillations, this step is disabled for a
6401 * short time interval after the limit happens to be decreased.
6402 *
6403 * (3) Periodically, after resetting the limit, to make sure that the
6404 * limit eventually drops in case the workload changes. This is
6405 * needed because, after the limit has gone safely up for a
6406 * certain workload, it is impossible to guess whether the
6407 * baseline total service time may have changed, without measuring
6408 * it again without injection. A more effective version of this
6409 * step might be to just sample the baseline, by interrupting
6410 * injection only once, and then to reset/lower the limit only if
6411 * the total service time with the current limit does happen to be
6412 * too large.
6413 *
6414 * More details on each step are provided in the comments on the
6415 * pieces of code that implement these steps: the branch handling the
6416 * transition from empty to non empty in bfq_add_request(), the branch
6417 * handling injection in bfq_select_queue(), and the function
6418 * bfq_choose_bfqq_for_injection(). These comments also explain some
6419 * exceptions, made by the injection mechanism in some special cases.
6420 */
6421static void bfq_update_inject_limit(struct bfq_data *bfqd,
6422 struct bfq_queue *bfqq)
6423{
6424 u64 tot_time_ns = ktime_get_ns() - bfqd->last_empty_occupied_ns;
6425 unsigned int old_limit = bfqq->inject_limit;
6426
6427 if (bfqq->last_serv_time_ns > 0 && bfqd->rqs_injected) {
6428 u64 threshold = (bfqq->last_serv_time_ns * 3)>>1;
6429
6430 if (tot_time_ns >= threshold && old_limit > 0) {
6431 bfqq->inject_limit--;
6432 bfqq->decrease_time_jif = jiffies;
6433 } else if (tot_time_ns < threshold &&
6434 old_limit <= bfqd->max_rq_in_driver)
6435 bfqq->inject_limit++;
6436 }
6437
6438 /*
6439 * Either we still have to compute the base value for the
6440 * total service time, and there seem to be the right
6441 * conditions to do it, or we can lower the last base value
6442 * computed.
6443 *
6444 * NOTE: (bfqd->rq_in_driver == 1) means that there is no I/O
6445 * request in flight, because this function is in the code
6446 * path that handles the completion of a request of bfqq, and,
6447 * in particular, this function is executed before
6448 * bfqd->rq_in_driver is decremented in such a code path.
6449 */
6450 if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 1) ||
6451 tot_time_ns < bfqq->last_serv_time_ns) {
6452 if (bfqq->last_serv_time_ns == 0) {
6453 /*
6454 * Now we certainly have a base value: make sure we
6455 * start trying injection.
6456 */
6457 bfqq->inject_limit = max_t(unsigned int, 1, old_limit);
6458 }
6459 bfqq->last_serv_time_ns = tot_time_ns;
6460 } else if (!bfqd->rqs_injected && bfqd->rq_in_driver == 1)
6461 /*
6462 * No I/O injected and no request still in service in
6463 * the drive: these are the exact conditions for
6464 * computing the base value of the total service time
6465 * for bfqq. So let's update this value, because it is
6466 * rather variable. For example, it varies if the size
6467 * or the spatial locality of the I/O requests in bfqq
6468 * change.
6469 */
6470 bfqq->last_serv_time_ns = tot_time_ns;
6471
6472
6473 /* update complete, not waiting for any request completion any longer */
6474 bfqd->waited_rq = NULL;
6475 bfqd->rqs_injected = false;
6476}
6477
6478/*
6479 * Handle either a requeue or a finish for rq. The things to do are
6480 * the same in both cases: all references to rq are to be dropped. In
6481 * particular, rq is considered completed from the point of view of
6482 * the scheduler.
6483 */
6484static void bfq_finish_requeue_request(struct request *rq)
6485{
6486 struct bfq_queue *bfqq = RQ_BFQQ(rq);
6487 struct bfq_data *bfqd;
6488 unsigned long flags;
6489
6490 /*
6491 * rq either is not associated with any icq, or is an already
6492 * requeued request that has not (yet) been re-inserted into
6493 * a bfq_queue.
6494 */
6495 if (!rq->elv.icq || !bfqq)
6496 return;
6497
6498 bfqd = bfqq->bfqd;
6499
6500 if (rq->rq_flags & RQF_STARTED)
6501 bfqg_stats_update_completion(bfqq_group(bfqq),
6502 rq->start_time_ns,
6503 rq->io_start_time_ns,
6504 rq->cmd_flags);
6505
6506 spin_lock_irqsave(&bfqd->lock, flags);
6507 if (likely(rq->rq_flags & RQF_STARTED)) {
6508 if (rq == bfqd->waited_rq)
6509 bfq_update_inject_limit(bfqd, bfqq);
6510
6511 bfq_completed_request(bfqq, bfqd);
6512 }
6513 bfqq_request_freed(bfqq);
6514 bfq_put_queue(bfqq);
6515 RQ_BIC(rq)->requests--;
6516 spin_unlock_irqrestore(&bfqd->lock, flags);
6517
6518 /*
6519 * Reset private fields. In case of a requeue, this allows
6520 * this function to correctly do nothing if it is spuriously
6521 * invoked again on this same request (see the check at the
6522 * beginning of the function). Probably, a better general
6523 * design would be to prevent blk-mq from invoking the requeue
6524 * or finish hooks of an elevator, for a request that is not
6525 * referred by that elevator.
6526 *
6527 * Resetting the following fields would break the
6528 * request-insertion logic if rq is re-inserted into a bfq
6529 * internal queue, without a re-preparation. Here we assume
6530 * that re-insertions of requeued requests, without
6531 * re-preparation, can happen only for pass_through or at_head
6532 * requests (which are not re-inserted into bfq internal
6533 * queues).
6534 */
6535 rq->elv.priv[0] = NULL;
6536 rq->elv.priv[1] = NULL;
6537}
6538
6539static void bfq_finish_request(struct request *rq)
6540{
6541 bfq_finish_requeue_request(rq);
6542
6543 if (rq->elv.icq) {
6544 put_io_context(rq->elv.icq->ioc);
6545 rq->elv.icq = NULL;
6546 }
6547}
6548
6549/*
6550 * Removes the association between the current task and bfqq, assuming
6551 * that bic points to the bfq iocontext of the task.
6552 * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
6553 * was the last process referring to that bfqq.
6554 */
6555static struct bfq_queue *
6556bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
6557{
6558 bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
6559
6560 if (bfqq_process_refs(bfqq) == 1) {
6561 bfqq->pid = current->pid;
6562 bfq_clear_bfqq_coop(bfqq);
6563 bfq_clear_bfqq_split_coop(bfqq);
6564 return bfqq;
6565 }
6566
6567 bic_set_bfqq(bic, NULL, true);
6568
6569 bfq_put_cooperator(bfqq);
6570
6571 bfq_release_process_ref(bfqq->bfqd, bfqq);
6572 return NULL;
6573}
6574
6575static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
6576 struct bfq_io_cq *bic,
6577 struct bio *bio,
6578 bool split, bool is_sync,
6579 bool *new_queue)
6580{
6581 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
6582
6583 if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
6584 return bfqq;
6585
6586 if (new_queue)
6587 *new_queue = true;
6588
6589 if (bfqq)
6590 bfq_put_queue(bfqq);
6591 bfqq = bfq_get_queue(bfqd, bio, is_sync, bic, split);
6592
6593 bic_set_bfqq(bic, bfqq, is_sync);
6594 if (split && is_sync) {
6595 if ((bic->was_in_burst_list && bfqd->large_burst) ||
6596 bic->saved_in_large_burst)
6597 bfq_mark_bfqq_in_large_burst(bfqq);
6598 else {
6599 bfq_clear_bfqq_in_large_burst(bfqq);
6600 if (bic->was_in_burst_list)
6601 /*
6602 * If bfqq was in the current
6603 * burst list before being
6604 * merged, then we have to add
6605 * it back. And we do not need
6606 * to increase burst_size, as
6607 * we did not decrement
6608 * burst_size when we removed
6609 * bfqq from the burst list as
6610 * a consequence of a merge
6611 * (see comments in
6612 * bfq_put_queue). In this
6613 * respect, it would be rather
6614 * costly to know whether the
6615 * current burst list is still
6616 * the same burst list from
6617 * which bfqq was removed on
6618 * the merge. To avoid this
6619 * cost, if bfqq was in a
6620 * burst list, then we add
6621 * bfqq to the current burst
6622 * list without any further
6623 * check. This can cause
6624 * inappropriate insertions,
6625 * but rarely enough to not
6626 * harm the detection of large
6627 * bursts significantly.
6628 */
6629 hlist_add_head(&bfqq->burst_list_node,
6630 &bfqd->burst_list);
6631 }
6632 bfqq->split_time = jiffies;
6633 }
6634
6635 return bfqq;
6636}
6637
6638/*
6639 * Only reset private fields. The actual request preparation will be
6640 * performed by bfq_init_rq, when rq is either inserted or merged. See
6641 * comments on bfq_init_rq for the reason behind this delayed
6642 * preparation.
6643 */
6644static void bfq_prepare_request(struct request *rq)
6645{
6646 rq->elv.icq = ioc_find_get_icq(rq->q);
6647
6648 /*
6649 * Regardless of whether we have an icq attached, we have to
6650 * clear the scheduler pointers, as they might point to
6651 * previously allocated bic/bfqq structs.
6652 */
6653 rq->elv.priv[0] = rq->elv.priv[1] = NULL;
6654}
6655
6656/*
6657 * If needed, init rq, allocate bfq data structures associated with
6658 * rq, and increment reference counters in the destination bfq_queue
6659 * for rq. Return the destination bfq_queue for rq, or NULL is rq is
6660 * not associated with any bfq_queue.
6661 *
6662 * This function is invoked by the functions that perform rq insertion
6663 * or merging. One may have expected the above preparation operations
6664 * to be performed in bfq_prepare_request, and not delayed to when rq
6665 * is inserted or merged. The rationale behind this delayed
6666 * preparation is that, after the prepare_request hook is invoked for
6667 * rq, rq may still be transformed into a request with no icq, i.e., a
6668 * request not associated with any queue. No bfq hook is invoked to
6669 * signal this transformation. As a consequence, should these
6670 * preparation operations be performed when the prepare_request hook
6671 * is invoked, and should rq be transformed one moment later, bfq
6672 * would end up in an inconsistent state, because it would have
6673 * incremented some queue counters for an rq destined to
6674 * transformation, without any chance to correctly lower these
6675 * counters back. In contrast, no transformation can still happen for
6676 * rq after rq has been inserted or merged. So, it is safe to execute
6677 * these preparation operations when rq is finally inserted or merged.
6678 */
6679static struct bfq_queue *bfq_init_rq(struct request *rq)
6680{
6681 struct request_queue *q = rq->q;
6682 struct bio *bio = rq->bio;
6683 struct bfq_data *bfqd = q->elevator->elevator_data;
6684 struct bfq_io_cq *bic;
6685 const int is_sync = rq_is_sync(rq);
6686 struct bfq_queue *bfqq;
6687 bool new_queue = false;
6688 bool bfqq_already_existing = false, split = false;
6689
6690 if (unlikely(!rq->elv.icq))
6691 return NULL;
6692
6693 /*
6694 * Assuming that elv.priv[1] is set only if everything is set
6695 * for this rq. This holds true, because this function is
6696 * invoked only for insertion or merging, and, after such
6697 * events, a request cannot be manipulated any longer before
6698 * being removed from bfq.
6699 */
6700 if (rq->elv.priv[1])
6701 return rq->elv.priv[1];
6702
6703 bic = icq_to_bic(rq->elv.icq);
6704
6705 bfq_check_ioprio_change(bic, bio);
6706
6707 bfq_bic_update_cgroup(bic, bio);
6708
6709 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
6710 &new_queue);
6711
6712 if (likely(!new_queue)) {
6713 /* If the queue was seeky for too long, break it apart. */
6714 if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) &&
6715 !bic->stably_merged) {
6716 struct bfq_queue *old_bfqq = bfqq;
6717
6718 /* Update bic before losing reference to bfqq */
6719 if (bfq_bfqq_in_large_burst(bfqq))
6720 bic->saved_in_large_burst = true;
6721
6722 bfqq = bfq_split_bfqq(bic, bfqq);
6723 split = true;
6724
6725 if (!bfqq) {
6726 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
6727 true, is_sync,
6728 NULL);
6729 if (unlikely(bfqq == &bfqd->oom_bfqq))
6730 bfqq_already_existing = true;
6731 } else
6732 bfqq_already_existing = true;
6733
6734 if (!bfqq_already_existing) {
6735 bfqq->waker_bfqq = old_bfqq->waker_bfqq;
6736 bfqq->tentative_waker_bfqq = NULL;
6737
6738 /*
6739 * If the waker queue disappears, then
6740 * new_bfqq->waker_bfqq must be
6741 * reset. So insert new_bfqq into the
6742 * woken_list of the waker. See
6743 * bfq_check_waker for details.
6744 */
6745 if (bfqq->waker_bfqq)
6746 hlist_add_head(&bfqq->woken_list_node,
6747 &bfqq->waker_bfqq->woken_list);
6748 }
6749 }
6750 }
6751
6752 bfqq_request_allocated(bfqq);
6753 bfqq->ref++;
6754 bic->requests++;
6755 bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
6756 rq, bfqq, bfqq->ref);
6757
6758 rq->elv.priv[0] = bic;
6759 rq->elv.priv[1] = bfqq;
6760
6761 /*
6762 * If a bfq_queue has only one process reference, it is owned
6763 * by only this bic: we can then set bfqq->bic = bic. in
6764 * addition, if the queue has also just been split, we have to
6765 * resume its state.
6766 */
6767 if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
6768 bfqq->bic = bic;
6769 if (split) {
6770 /*
6771 * The queue has just been split from a shared
6772 * queue: restore the idle window and the
6773 * possible weight raising period.
6774 */
6775 bfq_bfqq_resume_state(bfqq, bfqd, bic,
6776 bfqq_already_existing);
6777 }
6778 }
6779
6780 /*
6781 * Consider bfqq as possibly belonging to a burst of newly
6782 * created queues only if:
6783 * 1) A burst is actually happening (bfqd->burst_size > 0)
6784 * or
6785 * 2) There is no other active queue. In fact, if, in
6786 * contrast, there are active queues not belonging to the
6787 * possible burst bfqq may belong to, then there is no gain
6788 * in considering bfqq as belonging to a burst, and
6789 * therefore in not weight-raising bfqq. See comments on
6790 * bfq_handle_burst().
6791 *
6792 * This filtering also helps eliminating false positives,
6793 * occurring when bfqq does not belong to an actual large
6794 * burst, but some background task (e.g., a service) happens
6795 * to trigger the creation of new queues very close to when
6796 * bfqq and its possible companion queues are created. See
6797 * comments on bfq_handle_burst() for further details also on
6798 * this issue.
6799 */
6800 if (unlikely(bfq_bfqq_just_created(bfqq) &&
6801 (bfqd->burst_size > 0 ||
6802 bfq_tot_busy_queues(bfqd) == 0)))
6803 bfq_handle_burst(bfqd, bfqq);
6804
6805 return bfqq;
6806}
6807
6808static void
6809bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq)
6810{
6811 enum bfqq_expiration reason;
6812 unsigned long flags;
6813
6814 spin_lock_irqsave(&bfqd->lock, flags);
6815
6816 /*
6817 * Considering that bfqq may be in race, we should firstly check
6818 * whether bfqq is in service before doing something on it. If
6819 * the bfqq in race is not in service, it has already been expired
6820 * through __bfq_bfqq_expire func and its wait_request flags has
6821 * been cleared in __bfq_bfqd_reset_in_service func.
6822 */
6823 if (bfqq != bfqd->in_service_queue) {
6824 spin_unlock_irqrestore(&bfqd->lock, flags);
6825 return;
6826 }
6827
6828 bfq_clear_bfqq_wait_request(bfqq);
6829
6830 if (bfq_bfqq_budget_timeout(bfqq))
6831 /*
6832 * Also here the queue can be safely expired
6833 * for budget timeout without wasting
6834 * guarantees
6835 */
6836 reason = BFQQE_BUDGET_TIMEOUT;
6837 else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
6838 /*
6839 * The queue may not be empty upon timer expiration,
6840 * because we may not disable the timer when the
6841 * first request of the in-service queue arrives
6842 * during disk idling.
6843 */
6844 reason = BFQQE_TOO_IDLE;
6845 else
6846 goto schedule_dispatch;
6847
6848 bfq_bfqq_expire(bfqd, bfqq, true, reason);
6849
6850schedule_dispatch:
6851 bfq_schedule_dispatch(bfqd);
6852 spin_unlock_irqrestore(&bfqd->lock, flags);
6853}
6854
6855/*
6856 * Handler of the expiration of the timer running if the in-service queue
6857 * is idling inside its time slice.
6858 */
6859static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
6860{
6861 struct bfq_data *bfqd = container_of(timer, struct bfq_data,
6862 idle_slice_timer);
6863 struct bfq_queue *bfqq = bfqd->in_service_queue;
6864
6865 /*
6866 * Theoretical race here: the in-service queue can be NULL or
6867 * different from the queue that was idling if a new request
6868 * arrives for the current queue and there is a full dispatch
6869 * cycle that changes the in-service queue. This can hardly
6870 * happen, but in the worst case we just expire a queue too
6871 * early.
6872 */
6873 if (bfqq)
6874 bfq_idle_slice_timer_body(bfqd, bfqq);
6875
6876 return HRTIMER_NORESTART;
6877}
6878
6879static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
6880 struct bfq_queue **bfqq_ptr)
6881{
6882 struct bfq_queue *bfqq = *bfqq_ptr;
6883
6884 bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
6885 if (bfqq) {
6886 bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
6887
6888 bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
6889 bfqq, bfqq->ref);
6890 bfq_put_queue(bfqq);
6891 *bfqq_ptr = NULL;
6892 }
6893}
6894
6895/*
6896 * Release all the bfqg references to its async queues. If we are
6897 * deallocating the group these queues may still contain requests, so
6898 * we reparent them to the root cgroup (i.e., the only one that will
6899 * exist for sure until all the requests on a device are gone).
6900 */
6901void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
6902{
6903 int i, j;
6904
6905 for (i = 0; i < 2; i++)
6906 for (j = 0; j < IOPRIO_NR_LEVELS; j++)
6907 __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
6908
6909 __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
6910}
6911
6912/*
6913 * See the comments on bfq_limit_depth for the purpose of
6914 * the depths set in the function. Return minimum shallow depth we'll use.
6915 */
6916static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
6917{
6918 unsigned int depth = 1U << bt->sb.shift;
6919
6920 bfqd->full_depth_shift = bt->sb.shift;
6921 /*
6922 * In-word depths if no bfq_queue is being weight-raised:
6923 * leaving 25% of tags only for sync reads.
6924 *
6925 * In next formulas, right-shift the value
6926 * (1U<<bt->sb.shift), instead of computing directly
6927 * (1U<<(bt->sb.shift - something)), to be robust against
6928 * any possible value of bt->sb.shift, without having to
6929 * limit 'something'.
6930 */
6931 /* no more than 50% of tags for async I/O */
6932 bfqd->word_depths[0][0] = max(depth >> 1, 1U);
6933 /*
6934 * no more than 75% of tags for sync writes (25% extra tags
6935 * w.r.t. async I/O, to prevent async I/O from starving sync
6936 * writes)
6937 */
6938 bfqd->word_depths[0][1] = max((depth * 3) >> 2, 1U);
6939
6940 /*
6941 * In-word depths in case some bfq_queue is being weight-
6942 * raised: leaving ~63% of tags for sync reads. This is the
6943 * highest percentage for which, in our tests, application
6944 * start-up times didn't suffer from any regression due to tag
6945 * shortage.
6946 */
6947 /* no more than ~18% of tags for async I/O */
6948 bfqd->word_depths[1][0] = max((depth * 3) >> 4, 1U);
6949 /* no more than ~37% of tags for sync writes (~20% extra tags) */
6950 bfqd->word_depths[1][1] = max((depth * 6) >> 4, 1U);
6951}
6952
6953static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx)
6954{
6955 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
6956 struct blk_mq_tags *tags = hctx->sched_tags;
6957
6958 bfq_update_depths(bfqd, &tags->bitmap_tags);
6959 sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, 1);
6960}
6961
6962static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
6963{
6964 bfq_depth_updated(hctx);
6965 return 0;
6966}
6967
6968static void bfq_exit_queue(struct elevator_queue *e)
6969{
6970 struct bfq_data *bfqd = e->elevator_data;
6971 struct bfq_queue *bfqq, *n;
6972
6973 hrtimer_cancel(&bfqd->idle_slice_timer);
6974
6975 spin_lock_irq(&bfqd->lock);
6976 list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
6977 bfq_deactivate_bfqq(bfqd, bfqq, false, false);
6978 spin_unlock_irq(&bfqd->lock);
6979
6980 hrtimer_cancel(&bfqd->idle_slice_timer);
6981
6982 /* release oom-queue reference to root group */
6983 bfqg_and_blkg_put(bfqd->root_group);
6984
6985#ifdef CONFIG_BFQ_GROUP_IOSCHED
6986 blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
6987#else
6988 spin_lock_irq(&bfqd->lock);
6989 bfq_put_async_queues(bfqd, bfqd->root_group);
6990 kfree(bfqd->root_group);
6991 spin_unlock_irq(&bfqd->lock);
6992#endif
6993
6994 blk_stat_disable_accounting(bfqd->queue);
6995 clear_bit(ELEVATOR_FLAG_DISABLE_WBT, &e->flags);
6996 wbt_enable_default(bfqd->queue);
6997
6998 kfree(bfqd);
6999}
7000
7001static void bfq_init_root_group(struct bfq_group *root_group,
7002 struct bfq_data *bfqd)
7003{
7004 int i;
7005
7006#ifdef CONFIG_BFQ_GROUP_IOSCHED
7007 root_group->entity.parent = NULL;
7008 root_group->my_entity = NULL;
7009 root_group->bfqd = bfqd;
7010#endif
7011 root_group->rq_pos_tree = RB_ROOT;
7012 for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
7013 root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
7014 root_group->sched_data.bfq_class_idle_last_service = jiffies;
7015}
7016
7017static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
7018{
7019 struct bfq_data *bfqd;
7020 struct elevator_queue *eq;
7021
7022 eq = elevator_alloc(q, e);
7023 if (!eq)
7024 return -ENOMEM;
7025
7026 bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
7027 if (!bfqd) {
7028 kobject_put(&eq->kobj);
7029 return -ENOMEM;
7030 }
7031 eq->elevator_data = bfqd;
7032
7033 spin_lock_irq(&q->queue_lock);
7034 q->elevator = eq;
7035 spin_unlock_irq(&q->queue_lock);
7036
7037 /*
7038 * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
7039 * Grab a permanent reference to it, so that the normal code flow
7040 * will not attempt to free it.
7041 */
7042 bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
7043 bfqd->oom_bfqq.ref++;
7044 bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
7045 bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
7046 bfqd->oom_bfqq.entity.new_weight =
7047 bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
7048
7049 /* oom_bfqq does not participate to bursts */
7050 bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
7051
7052 /*
7053 * Trigger weight initialization, according to ioprio, at the
7054 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
7055 * class won't be changed any more.
7056 */
7057 bfqd->oom_bfqq.entity.prio_changed = 1;
7058
7059 bfqd->queue = q;
7060
7061 INIT_LIST_HEAD(&bfqd->dispatch);
7062
7063 hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
7064 HRTIMER_MODE_REL);
7065 bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
7066
7067 bfqd->queue_weights_tree = RB_ROOT_CACHED;
7068#ifdef CONFIG_BFQ_GROUP_IOSCHED
7069 bfqd->num_groups_with_pending_reqs = 0;
7070#endif
7071
7072 INIT_LIST_HEAD(&bfqd->active_list);
7073 INIT_LIST_HEAD(&bfqd->idle_list);
7074 INIT_HLIST_HEAD(&bfqd->burst_list);
7075
7076 bfqd->hw_tag = -1;
7077 bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue);
7078
7079 bfqd->bfq_max_budget = bfq_default_max_budget;
7080
7081 bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
7082 bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
7083 bfqd->bfq_back_max = bfq_back_max;
7084 bfqd->bfq_back_penalty = bfq_back_penalty;
7085 bfqd->bfq_slice_idle = bfq_slice_idle;
7086 bfqd->bfq_timeout = bfq_timeout;
7087
7088 bfqd->bfq_large_burst_thresh = 8;
7089 bfqd->bfq_burst_interval = msecs_to_jiffies(180);
7090
7091 bfqd->low_latency = true;
7092
7093 /*
7094 * Trade-off between responsiveness and fairness.
7095 */
7096 bfqd->bfq_wr_coeff = 30;
7097 bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
7098 bfqd->bfq_wr_max_time = 0;
7099 bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
7100 bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
7101 bfqd->bfq_wr_max_softrt_rate = 7000; /*
7102 * Approximate rate required
7103 * to playback or record a
7104 * high-definition compressed
7105 * video.
7106 */
7107 bfqd->wr_busy_queues = 0;
7108
7109 /*
7110 * Begin by assuming, optimistically, that the device peak
7111 * rate is equal to 2/3 of the highest reference rate.
7112 */
7113 bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] *
7114 ref_wr_duration[blk_queue_nonrot(bfqd->queue)];
7115 bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
7116
7117 spin_lock_init(&bfqd->lock);
7118
7119 /*
7120 * The invocation of the next bfq_create_group_hierarchy
7121 * function is the head of a chain of function calls
7122 * (bfq_create_group_hierarchy->blkcg_activate_policy->
7123 * blk_mq_freeze_queue) that may lead to the invocation of the
7124 * has_work hook function. For this reason,
7125 * bfq_create_group_hierarchy is invoked only after all
7126 * scheduler data has been initialized, apart from the fields
7127 * that can be initialized only after invoking
7128 * bfq_create_group_hierarchy. This, in particular, enables
7129 * has_work to correctly return false. Of course, to avoid
7130 * other inconsistencies, the blk-mq stack must then refrain
7131 * from invoking further scheduler hooks before this init
7132 * function is finished.
7133 */
7134 bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
7135 if (!bfqd->root_group)
7136 goto out_free;
7137 bfq_init_root_group(bfqd->root_group, bfqd);
7138 bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
7139
7140 /* We dispatch from request queue wide instead of hw queue */
7141 blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
7142
7143 set_bit(ELEVATOR_FLAG_DISABLE_WBT, &eq->flags);
7144 wbt_disable_default(q);
7145 blk_stat_enable_accounting(q);
7146
7147 return 0;
7148
7149out_free:
7150 kfree(bfqd);
7151 kobject_put(&eq->kobj);
7152 return -ENOMEM;
7153}
7154
7155static void bfq_slab_kill(void)
7156{
7157 kmem_cache_destroy(bfq_pool);
7158}
7159
7160static int __init bfq_slab_setup(void)
7161{
7162 bfq_pool = KMEM_CACHE(bfq_queue, 0);
7163 if (!bfq_pool)
7164 return -ENOMEM;
7165 return 0;
7166}
7167
7168static ssize_t bfq_var_show(unsigned int var, char *page)
7169{
7170 return sprintf(page, "%u\n", var);
7171}
7172
7173static int bfq_var_store(unsigned long *var, const char *page)
7174{
7175 unsigned long new_val;
7176 int ret = kstrtoul(page, 10, &new_val);
7177
7178 if (ret)
7179 return ret;
7180 *var = new_val;
7181 return 0;
7182}
7183
7184#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
7185static ssize_t __FUNC(struct elevator_queue *e, char *page) \
7186{ \
7187 struct bfq_data *bfqd = e->elevator_data; \
7188 u64 __data = __VAR; \
7189 if (__CONV == 1) \
7190 __data = jiffies_to_msecs(__data); \
7191 else if (__CONV == 2) \
7192 __data = div_u64(__data, NSEC_PER_MSEC); \
7193 return bfq_var_show(__data, (page)); \
7194}
7195SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
7196SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
7197SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
7198SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
7199SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
7200SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
7201SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
7202SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
7203SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
7204#undef SHOW_FUNCTION
7205
7206#define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
7207static ssize_t __FUNC(struct elevator_queue *e, char *page) \
7208{ \
7209 struct bfq_data *bfqd = e->elevator_data; \
7210 u64 __data = __VAR; \
7211 __data = div_u64(__data, NSEC_PER_USEC); \
7212 return bfq_var_show(__data, (page)); \
7213}
7214USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
7215#undef USEC_SHOW_FUNCTION
7216
7217#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
7218static ssize_t \
7219__FUNC(struct elevator_queue *e, const char *page, size_t count) \
7220{ \
7221 struct bfq_data *bfqd = e->elevator_data; \
7222 unsigned long __data, __min = (MIN), __max = (MAX); \
7223 int ret; \
7224 \
7225 ret = bfq_var_store(&__data, (page)); \
7226 if (ret) \
7227 return ret; \
7228 if (__data < __min) \
7229 __data = __min; \
7230 else if (__data > __max) \
7231 __data = __max; \
7232 if (__CONV == 1) \
7233 *(__PTR) = msecs_to_jiffies(__data); \
7234 else if (__CONV == 2) \
7235 *(__PTR) = (u64)__data * NSEC_PER_MSEC; \
7236 else \
7237 *(__PTR) = __data; \
7238 return count; \
7239}
7240STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
7241 INT_MAX, 2);
7242STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
7243 INT_MAX, 2);
7244STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
7245STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
7246 INT_MAX, 0);
7247STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
7248#undef STORE_FUNCTION
7249
7250#define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
7251static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
7252{ \
7253 struct bfq_data *bfqd = e->elevator_data; \
7254 unsigned long __data, __min = (MIN), __max = (MAX); \
7255 int ret; \
7256 \
7257 ret = bfq_var_store(&__data, (page)); \
7258 if (ret) \
7259 return ret; \
7260 if (__data < __min) \
7261 __data = __min; \
7262 else if (__data > __max) \
7263 __data = __max; \
7264 *(__PTR) = (u64)__data * NSEC_PER_USEC; \
7265 return count; \
7266}
7267USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
7268 UINT_MAX);
7269#undef USEC_STORE_FUNCTION
7270
7271static ssize_t bfq_max_budget_store(struct elevator_queue *e,
7272 const char *page, size_t count)
7273{
7274 struct bfq_data *bfqd = e->elevator_data;
7275 unsigned long __data;
7276 int ret;
7277
7278 ret = bfq_var_store(&__data, (page));
7279 if (ret)
7280 return ret;
7281
7282 if (__data == 0)
7283 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7284 else {
7285 if (__data > INT_MAX)
7286 __data = INT_MAX;
7287 bfqd->bfq_max_budget = __data;
7288 }
7289
7290 bfqd->bfq_user_max_budget = __data;
7291
7292 return count;
7293}
7294
7295/*
7296 * Leaving this name to preserve name compatibility with cfq
7297 * parameters, but this timeout is used for both sync and async.
7298 */
7299static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
7300 const char *page, size_t count)
7301{
7302 struct bfq_data *bfqd = e->elevator_data;
7303 unsigned long __data;
7304 int ret;
7305
7306 ret = bfq_var_store(&__data, (page));
7307 if (ret)
7308 return ret;
7309
7310 if (__data < 1)
7311 __data = 1;
7312 else if (__data > INT_MAX)
7313 __data = INT_MAX;
7314
7315 bfqd->bfq_timeout = msecs_to_jiffies(__data);
7316 if (bfqd->bfq_user_max_budget == 0)
7317 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7318
7319 return count;
7320}
7321
7322static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
7323 const char *page, size_t count)
7324{
7325 struct bfq_data *bfqd = e->elevator_data;
7326 unsigned long __data;
7327 int ret;
7328
7329 ret = bfq_var_store(&__data, (page));
7330 if (ret)
7331 return ret;
7332
7333 if (__data > 1)
7334 __data = 1;
7335 if (!bfqd->strict_guarantees && __data == 1
7336 && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
7337 bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
7338
7339 bfqd->strict_guarantees = __data;
7340
7341 return count;
7342}
7343
7344static ssize_t bfq_low_latency_store(struct elevator_queue *e,
7345 const char *page, size_t count)
7346{
7347 struct bfq_data *bfqd = e->elevator_data;
7348 unsigned long __data;
7349 int ret;
7350
7351 ret = bfq_var_store(&__data, (page));
7352 if (ret)
7353 return ret;
7354
7355 if (__data > 1)
7356 __data = 1;
7357 if (__data == 0 && bfqd->low_latency != 0)
7358 bfq_end_wr(bfqd);
7359 bfqd->low_latency = __data;
7360
7361 return count;
7362}
7363
7364#define BFQ_ATTR(name) \
7365 __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
7366
7367static struct elv_fs_entry bfq_attrs[] = {
7368 BFQ_ATTR(fifo_expire_sync),
7369 BFQ_ATTR(fifo_expire_async),
7370 BFQ_ATTR(back_seek_max),
7371 BFQ_ATTR(back_seek_penalty),
7372 BFQ_ATTR(slice_idle),
7373 BFQ_ATTR(slice_idle_us),
7374 BFQ_ATTR(max_budget),
7375 BFQ_ATTR(timeout_sync),
7376 BFQ_ATTR(strict_guarantees),
7377 BFQ_ATTR(low_latency),
7378 __ATTR_NULL
7379};
7380
7381static struct elevator_type iosched_bfq_mq = {
7382 .ops = {
7383 .limit_depth = bfq_limit_depth,
7384 .prepare_request = bfq_prepare_request,
7385 .requeue_request = bfq_finish_requeue_request,
7386 .finish_request = bfq_finish_request,
7387 .exit_icq = bfq_exit_icq,
7388 .insert_requests = bfq_insert_requests,
7389 .dispatch_request = bfq_dispatch_request,
7390 .next_request = elv_rb_latter_request,
7391 .former_request = elv_rb_former_request,
7392 .allow_merge = bfq_allow_bio_merge,
7393 .bio_merge = bfq_bio_merge,
7394 .request_merge = bfq_request_merge,
7395 .requests_merged = bfq_requests_merged,
7396 .request_merged = bfq_request_merged,
7397 .has_work = bfq_has_work,
7398 .depth_updated = bfq_depth_updated,
7399 .init_hctx = bfq_init_hctx,
7400 .init_sched = bfq_init_queue,
7401 .exit_sched = bfq_exit_queue,
7402 },
7403
7404 .icq_size = sizeof(struct bfq_io_cq),
7405 .icq_align = __alignof__(struct bfq_io_cq),
7406 .elevator_attrs = bfq_attrs,
7407 .elevator_name = "bfq",
7408 .elevator_owner = THIS_MODULE,
7409};
7410MODULE_ALIAS("bfq-iosched");
7411
7412static int __init bfq_init(void)
7413{
7414 int ret;
7415
7416#ifdef CONFIG_BFQ_GROUP_IOSCHED
7417 ret = blkcg_policy_register(&blkcg_policy_bfq);
7418 if (ret)
7419 return ret;
7420#endif
7421
7422 ret = -ENOMEM;
7423 if (bfq_slab_setup())
7424 goto err_pol_unreg;
7425
7426 /*
7427 * Times to load large popular applications for the typical
7428 * systems installed on the reference devices (see the
7429 * comments before the definition of the next
7430 * array). Actually, we use slightly lower values, as the
7431 * estimated peak rate tends to be smaller than the actual
7432 * peak rate. The reason for this last fact is that estimates
7433 * are computed over much shorter time intervals than the long
7434 * intervals typically used for benchmarking. Why? First, to
7435 * adapt more quickly to variations. Second, because an I/O
7436 * scheduler cannot rely on a peak-rate-evaluation workload to
7437 * be run for a long time.
7438 */
7439 ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */
7440 ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */
7441
7442 ret = elv_register(&iosched_bfq_mq);
7443 if (ret)
7444 goto slab_kill;
7445
7446 return 0;
7447
7448slab_kill:
7449 bfq_slab_kill();
7450err_pol_unreg:
7451#ifdef CONFIG_BFQ_GROUP_IOSCHED
7452 blkcg_policy_unregister(&blkcg_policy_bfq);
7453#endif
7454 return ret;
7455}
7456
7457static void __exit bfq_exit(void)
7458{
7459 elv_unregister(&iosched_bfq_mq);
7460#ifdef CONFIG_BFQ_GROUP_IOSCHED
7461 blkcg_policy_unregister(&blkcg_policy_bfq);
7462#endif
7463 bfq_slab_kill();
7464}
7465
7466module_init(bfq_init);
7467module_exit(bfq_exit);
7468
7469MODULE_AUTHOR("Paolo Valente");
7470MODULE_LICENSE("GPL");
7471MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Budget Fair Queueing (BFQ) I/O scheduler.
4 *
5 * Based on ideas and code from CFQ:
6 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7 *
8 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
9 * Paolo Valente <paolo.valente@unimore.it>
10 *
11 * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
12 * Arianna Avanzini <avanzini@google.com>
13 *
14 * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
15 *
16 * BFQ is a proportional-share I/O scheduler, with some extra
17 * low-latency capabilities. BFQ also supports full hierarchical
18 * scheduling through cgroups. Next paragraphs provide an introduction
19 * on BFQ inner workings. Details on BFQ benefits, usage and
20 * limitations can be found in Documentation/block/bfq-iosched.rst.
21 *
22 * BFQ is a proportional-share storage-I/O scheduling algorithm based
23 * on the slice-by-slice service scheme of CFQ. But BFQ assigns
24 * budgets, measured in number of sectors, to processes instead of
25 * time slices. The device is not granted to the in-service process
26 * for a given time slice, but until it has exhausted its assigned
27 * budget. This change from the time to the service domain enables BFQ
28 * to distribute the device throughput among processes as desired,
29 * without any distortion due to throughput fluctuations, or to device
30 * internal queueing. BFQ uses an ad hoc internal scheduler, called
31 * B-WF2Q+, to schedule processes according to their budgets. More
32 * precisely, BFQ schedules queues associated with processes. Each
33 * process/queue is assigned a user-configurable weight, and B-WF2Q+
34 * guarantees that each queue receives a fraction of the throughput
35 * proportional to its weight. Thanks to the accurate policy of
36 * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
37 * processes issuing sequential requests (to boost the throughput),
38 * and yet guarantee a low latency to interactive and soft real-time
39 * applications.
40 *
41 * In particular, to provide these low-latency guarantees, BFQ
42 * explicitly privileges the I/O of two classes of time-sensitive
43 * applications: interactive and soft real-time. In more detail, BFQ
44 * behaves this way if the low_latency parameter is set (default
45 * configuration). This feature enables BFQ to provide applications in
46 * these classes with a very low latency.
47 *
48 * To implement this feature, BFQ constantly tries to detect whether
49 * the I/O requests in a bfq_queue come from an interactive or a soft
50 * real-time application. For brevity, in these cases, the queue is
51 * said to be interactive or soft real-time. In both cases, BFQ
52 * privileges the service of the queue, over that of non-interactive
53 * and non-soft-real-time queues. This privileging is performed,
54 * mainly, by raising the weight of the queue. So, for brevity, we
55 * call just weight-raising periods the time periods during which a
56 * queue is privileged, because deemed interactive or soft real-time.
57 *
58 * The detection of soft real-time queues/applications is described in
59 * detail in the comments on the function
60 * bfq_bfqq_softrt_next_start. On the other hand, the detection of an
61 * interactive queue works as follows: a queue is deemed interactive
62 * if it is constantly non empty only for a limited time interval,
63 * after which it does become empty. The queue may be deemed
64 * interactive again (for a limited time), if it restarts being
65 * constantly non empty, provided that this happens only after the
66 * queue has remained empty for a given minimum idle time.
67 *
68 * By default, BFQ computes automatically the above maximum time
69 * interval, i.e., the time interval after which a constantly
70 * non-empty queue stops being deemed interactive. Since a queue is
71 * weight-raised while it is deemed interactive, this maximum time
72 * interval happens to coincide with the (maximum) duration of the
73 * weight-raising for interactive queues.
74 *
75 * Finally, BFQ also features additional heuristics for
76 * preserving both a low latency and a high throughput on NCQ-capable,
77 * rotational or flash-based devices, and to get the job done quickly
78 * for applications consisting in many I/O-bound processes.
79 *
80 * NOTE: if the main or only goal, with a given device, is to achieve
81 * the maximum-possible throughput at all times, then do switch off
82 * all low-latency heuristics for that device, by setting low_latency
83 * to 0.
84 *
85 * BFQ is described in [1], where also a reference to the initial,
86 * more theoretical paper on BFQ can be found. The interested reader
87 * can find in the latter paper full details on the main algorithm, as
88 * well as formulas of the guarantees and formal proofs of all the
89 * properties. With respect to the version of BFQ presented in these
90 * papers, this implementation adds a few more heuristics, such as the
91 * ones that guarantee a low latency to interactive and soft real-time
92 * applications, and a hierarchical extension based on H-WF2Q+.
93 *
94 * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
95 * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
96 * with O(log N) complexity derives from the one introduced with EEVDF
97 * in [3].
98 *
99 * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
100 * Scheduler", Proceedings of the First Workshop on Mobile System
101 * Technologies (MST-2015), May 2015.
102 * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
103 *
104 * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
105 * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
106 * Oct 1997.
107 *
108 * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
109 *
110 * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
111 * First: A Flexible and Accurate Mechanism for Proportional Share
112 * Resource Allocation", technical report.
113 *
114 * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
115 */
116#include <linux/module.h>
117#include <linux/slab.h>
118#include <linux/blkdev.h>
119#include <linux/cgroup.h>
120#include <linux/elevator.h>
121#include <linux/ktime.h>
122#include <linux/rbtree.h>
123#include <linux/ioprio.h>
124#include <linux/sbitmap.h>
125#include <linux/delay.h>
126#include <linux/backing-dev.h>
127
128#include "blk.h"
129#include "blk-mq.h"
130#include "blk-mq-tag.h"
131#include "blk-mq-sched.h"
132#include "bfq-iosched.h"
133#include "blk-wbt.h"
134
135#define BFQ_BFQQ_FNS(name) \
136void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
137{ \
138 __set_bit(BFQQF_##name, &(bfqq)->flags); \
139} \
140void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
141{ \
142 __clear_bit(BFQQF_##name, &(bfqq)->flags); \
143} \
144int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
145{ \
146 return test_bit(BFQQF_##name, &(bfqq)->flags); \
147}
148
149BFQ_BFQQ_FNS(just_created);
150BFQ_BFQQ_FNS(busy);
151BFQ_BFQQ_FNS(wait_request);
152BFQ_BFQQ_FNS(non_blocking_wait_rq);
153BFQ_BFQQ_FNS(fifo_expire);
154BFQ_BFQQ_FNS(has_short_ttime);
155BFQ_BFQQ_FNS(sync);
156BFQ_BFQQ_FNS(IO_bound);
157BFQ_BFQQ_FNS(in_large_burst);
158BFQ_BFQQ_FNS(coop);
159BFQ_BFQQ_FNS(split_coop);
160BFQ_BFQQ_FNS(softrt_update);
161BFQ_BFQQ_FNS(has_waker);
162#undef BFQ_BFQQ_FNS \
163
164/* Expiration time of sync (0) and async (1) requests, in ns. */
165static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
166
167/* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
168static const int bfq_back_max = 16 * 1024;
169
170/* Penalty of a backwards seek, in number of sectors. */
171static const int bfq_back_penalty = 2;
172
173/* Idling period duration, in ns. */
174static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
175
176/* Minimum number of assigned budgets for which stats are safe to compute. */
177static const int bfq_stats_min_budgets = 194;
178
179/* Default maximum budget values, in sectors and number of requests. */
180static const int bfq_default_max_budget = 16 * 1024;
181
182/*
183 * When a sync request is dispatched, the queue that contains that
184 * request, and all the ancestor entities of that queue, are charged
185 * with the number of sectors of the request. In contrast, if the
186 * request is async, then the queue and its ancestor entities are
187 * charged with the number of sectors of the request, multiplied by
188 * the factor below. This throttles the bandwidth for async I/O,
189 * w.r.t. to sync I/O, and it is done to counter the tendency of async
190 * writes to steal I/O throughput to reads.
191 *
192 * The current value of this parameter is the result of a tuning with
193 * several hardware and software configurations. We tried to find the
194 * lowest value for which writes do not cause noticeable problems to
195 * reads. In fact, the lower this parameter, the stabler I/O control,
196 * in the following respect. The lower this parameter is, the less
197 * the bandwidth enjoyed by a group decreases
198 * - when the group does writes, w.r.t. to when it does reads;
199 * - when other groups do reads, w.r.t. to when they do writes.
200 */
201static const int bfq_async_charge_factor = 3;
202
203/* Default timeout values, in jiffies, approximating CFQ defaults. */
204const int bfq_timeout = HZ / 8;
205
206/*
207 * Time limit for merging (see comments in bfq_setup_cooperator). Set
208 * to the slowest value that, in our tests, proved to be effective in
209 * removing false positives, while not causing true positives to miss
210 * queue merging.
211 *
212 * As can be deduced from the low time limit below, queue merging, if
213 * successful, happens at the very beginning of the I/O of the involved
214 * cooperating processes, as a consequence of the arrival of the very
215 * first requests from each cooperator. After that, there is very
216 * little chance to find cooperators.
217 */
218static const unsigned long bfq_merge_time_limit = HZ/10;
219
220static struct kmem_cache *bfq_pool;
221
222/* Below this threshold (in ns), we consider thinktime immediate. */
223#define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
224
225/* hw_tag detection: parallel requests threshold and min samples needed. */
226#define BFQ_HW_QUEUE_THRESHOLD 3
227#define BFQ_HW_QUEUE_SAMPLES 32
228
229#define BFQQ_SEEK_THR (sector_t)(8 * 100)
230#define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
231#define BFQ_RQ_SEEKY(bfqd, last_pos, rq) \
232 (get_sdist(last_pos, rq) > \
233 BFQQ_SEEK_THR && \
234 (!blk_queue_nonrot(bfqd->queue) || \
235 blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT))
236#define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
237#define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 19)
238/*
239 * Sync random I/O is likely to be confused with soft real-time I/O,
240 * because it is characterized by limited throughput and apparently
241 * isochronous arrival pattern. To avoid false positives, queues
242 * containing only random (seeky) I/O are prevented from being tagged
243 * as soft real-time.
244 */
245#define BFQQ_TOTALLY_SEEKY(bfqq) (bfqq->seek_history == -1)
246
247/* Min number of samples required to perform peak-rate update */
248#define BFQ_RATE_MIN_SAMPLES 32
249/* Min observation time interval required to perform a peak-rate update (ns) */
250#define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
251/* Target observation time interval for a peak-rate update (ns) */
252#define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
253
254/*
255 * Shift used for peak-rate fixed precision calculations.
256 * With
257 * - the current shift: 16 positions
258 * - the current type used to store rate: u32
259 * - the current unit of measure for rate: [sectors/usec], or, more precisely,
260 * [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
261 * the range of rates that can be stored is
262 * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
263 * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
264 * [15, 65G] sectors/sec
265 * Which, assuming a sector size of 512B, corresponds to a range of
266 * [7.5K, 33T] B/sec
267 */
268#define BFQ_RATE_SHIFT 16
269
270/*
271 * When configured for computing the duration of the weight-raising
272 * for interactive queues automatically (see the comments at the
273 * beginning of this file), BFQ does it using the following formula:
274 * duration = (ref_rate / r) * ref_wr_duration,
275 * where r is the peak rate of the device, and ref_rate and
276 * ref_wr_duration are two reference parameters. In particular,
277 * ref_rate is the peak rate of the reference storage device (see
278 * below), and ref_wr_duration is about the maximum time needed, with
279 * BFQ and while reading two files in parallel, to load typical large
280 * applications on the reference device (see the comments on
281 * max_service_from_wr below, for more details on how ref_wr_duration
282 * is obtained). In practice, the slower/faster the device at hand
283 * is, the more/less it takes to load applications with respect to the
284 * reference device. Accordingly, the longer/shorter BFQ grants
285 * weight raising to interactive applications.
286 *
287 * BFQ uses two different reference pairs (ref_rate, ref_wr_duration),
288 * depending on whether the device is rotational or non-rotational.
289 *
290 * In the following definitions, ref_rate[0] and ref_wr_duration[0]
291 * are the reference values for a rotational device, whereas
292 * ref_rate[1] and ref_wr_duration[1] are the reference values for a
293 * non-rotational device. The reference rates are not the actual peak
294 * rates of the devices used as a reference, but slightly lower
295 * values. The reason for using slightly lower values is that the
296 * peak-rate estimator tends to yield slightly lower values than the
297 * actual peak rate (it can yield the actual peak rate only if there
298 * is only one process doing I/O, and the process does sequential
299 * I/O).
300 *
301 * The reference peak rates are measured in sectors/usec, left-shifted
302 * by BFQ_RATE_SHIFT.
303 */
304static int ref_rate[2] = {14000, 33000};
305/*
306 * To improve readability, a conversion function is used to initialize
307 * the following array, which entails that the array can be
308 * initialized only in a function.
309 */
310static int ref_wr_duration[2];
311
312/*
313 * BFQ uses the above-detailed, time-based weight-raising mechanism to
314 * privilege interactive tasks. This mechanism is vulnerable to the
315 * following false positives: I/O-bound applications that will go on
316 * doing I/O for much longer than the duration of weight
317 * raising. These applications have basically no benefit from being
318 * weight-raised at the beginning of their I/O. On the opposite end,
319 * while being weight-raised, these applications
320 * a) unjustly steal throughput to applications that may actually need
321 * low latency;
322 * b) make BFQ uselessly perform device idling; device idling results
323 * in loss of device throughput with most flash-based storage, and may
324 * increase latencies when used purposelessly.
325 *
326 * BFQ tries to reduce these problems, by adopting the following
327 * countermeasure. To introduce this countermeasure, we need first to
328 * finish explaining how the duration of weight-raising for
329 * interactive tasks is computed.
330 *
331 * For a bfq_queue deemed as interactive, the duration of weight
332 * raising is dynamically adjusted, as a function of the estimated
333 * peak rate of the device, so as to be equal to the time needed to
334 * execute the 'largest' interactive task we benchmarked so far. By
335 * largest task, we mean the task for which each involved process has
336 * to do more I/O than for any of the other tasks we benchmarked. This
337 * reference interactive task is the start-up of LibreOffice Writer,
338 * and in this task each process/bfq_queue needs to have at most ~110K
339 * sectors transferred.
340 *
341 * This last piece of information enables BFQ to reduce the actual
342 * duration of weight-raising for at least one class of I/O-bound
343 * applications: those doing sequential or quasi-sequential I/O. An
344 * example is file copy. In fact, once started, the main I/O-bound
345 * processes of these applications usually consume the above 110K
346 * sectors in much less time than the processes of an application that
347 * is starting, because these I/O-bound processes will greedily devote
348 * almost all their CPU cycles only to their target,
349 * throughput-friendly I/O operations. This is even more true if BFQ
350 * happens to be underestimating the device peak rate, and thus
351 * overestimating the duration of weight raising. But, according to
352 * our measurements, once transferred 110K sectors, these processes
353 * have no right to be weight-raised any longer.
354 *
355 * Basing on the last consideration, BFQ ends weight-raising for a
356 * bfq_queue if the latter happens to have received an amount of
357 * service at least equal to the following constant. The constant is
358 * set to slightly more than 110K, to have a minimum safety margin.
359 *
360 * This early ending of weight-raising reduces the amount of time
361 * during which interactive false positives cause the two problems
362 * described at the beginning of these comments.
363 */
364static const unsigned long max_service_from_wr = 120000;
365
366#define RQ_BIC(rq) icq_to_bic((rq)->elv.priv[0])
367#define RQ_BFQQ(rq) ((rq)->elv.priv[1])
368
369struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
370{
371 return bic->bfqq[is_sync];
372}
373
374void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
375{
376 bic->bfqq[is_sync] = bfqq;
377}
378
379struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
380{
381 return bic->icq.q->elevator->elevator_data;
382}
383
384/**
385 * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
386 * @icq: the iocontext queue.
387 */
388static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
389{
390 /* bic->icq is the first member, %NULL will convert to %NULL */
391 return container_of(icq, struct bfq_io_cq, icq);
392}
393
394/**
395 * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
396 * @bfqd: the lookup key.
397 * @ioc: the io_context of the process doing I/O.
398 * @q: the request queue.
399 */
400static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd,
401 struct io_context *ioc,
402 struct request_queue *q)
403{
404 if (ioc) {
405 unsigned long flags;
406 struct bfq_io_cq *icq;
407
408 spin_lock_irqsave(&q->queue_lock, flags);
409 icq = icq_to_bic(ioc_lookup_icq(ioc, q));
410 spin_unlock_irqrestore(&q->queue_lock, flags);
411
412 return icq;
413 }
414
415 return NULL;
416}
417
418/*
419 * Scheduler run of queue, if there are requests pending and no one in the
420 * driver that will restart queueing.
421 */
422void bfq_schedule_dispatch(struct bfq_data *bfqd)
423{
424 if (bfqd->queued != 0) {
425 bfq_log(bfqd, "schedule dispatch");
426 blk_mq_run_hw_queues(bfqd->queue, true);
427 }
428}
429
430#define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
431
432#define bfq_sample_valid(samples) ((samples) > 80)
433
434/*
435 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
436 * We choose the request that is closer to the head right now. Distance
437 * behind the head is penalized and only allowed to a certain extent.
438 */
439static struct request *bfq_choose_req(struct bfq_data *bfqd,
440 struct request *rq1,
441 struct request *rq2,
442 sector_t last)
443{
444 sector_t s1, s2, d1 = 0, d2 = 0;
445 unsigned long back_max;
446#define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
447#define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
448 unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
449
450 if (!rq1 || rq1 == rq2)
451 return rq2;
452 if (!rq2)
453 return rq1;
454
455 if (rq_is_sync(rq1) && !rq_is_sync(rq2))
456 return rq1;
457 else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
458 return rq2;
459 if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
460 return rq1;
461 else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
462 return rq2;
463
464 s1 = blk_rq_pos(rq1);
465 s2 = blk_rq_pos(rq2);
466
467 /*
468 * By definition, 1KiB is 2 sectors.
469 */
470 back_max = bfqd->bfq_back_max * 2;
471
472 /*
473 * Strict one way elevator _except_ in the case where we allow
474 * short backward seeks which are biased as twice the cost of a
475 * similar forward seek.
476 */
477 if (s1 >= last)
478 d1 = s1 - last;
479 else if (s1 + back_max >= last)
480 d1 = (last - s1) * bfqd->bfq_back_penalty;
481 else
482 wrap |= BFQ_RQ1_WRAP;
483
484 if (s2 >= last)
485 d2 = s2 - last;
486 else if (s2 + back_max >= last)
487 d2 = (last - s2) * bfqd->bfq_back_penalty;
488 else
489 wrap |= BFQ_RQ2_WRAP;
490
491 /* Found required data */
492
493 /*
494 * By doing switch() on the bit mask "wrap" we avoid having to
495 * check two variables for all permutations: --> faster!
496 */
497 switch (wrap) {
498 case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
499 if (d1 < d2)
500 return rq1;
501 else if (d2 < d1)
502 return rq2;
503
504 if (s1 >= s2)
505 return rq1;
506 else
507 return rq2;
508
509 case BFQ_RQ2_WRAP:
510 return rq1;
511 case BFQ_RQ1_WRAP:
512 return rq2;
513 case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
514 default:
515 /*
516 * Since both rqs are wrapped,
517 * start with the one that's further behind head
518 * (--> only *one* back seek required),
519 * since back seek takes more time than forward.
520 */
521 if (s1 <= s2)
522 return rq1;
523 else
524 return rq2;
525 }
526}
527
528/*
529 * Async I/O can easily starve sync I/O (both sync reads and sync
530 * writes), by consuming all tags. Similarly, storms of sync writes,
531 * such as those that sync(2) may trigger, can starve sync reads.
532 * Limit depths of async I/O and sync writes so as to counter both
533 * problems.
534 */
535static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
536{
537 struct bfq_data *bfqd = data->q->elevator->elevator_data;
538
539 if (op_is_sync(op) && !op_is_write(op))
540 return;
541
542 data->shallow_depth =
543 bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)];
544
545 bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
546 __func__, bfqd->wr_busy_queues, op_is_sync(op),
547 data->shallow_depth);
548}
549
550static struct bfq_queue *
551bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
552 sector_t sector, struct rb_node **ret_parent,
553 struct rb_node ***rb_link)
554{
555 struct rb_node **p, *parent;
556 struct bfq_queue *bfqq = NULL;
557
558 parent = NULL;
559 p = &root->rb_node;
560 while (*p) {
561 struct rb_node **n;
562
563 parent = *p;
564 bfqq = rb_entry(parent, struct bfq_queue, pos_node);
565
566 /*
567 * Sort strictly based on sector. Smallest to the left,
568 * largest to the right.
569 */
570 if (sector > blk_rq_pos(bfqq->next_rq))
571 n = &(*p)->rb_right;
572 else if (sector < blk_rq_pos(bfqq->next_rq))
573 n = &(*p)->rb_left;
574 else
575 break;
576 p = n;
577 bfqq = NULL;
578 }
579
580 *ret_parent = parent;
581 if (rb_link)
582 *rb_link = p;
583
584 bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
585 (unsigned long long)sector,
586 bfqq ? bfqq->pid : 0);
587
588 return bfqq;
589}
590
591static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
592{
593 return bfqq->service_from_backlogged > 0 &&
594 time_is_before_jiffies(bfqq->first_IO_time +
595 bfq_merge_time_limit);
596}
597
598/*
599 * The following function is not marked as __cold because it is
600 * actually cold, but for the same performance goal described in the
601 * comments on the likely() at the beginning of
602 * bfq_setup_cooperator(). Unexpectedly, to reach an even lower
603 * execution time for the case where this function is not invoked, we
604 * had to add an unlikely() in each involved if().
605 */
606void __cold
607bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
608{
609 struct rb_node **p, *parent;
610 struct bfq_queue *__bfqq;
611
612 if (bfqq->pos_root) {
613 rb_erase(&bfqq->pos_node, bfqq->pos_root);
614 bfqq->pos_root = NULL;
615 }
616
617 /* oom_bfqq does not participate in queue merging */
618 if (bfqq == &bfqd->oom_bfqq)
619 return;
620
621 /*
622 * bfqq cannot be merged any longer (see comments in
623 * bfq_setup_cooperator): no point in adding bfqq into the
624 * position tree.
625 */
626 if (bfq_too_late_for_merging(bfqq))
627 return;
628
629 if (bfq_class_idle(bfqq))
630 return;
631 if (!bfqq->next_rq)
632 return;
633
634 bfqq->pos_root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
635 __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
636 blk_rq_pos(bfqq->next_rq), &parent, &p);
637 if (!__bfqq) {
638 rb_link_node(&bfqq->pos_node, parent, p);
639 rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
640 } else
641 bfqq->pos_root = NULL;
642}
643
644/*
645 * The following function returns false either if every active queue
646 * must receive the same share of the throughput (symmetric scenario),
647 * or, as a special case, if bfqq must receive a share of the
648 * throughput lower than or equal to the share that every other active
649 * queue must receive. If bfqq does sync I/O, then these are the only
650 * two cases where bfqq happens to be guaranteed its share of the
651 * throughput even if I/O dispatching is not plugged when bfqq remains
652 * temporarily empty (for more details, see the comments in the
653 * function bfq_better_to_idle()). For this reason, the return value
654 * of this function is used to check whether I/O-dispatch plugging can
655 * be avoided.
656 *
657 * The above first case (symmetric scenario) occurs when:
658 * 1) all active queues have the same weight,
659 * 2) all active queues belong to the same I/O-priority class,
660 * 3) all active groups at the same level in the groups tree have the same
661 * weight,
662 * 4) all active groups at the same level in the groups tree have the same
663 * number of children.
664 *
665 * Unfortunately, keeping the necessary state for evaluating exactly
666 * the last two symmetry sub-conditions above would be quite complex
667 * and time consuming. Therefore this function evaluates, instead,
668 * only the following stronger three sub-conditions, for which it is
669 * much easier to maintain the needed state:
670 * 1) all active queues have the same weight,
671 * 2) all active queues belong to the same I/O-priority class,
672 * 3) there are no active groups.
673 * In particular, the last condition is always true if hierarchical
674 * support or the cgroups interface are not enabled, thus no state
675 * needs to be maintained in this case.
676 */
677static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
678 struct bfq_queue *bfqq)
679{
680 bool smallest_weight = bfqq &&
681 bfqq->weight_counter &&
682 bfqq->weight_counter ==
683 container_of(
684 rb_first_cached(&bfqd->queue_weights_tree),
685 struct bfq_weight_counter,
686 weights_node);
687
688 /*
689 * For queue weights to differ, queue_weights_tree must contain
690 * at least two nodes.
691 */
692 bool varied_queue_weights = !smallest_weight &&
693 !RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) &&
694 (bfqd->queue_weights_tree.rb_root.rb_node->rb_left ||
695 bfqd->queue_weights_tree.rb_root.rb_node->rb_right);
696
697 bool multiple_classes_busy =
698 (bfqd->busy_queues[0] && bfqd->busy_queues[1]) ||
699 (bfqd->busy_queues[0] && bfqd->busy_queues[2]) ||
700 (bfqd->busy_queues[1] && bfqd->busy_queues[2]);
701
702 return varied_queue_weights || multiple_classes_busy
703#ifdef CONFIG_BFQ_GROUP_IOSCHED
704 || bfqd->num_groups_with_pending_reqs > 0
705#endif
706 ;
707}
708
709/*
710 * If the weight-counter tree passed as input contains no counter for
711 * the weight of the input queue, then add that counter; otherwise just
712 * increment the existing counter.
713 *
714 * Note that weight-counter trees contain few nodes in mostly symmetric
715 * scenarios. For example, if all queues have the same weight, then the
716 * weight-counter tree for the queues may contain at most one node.
717 * This holds even if low_latency is on, because weight-raised queues
718 * are not inserted in the tree.
719 * In most scenarios, the rate at which nodes are created/destroyed
720 * should be low too.
721 */
722void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
723 struct rb_root_cached *root)
724{
725 struct bfq_entity *entity = &bfqq->entity;
726 struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL;
727 bool leftmost = true;
728
729 /*
730 * Do not insert if the queue is already associated with a
731 * counter, which happens if:
732 * 1) a request arrival has caused the queue to become both
733 * non-weight-raised, and hence change its weight, and
734 * backlogged; in this respect, each of the two events
735 * causes an invocation of this function,
736 * 2) this is the invocation of this function caused by the
737 * second event. This second invocation is actually useless,
738 * and we handle this fact by exiting immediately. More
739 * efficient or clearer solutions might possibly be adopted.
740 */
741 if (bfqq->weight_counter)
742 return;
743
744 while (*new) {
745 struct bfq_weight_counter *__counter = container_of(*new,
746 struct bfq_weight_counter,
747 weights_node);
748 parent = *new;
749
750 if (entity->weight == __counter->weight) {
751 bfqq->weight_counter = __counter;
752 goto inc_counter;
753 }
754 if (entity->weight < __counter->weight)
755 new = &((*new)->rb_left);
756 else {
757 new = &((*new)->rb_right);
758 leftmost = false;
759 }
760 }
761
762 bfqq->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
763 GFP_ATOMIC);
764
765 /*
766 * In the unlucky event of an allocation failure, we just
767 * exit. This will cause the weight of queue to not be
768 * considered in bfq_asymmetric_scenario, which, in its turn,
769 * causes the scenario to be deemed wrongly symmetric in case
770 * bfqq's weight would have been the only weight making the
771 * scenario asymmetric. On the bright side, no unbalance will
772 * however occur when bfqq becomes inactive again (the
773 * invocation of this function is triggered by an activation
774 * of queue). In fact, bfq_weights_tree_remove does nothing
775 * if !bfqq->weight_counter.
776 */
777 if (unlikely(!bfqq->weight_counter))
778 return;
779
780 bfqq->weight_counter->weight = entity->weight;
781 rb_link_node(&bfqq->weight_counter->weights_node, parent, new);
782 rb_insert_color_cached(&bfqq->weight_counter->weights_node, root,
783 leftmost);
784
785inc_counter:
786 bfqq->weight_counter->num_active++;
787 bfqq->ref++;
788}
789
790/*
791 * Decrement the weight counter associated with the queue, and, if the
792 * counter reaches 0, remove the counter from the tree.
793 * See the comments to the function bfq_weights_tree_add() for considerations
794 * about overhead.
795 */
796void __bfq_weights_tree_remove(struct bfq_data *bfqd,
797 struct bfq_queue *bfqq,
798 struct rb_root_cached *root)
799{
800 if (!bfqq->weight_counter)
801 return;
802
803 bfqq->weight_counter->num_active--;
804 if (bfqq->weight_counter->num_active > 0)
805 goto reset_entity_pointer;
806
807 rb_erase_cached(&bfqq->weight_counter->weights_node, root);
808 kfree(bfqq->weight_counter);
809
810reset_entity_pointer:
811 bfqq->weight_counter = NULL;
812 bfq_put_queue(bfqq);
813}
814
815/*
816 * Invoke __bfq_weights_tree_remove on bfqq and decrement the number
817 * of active groups for each queue's inactive parent entity.
818 */
819void bfq_weights_tree_remove(struct bfq_data *bfqd,
820 struct bfq_queue *bfqq)
821{
822 struct bfq_entity *entity = bfqq->entity.parent;
823
824 for_each_entity(entity) {
825 struct bfq_sched_data *sd = entity->my_sched_data;
826
827 if (sd->next_in_service || sd->in_service_entity) {
828 /*
829 * entity is still active, because either
830 * next_in_service or in_service_entity is not
831 * NULL (see the comments on the definition of
832 * next_in_service for details on why
833 * in_service_entity must be checked too).
834 *
835 * As a consequence, its parent entities are
836 * active as well, and thus this loop must
837 * stop here.
838 */
839 break;
840 }
841
842 /*
843 * The decrement of num_groups_with_pending_reqs is
844 * not performed immediately upon the deactivation of
845 * entity, but it is delayed to when it also happens
846 * that the first leaf descendant bfqq of entity gets
847 * all its pending requests completed. The following
848 * instructions perform this delayed decrement, if
849 * needed. See the comments on
850 * num_groups_with_pending_reqs for details.
851 */
852 if (entity->in_groups_with_pending_reqs) {
853 entity->in_groups_with_pending_reqs = false;
854 bfqd->num_groups_with_pending_reqs--;
855 }
856 }
857
858 /*
859 * Next function is invoked last, because it causes bfqq to be
860 * freed if the following holds: bfqq is not in service and
861 * has no dispatched request. DO NOT use bfqq after the next
862 * function invocation.
863 */
864 __bfq_weights_tree_remove(bfqd, bfqq,
865 &bfqd->queue_weights_tree);
866}
867
868/*
869 * Return expired entry, or NULL to just start from scratch in rbtree.
870 */
871static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
872 struct request *last)
873{
874 struct request *rq;
875
876 if (bfq_bfqq_fifo_expire(bfqq))
877 return NULL;
878
879 bfq_mark_bfqq_fifo_expire(bfqq);
880
881 rq = rq_entry_fifo(bfqq->fifo.next);
882
883 if (rq == last || ktime_get_ns() < rq->fifo_time)
884 return NULL;
885
886 bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
887 return rq;
888}
889
890static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
891 struct bfq_queue *bfqq,
892 struct request *last)
893{
894 struct rb_node *rbnext = rb_next(&last->rb_node);
895 struct rb_node *rbprev = rb_prev(&last->rb_node);
896 struct request *next, *prev = NULL;
897
898 /* Follow expired path, else get first next available. */
899 next = bfq_check_fifo(bfqq, last);
900 if (next)
901 return next;
902
903 if (rbprev)
904 prev = rb_entry_rq(rbprev);
905
906 if (rbnext)
907 next = rb_entry_rq(rbnext);
908 else {
909 rbnext = rb_first(&bfqq->sort_list);
910 if (rbnext && rbnext != &last->rb_node)
911 next = rb_entry_rq(rbnext);
912 }
913
914 return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
915}
916
917/* see the definition of bfq_async_charge_factor for details */
918static unsigned long bfq_serv_to_charge(struct request *rq,
919 struct bfq_queue *bfqq)
920{
921 if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1 ||
922 bfq_asymmetric_scenario(bfqq->bfqd, bfqq))
923 return blk_rq_sectors(rq);
924
925 return blk_rq_sectors(rq) * bfq_async_charge_factor;
926}
927
928/**
929 * bfq_updated_next_req - update the queue after a new next_rq selection.
930 * @bfqd: the device data the queue belongs to.
931 * @bfqq: the queue to update.
932 *
933 * If the first request of a queue changes we make sure that the queue
934 * has enough budget to serve at least its first request (if the
935 * request has grown). We do this because if the queue has not enough
936 * budget for its first request, it has to go through two dispatch
937 * rounds to actually get it dispatched.
938 */
939static void bfq_updated_next_req(struct bfq_data *bfqd,
940 struct bfq_queue *bfqq)
941{
942 struct bfq_entity *entity = &bfqq->entity;
943 struct request *next_rq = bfqq->next_rq;
944 unsigned long new_budget;
945
946 if (!next_rq)
947 return;
948
949 if (bfqq == bfqd->in_service_queue)
950 /*
951 * In order not to break guarantees, budgets cannot be
952 * changed after an entity has been selected.
953 */
954 return;
955
956 new_budget = max_t(unsigned long,
957 max_t(unsigned long, bfqq->max_budget,
958 bfq_serv_to_charge(next_rq, bfqq)),
959 entity->service);
960 if (entity->budget != new_budget) {
961 entity->budget = new_budget;
962 bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
963 new_budget);
964 bfq_requeue_bfqq(bfqd, bfqq, false);
965 }
966}
967
968static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
969{
970 u64 dur;
971
972 if (bfqd->bfq_wr_max_time > 0)
973 return bfqd->bfq_wr_max_time;
974
975 dur = bfqd->rate_dur_prod;
976 do_div(dur, bfqd->peak_rate);
977
978 /*
979 * Limit duration between 3 and 25 seconds. The upper limit
980 * has been conservatively set after the following worst case:
981 * on a QEMU/KVM virtual machine
982 * - running in a slow PC
983 * - with a virtual disk stacked on a slow low-end 5400rpm HDD
984 * - serving a heavy I/O workload, such as the sequential reading
985 * of several files
986 * mplayer took 23 seconds to start, if constantly weight-raised.
987 *
988 * As for higher values than that accommodating the above bad
989 * scenario, tests show that higher values would often yield
990 * the opposite of the desired result, i.e., would worsen
991 * responsiveness by allowing non-interactive applications to
992 * preserve weight raising for too long.
993 *
994 * On the other end, lower values than 3 seconds make it
995 * difficult for most interactive tasks to complete their jobs
996 * before weight-raising finishes.
997 */
998 return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000));
999}
1000
1001/* switch back from soft real-time to interactive weight raising */
1002static void switch_back_to_interactive_wr(struct bfq_queue *bfqq,
1003 struct bfq_data *bfqd)
1004{
1005 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1006 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1007 bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt;
1008}
1009
1010static void
1011bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
1012 struct bfq_io_cq *bic, bool bfq_already_existing)
1013{
1014 unsigned int old_wr_coeff = bfqq->wr_coeff;
1015 bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
1016
1017 if (bic->saved_has_short_ttime)
1018 bfq_mark_bfqq_has_short_ttime(bfqq);
1019 else
1020 bfq_clear_bfqq_has_short_ttime(bfqq);
1021
1022 if (bic->saved_IO_bound)
1023 bfq_mark_bfqq_IO_bound(bfqq);
1024 else
1025 bfq_clear_bfqq_IO_bound(bfqq);
1026
1027 bfqq->entity.new_weight = bic->saved_weight;
1028 bfqq->ttime = bic->saved_ttime;
1029 bfqq->wr_coeff = bic->saved_wr_coeff;
1030 bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
1031 bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
1032 bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
1033
1034 if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
1035 time_is_before_jiffies(bfqq->last_wr_start_finish +
1036 bfqq->wr_cur_max_time))) {
1037 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
1038 !bfq_bfqq_in_large_burst(bfqq) &&
1039 time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt +
1040 bfq_wr_duration(bfqd))) {
1041 switch_back_to_interactive_wr(bfqq, bfqd);
1042 } else {
1043 bfqq->wr_coeff = 1;
1044 bfq_log_bfqq(bfqq->bfqd, bfqq,
1045 "resume state: switching off wr");
1046 }
1047 }
1048
1049 /* make sure weight will be updated, however we got here */
1050 bfqq->entity.prio_changed = 1;
1051
1052 if (likely(!busy))
1053 return;
1054
1055 if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
1056 bfqd->wr_busy_queues++;
1057 else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
1058 bfqd->wr_busy_queues--;
1059}
1060
1061static int bfqq_process_refs(struct bfq_queue *bfqq)
1062{
1063 return bfqq->ref - bfqq->allocated - bfqq->entity.on_st_or_in_serv -
1064 (bfqq->weight_counter != NULL);
1065}
1066
1067/* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
1068static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1069{
1070 struct bfq_queue *item;
1071 struct hlist_node *n;
1072
1073 hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
1074 hlist_del_init(&item->burst_list_node);
1075
1076 /*
1077 * Start the creation of a new burst list only if there is no
1078 * active queue. See comments on the conditional invocation of
1079 * bfq_handle_burst().
1080 */
1081 if (bfq_tot_busy_queues(bfqd) == 0) {
1082 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1083 bfqd->burst_size = 1;
1084 } else
1085 bfqd->burst_size = 0;
1086
1087 bfqd->burst_parent_entity = bfqq->entity.parent;
1088}
1089
1090/* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
1091static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1092{
1093 /* Increment burst size to take into account also bfqq */
1094 bfqd->burst_size++;
1095
1096 if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
1097 struct bfq_queue *pos, *bfqq_item;
1098 struct hlist_node *n;
1099
1100 /*
1101 * Enough queues have been activated shortly after each
1102 * other to consider this burst as large.
1103 */
1104 bfqd->large_burst = true;
1105
1106 /*
1107 * We can now mark all queues in the burst list as
1108 * belonging to a large burst.
1109 */
1110 hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
1111 burst_list_node)
1112 bfq_mark_bfqq_in_large_burst(bfqq_item);
1113 bfq_mark_bfqq_in_large_burst(bfqq);
1114
1115 /*
1116 * From now on, and until the current burst finishes, any
1117 * new queue being activated shortly after the last queue
1118 * was inserted in the burst can be immediately marked as
1119 * belonging to a large burst. So the burst list is not
1120 * needed any more. Remove it.
1121 */
1122 hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
1123 burst_list_node)
1124 hlist_del_init(&pos->burst_list_node);
1125 } else /*
1126 * Burst not yet large: add bfqq to the burst list. Do
1127 * not increment the ref counter for bfqq, because bfqq
1128 * is removed from the burst list before freeing bfqq
1129 * in put_queue.
1130 */
1131 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1132}
1133
1134/*
1135 * If many queues belonging to the same group happen to be created
1136 * shortly after each other, then the processes associated with these
1137 * queues have typically a common goal. In particular, bursts of queue
1138 * creations are usually caused by services or applications that spawn
1139 * many parallel threads/processes. Examples are systemd during boot,
1140 * or git grep. To help these processes get their job done as soon as
1141 * possible, it is usually better to not grant either weight-raising
1142 * or device idling to their queues, unless these queues must be
1143 * protected from the I/O flowing through other active queues.
1144 *
1145 * In this comment we describe, firstly, the reasons why this fact
1146 * holds, and, secondly, the next function, which implements the main
1147 * steps needed to properly mark these queues so that they can then be
1148 * treated in a different way.
1149 *
1150 * The above services or applications benefit mostly from a high
1151 * throughput: the quicker the requests of the activated queues are
1152 * cumulatively served, the sooner the target job of these queues gets
1153 * completed. As a consequence, weight-raising any of these queues,
1154 * which also implies idling the device for it, is almost always
1155 * counterproductive, unless there are other active queues to isolate
1156 * these new queues from. If there no other active queues, then
1157 * weight-raising these new queues just lowers throughput in most
1158 * cases.
1159 *
1160 * On the other hand, a burst of queue creations may be caused also by
1161 * the start of an application that does not consist of a lot of
1162 * parallel I/O-bound threads. In fact, with a complex application,
1163 * several short processes may need to be executed to start-up the
1164 * application. In this respect, to start an application as quickly as
1165 * possible, the best thing to do is in any case to privilege the I/O
1166 * related to the application with respect to all other
1167 * I/O. Therefore, the best strategy to start as quickly as possible
1168 * an application that causes a burst of queue creations is to
1169 * weight-raise all the queues created during the burst. This is the
1170 * exact opposite of the best strategy for the other type of bursts.
1171 *
1172 * In the end, to take the best action for each of the two cases, the
1173 * two types of bursts need to be distinguished. Fortunately, this
1174 * seems relatively easy, by looking at the sizes of the bursts. In
1175 * particular, we found a threshold such that only bursts with a
1176 * larger size than that threshold are apparently caused by
1177 * services or commands such as systemd or git grep. For brevity,
1178 * hereafter we call just 'large' these bursts. BFQ *does not*
1179 * weight-raise queues whose creation occurs in a large burst. In
1180 * addition, for each of these queues BFQ performs or does not perform
1181 * idling depending on which choice boosts the throughput more. The
1182 * exact choice depends on the device and request pattern at
1183 * hand.
1184 *
1185 * Unfortunately, false positives may occur while an interactive task
1186 * is starting (e.g., an application is being started). The
1187 * consequence is that the queues associated with the task do not
1188 * enjoy weight raising as expected. Fortunately these false positives
1189 * are very rare. They typically occur if some service happens to
1190 * start doing I/O exactly when the interactive task starts.
1191 *
1192 * Turning back to the next function, it is invoked only if there are
1193 * no active queues (apart from active queues that would belong to the
1194 * same, possible burst bfqq would belong to), and it implements all
1195 * the steps needed to detect the occurrence of a large burst and to
1196 * properly mark all the queues belonging to it (so that they can then
1197 * be treated in a different way). This goal is achieved by
1198 * maintaining a "burst list" that holds, temporarily, the queues that
1199 * belong to the burst in progress. The list is then used to mark
1200 * these queues as belonging to a large burst if the burst does become
1201 * large. The main steps are the following.
1202 *
1203 * . when the very first queue is created, the queue is inserted into the
1204 * list (as it could be the first queue in a possible burst)
1205 *
1206 * . if the current burst has not yet become large, and a queue Q that does
1207 * not yet belong to the burst is activated shortly after the last time
1208 * at which a new queue entered the burst list, then the function appends
1209 * Q to the burst list
1210 *
1211 * . if, as a consequence of the previous step, the burst size reaches
1212 * the large-burst threshold, then
1213 *
1214 * . all the queues in the burst list are marked as belonging to a
1215 * large burst
1216 *
1217 * . the burst list is deleted; in fact, the burst list already served
1218 * its purpose (keeping temporarily track of the queues in a burst,
1219 * so as to be able to mark them as belonging to a large burst in the
1220 * previous sub-step), and now is not needed any more
1221 *
1222 * . the device enters a large-burst mode
1223 *
1224 * . if a queue Q that does not belong to the burst is created while
1225 * the device is in large-burst mode and shortly after the last time
1226 * at which a queue either entered the burst list or was marked as
1227 * belonging to the current large burst, then Q is immediately marked
1228 * as belonging to a large burst.
1229 *
1230 * . if a queue Q that does not belong to the burst is created a while
1231 * later, i.e., not shortly after, than the last time at which a queue
1232 * either entered the burst list or was marked as belonging to the
1233 * current large burst, then the current burst is deemed as finished and:
1234 *
1235 * . the large-burst mode is reset if set
1236 *
1237 * . the burst list is emptied
1238 *
1239 * . Q is inserted in the burst list, as Q may be the first queue
1240 * in a possible new burst (then the burst list contains just Q
1241 * after this step).
1242 */
1243static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1244{
1245 /*
1246 * If bfqq is already in the burst list or is part of a large
1247 * burst, or finally has just been split, then there is
1248 * nothing else to do.
1249 */
1250 if (!hlist_unhashed(&bfqq->burst_list_node) ||
1251 bfq_bfqq_in_large_burst(bfqq) ||
1252 time_is_after_eq_jiffies(bfqq->split_time +
1253 msecs_to_jiffies(10)))
1254 return;
1255
1256 /*
1257 * If bfqq's creation happens late enough, or bfqq belongs to
1258 * a different group than the burst group, then the current
1259 * burst is finished, and related data structures must be
1260 * reset.
1261 *
1262 * In this respect, consider the special case where bfqq is
1263 * the very first queue created after BFQ is selected for this
1264 * device. In this case, last_ins_in_burst and
1265 * burst_parent_entity are not yet significant when we get
1266 * here. But it is easy to verify that, whether or not the
1267 * following condition is true, bfqq will end up being
1268 * inserted into the burst list. In particular the list will
1269 * happen to contain only bfqq. And this is exactly what has
1270 * to happen, as bfqq may be the first queue of the first
1271 * burst.
1272 */
1273 if (time_is_before_jiffies(bfqd->last_ins_in_burst +
1274 bfqd->bfq_burst_interval) ||
1275 bfqq->entity.parent != bfqd->burst_parent_entity) {
1276 bfqd->large_burst = false;
1277 bfq_reset_burst_list(bfqd, bfqq);
1278 goto end;
1279 }
1280
1281 /*
1282 * If we get here, then bfqq is being activated shortly after the
1283 * last queue. So, if the current burst is also large, we can mark
1284 * bfqq as belonging to this large burst immediately.
1285 */
1286 if (bfqd->large_burst) {
1287 bfq_mark_bfqq_in_large_burst(bfqq);
1288 goto end;
1289 }
1290
1291 /*
1292 * If we get here, then a large-burst state has not yet been
1293 * reached, but bfqq is being activated shortly after the last
1294 * queue. Then we add bfqq to the burst.
1295 */
1296 bfq_add_to_burst(bfqd, bfqq);
1297end:
1298 /*
1299 * At this point, bfqq either has been added to the current
1300 * burst or has caused the current burst to terminate and a
1301 * possible new burst to start. In particular, in the second
1302 * case, bfqq has become the first queue in the possible new
1303 * burst. In both cases last_ins_in_burst needs to be moved
1304 * forward.
1305 */
1306 bfqd->last_ins_in_burst = jiffies;
1307}
1308
1309static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1310{
1311 struct bfq_entity *entity = &bfqq->entity;
1312
1313 return entity->budget - entity->service;
1314}
1315
1316/*
1317 * If enough samples have been computed, return the current max budget
1318 * stored in bfqd, which is dynamically updated according to the
1319 * estimated disk peak rate; otherwise return the default max budget
1320 */
1321static int bfq_max_budget(struct bfq_data *bfqd)
1322{
1323 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1324 return bfq_default_max_budget;
1325 else
1326 return bfqd->bfq_max_budget;
1327}
1328
1329/*
1330 * Return min budget, which is a fraction of the current or default
1331 * max budget (trying with 1/32)
1332 */
1333static int bfq_min_budget(struct bfq_data *bfqd)
1334{
1335 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1336 return bfq_default_max_budget / 32;
1337 else
1338 return bfqd->bfq_max_budget / 32;
1339}
1340
1341/*
1342 * The next function, invoked after the input queue bfqq switches from
1343 * idle to busy, updates the budget of bfqq. The function also tells
1344 * whether the in-service queue should be expired, by returning
1345 * true. The purpose of expiring the in-service queue is to give bfqq
1346 * the chance to possibly preempt the in-service queue, and the reason
1347 * for preempting the in-service queue is to achieve one of the two
1348 * goals below.
1349 *
1350 * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1351 * expired because it has remained idle. In particular, bfqq may have
1352 * expired for one of the following two reasons:
1353 *
1354 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1355 * and did not make it to issue a new request before its last
1356 * request was served;
1357 *
1358 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1359 * a new request before the expiration of the idling-time.
1360 *
1361 * Even if bfqq has expired for one of the above reasons, the process
1362 * associated with the queue may be however issuing requests greedily,
1363 * and thus be sensitive to the bandwidth it receives (bfqq may have
1364 * remained idle for other reasons: CPU high load, bfqq not enjoying
1365 * idling, I/O throttling somewhere in the path from the process to
1366 * the I/O scheduler, ...). But if, after every expiration for one of
1367 * the above two reasons, bfqq has to wait for the service of at least
1368 * one full budget of another queue before being served again, then
1369 * bfqq is likely to get a much lower bandwidth or resource time than
1370 * its reserved ones. To address this issue, two countermeasures need
1371 * to be taken.
1372 *
1373 * First, the budget and the timestamps of bfqq need to be updated in
1374 * a special way on bfqq reactivation: they need to be updated as if
1375 * bfqq did not remain idle and did not expire. In fact, if they are
1376 * computed as if bfqq expired and remained idle until reactivation,
1377 * then the process associated with bfqq is treated as if, instead of
1378 * being greedy, it stopped issuing requests when bfqq remained idle,
1379 * and restarts issuing requests only on this reactivation. In other
1380 * words, the scheduler does not help the process recover the "service
1381 * hole" between bfqq expiration and reactivation. As a consequence,
1382 * the process receives a lower bandwidth than its reserved one. In
1383 * contrast, to recover this hole, the budget must be updated as if
1384 * bfqq was not expired at all before this reactivation, i.e., it must
1385 * be set to the value of the remaining budget when bfqq was
1386 * expired. Along the same line, timestamps need to be assigned the
1387 * value they had the last time bfqq was selected for service, i.e.,
1388 * before last expiration. Thus timestamps need to be back-shifted
1389 * with respect to their normal computation (see [1] for more details
1390 * on this tricky aspect).
1391 *
1392 * Secondly, to allow the process to recover the hole, the in-service
1393 * queue must be expired too, to give bfqq the chance to preempt it
1394 * immediately. In fact, if bfqq has to wait for a full budget of the
1395 * in-service queue to be completed, then it may become impossible to
1396 * let the process recover the hole, even if the back-shifted
1397 * timestamps of bfqq are lower than those of the in-service queue. If
1398 * this happens for most or all of the holes, then the process may not
1399 * receive its reserved bandwidth. In this respect, it is worth noting
1400 * that, being the service of outstanding requests unpreemptible, a
1401 * little fraction of the holes may however be unrecoverable, thereby
1402 * causing a little loss of bandwidth.
1403 *
1404 * The last important point is detecting whether bfqq does need this
1405 * bandwidth recovery. In this respect, the next function deems the
1406 * process associated with bfqq greedy, and thus allows it to recover
1407 * the hole, if: 1) the process is waiting for the arrival of a new
1408 * request (which implies that bfqq expired for one of the above two
1409 * reasons), and 2) such a request has arrived soon. The first
1410 * condition is controlled through the flag non_blocking_wait_rq,
1411 * while the second through the flag arrived_in_time. If both
1412 * conditions hold, then the function computes the budget in the
1413 * above-described special way, and signals that the in-service queue
1414 * should be expired. Timestamp back-shifting is done later in
1415 * __bfq_activate_entity.
1416 *
1417 * 2. Reduce latency. Even if timestamps are not backshifted to let
1418 * the process associated with bfqq recover a service hole, bfqq may
1419 * however happen to have, after being (re)activated, a lower finish
1420 * timestamp than the in-service queue. That is, the next budget of
1421 * bfqq may have to be completed before the one of the in-service
1422 * queue. If this is the case, then preempting the in-service queue
1423 * allows this goal to be achieved, apart from the unpreemptible,
1424 * outstanding requests mentioned above.
1425 *
1426 * Unfortunately, regardless of which of the above two goals one wants
1427 * to achieve, service trees need first to be updated to know whether
1428 * the in-service queue must be preempted. To have service trees
1429 * correctly updated, the in-service queue must be expired and
1430 * rescheduled, and bfqq must be scheduled too. This is one of the
1431 * most costly operations (in future versions, the scheduling
1432 * mechanism may be re-designed in such a way to make it possible to
1433 * know whether preemption is needed without needing to update service
1434 * trees). In addition, queue preemptions almost always cause random
1435 * I/O, which may in turn cause loss of throughput. Finally, there may
1436 * even be no in-service queue when the next function is invoked (so,
1437 * no queue to compare timestamps with). Because of these facts, the
1438 * next function adopts the following simple scheme to avoid costly
1439 * operations, too frequent preemptions and too many dependencies on
1440 * the state of the scheduler: it requests the expiration of the
1441 * in-service queue (unconditionally) only for queues that need to
1442 * recover a hole. Then it delegates to other parts of the code the
1443 * responsibility of handling the above case 2.
1444 */
1445static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1446 struct bfq_queue *bfqq,
1447 bool arrived_in_time)
1448{
1449 struct bfq_entity *entity = &bfqq->entity;
1450
1451 /*
1452 * In the next compound condition, we check also whether there
1453 * is some budget left, because otherwise there is no point in
1454 * trying to go on serving bfqq with this same budget: bfqq
1455 * would be expired immediately after being selected for
1456 * service. This would only cause useless overhead.
1457 */
1458 if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
1459 bfq_bfqq_budget_left(bfqq) > 0) {
1460 /*
1461 * We do not clear the flag non_blocking_wait_rq here, as
1462 * the latter is used in bfq_activate_bfqq to signal
1463 * that timestamps need to be back-shifted (and is
1464 * cleared right after).
1465 */
1466
1467 /*
1468 * In next assignment we rely on that either
1469 * entity->service or entity->budget are not updated
1470 * on expiration if bfqq is empty (see
1471 * __bfq_bfqq_recalc_budget). Thus both quantities
1472 * remain unchanged after such an expiration, and the
1473 * following statement therefore assigns to
1474 * entity->budget the remaining budget on such an
1475 * expiration.
1476 */
1477 entity->budget = min_t(unsigned long,
1478 bfq_bfqq_budget_left(bfqq),
1479 bfqq->max_budget);
1480
1481 /*
1482 * At this point, we have used entity->service to get
1483 * the budget left (needed for updating
1484 * entity->budget). Thus we finally can, and have to,
1485 * reset entity->service. The latter must be reset
1486 * because bfqq would otherwise be charged again for
1487 * the service it has received during its previous
1488 * service slot(s).
1489 */
1490 entity->service = 0;
1491
1492 return true;
1493 }
1494
1495 /*
1496 * We can finally complete expiration, by setting service to 0.
1497 */
1498 entity->service = 0;
1499 entity->budget = max_t(unsigned long, bfqq->max_budget,
1500 bfq_serv_to_charge(bfqq->next_rq, bfqq));
1501 bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1502 return false;
1503}
1504
1505/*
1506 * Return the farthest past time instant according to jiffies
1507 * macros.
1508 */
1509static unsigned long bfq_smallest_from_now(void)
1510{
1511 return jiffies - MAX_JIFFY_OFFSET;
1512}
1513
1514static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1515 struct bfq_queue *bfqq,
1516 unsigned int old_wr_coeff,
1517 bool wr_or_deserves_wr,
1518 bool interactive,
1519 bool in_burst,
1520 bool soft_rt)
1521{
1522 if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1523 /* start a weight-raising period */
1524 if (interactive) {
1525 bfqq->service_from_wr = 0;
1526 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1527 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1528 } else {
1529 /*
1530 * No interactive weight raising in progress
1531 * here: assign minus infinity to
1532 * wr_start_at_switch_to_srt, to make sure
1533 * that, at the end of the soft-real-time
1534 * weight raising periods that is starting
1535 * now, no interactive weight-raising period
1536 * may be wrongly considered as still in
1537 * progress (and thus actually started by
1538 * mistake).
1539 */
1540 bfqq->wr_start_at_switch_to_srt =
1541 bfq_smallest_from_now();
1542 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1543 BFQ_SOFTRT_WEIGHT_FACTOR;
1544 bfqq->wr_cur_max_time =
1545 bfqd->bfq_wr_rt_max_time;
1546 }
1547
1548 /*
1549 * If needed, further reduce budget to make sure it is
1550 * close to bfqq's backlog, so as to reduce the
1551 * scheduling-error component due to a too large
1552 * budget. Do not care about throughput consequences,
1553 * but only about latency. Finally, do not assign a
1554 * too small budget either, to avoid increasing
1555 * latency by causing too frequent expirations.
1556 */
1557 bfqq->entity.budget = min_t(unsigned long,
1558 bfqq->entity.budget,
1559 2 * bfq_min_budget(bfqd));
1560 } else if (old_wr_coeff > 1) {
1561 if (interactive) { /* update wr coeff and duration */
1562 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1563 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1564 } else if (in_burst)
1565 bfqq->wr_coeff = 1;
1566 else if (soft_rt) {
1567 /*
1568 * The application is now or still meeting the
1569 * requirements for being deemed soft rt. We
1570 * can then correctly and safely (re)charge
1571 * the weight-raising duration for the
1572 * application with the weight-raising
1573 * duration for soft rt applications.
1574 *
1575 * In particular, doing this recharge now, i.e.,
1576 * before the weight-raising period for the
1577 * application finishes, reduces the probability
1578 * of the following negative scenario:
1579 * 1) the weight of a soft rt application is
1580 * raised at startup (as for any newly
1581 * created application),
1582 * 2) since the application is not interactive,
1583 * at a certain time weight-raising is
1584 * stopped for the application,
1585 * 3) at that time the application happens to
1586 * still have pending requests, and hence
1587 * is destined to not have a chance to be
1588 * deemed soft rt before these requests are
1589 * completed (see the comments to the
1590 * function bfq_bfqq_softrt_next_start()
1591 * for details on soft rt detection),
1592 * 4) these pending requests experience a high
1593 * latency because the application is not
1594 * weight-raised while they are pending.
1595 */
1596 if (bfqq->wr_cur_max_time !=
1597 bfqd->bfq_wr_rt_max_time) {
1598 bfqq->wr_start_at_switch_to_srt =
1599 bfqq->last_wr_start_finish;
1600
1601 bfqq->wr_cur_max_time =
1602 bfqd->bfq_wr_rt_max_time;
1603 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1604 BFQ_SOFTRT_WEIGHT_FACTOR;
1605 }
1606 bfqq->last_wr_start_finish = jiffies;
1607 }
1608 }
1609}
1610
1611static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1612 struct bfq_queue *bfqq)
1613{
1614 return bfqq->dispatched == 0 &&
1615 time_is_before_jiffies(
1616 bfqq->budget_timeout +
1617 bfqd->bfq_wr_min_idle_time);
1618}
1619
1620
1621/*
1622 * Return true if bfqq is in a higher priority class, or has a higher
1623 * weight than the in-service queue.
1624 */
1625static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
1626 struct bfq_queue *in_serv_bfqq)
1627{
1628 int bfqq_weight, in_serv_weight;
1629
1630 if (bfqq->ioprio_class < in_serv_bfqq->ioprio_class)
1631 return true;
1632
1633 if (in_serv_bfqq->entity.parent == bfqq->entity.parent) {
1634 bfqq_weight = bfqq->entity.weight;
1635 in_serv_weight = in_serv_bfqq->entity.weight;
1636 } else {
1637 if (bfqq->entity.parent)
1638 bfqq_weight = bfqq->entity.parent->weight;
1639 else
1640 bfqq_weight = bfqq->entity.weight;
1641 if (in_serv_bfqq->entity.parent)
1642 in_serv_weight = in_serv_bfqq->entity.parent->weight;
1643 else
1644 in_serv_weight = in_serv_bfqq->entity.weight;
1645 }
1646
1647 return bfqq_weight > in_serv_weight;
1648}
1649
1650static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1651 struct bfq_queue *bfqq,
1652 int old_wr_coeff,
1653 struct request *rq,
1654 bool *interactive)
1655{
1656 bool soft_rt, in_burst, wr_or_deserves_wr,
1657 bfqq_wants_to_preempt,
1658 idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1659 /*
1660 * See the comments on
1661 * bfq_bfqq_update_budg_for_activation for
1662 * details on the usage of the next variable.
1663 */
1664 arrived_in_time = ktime_get_ns() <=
1665 bfqq->ttime.last_end_request +
1666 bfqd->bfq_slice_idle * 3;
1667
1668
1669 /*
1670 * bfqq deserves to be weight-raised if:
1671 * - it is sync,
1672 * - it does not belong to a large burst,
1673 * - it has been idle for enough time or is soft real-time,
1674 * - is linked to a bfq_io_cq (it is not shared in any sense).
1675 */
1676 in_burst = bfq_bfqq_in_large_burst(bfqq);
1677 soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1678 !BFQQ_TOTALLY_SEEKY(bfqq) &&
1679 !in_burst &&
1680 time_is_before_jiffies(bfqq->soft_rt_next_start) &&
1681 bfqq->dispatched == 0;
1682 *interactive = !in_burst && idle_for_long_time;
1683 wr_or_deserves_wr = bfqd->low_latency &&
1684 (bfqq->wr_coeff > 1 ||
1685 (bfq_bfqq_sync(bfqq) &&
1686 bfqq->bic && (*interactive || soft_rt)));
1687
1688 /*
1689 * Using the last flag, update budget and check whether bfqq
1690 * may want to preempt the in-service queue.
1691 */
1692 bfqq_wants_to_preempt =
1693 bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1694 arrived_in_time);
1695
1696 /*
1697 * If bfqq happened to be activated in a burst, but has been
1698 * idle for much more than an interactive queue, then we
1699 * assume that, in the overall I/O initiated in the burst, the
1700 * I/O associated with bfqq is finished. So bfqq does not need
1701 * to be treated as a queue belonging to a burst
1702 * anymore. Accordingly, we reset bfqq's in_large_burst flag
1703 * if set, and remove bfqq from the burst list if it's
1704 * there. We do not decrement burst_size, because the fact
1705 * that bfqq does not need to belong to the burst list any
1706 * more does not invalidate the fact that bfqq was created in
1707 * a burst.
1708 */
1709 if (likely(!bfq_bfqq_just_created(bfqq)) &&
1710 idle_for_long_time &&
1711 time_is_before_jiffies(
1712 bfqq->budget_timeout +
1713 msecs_to_jiffies(10000))) {
1714 hlist_del_init(&bfqq->burst_list_node);
1715 bfq_clear_bfqq_in_large_burst(bfqq);
1716 }
1717
1718 bfq_clear_bfqq_just_created(bfqq);
1719
1720
1721 if (!bfq_bfqq_IO_bound(bfqq)) {
1722 if (arrived_in_time) {
1723 bfqq->requests_within_timer++;
1724 if (bfqq->requests_within_timer >=
1725 bfqd->bfq_requests_within_timer)
1726 bfq_mark_bfqq_IO_bound(bfqq);
1727 } else
1728 bfqq->requests_within_timer = 0;
1729 }
1730
1731 if (bfqd->low_latency) {
1732 if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1733 /* wraparound */
1734 bfqq->split_time =
1735 jiffies - bfqd->bfq_wr_min_idle_time - 1;
1736
1737 if (time_is_before_jiffies(bfqq->split_time +
1738 bfqd->bfq_wr_min_idle_time)) {
1739 bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1740 old_wr_coeff,
1741 wr_or_deserves_wr,
1742 *interactive,
1743 in_burst,
1744 soft_rt);
1745
1746 if (old_wr_coeff != bfqq->wr_coeff)
1747 bfqq->entity.prio_changed = 1;
1748 }
1749 }
1750
1751 bfqq->last_idle_bklogged = jiffies;
1752 bfqq->service_from_backlogged = 0;
1753 bfq_clear_bfqq_softrt_update(bfqq);
1754
1755 bfq_add_bfqq_busy(bfqd, bfqq);
1756
1757 /*
1758 * Expire in-service queue only if preemption may be needed
1759 * for guarantees. In particular, we care only about two
1760 * cases. The first is that bfqq has to recover a service
1761 * hole, as explained in the comments on
1762 * bfq_bfqq_update_budg_for_activation(), i.e., that
1763 * bfqq_wants_to_preempt is true. However, if bfqq does not
1764 * carry time-critical I/O, then bfqq's bandwidth is less
1765 * important than that of queues that carry time-critical I/O.
1766 * So, as a further constraint, we consider this case only if
1767 * bfqq is at least as weight-raised, i.e., at least as time
1768 * critical, as the in-service queue.
1769 *
1770 * The second case is that bfqq is in a higher priority class,
1771 * or has a higher weight than the in-service queue. If this
1772 * condition does not hold, we don't care because, even if
1773 * bfqq does not start to be served immediately, the resulting
1774 * delay for bfqq's I/O is however lower or much lower than
1775 * the ideal completion time to be guaranteed to bfqq's I/O.
1776 *
1777 * In both cases, preemption is needed only if, according to
1778 * the timestamps of both bfqq and of the in-service queue,
1779 * bfqq actually is the next queue to serve. So, to reduce
1780 * useless preemptions, the return value of
1781 * next_queue_may_preempt() is considered in the next compound
1782 * condition too. Yet next_queue_may_preempt() just checks a
1783 * simple, necessary condition for bfqq to be the next queue
1784 * to serve. In fact, to evaluate a sufficient condition, the
1785 * timestamps of the in-service queue would need to be
1786 * updated, and this operation is quite costly (see the
1787 * comments on bfq_bfqq_update_budg_for_activation()).
1788 */
1789 if (bfqd->in_service_queue &&
1790 ((bfqq_wants_to_preempt &&
1791 bfqq->wr_coeff >= bfqd->in_service_queue->wr_coeff) ||
1792 bfq_bfqq_higher_class_or_weight(bfqq, bfqd->in_service_queue)) &&
1793 next_queue_may_preempt(bfqd))
1794 bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
1795 false, BFQQE_PREEMPTED);
1796}
1797
1798static void bfq_reset_inject_limit(struct bfq_data *bfqd,
1799 struct bfq_queue *bfqq)
1800{
1801 /* invalidate baseline total service time */
1802 bfqq->last_serv_time_ns = 0;
1803
1804 /*
1805 * Reset pointer in case we are waiting for
1806 * some request completion.
1807 */
1808 bfqd->waited_rq = NULL;
1809
1810 /*
1811 * If bfqq has a short think time, then start by setting the
1812 * inject limit to 0 prudentially, because the service time of
1813 * an injected I/O request may be higher than the think time
1814 * of bfqq, and therefore, if one request was injected when
1815 * bfqq remains empty, this injected request might delay the
1816 * service of the next I/O request for bfqq significantly. In
1817 * case bfqq can actually tolerate some injection, then the
1818 * adaptive update will however raise the limit soon. This
1819 * lucky circumstance holds exactly because bfqq has a short
1820 * think time, and thus, after remaining empty, is likely to
1821 * get new I/O enqueued---and then completed---before being
1822 * expired. This is the very pattern that gives the
1823 * limit-update algorithm the chance to measure the effect of
1824 * injection on request service times, and then to update the
1825 * limit accordingly.
1826 *
1827 * However, in the following special case, the inject limit is
1828 * left to 1 even if the think time is short: bfqq's I/O is
1829 * synchronized with that of some other queue, i.e., bfqq may
1830 * receive new I/O only after the I/O of the other queue is
1831 * completed. Keeping the inject limit to 1 allows the
1832 * blocking I/O to be served while bfqq is in service. And
1833 * this is very convenient both for bfqq and for overall
1834 * throughput, as explained in detail in the comments in
1835 * bfq_update_has_short_ttime().
1836 *
1837 * On the opposite end, if bfqq has a long think time, then
1838 * start directly by 1, because:
1839 * a) on the bright side, keeping at most one request in
1840 * service in the drive is unlikely to cause any harm to the
1841 * latency of bfqq's requests, as the service time of a single
1842 * request is likely to be lower than the think time of bfqq;
1843 * b) on the downside, after becoming empty, bfqq is likely to
1844 * expire before getting its next request. With this request
1845 * arrival pattern, it is very hard to sample total service
1846 * times and update the inject limit accordingly (see comments
1847 * on bfq_update_inject_limit()). So the limit is likely to be
1848 * never, or at least seldom, updated. As a consequence, by
1849 * setting the limit to 1, we avoid that no injection ever
1850 * occurs with bfqq. On the downside, this proactive step
1851 * further reduces chances to actually compute the baseline
1852 * total service time. Thus it reduces chances to execute the
1853 * limit-update algorithm and possibly raise the limit to more
1854 * than 1.
1855 */
1856 if (bfq_bfqq_has_short_ttime(bfqq))
1857 bfqq->inject_limit = 0;
1858 else
1859 bfqq->inject_limit = 1;
1860
1861 bfqq->decrease_time_jif = jiffies;
1862}
1863
1864static void bfq_add_request(struct request *rq)
1865{
1866 struct bfq_queue *bfqq = RQ_BFQQ(rq);
1867 struct bfq_data *bfqd = bfqq->bfqd;
1868 struct request *next_rq, *prev;
1869 unsigned int old_wr_coeff = bfqq->wr_coeff;
1870 bool interactive = false;
1871
1872 bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
1873 bfqq->queued[rq_is_sync(rq)]++;
1874 bfqd->queued++;
1875
1876 if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_sync(bfqq)) {
1877 /*
1878 * Detect whether bfqq's I/O seems synchronized with
1879 * that of some other queue, i.e., whether bfqq, after
1880 * remaining empty, happens to receive new I/O only
1881 * right after some I/O request of the other queue has
1882 * been completed. We call waker queue the other
1883 * queue, and we assume, for simplicity, that bfqq may
1884 * have at most one waker queue.
1885 *
1886 * A remarkable throughput boost can be reached by
1887 * unconditionally injecting the I/O of the waker
1888 * queue, every time a new bfq_dispatch_request
1889 * happens to be invoked while I/O is being plugged
1890 * for bfqq. In addition to boosting throughput, this
1891 * unblocks bfqq's I/O, thereby improving bandwidth
1892 * and latency for bfqq. Note that these same results
1893 * may be achieved with the general injection
1894 * mechanism, but less effectively. For details on
1895 * this aspect, see the comments on the choice of the
1896 * queue for injection in bfq_select_queue().
1897 *
1898 * Turning back to the detection of a waker queue, a
1899 * queue Q is deemed as a waker queue for bfqq if, for
1900 * two consecutive times, bfqq happens to become non
1901 * empty right after a request of Q has been
1902 * completed. In particular, on the first time, Q is
1903 * tentatively set as a candidate waker queue, while
1904 * on the second time, the flag
1905 * bfq_bfqq_has_waker(bfqq) is set to confirm that Q
1906 * is a waker queue for bfqq. These detection steps
1907 * are performed only if bfqq has a long think time,
1908 * so as to make it more likely that bfqq's I/O is
1909 * actually being blocked by a synchronization. This
1910 * last filter, plus the above two-times requirement,
1911 * make false positives less likely.
1912 *
1913 * NOTE
1914 *
1915 * The sooner a waker queue is detected, the sooner
1916 * throughput can be boosted by injecting I/O from the
1917 * waker queue. Fortunately, detection is likely to be
1918 * actually fast, for the following reasons. While
1919 * blocked by synchronization, bfqq has a long think
1920 * time. This implies that bfqq's inject limit is at
1921 * least equal to 1 (see the comments in
1922 * bfq_update_inject_limit()). So, thanks to
1923 * injection, the waker queue is likely to be served
1924 * during the very first I/O-plugging time interval
1925 * for bfqq. This triggers the first step of the
1926 * detection mechanism. Thanks again to injection, the
1927 * candidate waker queue is then likely to be
1928 * confirmed no later than during the next
1929 * I/O-plugging interval for bfqq.
1930 */
1931 if (bfqd->last_completed_rq_bfqq &&
1932 !bfq_bfqq_has_short_ttime(bfqq) &&
1933 ktime_get_ns() - bfqd->last_completion <
1934 200 * NSEC_PER_USEC) {
1935 if (bfqd->last_completed_rq_bfqq != bfqq &&
1936 bfqd->last_completed_rq_bfqq !=
1937 bfqq->waker_bfqq) {
1938 /*
1939 * First synchronization detected with
1940 * a candidate waker queue, or with a
1941 * different candidate waker queue
1942 * from the current one.
1943 */
1944 bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq;
1945
1946 /*
1947 * If the waker queue disappears, then
1948 * bfqq->waker_bfqq must be reset. To
1949 * this goal, we maintain in each
1950 * waker queue a list, woken_list, of
1951 * all the queues that reference the
1952 * waker queue through their
1953 * waker_bfqq pointer. When the waker
1954 * queue exits, the waker_bfqq pointer
1955 * of all the queues in the woken_list
1956 * is reset.
1957 *
1958 * In addition, if bfqq is already in
1959 * the woken_list of a waker queue,
1960 * then, before being inserted into
1961 * the woken_list of a new waker
1962 * queue, bfqq must be removed from
1963 * the woken_list of the old waker
1964 * queue.
1965 */
1966 if (!hlist_unhashed(&bfqq->woken_list_node))
1967 hlist_del_init(&bfqq->woken_list_node);
1968 hlist_add_head(&bfqq->woken_list_node,
1969 &bfqd->last_completed_rq_bfqq->woken_list);
1970
1971 bfq_clear_bfqq_has_waker(bfqq);
1972 } else if (bfqd->last_completed_rq_bfqq ==
1973 bfqq->waker_bfqq &&
1974 !bfq_bfqq_has_waker(bfqq)) {
1975 /*
1976 * synchronization with waker_bfqq
1977 * seen for the second time
1978 */
1979 bfq_mark_bfqq_has_waker(bfqq);
1980 }
1981 }
1982
1983 /*
1984 * Periodically reset inject limit, to make sure that
1985 * the latter eventually drops in case workload
1986 * changes, see step (3) in the comments on
1987 * bfq_update_inject_limit().
1988 */
1989 if (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
1990 msecs_to_jiffies(1000)))
1991 bfq_reset_inject_limit(bfqd, bfqq);
1992
1993 /*
1994 * The following conditions must hold to setup a new
1995 * sampling of total service time, and then a new
1996 * update of the inject limit:
1997 * - bfqq is in service, because the total service
1998 * time is evaluated only for the I/O requests of
1999 * the queues in service;
2000 * - this is the right occasion to compute or to
2001 * lower the baseline total service time, because
2002 * there are actually no requests in the drive,
2003 * or
2004 * the baseline total service time is available, and
2005 * this is the right occasion to compute the other
2006 * quantity needed to update the inject limit, i.e.,
2007 * the total service time caused by the amount of
2008 * injection allowed by the current value of the
2009 * limit. It is the right occasion because injection
2010 * has actually been performed during the service
2011 * hole, and there are still in-flight requests,
2012 * which are very likely to be exactly the injected
2013 * requests, or part of them;
2014 * - the minimum interval for sampling the total
2015 * service time and updating the inject limit has
2016 * elapsed.
2017 */
2018 if (bfqq == bfqd->in_service_queue &&
2019 (bfqd->rq_in_driver == 0 ||
2020 (bfqq->last_serv_time_ns > 0 &&
2021 bfqd->rqs_injected && bfqd->rq_in_driver > 0)) &&
2022 time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2023 msecs_to_jiffies(10))) {
2024 bfqd->last_empty_occupied_ns = ktime_get_ns();
2025 /*
2026 * Start the state machine for measuring the
2027 * total service time of rq: setting
2028 * wait_dispatch will cause bfqd->waited_rq to
2029 * be set when rq will be dispatched.
2030 */
2031 bfqd->wait_dispatch = true;
2032 /*
2033 * If there is no I/O in service in the drive,
2034 * then possible injection occurred before the
2035 * arrival of rq will not affect the total
2036 * service time of rq. So the injection limit
2037 * must not be updated as a function of such
2038 * total service time, unless new injection
2039 * occurs before rq is completed. To have the
2040 * injection limit updated only in the latter
2041 * case, reset rqs_injected here (rqs_injected
2042 * will be set in case injection is performed
2043 * on bfqq before rq is completed).
2044 */
2045 if (bfqd->rq_in_driver == 0)
2046 bfqd->rqs_injected = false;
2047 }
2048 }
2049
2050 elv_rb_add(&bfqq->sort_list, rq);
2051
2052 /*
2053 * Check if this request is a better next-serve candidate.
2054 */
2055 prev = bfqq->next_rq;
2056 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
2057 bfqq->next_rq = next_rq;
2058
2059 /*
2060 * Adjust priority tree position, if next_rq changes.
2061 * See comments on bfq_pos_tree_add_move() for the unlikely().
2062 */
2063 if (unlikely(!bfqd->nonrot_with_queueing && prev != bfqq->next_rq))
2064 bfq_pos_tree_add_move(bfqd, bfqq);
2065
2066 if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
2067 bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
2068 rq, &interactive);
2069 else {
2070 if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
2071 time_is_before_jiffies(
2072 bfqq->last_wr_start_finish +
2073 bfqd->bfq_wr_min_inter_arr_async)) {
2074 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
2075 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
2076
2077 bfqd->wr_busy_queues++;
2078 bfqq->entity.prio_changed = 1;
2079 }
2080 if (prev != bfqq->next_rq)
2081 bfq_updated_next_req(bfqd, bfqq);
2082 }
2083
2084 /*
2085 * Assign jiffies to last_wr_start_finish in the following
2086 * cases:
2087 *
2088 * . if bfqq is not going to be weight-raised, because, for
2089 * non weight-raised queues, last_wr_start_finish stores the
2090 * arrival time of the last request; as of now, this piece
2091 * of information is used only for deciding whether to
2092 * weight-raise async queues
2093 *
2094 * . if bfqq is not weight-raised, because, if bfqq is now
2095 * switching to weight-raised, then last_wr_start_finish
2096 * stores the time when weight-raising starts
2097 *
2098 * . if bfqq is interactive, because, regardless of whether
2099 * bfqq is currently weight-raised, the weight-raising
2100 * period must start or restart (this case is considered
2101 * separately because it is not detected by the above
2102 * conditions, if bfqq is already weight-raised)
2103 *
2104 * last_wr_start_finish has to be updated also if bfqq is soft
2105 * real-time, because the weight-raising period is constantly
2106 * restarted on idle-to-busy transitions for these queues, but
2107 * this is already done in bfq_bfqq_handle_idle_busy_switch if
2108 * needed.
2109 */
2110 if (bfqd->low_latency &&
2111 (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
2112 bfqq->last_wr_start_finish = jiffies;
2113}
2114
2115static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
2116 struct bio *bio,
2117 struct request_queue *q)
2118{
2119 struct bfq_queue *bfqq = bfqd->bio_bfqq;
2120
2121
2122 if (bfqq)
2123 return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
2124
2125 return NULL;
2126}
2127
2128static sector_t get_sdist(sector_t last_pos, struct request *rq)
2129{
2130 if (last_pos)
2131 return abs(blk_rq_pos(rq) - last_pos);
2132
2133 return 0;
2134}
2135
2136#if 0 /* Still not clear if we can do without next two functions */
2137static void bfq_activate_request(struct request_queue *q, struct request *rq)
2138{
2139 struct bfq_data *bfqd = q->elevator->elevator_data;
2140
2141 bfqd->rq_in_driver++;
2142}
2143
2144static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
2145{
2146 struct bfq_data *bfqd = q->elevator->elevator_data;
2147
2148 bfqd->rq_in_driver--;
2149}
2150#endif
2151
2152static void bfq_remove_request(struct request_queue *q,
2153 struct request *rq)
2154{
2155 struct bfq_queue *bfqq = RQ_BFQQ(rq);
2156 struct bfq_data *bfqd = bfqq->bfqd;
2157 const int sync = rq_is_sync(rq);
2158
2159 if (bfqq->next_rq == rq) {
2160 bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
2161 bfq_updated_next_req(bfqd, bfqq);
2162 }
2163
2164 if (rq->queuelist.prev != &rq->queuelist)
2165 list_del_init(&rq->queuelist);
2166 bfqq->queued[sync]--;
2167 bfqd->queued--;
2168 elv_rb_del(&bfqq->sort_list, rq);
2169
2170 elv_rqhash_del(q, rq);
2171 if (q->last_merge == rq)
2172 q->last_merge = NULL;
2173
2174 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2175 bfqq->next_rq = NULL;
2176
2177 if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
2178 bfq_del_bfqq_busy(bfqd, bfqq, false);
2179 /*
2180 * bfqq emptied. In normal operation, when
2181 * bfqq is empty, bfqq->entity.service and
2182 * bfqq->entity.budget must contain,
2183 * respectively, the service received and the
2184 * budget used last time bfqq emptied. These
2185 * facts do not hold in this case, as at least
2186 * this last removal occurred while bfqq is
2187 * not in service. To avoid inconsistencies,
2188 * reset both bfqq->entity.service and
2189 * bfqq->entity.budget, if bfqq has still a
2190 * process that may issue I/O requests to it.
2191 */
2192 bfqq->entity.budget = bfqq->entity.service = 0;
2193 }
2194
2195 /*
2196 * Remove queue from request-position tree as it is empty.
2197 */
2198 if (bfqq->pos_root) {
2199 rb_erase(&bfqq->pos_node, bfqq->pos_root);
2200 bfqq->pos_root = NULL;
2201 }
2202 } else {
2203 /* see comments on bfq_pos_tree_add_move() for the unlikely() */
2204 if (unlikely(!bfqd->nonrot_with_queueing))
2205 bfq_pos_tree_add_move(bfqd, bfqq);
2206 }
2207
2208 if (rq->cmd_flags & REQ_META)
2209 bfqq->meta_pending--;
2210
2211}
2212
2213static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio,
2214 unsigned int nr_segs)
2215{
2216 struct request_queue *q = hctx->queue;
2217 struct bfq_data *bfqd = q->elevator->elevator_data;
2218 struct request *free = NULL;
2219 /*
2220 * bfq_bic_lookup grabs the queue_lock: invoke it now and
2221 * store its return value for later use, to avoid nesting
2222 * queue_lock inside the bfqd->lock. We assume that the bic
2223 * returned by bfq_bic_lookup does not go away before
2224 * bfqd->lock is taken.
2225 */
2226 struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q);
2227 bool ret;
2228
2229 spin_lock_irq(&bfqd->lock);
2230
2231 if (bic)
2232 bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
2233 else
2234 bfqd->bio_bfqq = NULL;
2235 bfqd->bio_bic = bic;
2236
2237 ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);
2238
2239 if (free)
2240 blk_mq_free_request(free);
2241 spin_unlock_irq(&bfqd->lock);
2242
2243 return ret;
2244}
2245
2246static int bfq_request_merge(struct request_queue *q, struct request **req,
2247 struct bio *bio)
2248{
2249 struct bfq_data *bfqd = q->elevator->elevator_data;
2250 struct request *__rq;
2251
2252 __rq = bfq_find_rq_fmerge(bfqd, bio, q);
2253 if (__rq && elv_bio_merge_ok(__rq, bio)) {
2254 *req = __rq;
2255 return ELEVATOR_FRONT_MERGE;
2256 }
2257
2258 return ELEVATOR_NO_MERGE;
2259}
2260
2261static struct bfq_queue *bfq_init_rq(struct request *rq);
2262
2263static void bfq_request_merged(struct request_queue *q, struct request *req,
2264 enum elv_merge type)
2265{
2266 if (type == ELEVATOR_FRONT_MERGE &&
2267 rb_prev(&req->rb_node) &&
2268 blk_rq_pos(req) <
2269 blk_rq_pos(container_of(rb_prev(&req->rb_node),
2270 struct request, rb_node))) {
2271 struct bfq_queue *bfqq = bfq_init_rq(req);
2272 struct bfq_data *bfqd;
2273 struct request *prev, *next_rq;
2274
2275 if (!bfqq)
2276 return;
2277
2278 bfqd = bfqq->bfqd;
2279
2280 /* Reposition request in its sort_list */
2281 elv_rb_del(&bfqq->sort_list, req);
2282 elv_rb_add(&bfqq->sort_list, req);
2283
2284 /* Choose next request to be served for bfqq */
2285 prev = bfqq->next_rq;
2286 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
2287 bfqd->last_position);
2288 bfqq->next_rq = next_rq;
2289 /*
2290 * If next_rq changes, update both the queue's budget to
2291 * fit the new request and the queue's position in its
2292 * rq_pos_tree.
2293 */
2294 if (prev != bfqq->next_rq) {
2295 bfq_updated_next_req(bfqd, bfqq);
2296 /*
2297 * See comments on bfq_pos_tree_add_move() for
2298 * the unlikely().
2299 */
2300 if (unlikely(!bfqd->nonrot_with_queueing))
2301 bfq_pos_tree_add_move(bfqd, bfqq);
2302 }
2303 }
2304}
2305
2306/*
2307 * This function is called to notify the scheduler that the requests
2308 * rq and 'next' have been merged, with 'next' going away. BFQ
2309 * exploits this hook to address the following issue: if 'next' has a
2310 * fifo_time lower that rq, then the fifo_time of rq must be set to
2311 * the value of 'next', to not forget the greater age of 'next'.
2312 *
2313 * NOTE: in this function we assume that rq is in a bfq_queue, basing
2314 * on that rq is picked from the hash table q->elevator->hash, which,
2315 * in its turn, is filled only with I/O requests present in
2316 * bfq_queues, while BFQ is in use for the request queue q. In fact,
2317 * the function that fills this hash table (elv_rqhash_add) is called
2318 * only by bfq_insert_request.
2319 */
2320static void bfq_requests_merged(struct request_queue *q, struct request *rq,
2321 struct request *next)
2322{
2323 struct bfq_queue *bfqq = bfq_init_rq(rq),
2324 *next_bfqq = bfq_init_rq(next);
2325
2326 if (!bfqq)
2327 return;
2328
2329 /*
2330 * If next and rq belong to the same bfq_queue and next is older
2331 * than rq, then reposition rq in the fifo (by substituting next
2332 * with rq). Otherwise, if next and rq belong to different
2333 * bfq_queues, never reposition rq: in fact, we would have to
2334 * reposition it with respect to next's position in its own fifo,
2335 * which would most certainly be too expensive with respect to
2336 * the benefits.
2337 */
2338 if (bfqq == next_bfqq &&
2339 !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
2340 next->fifo_time < rq->fifo_time) {
2341 list_del_init(&rq->queuelist);
2342 list_replace_init(&next->queuelist, &rq->queuelist);
2343 rq->fifo_time = next->fifo_time;
2344 }
2345
2346 if (bfqq->next_rq == next)
2347 bfqq->next_rq = rq;
2348
2349 bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
2350}
2351
2352/* Must be called with bfqq != NULL */
2353static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
2354{
2355 if (bfq_bfqq_busy(bfqq))
2356 bfqq->bfqd->wr_busy_queues--;
2357 bfqq->wr_coeff = 1;
2358 bfqq->wr_cur_max_time = 0;
2359 bfqq->last_wr_start_finish = jiffies;
2360 /*
2361 * Trigger a weight change on the next invocation of
2362 * __bfq_entity_update_weight_prio.
2363 */
2364 bfqq->entity.prio_changed = 1;
2365}
2366
2367void bfq_end_wr_async_queues(struct bfq_data *bfqd,
2368 struct bfq_group *bfqg)
2369{
2370 int i, j;
2371
2372 for (i = 0; i < 2; i++)
2373 for (j = 0; j < IOPRIO_BE_NR; j++)
2374 if (bfqg->async_bfqq[i][j])
2375 bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
2376 if (bfqg->async_idle_bfqq)
2377 bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
2378}
2379
2380static void bfq_end_wr(struct bfq_data *bfqd)
2381{
2382 struct bfq_queue *bfqq;
2383
2384 spin_lock_irq(&bfqd->lock);
2385
2386 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
2387 bfq_bfqq_end_wr(bfqq);
2388 list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
2389 bfq_bfqq_end_wr(bfqq);
2390 bfq_end_wr_async(bfqd);
2391
2392 spin_unlock_irq(&bfqd->lock);
2393}
2394
2395static sector_t bfq_io_struct_pos(void *io_struct, bool request)
2396{
2397 if (request)
2398 return blk_rq_pos(io_struct);
2399 else
2400 return ((struct bio *)io_struct)->bi_iter.bi_sector;
2401}
2402
2403static int bfq_rq_close_to_sector(void *io_struct, bool request,
2404 sector_t sector)
2405{
2406 return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
2407 BFQQ_CLOSE_THR;
2408}
2409
2410static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
2411 struct bfq_queue *bfqq,
2412 sector_t sector)
2413{
2414 struct rb_root *root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
2415 struct rb_node *parent, *node;
2416 struct bfq_queue *__bfqq;
2417
2418 if (RB_EMPTY_ROOT(root))
2419 return NULL;
2420
2421 /*
2422 * First, if we find a request starting at the end of the last
2423 * request, choose it.
2424 */
2425 __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
2426 if (__bfqq)
2427 return __bfqq;
2428
2429 /*
2430 * If the exact sector wasn't found, the parent of the NULL leaf
2431 * will contain the closest sector (rq_pos_tree sorted by
2432 * next_request position).
2433 */
2434 __bfqq = rb_entry(parent, struct bfq_queue, pos_node);
2435 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2436 return __bfqq;
2437
2438 if (blk_rq_pos(__bfqq->next_rq) < sector)
2439 node = rb_next(&__bfqq->pos_node);
2440 else
2441 node = rb_prev(&__bfqq->pos_node);
2442 if (!node)
2443 return NULL;
2444
2445 __bfqq = rb_entry(node, struct bfq_queue, pos_node);
2446 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2447 return __bfqq;
2448
2449 return NULL;
2450}
2451
2452static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
2453 struct bfq_queue *cur_bfqq,
2454 sector_t sector)
2455{
2456 struct bfq_queue *bfqq;
2457
2458 /*
2459 * We shall notice if some of the queues are cooperating,
2460 * e.g., working closely on the same area of the device. In
2461 * that case, we can group them together and: 1) don't waste
2462 * time idling, and 2) serve the union of their requests in
2463 * the best possible order for throughput.
2464 */
2465 bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
2466 if (!bfqq || bfqq == cur_bfqq)
2467 return NULL;
2468
2469 return bfqq;
2470}
2471
2472static struct bfq_queue *
2473bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2474{
2475 int process_refs, new_process_refs;
2476 struct bfq_queue *__bfqq;
2477
2478 /*
2479 * If there are no process references on the new_bfqq, then it is
2480 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
2481 * may have dropped their last reference (not just their last process
2482 * reference).
2483 */
2484 if (!bfqq_process_refs(new_bfqq))
2485 return NULL;
2486
2487 /* Avoid a circular list and skip interim queue merges. */
2488 while ((__bfqq = new_bfqq->new_bfqq)) {
2489 if (__bfqq == bfqq)
2490 return NULL;
2491 new_bfqq = __bfqq;
2492 }
2493
2494 process_refs = bfqq_process_refs(bfqq);
2495 new_process_refs = bfqq_process_refs(new_bfqq);
2496 /*
2497 * If the process for the bfqq has gone away, there is no
2498 * sense in merging the queues.
2499 */
2500 if (process_refs == 0 || new_process_refs == 0)
2501 return NULL;
2502
2503 bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
2504 new_bfqq->pid);
2505
2506 /*
2507 * Merging is just a redirection: the requests of the process
2508 * owning one of the two queues are redirected to the other queue.
2509 * The latter queue, in its turn, is set as shared if this is the
2510 * first time that the requests of some process are redirected to
2511 * it.
2512 *
2513 * We redirect bfqq to new_bfqq and not the opposite, because
2514 * we are in the context of the process owning bfqq, thus we
2515 * have the io_cq of this process. So we can immediately
2516 * configure this io_cq to redirect the requests of the
2517 * process to new_bfqq. In contrast, the io_cq of new_bfqq is
2518 * not available any more (new_bfqq->bic == NULL).
2519 *
2520 * Anyway, even in case new_bfqq coincides with the in-service
2521 * queue, redirecting requests the in-service queue is the
2522 * best option, as we feed the in-service queue with new
2523 * requests close to the last request served and, by doing so,
2524 * are likely to increase the throughput.
2525 */
2526 bfqq->new_bfqq = new_bfqq;
2527 new_bfqq->ref += process_refs;
2528 return new_bfqq;
2529}
2530
2531static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
2532 struct bfq_queue *new_bfqq)
2533{
2534 if (bfq_too_late_for_merging(new_bfqq))
2535 return false;
2536
2537 if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
2538 (bfqq->ioprio_class != new_bfqq->ioprio_class))
2539 return false;
2540
2541 /*
2542 * If either of the queues has already been detected as seeky,
2543 * then merging it with the other queue is unlikely to lead to
2544 * sequential I/O.
2545 */
2546 if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
2547 return false;
2548
2549 /*
2550 * Interleaved I/O is known to be done by (some) applications
2551 * only for reads, so it does not make sense to merge async
2552 * queues.
2553 */
2554 if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
2555 return false;
2556
2557 return true;
2558}
2559
2560/*
2561 * Attempt to schedule a merge of bfqq with the currently in-service
2562 * queue or with a close queue among the scheduled queues. Return
2563 * NULL if no merge was scheduled, a pointer to the shared bfq_queue
2564 * structure otherwise.
2565 *
2566 * The OOM queue is not allowed to participate to cooperation: in fact, since
2567 * the requests temporarily redirected to the OOM queue could be redirected
2568 * again to dedicated queues at any time, the state needed to correctly
2569 * handle merging with the OOM queue would be quite complex and expensive
2570 * to maintain. Besides, in such a critical condition as an out of memory,
2571 * the benefits of queue merging may be little relevant, or even negligible.
2572 *
2573 * WARNING: queue merging may impair fairness among non-weight raised
2574 * queues, for at least two reasons: 1) the original weight of a
2575 * merged queue may change during the merged state, 2) even being the
2576 * weight the same, a merged queue may be bloated with many more
2577 * requests than the ones produced by its originally-associated
2578 * process.
2579 */
2580static struct bfq_queue *
2581bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2582 void *io_struct, bool request)
2583{
2584 struct bfq_queue *in_service_bfqq, *new_bfqq;
2585
2586 /*
2587 * Do not perform queue merging if the device is non
2588 * rotational and performs internal queueing. In fact, such a
2589 * device reaches a high speed through internal parallelism
2590 * and pipelining. This means that, to reach a high
2591 * throughput, it must have many requests enqueued at the same
2592 * time. But, in this configuration, the internal scheduling
2593 * algorithm of the device does exactly the job of queue
2594 * merging: it reorders requests so as to obtain as much as
2595 * possible a sequential I/O pattern. As a consequence, with
2596 * the workload generated by processes doing interleaved I/O,
2597 * the throughput reached by the device is likely to be the
2598 * same, with and without queue merging.
2599 *
2600 * Disabling merging also provides a remarkable benefit in
2601 * terms of throughput. Merging tends to make many workloads
2602 * artificially more uneven, because of shared queues
2603 * remaining non empty for incomparably more time than
2604 * non-merged queues. This may accentuate workload
2605 * asymmetries. For example, if one of the queues in a set of
2606 * merged queues has a higher weight than a normal queue, then
2607 * the shared queue may inherit such a high weight and, by
2608 * staying almost always active, may force BFQ to perform I/O
2609 * plugging most of the time. This evidently makes it harder
2610 * for BFQ to let the device reach a high throughput.
2611 *
2612 * Finally, the likely() macro below is not used because one
2613 * of the two branches is more likely than the other, but to
2614 * have the code path after the following if() executed as
2615 * fast as possible for the case of a non rotational device
2616 * with queueing. We want it because this is the fastest kind
2617 * of device. On the opposite end, the likely() may lengthen
2618 * the execution time of BFQ for the case of slower devices
2619 * (rotational or at least without queueing). But in this case
2620 * the execution time of BFQ matters very little, if not at
2621 * all.
2622 */
2623 if (likely(bfqd->nonrot_with_queueing))
2624 return NULL;
2625
2626 /*
2627 * Prevent bfqq from being merged if it has been created too
2628 * long ago. The idea is that true cooperating processes, and
2629 * thus their associated bfq_queues, are supposed to be
2630 * created shortly after each other. This is the case, e.g.,
2631 * for KVM/QEMU and dump I/O threads. Basing on this
2632 * assumption, the following filtering greatly reduces the
2633 * probability that two non-cooperating processes, which just
2634 * happen to do close I/O for some short time interval, have
2635 * their queues merged by mistake.
2636 */
2637 if (bfq_too_late_for_merging(bfqq))
2638 return NULL;
2639
2640 if (bfqq->new_bfqq)
2641 return bfqq->new_bfqq;
2642
2643 if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
2644 return NULL;
2645
2646 /* If there is only one backlogged queue, don't search. */
2647 if (bfq_tot_busy_queues(bfqd) == 1)
2648 return NULL;
2649
2650 in_service_bfqq = bfqd->in_service_queue;
2651
2652 if (in_service_bfqq && in_service_bfqq != bfqq &&
2653 likely(in_service_bfqq != &bfqd->oom_bfqq) &&
2654 bfq_rq_close_to_sector(io_struct, request,
2655 bfqd->in_serv_last_pos) &&
2656 bfqq->entity.parent == in_service_bfqq->entity.parent &&
2657 bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
2658 new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
2659 if (new_bfqq)
2660 return new_bfqq;
2661 }
2662 /*
2663 * Check whether there is a cooperator among currently scheduled
2664 * queues. The only thing we need is that the bio/request is not
2665 * NULL, as we need it to establish whether a cooperator exists.
2666 */
2667 new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
2668 bfq_io_struct_pos(io_struct, request));
2669
2670 if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
2671 bfq_may_be_close_cooperator(bfqq, new_bfqq))
2672 return bfq_setup_merge(bfqq, new_bfqq);
2673
2674 return NULL;
2675}
2676
2677static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
2678{
2679 struct bfq_io_cq *bic = bfqq->bic;
2680
2681 /*
2682 * If !bfqq->bic, the queue is already shared or its requests
2683 * have already been redirected to a shared queue; both idle window
2684 * and weight raising state have already been saved. Do nothing.
2685 */
2686 if (!bic)
2687 return;
2688
2689 bic->saved_weight = bfqq->entity.orig_weight;
2690 bic->saved_ttime = bfqq->ttime;
2691 bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
2692 bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
2693 bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
2694 bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
2695 if (unlikely(bfq_bfqq_just_created(bfqq) &&
2696 !bfq_bfqq_in_large_burst(bfqq) &&
2697 bfqq->bfqd->low_latency)) {
2698 /*
2699 * bfqq being merged right after being created: bfqq
2700 * would have deserved interactive weight raising, but
2701 * did not make it to be set in a weight-raised state,
2702 * because of this early merge. Store directly the
2703 * weight-raising state that would have been assigned
2704 * to bfqq, so that to avoid that bfqq unjustly fails
2705 * to enjoy weight raising if split soon.
2706 */
2707 bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
2708 bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
2709 bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
2710 bic->saved_last_wr_start_finish = jiffies;
2711 } else {
2712 bic->saved_wr_coeff = bfqq->wr_coeff;
2713 bic->saved_wr_start_at_switch_to_srt =
2714 bfqq->wr_start_at_switch_to_srt;
2715 bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
2716 bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
2717 }
2718}
2719
2720void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq)
2721{
2722 /*
2723 * To prevent bfqq's service guarantees from being violated,
2724 * bfqq may be left busy, i.e., queued for service, even if
2725 * empty (see comments in __bfq_bfqq_expire() for
2726 * details). But, if no process will send requests to bfqq any
2727 * longer, then there is no point in keeping bfqq queued for
2728 * service. In addition, keeping bfqq queued for service, but
2729 * with no process ref any longer, may have caused bfqq to be
2730 * freed when dequeued from service. But this is assumed to
2731 * never happen.
2732 */
2733 if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) &&
2734 bfqq != bfqd->in_service_queue)
2735 bfq_del_bfqq_busy(bfqd, bfqq, false);
2736
2737 bfq_put_queue(bfqq);
2738}
2739
2740static void
2741bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
2742 struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2743{
2744 bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
2745 (unsigned long)new_bfqq->pid);
2746 /* Save weight raising and idle window of the merged queues */
2747 bfq_bfqq_save_state(bfqq);
2748 bfq_bfqq_save_state(new_bfqq);
2749 if (bfq_bfqq_IO_bound(bfqq))
2750 bfq_mark_bfqq_IO_bound(new_bfqq);
2751 bfq_clear_bfqq_IO_bound(bfqq);
2752
2753 /*
2754 * If bfqq is weight-raised, then let new_bfqq inherit
2755 * weight-raising. To reduce false positives, neglect the case
2756 * where bfqq has just been created, but has not yet made it
2757 * to be weight-raised (which may happen because EQM may merge
2758 * bfqq even before bfq_add_request is executed for the first
2759 * time for bfqq). Handling this case would however be very
2760 * easy, thanks to the flag just_created.
2761 */
2762 if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
2763 new_bfqq->wr_coeff = bfqq->wr_coeff;
2764 new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
2765 new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
2766 new_bfqq->wr_start_at_switch_to_srt =
2767 bfqq->wr_start_at_switch_to_srt;
2768 if (bfq_bfqq_busy(new_bfqq))
2769 bfqd->wr_busy_queues++;
2770 new_bfqq->entity.prio_changed = 1;
2771 }
2772
2773 if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
2774 bfqq->wr_coeff = 1;
2775 bfqq->entity.prio_changed = 1;
2776 if (bfq_bfqq_busy(bfqq))
2777 bfqd->wr_busy_queues--;
2778 }
2779
2780 bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
2781 bfqd->wr_busy_queues);
2782
2783 /*
2784 * Merge queues (that is, let bic redirect its requests to new_bfqq)
2785 */
2786 bic_set_bfqq(bic, new_bfqq, 1);
2787 bfq_mark_bfqq_coop(new_bfqq);
2788 /*
2789 * new_bfqq now belongs to at least two bics (it is a shared queue):
2790 * set new_bfqq->bic to NULL. bfqq either:
2791 * - does not belong to any bic any more, and hence bfqq->bic must
2792 * be set to NULL, or
2793 * - is a queue whose owning bics have already been redirected to a
2794 * different queue, hence the queue is destined to not belong to
2795 * any bic soon and bfqq->bic is already NULL (therefore the next
2796 * assignment causes no harm).
2797 */
2798 new_bfqq->bic = NULL;
2799 /*
2800 * If the queue is shared, the pid is the pid of one of the associated
2801 * processes. Which pid depends on the exact sequence of merge events
2802 * the queue underwent. So printing such a pid is useless and confusing
2803 * because it reports a random pid between those of the associated
2804 * processes.
2805 * We mark such a queue with a pid -1, and then print SHARED instead of
2806 * a pid in logging messages.
2807 */
2808 new_bfqq->pid = -1;
2809 bfqq->bic = NULL;
2810 bfq_release_process_ref(bfqd, bfqq);
2811}
2812
2813static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
2814 struct bio *bio)
2815{
2816 struct bfq_data *bfqd = q->elevator->elevator_data;
2817 bool is_sync = op_is_sync(bio->bi_opf);
2818 struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
2819
2820 /*
2821 * Disallow merge of a sync bio into an async request.
2822 */
2823 if (is_sync && !rq_is_sync(rq))
2824 return false;
2825
2826 /*
2827 * Lookup the bfqq that this bio will be queued with. Allow
2828 * merge only if rq is queued there.
2829 */
2830 if (!bfqq)
2831 return false;
2832
2833 /*
2834 * We take advantage of this function to perform an early merge
2835 * of the queues of possible cooperating processes.
2836 */
2837 new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false);
2838 if (new_bfqq) {
2839 /*
2840 * bic still points to bfqq, then it has not yet been
2841 * redirected to some other bfq_queue, and a queue
2842 * merge between bfqq and new_bfqq can be safely
2843 * fulfilled, i.e., bic can be redirected to new_bfqq
2844 * and bfqq can be put.
2845 */
2846 bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
2847 new_bfqq);
2848 /*
2849 * If we get here, bio will be queued into new_queue,
2850 * so use new_bfqq to decide whether bio and rq can be
2851 * merged.
2852 */
2853 bfqq = new_bfqq;
2854
2855 /*
2856 * Change also bqfd->bio_bfqq, as
2857 * bfqd->bio_bic now points to new_bfqq, and
2858 * this function may be invoked again (and then may
2859 * use again bqfd->bio_bfqq).
2860 */
2861 bfqd->bio_bfqq = bfqq;
2862 }
2863
2864 return bfqq == RQ_BFQQ(rq);
2865}
2866
2867/*
2868 * Set the maximum time for the in-service queue to consume its
2869 * budget. This prevents seeky processes from lowering the throughput.
2870 * In practice, a time-slice service scheme is used with seeky
2871 * processes.
2872 */
2873static void bfq_set_budget_timeout(struct bfq_data *bfqd,
2874 struct bfq_queue *bfqq)
2875{
2876 unsigned int timeout_coeff;
2877
2878 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
2879 timeout_coeff = 1;
2880 else
2881 timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
2882
2883 bfqd->last_budget_start = ktime_get();
2884
2885 bfqq->budget_timeout = jiffies +
2886 bfqd->bfq_timeout * timeout_coeff;
2887}
2888
2889static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
2890 struct bfq_queue *bfqq)
2891{
2892 if (bfqq) {
2893 bfq_clear_bfqq_fifo_expire(bfqq);
2894
2895 bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
2896
2897 if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
2898 bfqq->wr_coeff > 1 &&
2899 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
2900 time_is_before_jiffies(bfqq->budget_timeout)) {
2901 /*
2902 * For soft real-time queues, move the start
2903 * of the weight-raising period forward by the
2904 * time the queue has not received any
2905 * service. Otherwise, a relatively long
2906 * service delay is likely to cause the
2907 * weight-raising period of the queue to end,
2908 * because of the short duration of the
2909 * weight-raising period of a soft real-time
2910 * queue. It is worth noting that this move
2911 * is not so dangerous for the other queues,
2912 * because soft real-time queues are not
2913 * greedy.
2914 *
2915 * To not add a further variable, we use the
2916 * overloaded field budget_timeout to
2917 * determine for how long the queue has not
2918 * received service, i.e., how much time has
2919 * elapsed since the queue expired. However,
2920 * this is a little imprecise, because
2921 * budget_timeout is set to jiffies if bfqq
2922 * not only expires, but also remains with no
2923 * request.
2924 */
2925 if (time_after(bfqq->budget_timeout,
2926 bfqq->last_wr_start_finish))
2927 bfqq->last_wr_start_finish +=
2928 jiffies - bfqq->budget_timeout;
2929 else
2930 bfqq->last_wr_start_finish = jiffies;
2931 }
2932
2933 bfq_set_budget_timeout(bfqd, bfqq);
2934 bfq_log_bfqq(bfqd, bfqq,
2935 "set_in_service_queue, cur-budget = %d",
2936 bfqq->entity.budget);
2937 }
2938
2939 bfqd->in_service_queue = bfqq;
2940}
2941
2942/*
2943 * Get and set a new queue for service.
2944 */
2945static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
2946{
2947 struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
2948
2949 __bfq_set_in_service_queue(bfqd, bfqq);
2950 return bfqq;
2951}
2952
2953static void bfq_arm_slice_timer(struct bfq_data *bfqd)
2954{
2955 struct bfq_queue *bfqq = bfqd->in_service_queue;
2956 u32 sl;
2957
2958 bfq_mark_bfqq_wait_request(bfqq);
2959
2960 /*
2961 * We don't want to idle for seeks, but we do want to allow
2962 * fair distribution of slice time for a process doing back-to-back
2963 * seeks. So allow a little bit of time for him to submit a new rq.
2964 */
2965 sl = bfqd->bfq_slice_idle;
2966 /*
2967 * Unless the queue is being weight-raised or the scenario is
2968 * asymmetric, grant only minimum idle time if the queue
2969 * is seeky. A long idling is preserved for a weight-raised
2970 * queue, or, more in general, in an asymmetric scenario,
2971 * because a long idling is needed for guaranteeing to a queue
2972 * its reserved share of the throughput (in particular, it is
2973 * needed if the queue has a higher weight than some other
2974 * queue).
2975 */
2976 if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
2977 !bfq_asymmetric_scenario(bfqd, bfqq))
2978 sl = min_t(u64, sl, BFQ_MIN_TT);
2979 else if (bfqq->wr_coeff > 1)
2980 sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC);
2981
2982 bfqd->last_idling_start = ktime_get();
2983 bfqd->last_idling_start_jiffies = jiffies;
2984
2985 hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
2986 HRTIMER_MODE_REL);
2987 bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
2988}
2989
2990/*
2991 * In autotuning mode, max_budget is dynamically recomputed as the
2992 * amount of sectors transferred in timeout at the estimated peak
2993 * rate. This enables BFQ to utilize a full timeslice with a full
2994 * budget, even if the in-service queue is served at peak rate. And
2995 * this maximises throughput with sequential workloads.
2996 */
2997static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
2998{
2999 return (u64)bfqd->peak_rate * USEC_PER_MSEC *
3000 jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
3001}
3002
3003/*
3004 * Update parameters related to throughput and responsiveness, as a
3005 * function of the estimated peak rate. See comments on
3006 * bfq_calc_max_budget(), and on the ref_wr_duration array.
3007 */
3008static void update_thr_responsiveness_params(struct bfq_data *bfqd)
3009{
3010 if (bfqd->bfq_user_max_budget == 0) {
3011 bfqd->bfq_max_budget =
3012 bfq_calc_max_budget(bfqd);
3013 bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget);
3014 }
3015}
3016
3017static void bfq_reset_rate_computation(struct bfq_data *bfqd,
3018 struct request *rq)
3019{
3020 if (rq != NULL) { /* new rq dispatch now, reset accordingly */
3021 bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
3022 bfqd->peak_rate_samples = 1;
3023 bfqd->sequential_samples = 0;
3024 bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
3025 blk_rq_sectors(rq);
3026 } else /* no new rq dispatched, just reset the number of samples */
3027 bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
3028
3029 bfq_log(bfqd,
3030 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
3031 bfqd->peak_rate_samples, bfqd->sequential_samples,
3032 bfqd->tot_sectors_dispatched);
3033}
3034
3035static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
3036{
3037 u32 rate, weight, divisor;
3038
3039 /*
3040 * For the convergence property to hold (see comments on
3041 * bfq_update_peak_rate()) and for the assessment to be
3042 * reliable, a minimum number of samples must be present, and
3043 * a minimum amount of time must have elapsed. If not so, do
3044 * not compute new rate. Just reset parameters, to get ready
3045 * for a new evaluation attempt.
3046 */
3047 if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
3048 bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
3049 goto reset_computation;
3050
3051 /*
3052 * If a new request completion has occurred after last
3053 * dispatch, then, to approximate the rate at which requests
3054 * have been served by the device, it is more precise to
3055 * extend the observation interval to the last completion.
3056 */
3057 bfqd->delta_from_first =
3058 max_t(u64, bfqd->delta_from_first,
3059 bfqd->last_completion - bfqd->first_dispatch);
3060
3061 /*
3062 * Rate computed in sects/usec, and not sects/nsec, for
3063 * precision issues.
3064 */
3065 rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
3066 div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
3067
3068 /*
3069 * Peak rate not updated if:
3070 * - the percentage of sequential dispatches is below 3/4 of the
3071 * total, and rate is below the current estimated peak rate
3072 * - rate is unreasonably high (> 20M sectors/sec)
3073 */
3074 if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
3075 rate <= bfqd->peak_rate) ||
3076 rate > 20<<BFQ_RATE_SHIFT)
3077 goto reset_computation;
3078
3079 /*
3080 * We have to update the peak rate, at last! To this purpose,
3081 * we use a low-pass filter. We compute the smoothing constant
3082 * of the filter as a function of the 'weight' of the new
3083 * measured rate.
3084 *
3085 * As can be seen in next formulas, we define this weight as a
3086 * quantity proportional to how sequential the workload is,
3087 * and to how long the observation time interval is.
3088 *
3089 * The weight runs from 0 to 8. The maximum value of the
3090 * weight, 8, yields the minimum value for the smoothing
3091 * constant. At this minimum value for the smoothing constant,
3092 * the measured rate contributes for half of the next value of
3093 * the estimated peak rate.
3094 *
3095 * So, the first step is to compute the weight as a function
3096 * of how sequential the workload is. Note that the weight
3097 * cannot reach 9, because bfqd->sequential_samples cannot
3098 * become equal to bfqd->peak_rate_samples, which, in its
3099 * turn, holds true because bfqd->sequential_samples is not
3100 * incremented for the first sample.
3101 */
3102 weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
3103
3104 /*
3105 * Second step: further refine the weight as a function of the
3106 * duration of the observation interval.
3107 */
3108 weight = min_t(u32, 8,
3109 div_u64(weight * bfqd->delta_from_first,
3110 BFQ_RATE_REF_INTERVAL));
3111
3112 /*
3113 * Divisor ranging from 10, for minimum weight, to 2, for
3114 * maximum weight.
3115 */
3116 divisor = 10 - weight;
3117
3118 /*
3119 * Finally, update peak rate:
3120 *
3121 * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
3122 */
3123 bfqd->peak_rate *= divisor-1;
3124 bfqd->peak_rate /= divisor;
3125 rate /= divisor; /* smoothing constant alpha = 1/divisor */
3126
3127 bfqd->peak_rate += rate;
3128
3129 /*
3130 * For a very slow device, bfqd->peak_rate can reach 0 (see
3131 * the minimum representable values reported in the comments
3132 * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
3133 * divisions by zero where bfqd->peak_rate is used as a
3134 * divisor.
3135 */
3136 bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
3137
3138 update_thr_responsiveness_params(bfqd);
3139
3140reset_computation:
3141 bfq_reset_rate_computation(bfqd, rq);
3142}
3143
3144/*
3145 * Update the read/write peak rate (the main quantity used for
3146 * auto-tuning, see update_thr_responsiveness_params()).
3147 *
3148 * It is not trivial to estimate the peak rate (correctly): because of
3149 * the presence of sw and hw queues between the scheduler and the
3150 * device components that finally serve I/O requests, it is hard to
3151 * say exactly when a given dispatched request is served inside the
3152 * device, and for how long. As a consequence, it is hard to know
3153 * precisely at what rate a given set of requests is actually served
3154 * by the device.
3155 *
3156 * On the opposite end, the dispatch time of any request is trivially
3157 * available, and, from this piece of information, the "dispatch rate"
3158 * of requests can be immediately computed. So, the idea in the next
3159 * function is to use what is known, namely request dispatch times
3160 * (plus, when useful, request completion times), to estimate what is
3161 * unknown, namely in-device request service rate.
3162 *
3163 * The main issue is that, because of the above facts, the rate at
3164 * which a certain set of requests is dispatched over a certain time
3165 * interval can vary greatly with respect to the rate at which the
3166 * same requests are then served. But, since the size of any
3167 * intermediate queue is limited, and the service scheme is lossless
3168 * (no request is silently dropped), the following obvious convergence
3169 * property holds: the number of requests dispatched MUST become
3170 * closer and closer to the number of requests completed as the
3171 * observation interval grows. This is the key property used in
3172 * the next function to estimate the peak service rate as a function
3173 * of the observed dispatch rate. The function assumes to be invoked
3174 * on every request dispatch.
3175 */
3176static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
3177{
3178 u64 now_ns = ktime_get_ns();
3179
3180 if (bfqd->peak_rate_samples == 0) { /* first dispatch */
3181 bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
3182 bfqd->peak_rate_samples);
3183 bfq_reset_rate_computation(bfqd, rq);
3184 goto update_last_values; /* will add one sample */
3185 }
3186
3187 /*
3188 * Device idle for very long: the observation interval lasting
3189 * up to this dispatch cannot be a valid observation interval
3190 * for computing a new peak rate (similarly to the late-
3191 * completion event in bfq_completed_request()). Go to
3192 * update_rate_and_reset to have the following three steps
3193 * taken:
3194 * - close the observation interval at the last (previous)
3195 * request dispatch or completion
3196 * - compute rate, if possible, for that observation interval
3197 * - start a new observation interval with this dispatch
3198 */
3199 if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
3200 bfqd->rq_in_driver == 0)
3201 goto update_rate_and_reset;
3202
3203 /* Update sampling information */
3204 bfqd->peak_rate_samples++;
3205
3206 if ((bfqd->rq_in_driver > 0 ||
3207 now_ns - bfqd->last_completion < BFQ_MIN_TT)
3208 && !BFQ_RQ_SEEKY(bfqd, bfqd->last_position, rq))
3209 bfqd->sequential_samples++;
3210
3211 bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
3212
3213 /* Reset max observed rq size every 32 dispatches */
3214 if (likely(bfqd->peak_rate_samples % 32))
3215 bfqd->last_rq_max_size =
3216 max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
3217 else
3218 bfqd->last_rq_max_size = blk_rq_sectors(rq);
3219
3220 bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
3221
3222 /* Target observation interval not yet reached, go on sampling */
3223 if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
3224 goto update_last_values;
3225
3226update_rate_and_reset:
3227 bfq_update_rate_reset(bfqd, rq);
3228update_last_values:
3229 bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
3230 if (RQ_BFQQ(rq) == bfqd->in_service_queue)
3231 bfqd->in_serv_last_pos = bfqd->last_position;
3232 bfqd->last_dispatch = now_ns;
3233}
3234
3235/*
3236 * Remove request from internal lists.
3237 */
3238static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
3239{
3240 struct bfq_queue *bfqq = RQ_BFQQ(rq);
3241
3242 /*
3243 * For consistency, the next instruction should have been
3244 * executed after removing the request from the queue and
3245 * dispatching it. We execute instead this instruction before
3246 * bfq_remove_request() (and hence introduce a temporary
3247 * inconsistency), for efficiency. In fact, should this
3248 * dispatch occur for a non in-service bfqq, this anticipated
3249 * increment prevents two counters related to bfqq->dispatched
3250 * from risking to be, first, uselessly decremented, and then
3251 * incremented again when the (new) value of bfqq->dispatched
3252 * happens to be taken into account.
3253 */
3254 bfqq->dispatched++;
3255 bfq_update_peak_rate(q->elevator->elevator_data, rq);
3256
3257 bfq_remove_request(q, rq);
3258}
3259
3260/*
3261 * There is a case where idling does not have to be performed for
3262 * throughput concerns, but to preserve the throughput share of
3263 * the process associated with bfqq.
3264 *
3265 * To introduce this case, we can note that allowing the drive
3266 * to enqueue more than one request at a time, and hence
3267 * delegating de facto final scheduling decisions to the
3268 * drive's internal scheduler, entails loss of control on the
3269 * actual request service order. In particular, the critical
3270 * situation is when requests from different processes happen
3271 * to be present, at the same time, in the internal queue(s)
3272 * of the drive. In such a situation, the drive, by deciding
3273 * the service order of the internally-queued requests, does
3274 * determine also the actual throughput distribution among
3275 * these processes. But the drive typically has no notion or
3276 * concern about per-process throughput distribution, and
3277 * makes its decisions only on a per-request basis. Therefore,
3278 * the service distribution enforced by the drive's internal
3279 * scheduler is likely to coincide with the desired throughput
3280 * distribution only in a completely symmetric, or favorably
3281 * skewed scenario where:
3282 * (i-a) each of these processes must get the same throughput as
3283 * the others,
3284 * (i-b) in case (i-a) does not hold, it holds that the process
3285 * associated with bfqq must receive a lower or equal
3286 * throughput than any of the other processes;
3287 * (ii) the I/O of each process has the same properties, in
3288 * terms of locality (sequential or random), direction
3289 * (reads or writes), request sizes, greediness
3290 * (from I/O-bound to sporadic), and so on;
3291
3292 * In fact, in such a scenario, the drive tends to treat the requests
3293 * of each process in about the same way as the requests of the
3294 * others, and thus to provide each of these processes with about the
3295 * same throughput. This is exactly the desired throughput
3296 * distribution if (i-a) holds, or, if (i-b) holds instead, this is an
3297 * even more convenient distribution for (the process associated with)
3298 * bfqq.
3299 *
3300 * In contrast, in any asymmetric or unfavorable scenario, device
3301 * idling (I/O-dispatch plugging) is certainly needed to guarantee
3302 * that bfqq receives its assigned fraction of the device throughput
3303 * (see [1] for details).
3304 *
3305 * The problem is that idling may significantly reduce throughput with
3306 * certain combinations of types of I/O and devices. An important
3307 * example is sync random I/O on flash storage with command
3308 * queueing. So, unless bfqq falls in cases where idling also boosts
3309 * throughput, it is important to check conditions (i-a), i(-b) and
3310 * (ii) accurately, so as to avoid idling when not strictly needed for
3311 * service guarantees.
3312 *
3313 * Unfortunately, it is extremely difficult to thoroughly check
3314 * condition (ii). And, in case there are active groups, it becomes
3315 * very difficult to check conditions (i-a) and (i-b) too. In fact,
3316 * if there are active groups, then, for conditions (i-a) or (i-b) to
3317 * become false 'indirectly', it is enough that an active group
3318 * contains more active processes or sub-groups than some other active
3319 * group. More precisely, for conditions (i-a) or (i-b) to become
3320 * false because of such a group, it is not even necessary that the
3321 * group is (still) active: it is sufficient that, even if the group
3322 * has become inactive, some of its descendant processes still have
3323 * some request already dispatched but still waiting for
3324 * completion. In fact, requests have still to be guaranteed their
3325 * share of the throughput even after being dispatched. In this
3326 * respect, it is easy to show that, if a group frequently becomes
3327 * inactive while still having in-flight requests, and if, when this
3328 * happens, the group is not considered in the calculation of whether
3329 * the scenario is asymmetric, then the group may fail to be
3330 * guaranteed its fair share of the throughput (basically because
3331 * idling may not be performed for the descendant processes of the
3332 * group, but it had to be). We address this issue with the following
3333 * bi-modal behavior, implemented in the function
3334 * bfq_asymmetric_scenario().
3335 *
3336 * If there are groups with requests waiting for completion
3337 * (as commented above, some of these groups may even be
3338 * already inactive), then the scenario is tagged as
3339 * asymmetric, conservatively, without checking any of the
3340 * conditions (i-a), (i-b) or (ii). So the device is idled for bfqq.
3341 * This behavior matches also the fact that groups are created
3342 * exactly if controlling I/O is a primary concern (to
3343 * preserve bandwidth and latency guarantees).
3344 *
3345 * On the opposite end, if there are no groups with requests waiting
3346 * for completion, then only conditions (i-a) and (i-b) are actually
3347 * controlled, i.e., provided that conditions (i-a) or (i-b) holds,
3348 * idling is not performed, regardless of whether condition (ii)
3349 * holds. In other words, only if conditions (i-a) and (i-b) do not
3350 * hold, then idling is allowed, and the device tends to be prevented
3351 * from queueing many requests, possibly of several processes. Since
3352 * there are no groups with requests waiting for completion, then, to
3353 * control conditions (i-a) and (i-b) it is enough to check just
3354 * whether all the queues with requests waiting for completion also
3355 * have the same weight.
3356 *
3357 * Not checking condition (ii) evidently exposes bfqq to the
3358 * risk of getting less throughput than its fair share.
3359 * However, for queues with the same weight, a further
3360 * mechanism, preemption, mitigates or even eliminates this
3361 * problem. And it does so without consequences on overall
3362 * throughput. This mechanism and its benefits are explained
3363 * in the next three paragraphs.
3364 *
3365 * Even if a queue, say Q, is expired when it remains idle, Q
3366 * can still preempt the new in-service queue if the next
3367 * request of Q arrives soon (see the comments on
3368 * bfq_bfqq_update_budg_for_activation). If all queues and
3369 * groups have the same weight, this form of preemption,
3370 * combined with the hole-recovery heuristic described in the
3371 * comments on function bfq_bfqq_update_budg_for_activation,
3372 * are enough to preserve a correct bandwidth distribution in
3373 * the mid term, even without idling. In fact, even if not
3374 * idling allows the internal queues of the device to contain
3375 * many requests, and thus to reorder requests, we can rather
3376 * safely assume that the internal scheduler still preserves a
3377 * minimum of mid-term fairness.
3378 *
3379 * More precisely, this preemption-based, idleless approach
3380 * provides fairness in terms of IOPS, and not sectors per
3381 * second. This can be seen with a simple example. Suppose
3382 * that there are two queues with the same weight, but that
3383 * the first queue receives requests of 8 sectors, while the
3384 * second queue receives requests of 1024 sectors. In
3385 * addition, suppose that each of the two queues contains at
3386 * most one request at a time, which implies that each queue
3387 * always remains idle after it is served. Finally, after
3388 * remaining idle, each queue receives very quickly a new
3389 * request. It follows that the two queues are served
3390 * alternatively, preempting each other if needed. This
3391 * implies that, although both queues have the same weight,
3392 * the queue with large requests receives a service that is
3393 * 1024/8 times as high as the service received by the other
3394 * queue.
3395 *
3396 * The motivation for using preemption instead of idling (for
3397 * queues with the same weight) is that, by not idling,
3398 * service guarantees are preserved (completely or at least in
3399 * part) without minimally sacrificing throughput. And, if
3400 * there is no active group, then the primary expectation for
3401 * this device is probably a high throughput.
3402 *
3403 * We are now left only with explaining the two sub-conditions in the
3404 * additional compound condition that is checked below for deciding
3405 * whether the scenario is asymmetric. To explain the first
3406 * sub-condition, we need to add that the function
3407 * bfq_asymmetric_scenario checks the weights of only
3408 * non-weight-raised queues, for efficiency reasons (see comments on
3409 * bfq_weights_tree_add()). Then the fact that bfqq is weight-raised
3410 * is checked explicitly here. More precisely, the compound condition
3411 * below takes into account also the fact that, even if bfqq is being
3412 * weight-raised, the scenario is still symmetric if all queues with
3413 * requests waiting for completion happen to be
3414 * weight-raised. Actually, we should be even more precise here, and
3415 * differentiate between interactive weight raising and soft real-time
3416 * weight raising.
3417 *
3418 * The second sub-condition checked in the compound condition is
3419 * whether there is a fair amount of already in-flight I/O not
3420 * belonging to bfqq. If so, I/O dispatching is to be plugged, for the
3421 * following reason. The drive may decide to serve in-flight
3422 * non-bfqq's I/O requests before bfqq's ones, thereby delaying the
3423 * arrival of new I/O requests for bfqq (recall that bfqq is sync). If
3424 * I/O-dispatching is not plugged, then, while bfqq remains empty, a
3425 * basically uncontrolled amount of I/O from other queues may be
3426 * dispatched too, possibly causing the service of bfqq's I/O to be
3427 * delayed even longer in the drive. This problem gets more and more
3428 * serious as the speed and the queue depth of the drive grow,
3429 * because, as these two quantities grow, the probability to find no
3430 * queue busy but many requests in flight grows too. By contrast,
3431 * plugging I/O dispatching minimizes the delay induced by already
3432 * in-flight I/O, and enables bfqq to recover the bandwidth it may
3433 * lose because of this delay.
3434 *
3435 * As a side note, it is worth considering that the above
3436 * device-idling countermeasures may however fail in the following
3437 * unlucky scenario: if I/O-dispatch plugging is (correctly) disabled
3438 * in a time period during which all symmetry sub-conditions hold, and
3439 * therefore the device is allowed to enqueue many requests, but at
3440 * some later point in time some sub-condition stops to hold, then it
3441 * may become impossible to make requests be served in the desired
3442 * order until all the requests already queued in the device have been
3443 * served. The last sub-condition commented above somewhat mitigates
3444 * this problem for weight-raised queues.
3445 */
3446static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
3447 struct bfq_queue *bfqq)
3448{
3449 /* No point in idling for bfqq if it won't get requests any longer */
3450 if (unlikely(!bfqq_process_refs(bfqq)))
3451 return false;
3452
3453 return (bfqq->wr_coeff > 1 &&
3454 (bfqd->wr_busy_queues <
3455 bfq_tot_busy_queues(bfqd) ||
3456 bfqd->rq_in_driver >=
3457 bfqq->dispatched + 4)) ||
3458 bfq_asymmetric_scenario(bfqd, bfqq);
3459}
3460
3461static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3462 enum bfqq_expiration reason)
3463{
3464 /*
3465 * If this bfqq is shared between multiple processes, check
3466 * to make sure that those processes are still issuing I/Os
3467 * within the mean seek distance. If not, it may be time to
3468 * break the queues apart again.
3469 */
3470 if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
3471 bfq_mark_bfqq_split_coop(bfqq);
3472
3473 /*
3474 * Consider queues with a higher finish virtual time than
3475 * bfqq. If idling_needed_for_service_guarantees(bfqq) returns
3476 * true, then bfqq's bandwidth would be violated if an
3477 * uncontrolled amount of I/O from these queues were
3478 * dispatched while bfqq is waiting for its new I/O to
3479 * arrive. This is exactly what may happen if this is a forced
3480 * expiration caused by a preemption attempt, and if bfqq is
3481 * not re-scheduled. To prevent this from happening, re-queue
3482 * bfqq if it needs I/O-dispatch plugging, even if it is
3483 * empty. By doing so, bfqq is granted to be served before the
3484 * above queues (provided that bfqq is of course eligible).
3485 */
3486 if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
3487 !(reason == BFQQE_PREEMPTED &&
3488 idling_needed_for_service_guarantees(bfqd, bfqq))) {
3489 if (bfqq->dispatched == 0)
3490 /*
3491 * Overloading budget_timeout field to store
3492 * the time at which the queue remains with no
3493 * backlog and no outstanding request; used by
3494 * the weight-raising mechanism.
3495 */
3496 bfqq->budget_timeout = jiffies;
3497
3498 bfq_del_bfqq_busy(bfqd, bfqq, true);
3499 } else {
3500 bfq_requeue_bfqq(bfqd, bfqq, true);
3501 /*
3502 * Resort priority tree of potential close cooperators.
3503 * See comments on bfq_pos_tree_add_move() for the unlikely().
3504 */
3505 if (unlikely(!bfqd->nonrot_with_queueing &&
3506 !RB_EMPTY_ROOT(&bfqq->sort_list)))
3507 bfq_pos_tree_add_move(bfqd, bfqq);
3508 }
3509
3510 /*
3511 * All in-service entities must have been properly deactivated
3512 * or requeued before executing the next function, which
3513 * resets all in-service entities as no more in service. This
3514 * may cause bfqq to be freed. If this happens, the next
3515 * function returns true.
3516 */
3517 return __bfq_bfqd_reset_in_service(bfqd);
3518}
3519
3520/**
3521 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
3522 * @bfqd: device data.
3523 * @bfqq: queue to update.
3524 * @reason: reason for expiration.
3525 *
3526 * Handle the feedback on @bfqq budget at queue expiration.
3527 * See the body for detailed comments.
3528 */
3529static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
3530 struct bfq_queue *bfqq,
3531 enum bfqq_expiration reason)
3532{
3533 struct request *next_rq;
3534 int budget, min_budget;
3535
3536 min_budget = bfq_min_budget(bfqd);
3537
3538 if (bfqq->wr_coeff == 1)
3539 budget = bfqq->max_budget;
3540 else /*
3541 * Use a constant, low budget for weight-raised queues,
3542 * to help achieve a low latency. Keep it slightly higher
3543 * than the minimum possible budget, to cause a little
3544 * bit fewer expirations.
3545 */
3546 budget = 2 * min_budget;
3547
3548 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
3549 bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
3550 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
3551 budget, bfq_min_budget(bfqd));
3552 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
3553 bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
3554
3555 if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
3556 switch (reason) {
3557 /*
3558 * Caveat: in all the following cases we trade latency
3559 * for throughput.
3560 */
3561 case BFQQE_TOO_IDLE:
3562 /*
3563 * This is the only case where we may reduce
3564 * the budget: if there is no request of the
3565 * process still waiting for completion, then
3566 * we assume (tentatively) that the timer has
3567 * expired because the batch of requests of
3568 * the process could have been served with a
3569 * smaller budget. Hence, betting that
3570 * process will behave in the same way when it
3571 * becomes backlogged again, we reduce its
3572 * next budget. As long as we guess right,
3573 * this budget cut reduces the latency
3574 * experienced by the process.
3575 *
3576 * However, if there are still outstanding
3577 * requests, then the process may have not yet
3578 * issued its next request just because it is
3579 * still waiting for the completion of some of
3580 * the still outstanding ones. So in this
3581 * subcase we do not reduce its budget, on the
3582 * contrary we increase it to possibly boost
3583 * the throughput, as discussed in the
3584 * comments to the BUDGET_TIMEOUT case.
3585 */
3586 if (bfqq->dispatched > 0) /* still outstanding reqs */
3587 budget = min(budget * 2, bfqd->bfq_max_budget);
3588 else {
3589 if (budget > 5 * min_budget)
3590 budget -= 4 * min_budget;
3591 else
3592 budget = min_budget;
3593 }
3594 break;
3595 case BFQQE_BUDGET_TIMEOUT:
3596 /*
3597 * We double the budget here because it gives
3598 * the chance to boost the throughput if this
3599 * is not a seeky process (and has bumped into
3600 * this timeout because of, e.g., ZBR).
3601 */
3602 budget = min(budget * 2, bfqd->bfq_max_budget);
3603 break;
3604 case BFQQE_BUDGET_EXHAUSTED:
3605 /*
3606 * The process still has backlog, and did not
3607 * let either the budget timeout or the disk
3608 * idling timeout expire. Hence it is not
3609 * seeky, has a short thinktime and may be
3610 * happy with a higher budget too. So
3611 * definitely increase the budget of this good
3612 * candidate to boost the disk throughput.
3613 */
3614 budget = min(budget * 4, bfqd->bfq_max_budget);
3615 break;
3616 case BFQQE_NO_MORE_REQUESTS:
3617 /*
3618 * For queues that expire for this reason, it
3619 * is particularly important to keep the
3620 * budget close to the actual service they
3621 * need. Doing so reduces the timestamp
3622 * misalignment problem described in the
3623 * comments in the body of
3624 * __bfq_activate_entity. In fact, suppose
3625 * that a queue systematically expires for
3626 * BFQQE_NO_MORE_REQUESTS and presents a
3627 * new request in time to enjoy timestamp
3628 * back-shifting. The larger the budget of the
3629 * queue is with respect to the service the
3630 * queue actually requests in each service
3631 * slot, the more times the queue can be
3632 * reactivated with the same virtual finish
3633 * time. It follows that, even if this finish
3634 * time is pushed to the system virtual time
3635 * to reduce the consequent timestamp
3636 * misalignment, the queue unjustly enjoys for
3637 * many re-activations a lower finish time
3638 * than all newly activated queues.
3639 *
3640 * The service needed by bfqq is measured
3641 * quite precisely by bfqq->entity.service.
3642 * Since bfqq does not enjoy device idling,
3643 * bfqq->entity.service is equal to the number
3644 * of sectors that the process associated with
3645 * bfqq requested to read/write before waiting
3646 * for request completions, or blocking for
3647 * other reasons.
3648 */
3649 budget = max_t(int, bfqq->entity.service, min_budget);
3650 break;
3651 default:
3652 return;
3653 }
3654 } else if (!bfq_bfqq_sync(bfqq)) {
3655 /*
3656 * Async queues get always the maximum possible
3657 * budget, as for them we do not care about latency
3658 * (in addition, their ability to dispatch is limited
3659 * by the charging factor).
3660 */
3661 budget = bfqd->bfq_max_budget;
3662 }
3663
3664 bfqq->max_budget = budget;
3665
3666 if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
3667 !bfqd->bfq_user_max_budget)
3668 bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
3669
3670 /*
3671 * If there is still backlog, then assign a new budget, making
3672 * sure that it is large enough for the next request. Since
3673 * the finish time of bfqq must be kept in sync with the
3674 * budget, be sure to call __bfq_bfqq_expire() *after* this
3675 * update.
3676 *
3677 * If there is no backlog, then no need to update the budget;
3678 * it will be updated on the arrival of a new request.
3679 */
3680 next_rq = bfqq->next_rq;
3681 if (next_rq)
3682 bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
3683 bfq_serv_to_charge(next_rq, bfqq));
3684
3685 bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
3686 next_rq ? blk_rq_sectors(next_rq) : 0,
3687 bfqq->entity.budget);
3688}
3689
3690/*
3691 * Return true if the process associated with bfqq is "slow". The slow
3692 * flag is used, in addition to the budget timeout, to reduce the
3693 * amount of service provided to seeky processes, and thus reduce
3694 * their chances to lower the throughput. More details in the comments
3695 * on the function bfq_bfqq_expire().
3696 *
3697 * An important observation is in order: as discussed in the comments
3698 * on the function bfq_update_peak_rate(), with devices with internal
3699 * queues, it is hard if ever possible to know when and for how long
3700 * an I/O request is processed by the device (apart from the trivial
3701 * I/O pattern where a new request is dispatched only after the
3702 * previous one has been completed). This makes it hard to evaluate
3703 * the real rate at which the I/O requests of each bfq_queue are
3704 * served. In fact, for an I/O scheduler like BFQ, serving a
3705 * bfq_queue means just dispatching its requests during its service
3706 * slot (i.e., until the budget of the queue is exhausted, or the
3707 * queue remains idle, or, finally, a timeout fires). But, during the
3708 * service slot of a bfq_queue, around 100 ms at most, the device may
3709 * be even still processing requests of bfq_queues served in previous
3710 * service slots. On the opposite end, the requests of the in-service
3711 * bfq_queue may be completed after the service slot of the queue
3712 * finishes.
3713 *
3714 * Anyway, unless more sophisticated solutions are used
3715 * (where possible), the sum of the sizes of the requests dispatched
3716 * during the service slot of a bfq_queue is probably the only
3717 * approximation available for the service received by the bfq_queue
3718 * during its service slot. And this sum is the quantity used in this
3719 * function to evaluate the I/O speed of a process.
3720 */
3721static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3722 bool compensate, enum bfqq_expiration reason,
3723 unsigned long *delta_ms)
3724{
3725 ktime_t delta_ktime;
3726 u32 delta_usecs;
3727 bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
3728
3729 if (!bfq_bfqq_sync(bfqq))
3730 return false;
3731
3732 if (compensate)
3733 delta_ktime = bfqd->last_idling_start;
3734 else
3735 delta_ktime = ktime_get();
3736 delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
3737 delta_usecs = ktime_to_us(delta_ktime);
3738
3739 /* don't use too short time intervals */
3740 if (delta_usecs < 1000) {
3741 if (blk_queue_nonrot(bfqd->queue))
3742 /*
3743 * give same worst-case guarantees as idling
3744 * for seeky
3745 */
3746 *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
3747 else /* charge at least one seek */
3748 *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
3749
3750 return slow;
3751 }
3752
3753 *delta_ms = delta_usecs / USEC_PER_MSEC;
3754
3755 /*
3756 * Use only long (> 20ms) intervals to filter out excessive
3757 * spikes in service rate estimation.
3758 */
3759 if (delta_usecs > 20000) {
3760 /*
3761 * Caveat for rotational devices: processes doing I/O
3762 * in the slower disk zones tend to be slow(er) even
3763 * if not seeky. In this respect, the estimated peak
3764 * rate is likely to be an average over the disk
3765 * surface. Accordingly, to not be too harsh with
3766 * unlucky processes, a process is deemed slow only if
3767 * its rate has been lower than half of the estimated
3768 * peak rate.
3769 */
3770 slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
3771 }
3772
3773 bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
3774
3775 return slow;
3776}
3777
3778/*
3779 * To be deemed as soft real-time, an application must meet two
3780 * requirements. First, the application must not require an average
3781 * bandwidth higher than the approximate bandwidth required to playback or
3782 * record a compressed high-definition video.
3783 * The next function is invoked on the completion of the last request of a
3784 * batch, to compute the next-start time instant, soft_rt_next_start, such
3785 * that, if the next request of the application does not arrive before
3786 * soft_rt_next_start, then the above requirement on the bandwidth is met.
3787 *
3788 * The second requirement is that the request pattern of the application is
3789 * isochronous, i.e., that, after issuing a request or a batch of requests,
3790 * the application stops issuing new requests until all its pending requests
3791 * have been completed. After that, the application may issue a new batch,
3792 * and so on.
3793 * For this reason the next function is invoked to compute
3794 * soft_rt_next_start only for applications that meet this requirement,
3795 * whereas soft_rt_next_start is set to infinity for applications that do
3796 * not.
3797 *
3798 * Unfortunately, even a greedy (i.e., I/O-bound) application may
3799 * happen to meet, occasionally or systematically, both the above
3800 * bandwidth and isochrony requirements. This may happen at least in
3801 * the following circumstances. First, if the CPU load is high. The
3802 * application may stop issuing requests while the CPUs are busy
3803 * serving other processes, then restart, then stop again for a while,
3804 * and so on. The other circumstances are related to the storage
3805 * device: the storage device is highly loaded or reaches a low-enough
3806 * throughput with the I/O of the application (e.g., because the I/O
3807 * is random and/or the device is slow). In all these cases, the
3808 * I/O of the application may be simply slowed down enough to meet
3809 * the bandwidth and isochrony requirements. To reduce the probability
3810 * that greedy applications are deemed as soft real-time in these
3811 * corner cases, a further rule is used in the computation of
3812 * soft_rt_next_start: the return value of this function is forced to
3813 * be higher than the maximum between the following two quantities.
3814 *
3815 * (a) Current time plus: (1) the maximum time for which the arrival
3816 * of a request is waited for when a sync queue becomes idle,
3817 * namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We
3818 * postpone for a moment the reason for adding a few extra
3819 * jiffies; we get back to it after next item (b). Lower-bounding
3820 * the return value of this function with the current time plus
3821 * bfqd->bfq_slice_idle tends to filter out greedy applications,
3822 * because the latter issue their next request as soon as possible
3823 * after the last one has been completed. In contrast, a soft
3824 * real-time application spends some time processing data, after a
3825 * batch of its requests has been completed.
3826 *
3827 * (b) Current value of bfqq->soft_rt_next_start. As pointed out
3828 * above, greedy applications may happen to meet both the
3829 * bandwidth and isochrony requirements under heavy CPU or
3830 * storage-device load. In more detail, in these scenarios, these
3831 * applications happen, only for limited time periods, to do I/O
3832 * slowly enough to meet all the requirements described so far,
3833 * including the filtering in above item (a). These slow-speed
3834 * time intervals are usually interspersed between other time
3835 * intervals during which these applications do I/O at a very high
3836 * speed. Fortunately, exactly because of the high speed of the
3837 * I/O in the high-speed intervals, the values returned by this
3838 * function happen to be so high, near the end of any such
3839 * high-speed interval, to be likely to fall *after* the end of
3840 * the low-speed time interval that follows. These high values are
3841 * stored in bfqq->soft_rt_next_start after each invocation of
3842 * this function. As a consequence, if the last value of
3843 * bfqq->soft_rt_next_start is constantly used to lower-bound the
3844 * next value that this function may return, then, from the very
3845 * beginning of a low-speed interval, bfqq->soft_rt_next_start is
3846 * likely to be constantly kept so high that any I/O request
3847 * issued during the low-speed interval is considered as arriving
3848 * to soon for the application to be deemed as soft
3849 * real-time. Then, in the high-speed interval that follows, the
3850 * application will not be deemed as soft real-time, just because
3851 * it will do I/O at a high speed. And so on.
3852 *
3853 * Getting back to the filtering in item (a), in the following two
3854 * cases this filtering might be easily passed by a greedy
3855 * application, if the reference quantity was just
3856 * bfqd->bfq_slice_idle:
3857 * 1) HZ is so low that the duration of a jiffy is comparable to or
3858 * higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
3859 * devices with HZ=100. The time granularity may be so coarse
3860 * that the approximation, in jiffies, of bfqd->bfq_slice_idle
3861 * is rather lower than the exact value.
3862 * 2) jiffies, instead of increasing at a constant rate, may stop increasing
3863 * for a while, then suddenly 'jump' by several units to recover the lost
3864 * increments. This seems to happen, e.g., inside virtual machines.
3865 * To address this issue, in the filtering in (a) we do not use as a
3866 * reference time interval just bfqd->bfq_slice_idle, but
3867 * bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the
3868 * minimum number of jiffies for which the filter seems to be quite
3869 * precise also in embedded systems and KVM/QEMU virtual machines.
3870 */
3871static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
3872 struct bfq_queue *bfqq)
3873{
3874 return max3(bfqq->soft_rt_next_start,
3875 bfqq->last_idle_bklogged +
3876 HZ * bfqq->service_from_backlogged /
3877 bfqd->bfq_wr_max_softrt_rate,
3878 jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
3879}
3880
3881/**
3882 * bfq_bfqq_expire - expire a queue.
3883 * @bfqd: device owning the queue.
3884 * @bfqq: the queue to expire.
3885 * @compensate: if true, compensate for the time spent idling.
3886 * @reason: the reason causing the expiration.
3887 *
3888 * If the process associated with bfqq does slow I/O (e.g., because it
3889 * issues random requests), we charge bfqq with the time it has been
3890 * in service instead of the service it has received (see
3891 * bfq_bfqq_charge_time for details on how this goal is achieved). As
3892 * a consequence, bfqq will typically get higher timestamps upon
3893 * reactivation, and hence it will be rescheduled as if it had
3894 * received more service than what it has actually received. In the
3895 * end, bfqq receives less service in proportion to how slowly its
3896 * associated process consumes its budgets (and hence how seriously it
3897 * tends to lower the throughput). In addition, this time-charging
3898 * strategy guarantees time fairness among slow processes. In
3899 * contrast, if the process associated with bfqq is not slow, we
3900 * charge bfqq exactly with the service it has received.
3901 *
3902 * Charging time to the first type of queues and the exact service to
3903 * the other has the effect of using the WF2Q+ policy to schedule the
3904 * former on a timeslice basis, without violating service domain
3905 * guarantees among the latter.
3906 */
3907void bfq_bfqq_expire(struct bfq_data *bfqd,
3908 struct bfq_queue *bfqq,
3909 bool compensate,
3910 enum bfqq_expiration reason)
3911{
3912 bool slow;
3913 unsigned long delta = 0;
3914 struct bfq_entity *entity = &bfqq->entity;
3915
3916 /*
3917 * Check whether the process is slow (see bfq_bfqq_is_slow).
3918 */
3919 slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
3920
3921 /*
3922 * As above explained, charge slow (typically seeky) and
3923 * timed-out queues with the time and not the service
3924 * received, to favor sequential workloads.
3925 *
3926 * Processes doing I/O in the slower disk zones will tend to
3927 * be slow(er) even if not seeky. Therefore, since the
3928 * estimated peak rate is actually an average over the disk
3929 * surface, these processes may timeout just for bad luck. To
3930 * avoid punishing them, do not charge time to processes that
3931 * succeeded in consuming at least 2/3 of their budget. This
3932 * allows BFQ to preserve enough elasticity to still perform
3933 * bandwidth, and not time, distribution with little unlucky
3934 * or quasi-sequential processes.
3935 */
3936 if (bfqq->wr_coeff == 1 &&
3937 (slow ||
3938 (reason == BFQQE_BUDGET_TIMEOUT &&
3939 bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
3940 bfq_bfqq_charge_time(bfqd, bfqq, delta);
3941
3942 if (reason == BFQQE_TOO_IDLE &&
3943 entity->service <= 2 * entity->budget / 10)
3944 bfq_clear_bfqq_IO_bound(bfqq);
3945
3946 if (bfqd->low_latency && bfqq->wr_coeff == 1)
3947 bfqq->last_wr_start_finish = jiffies;
3948
3949 if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
3950 RB_EMPTY_ROOT(&bfqq->sort_list)) {
3951 /*
3952 * If we get here, and there are no outstanding
3953 * requests, then the request pattern is isochronous
3954 * (see the comments on the function
3955 * bfq_bfqq_softrt_next_start()). Thus we can compute
3956 * soft_rt_next_start. And we do it, unless bfqq is in
3957 * interactive weight raising. We do not do it in the
3958 * latter subcase, for the following reason. bfqq may
3959 * be conveying the I/O needed to load a soft
3960 * real-time application. Such an application will
3961 * actually exhibit a soft real-time I/O pattern after
3962 * it finally starts doing its job. But, if
3963 * soft_rt_next_start is computed here for an
3964 * interactive bfqq, and bfqq had received a lot of
3965 * service before remaining with no outstanding
3966 * request (likely to happen on a fast device), then
3967 * soft_rt_next_start would be assigned such a high
3968 * value that, for a very long time, bfqq would be
3969 * prevented from being possibly considered as soft
3970 * real time.
3971 *
3972 * If, instead, the queue still has outstanding
3973 * requests, then we have to wait for the completion
3974 * of all the outstanding requests to discover whether
3975 * the request pattern is actually isochronous.
3976 */
3977 if (bfqq->dispatched == 0 &&
3978 bfqq->wr_coeff != bfqd->bfq_wr_coeff)
3979 bfqq->soft_rt_next_start =
3980 bfq_bfqq_softrt_next_start(bfqd, bfqq);
3981 else if (bfqq->dispatched > 0) {
3982 /*
3983 * Schedule an update of soft_rt_next_start to when
3984 * the task may be discovered to be isochronous.
3985 */
3986 bfq_mark_bfqq_softrt_update(bfqq);
3987 }
3988 }
3989
3990 bfq_log_bfqq(bfqd, bfqq,
3991 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
3992 slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
3993
3994 /*
3995 * bfqq expired, so no total service time needs to be computed
3996 * any longer: reset state machine for measuring total service
3997 * times.
3998 */
3999 bfqd->rqs_injected = bfqd->wait_dispatch = false;
4000 bfqd->waited_rq = NULL;
4001
4002 /*
4003 * Increase, decrease or leave budget unchanged according to
4004 * reason.
4005 */
4006 __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
4007 if (__bfq_bfqq_expire(bfqd, bfqq, reason))
4008 /* bfqq is gone, no more actions on it */
4009 return;
4010
4011 /* mark bfqq as waiting a request only if a bic still points to it */
4012 if (!bfq_bfqq_busy(bfqq) &&
4013 reason != BFQQE_BUDGET_TIMEOUT &&
4014 reason != BFQQE_BUDGET_EXHAUSTED) {
4015 bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
4016 /*
4017 * Not setting service to 0, because, if the next rq
4018 * arrives in time, the queue will go on receiving
4019 * service with this same budget (as if it never expired)
4020 */
4021 } else
4022 entity->service = 0;
4023
4024 /*
4025 * Reset the received-service counter for every parent entity.
4026 * Differently from what happens with bfqq->entity.service,
4027 * the resetting of this counter never needs to be postponed
4028 * for parent entities. In fact, in case bfqq may have a
4029 * chance to go on being served using the last, partially
4030 * consumed budget, bfqq->entity.service needs to be kept,
4031 * because if bfqq then actually goes on being served using
4032 * the same budget, the last value of bfqq->entity.service is
4033 * needed to properly decrement bfqq->entity.budget by the
4034 * portion already consumed. In contrast, it is not necessary
4035 * to keep entity->service for parent entities too, because
4036 * the bubble up of the new value of bfqq->entity.budget will
4037 * make sure that the budgets of parent entities are correct,
4038 * even in case bfqq and thus parent entities go on receiving
4039 * service with the same budget.
4040 */
4041 entity = entity->parent;
4042 for_each_entity(entity)
4043 entity->service = 0;
4044}
4045
4046/*
4047 * Budget timeout is not implemented through a dedicated timer, but
4048 * just checked on request arrivals and completions, as well as on
4049 * idle timer expirations.
4050 */
4051static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
4052{
4053 return time_is_before_eq_jiffies(bfqq->budget_timeout);
4054}
4055
4056/*
4057 * If we expire a queue that is actively waiting (i.e., with the
4058 * device idled) for the arrival of a new request, then we may incur
4059 * the timestamp misalignment problem described in the body of the
4060 * function __bfq_activate_entity. Hence we return true only if this
4061 * condition does not hold, or if the queue is slow enough to deserve
4062 * only to be kicked off for preserving a high throughput.
4063 */
4064static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
4065{
4066 bfq_log_bfqq(bfqq->bfqd, bfqq,
4067 "may_budget_timeout: wait_request %d left %d timeout %d",
4068 bfq_bfqq_wait_request(bfqq),
4069 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3,
4070 bfq_bfqq_budget_timeout(bfqq));
4071
4072 return (!bfq_bfqq_wait_request(bfqq) ||
4073 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3)
4074 &&
4075 bfq_bfqq_budget_timeout(bfqq);
4076}
4077
4078static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
4079 struct bfq_queue *bfqq)
4080{
4081 bool rot_without_queueing =
4082 !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
4083 bfqq_sequential_and_IO_bound,
4084 idling_boosts_thr;
4085
4086 /* No point in idling for bfqq if it won't get requests any longer */
4087 if (unlikely(!bfqq_process_refs(bfqq)))
4088 return false;
4089
4090 bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
4091 bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
4092
4093 /*
4094 * The next variable takes into account the cases where idling
4095 * boosts the throughput.
4096 *
4097 * The value of the variable is computed considering, first, that
4098 * idling is virtually always beneficial for the throughput if:
4099 * (a) the device is not NCQ-capable and rotational, or
4100 * (b) regardless of the presence of NCQ, the device is rotational and
4101 * the request pattern for bfqq is I/O-bound and sequential, or
4102 * (c) regardless of whether it is rotational, the device is
4103 * not NCQ-capable and the request pattern for bfqq is
4104 * I/O-bound and sequential.
4105 *
4106 * Secondly, and in contrast to the above item (b), idling an
4107 * NCQ-capable flash-based device would not boost the
4108 * throughput even with sequential I/O; rather it would lower
4109 * the throughput in proportion to how fast the device
4110 * is. Accordingly, the next variable is true if any of the
4111 * above conditions (a), (b) or (c) is true, and, in
4112 * particular, happens to be false if bfqd is an NCQ-capable
4113 * flash-based device.
4114 */
4115 idling_boosts_thr = rot_without_queueing ||
4116 ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
4117 bfqq_sequential_and_IO_bound);
4118
4119 /*
4120 * The return value of this function is equal to that of
4121 * idling_boosts_thr, unless a special case holds. In this
4122 * special case, described below, idling may cause problems to
4123 * weight-raised queues.
4124 *
4125 * When the request pool is saturated (e.g., in the presence
4126 * of write hogs), if the processes associated with
4127 * non-weight-raised queues ask for requests at a lower rate,
4128 * then processes associated with weight-raised queues have a
4129 * higher probability to get a request from the pool
4130 * immediately (or at least soon) when they need one. Thus
4131 * they have a higher probability to actually get a fraction
4132 * of the device throughput proportional to their high
4133 * weight. This is especially true with NCQ-capable drives,
4134 * which enqueue several requests in advance, and further
4135 * reorder internally-queued requests.
4136 *
4137 * For this reason, we force to false the return value if
4138 * there are weight-raised busy queues. In this case, and if
4139 * bfqq is not weight-raised, this guarantees that the device
4140 * is not idled for bfqq (if, instead, bfqq is weight-raised,
4141 * then idling will be guaranteed by another variable, see
4142 * below). Combined with the timestamping rules of BFQ (see
4143 * [1] for details), this behavior causes bfqq, and hence any
4144 * sync non-weight-raised queue, to get a lower number of
4145 * requests served, and thus to ask for a lower number of
4146 * requests from the request pool, before the busy
4147 * weight-raised queues get served again. This often mitigates
4148 * starvation problems in the presence of heavy write
4149 * workloads and NCQ, thereby guaranteeing a higher
4150 * application and system responsiveness in these hostile
4151 * scenarios.
4152 */
4153 return idling_boosts_thr &&
4154 bfqd->wr_busy_queues == 0;
4155}
4156
4157/*
4158 * For a queue that becomes empty, device idling is allowed only if
4159 * this function returns true for that queue. As a consequence, since
4160 * device idling plays a critical role for both throughput boosting
4161 * and service guarantees, the return value of this function plays a
4162 * critical role as well.
4163 *
4164 * In a nutshell, this function returns true only if idling is
4165 * beneficial for throughput or, even if detrimental for throughput,
4166 * idling is however necessary to preserve service guarantees (low
4167 * latency, desired throughput distribution, ...). In particular, on
4168 * NCQ-capable devices, this function tries to return false, so as to
4169 * help keep the drives' internal queues full, whenever this helps the
4170 * device boost the throughput without causing any service-guarantee
4171 * issue.
4172 *
4173 * Most of the issues taken into account to get the return value of
4174 * this function are not trivial. We discuss these issues in the two
4175 * functions providing the main pieces of information needed by this
4176 * function.
4177 */
4178static bool bfq_better_to_idle(struct bfq_queue *bfqq)
4179{
4180 struct bfq_data *bfqd = bfqq->bfqd;
4181 bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar;
4182
4183 /* No point in idling for bfqq if it won't get requests any longer */
4184 if (unlikely(!bfqq_process_refs(bfqq)))
4185 return false;
4186
4187 if (unlikely(bfqd->strict_guarantees))
4188 return true;
4189
4190 /*
4191 * Idling is performed only if slice_idle > 0. In addition, we
4192 * do not idle if
4193 * (a) bfqq is async
4194 * (b) bfqq is in the idle io prio class: in this case we do
4195 * not idle because we want to minimize the bandwidth that
4196 * queues in this class can steal to higher-priority queues
4197 */
4198 if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
4199 bfq_class_idle(bfqq))
4200 return false;
4201
4202 idling_boosts_thr_with_no_issue =
4203 idling_boosts_thr_without_issues(bfqd, bfqq);
4204
4205 idling_needed_for_service_guar =
4206 idling_needed_for_service_guarantees(bfqd, bfqq);
4207
4208 /*
4209 * We have now the two components we need to compute the
4210 * return value of the function, which is true only if idling
4211 * either boosts the throughput (without issues), or is
4212 * necessary to preserve service guarantees.
4213 */
4214 return idling_boosts_thr_with_no_issue ||
4215 idling_needed_for_service_guar;
4216}
4217
4218/*
4219 * If the in-service queue is empty but the function bfq_better_to_idle
4220 * returns true, then:
4221 * 1) the queue must remain in service and cannot be expired, and
4222 * 2) the device must be idled to wait for the possible arrival of a new
4223 * request for the queue.
4224 * See the comments on the function bfq_better_to_idle for the reasons
4225 * why performing device idling is the best choice to boost the throughput
4226 * and preserve service guarantees when bfq_better_to_idle itself
4227 * returns true.
4228 */
4229static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
4230{
4231 return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq);
4232}
4233
4234/*
4235 * This function chooses the queue from which to pick the next extra
4236 * I/O request to inject, if it finds a compatible queue. See the
4237 * comments on bfq_update_inject_limit() for details on the injection
4238 * mechanism, and for the definitions of the quantities mentioned
4239 * below.
4240 */
4241static struct bfq_queue *
4242bfq_choose_bfqq_for_injection(struct bfq_data *bfqd)
4243{
4244 struct bfq_queue *bfqq, *in_serv_bfqq = bfqd->in_service_queue;
4245 unsigned int limit = in_serv_bfqq->inject_limit;
4246 /*
4247 * If
4248 * - bfqq is not weight-raised and therefore does not carry
4249 * time-critical I/O,
4250 * or
4251 * - regardless of whether bfqq is weight-raised, bfqq has
4252 * however a long think time, during which it can absorb the
4253 * effect of an appropriate number of extra I/O requests
4254 * from other queues (see bfq_update_inject_limit for
4255 * details on the computation of this number);
4256 * then injection can be performed without restrictions.
4257 */
4258 bool in_serv_always_inject = in_serv_bfqq->wr_coeff == 1 ||
4259 !bfq_bfqq_has_short_ttime(in_serv_bfqq);
4260
4261 /*
4262 * If
4263 * - the baseline total service time could not be sampled yet,
4264 * so the inject limit happens to be still 0, and
4265 * - a lot of time has elapsed since the plugging of I/O
4266 * dispatching started, so drive speed is being wasted
4267 * significantly;
4268 * then temporarily raise inject limit to one request.
4269 */
4270 if (limit == 0 && in_serv_bfqq->last_serv_time_ns == 0 &&
4271 bfq_bfqq_wait_request(in_serv_bfqq) &&
4272 time_is_before_eq_jiffies(bfqd->last_idling_start_jiffies +
4273 bfqd->bfq_slice_idle)
4274 )
4275 limit = 1;
4276
4277 if (bfqd->rq_in_driver >= limit)
4278 return NULL;
4279
4280 /*
4281 * Linear search of the source queue for injection; but, with
4282 * a high probability, very few steps are needed to find a
4283 * candidate queue, i.e., a queue with enough budget left for
4284 * its next request. In fact:
4285 * - BFQ dynamically updates the budget of every queue so as
4286 * to accommodate the expected backlog of the queue;
4287 * - if a queue gets all its requests dispatched as injected
4288 * service, then the queue is removed from the active list
4289 * (and re-added only if it gets new requests, but then it
4290 * is assigned again enough budget for its new backlog).
4291 */
4292 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
4293 if (!RB_EMPTY_ROOT(&bfqq->sort_list) &&
4294 (in_serv_always_inject || bfqq->wr_coeff > 1) &&
4295 bfq_serv_to_charge(bfqq->next_rq, bfqq) <=
4296 bfq_bfqq_budget_left(bfqq)) {
4297 /*
4298 * Allow for only one large in-flight request
4299 * on non-rotational devices, for the
4300 * following reason. On non-rotationl drives,
4301 * large requests take much longer than
4302 * smaller requests to be served. In addition,
4303 * the drive prefers to serve large requests
4304 * w.r.t. to small ones, if it can choose. So,
4305 * having more than one large requests queued
4306 * in the drive may easily make the next first
4307 * request of the in-service queue wait for so
4308 * long to break bfqq's service guarantees. On
4309 * the bright side, large requests let the
4310 * drive reach a very high throughput, even if
4311 * there is only one in-flight large request
4312 * at a time.
4313 */
4314 if (blk_queue_nonrot(bfqd->queue) &&
4315 blk_rq_sectors(bfqq->next_rq) >=
4316 BFQQ_SECT_THR_NONROT)
4317 limit = min_t(unsigned int, 1, limit);
4318 else
4319 limit = in_serv_bfqq->inject_limit;
4320
4321 if (bfqd->rq_in_driver < limit) {
4322 bfqd->rqs_injected = true;
4323 return bfqq;
4324 }
4325 }
4326
4327 return NULL;
4328}
4329
4330/*
4331 * Select a queue for service. If we have a current queue in service,
4332 * check whether to continue servicing it, or retrieve and set a new one.
4333 */
4334static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
4335{
4336 struct bfq_queue *bfqq;
4337 struct request *next_rq;
4338 enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
4339
4340 bfqq = bfqd->in_service_queue;
4341 if (!bfqq)
4342 goto new_queue;
4343
4344 bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
4345
4346 /*
4347 * Do not expire bfqq for budget timeout if bfqq may be about
4348 * to enjoy device idling. The reason why, in this case, we
4349 * prevent bfqq from expiring is the same as in the comments
4350 * on the case where bfq_bfqq_must_idle() returns true, in
4351 * bfq_completed_request().
4352 */
4353 if (bfq_may_expire_for_budg_timeout(bfqq) &&
4354 !bfq_bfqq_must_idle(bfqq))
4355 goto expire;
4356
4357check_queue:
4358 /*
4359 * This loop is rarely executed more than once. Even when it
4360 * happens, it is much more convenient to re-execute this loop
4361 * than to return NULL and trigger a new dispatch to get a
4362 * request served.
4363 */
4364 next_rq = bfqq->next_rq;
4365 /*
4366 * If bfqq has requests queued and it has enough budget left to
4367 * serve them, keep the queue, otherwise expire it.
4368 */
4369 if (next_rq) {
4370 if (bfq_serv_to_charge(next_rq, bfqq) >
4371 bfq_bfqq_budget_left(bfqq)) {
4372 /*
4373 * Expire the queue for budget exhaustion,
4374 * which makes sure that the next budget is
4375 * enough to serve the next request, even if
4376 * it comes from the fifo expired path.
4377 */
4378 reason = BFQQE_BUDGET_EXHAUSTED;
4379 goto expire;
4380 } else {
4381 /*
4382 * The idle timer may be pending because we may
4383 * not disable disk idling even when a new request
4384 * arrives.
4385 */
4386 if (bfq_bfqq_wait_request(bfqq)) {
4387 /*
4388 * If we get here: 1) at least a new request
4389 * has arrived but we have not disabled the
4390 * timer because the request was too small,
4391 * 2) then the block layer has unplugged
4392 * the device, causing the dispatch to be
4393 * invoked.
4394 *
4395 * Since the device is unplugged, now the
4396 * requests are probably large enough to
4397 * provide a reasonable throughput.
4398 * So we disable idling.
4399 */
4400 bfq_clear_bfqq_wait_request(bfqq);
4401 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
4402 }
4403 goto keep_queue;
4404 }
4405 }
4406
4407 /*
4408 * No requests pending. However, if the in-service queue is idling
4409 * for a new request, or has requests waiting for a completion and
4410 * may idle after their completion, then keep it anyway.
4411 *
4412 * Yet, inject service from other queues if it boosts
4413 * throughput and is possible.
4414 */
4415 if (bfq_bfqq_wait_request(bfqq) ||
4416 (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) {
4417 struct bfq_queue *async_bfqq =
4418 bfqq->bic && bfqq->bic->bfqq[0] &&
4419 bfq_bfqq_busy(bfqq->bic->bfqq[0]) &&
4420 bfqq->bic->bfqq[0]->next_rq ?
4421 bfqq->bic->bfqq[0] : NULL;
4422
4423 /*
4424 * The next three mutually-exclusive ifs decide
4425 * whether to try injection, and choose the queue to
4426 * pick an I/O request from.
4427 *
4428 * The first if checks whether the process associated
4429 * with bfqq has also async I/O pending. If so, it
4430 * injects such I/O unconditionally. Injecting async
4431 * I/O from the same process can cause no harm to the
4432 * process. On the contrary, it can only increase
4433 * bandwidth and reduce latency for the process.
4434 *
4435 * The second if checks whether there happens to be a
4436 * non-empty waker queue for bfqq, i.e., a queue whose
4437 * I/O needs to be completed for bfqq to receive new
4438 * I/O. This happens, e.g., if bfqq is associated with
4439 * a process that does some sync. A sync generates
4440 * extra blocking I/O, which must be completed before
4441 * the process associated with bfqq can go on with its
4442 * I/O. If the I/O of the waker queue is not served,
4443 * then bfqq remains empty, and no I/O is dispatched,
4444 * until the idle timeout fires for bfqq. This is
4445 * likely to result in lower bandwidth and higher
4446 * latencies for bfqq, and in a severe loss of total
4447 * throughput. The best action to take is therefore to
4448 * serve the waker queue as soon as possible. So do it
4449 * (without relying on the third alternative below for
4450 * eventually serving waker_bfqq's I/O; see the last
4451 * paragraph for further details). This systematic
4452 * injection of I/O from the waker queue does not
4453 * cause any delay to bfqq's I/O. On the contrary,
4454 * next bfqq's I/O is brought forward dramatically,
4455 * for it is not blocked for milliseconds.
4456 *
4457 * The third if checks whether bfqq is a queue for
4458 * which it is better to avoid injection. It is so if
4459 * bfqq delivers more throughput when served without
4460 * any further I/O from other queues in the middle, or
4461 * if the service times of bfqq's I/O requests both
4462 * count more than overall throughput, and may be
4463 * easily increased by injection (this happens if bfqq
4464 * has a short think time). If none of these
4465 * conditions holds, then a candidate queue for
4466 * injection is looked for through
4467 * bfq_choose_bfqq_for_injection(). Note that the
4468 * latter may return NULL (for example if the inject
4469 * limit for bfqq is currently 0).
4470 *
4471 * NOTE: motivation for the second alternative
4472 *
4473 * Thanks to the way the inject limit is updated in
4474 * bfq_update_has_short_ttime(), it is rather likely
4475 * that, if I/O is being plugged for bfqq and the
4476 * waker queue has pending I/O requests that are
4477 * blocking bfqq's I/O, then the third alternative
4478 * above lets the waker queue get served before the
4479 * I/O-plugging timeout fires. So one may deem the
4480 * second alternative superfluous. It is not, because
4481 * the third alternative may be way less effective in
4482 * case of a synchronization. For two main
4483 * reasons. First, throughput may be low because the
4484 * inject limit may be too low to guarantee the same
4485 * amount of injected I/O, from the waker queue or
4486 * other queues, that the second alternative
4487 * guarantees (the second alternative unconditionally
4488 * injects a pending I/O request of the waker queue
4489 * for each bfq_dispatch_request()). Second, with the
4490 * third alternative, the duration of the plugging,
4491 * i.e., the time before bfqq finally receives new I/O,
4492 * may not be minimized, because the waker queue may
4493 * happen to be served only after other queues.
4494 */
4495 if (async_bfqq &&
4496 icq_to_bic(async_bfqq->next_rq->elv.icq) == bfqq->bic &&
4497 bfq_serv_to_charge(async_bfqq->next_rq, async_bfqq) <=
4498 bfq_bfqq_budget_left(async_bfqq))
4499 bfqq = bfqq->bic->bfqq[0];
4500 else if (bfq_bfqq_has_waker(bfqq) &&
4501 bfq_bfqq_busy(bfqq->waker_bfqq) &&
4502 bfqq->next_rq &&
4503 bfq_serv_to_charge(bfqq->waker_bfqq->next_rq,
4504 bfqq->waker_bfqq) <=
4505 bfq_bfqq_budget_left(bfqq->waker_bfqq)
4506 )
4507 bfqq = bfqq->waker_bfqq;
4508 else if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
4509 (bfqq->wr_coeff == 1 || bfqd->wr_busy_queues > 1 ||
4510 !bfq_bfqq_has_short_ttime(bfqq)))
4511 bfqq = bfq_choose_bfqq_for_injection(bfqd);
4512 else
4513 bfqq = NULL;
4514
4515 goto keep_queue;
4516 }
4517
4518 reason = BFQQE_NO_MORE_REQUESTS;
4519expire:
4520 bfq_bfqq_expire(bfqd, bfqq, false, reason);
4521new_queue:
4522 bfqq = bfq_set_in_service_queue(bfqd);
4523 if (bfqq) {
4524 bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
4525 goto check_queue;
4526 }
4527keep_queue:
4528 if (bfqq)
4529 bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
4530 else
4531 bfq_log(bfqd, "select_queue: no queue returned");
4532
4533 return bfqq;
4534}
4535
4536static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4537{
4538 struct bfq_entity *entity = &bfqq->entity;
4539
4540 if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
4541 bfq_log_bfqq(bfqd, bfqq,
4542 "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
4543 jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
4544 jiffies_to_msecs(bfqq->wr_cur_max_time),
4545 bfqq->wr_coeff,
4546 bfqq->entity.weight, bfqq->entity.orig_weight);
4547
4548 if (entity->prio_changed)
4549 bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
4550
4551 /*
4552 * If the queue was activated in a burst, or too much
4553 * time has elapsed from the beginning of this
4554 * weight-raising period, then end weight raising.
4555 */
4556 if (bfq_bfqq_in_large_burst(bfqq))
4557 bfq_bfqq_end_wr(bfqq);
4558 else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
4559 bfqq->wr_cur_max_time)) {
4560 if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
4561 time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
4562 bfq_wr_duration(bfqd)))
4563 bfq_bfqq_end_wr(bfqq);
4564 else {
4565 switch_back_to_interactive_wr(bfqq, bfqd);
4566 bfqq->entity.prio_changed = 1;
4567 }
4568 }
4569 if (bfqq->wr_coeff > 1 &&
4570 bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time &&
4571 bfqq->service_from_wr > max_service_from_wr) {
4572 /* see comments on max_service_from_wr */
4573 bfq_bfqq_end_wr(bfqq);
4574 }
4575 }
4576 /*
4577 * To improve latency (for this or other queues), immediately
4578 * update weight both if it must be raised and if it must be
4579 * lowered. Since, entity may be on some active tree here, and
4580 * might have a pending change of its ioprio class, invoke
4581 * next function with the last parameter unset (see the
4582 * comments on the function).
4583 */
4584 if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
4585 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
4586 entity, false);
4587}
4588
4589/*
4590 * Dispatch next request from bfqq.
4591 */
4592static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
4593 struct bfq_queue *bfqq)
4594{
4595 struct request *rq = bfqq->next_rq;
4596 unsigned long service_to_charge;
4597
4598 service_to_charge = bfq_serv_to_charge(rq, bfqq);
4599
4600 bfq_bfqq_served(bfqq, service_to_charge);
4601
4602 if (bfqq == bfqd->in_service_queue && bfqd->wait_dispatch) {
4603 bfqd->wait_dispatch = false;
4604 bfqd->waited_rq = rq;
4605 }
4606
4607 bfq_dispatch_remove(bfqd->queue, rq);
4608
4609 if (bfqq != bfqd->in_service_queue)
4610 goto return_rq;
4611
4612 /*
4613 * If weight raising has to terminate for bfqq, then next
4614 * function causes an immediate update of bfqq's weight,
4615 * without waiting for next activation. As a consequence, on
4616 * expiration, bfqq will be timestamped as if has never been
4617 * weight-raised during this service slot, even if it has
4618 * received part or even most of the service as a
4619 * weight-raised queue. This inflates bfqq's timestamps, which
4620 * is beneficial, as bfqq is then more willing to leave the
4621 * device immediately to possible other weight-raised queues.
4622 */
4623 bfq_update_wr_data(bfqd, bfqq);
4624
4625 /*
4626 * Expire bfqq, pretending that its budget expired, if bfqq
4627 * belongs to CLASS_IDLE and other queues are waiting for
4628 * service.
4629 */
4630 if (!(bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq)))
4631 goto return_rq;
4632
4633 bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
4634
4635return_rq:
4636 return rq;
4637}
4638
4639static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
4640{
4641 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
4642
4643 /*
4644 * Avoiding lock: a race on bfqd->busy_queues should cause at
4645 * most a call to dispatch for nothing
4646 */
4647 return !list_empty_careful(&bfqd->dispatch) ||
4648 bfq_tot_busy_queues(bfqd) > 0;
4649}
4650
4651static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
4652{
4653 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
4654 struct request *rq = NULL;
4655 struct bfq_queue *bfqq = NULL;
4656
4657 if (!list_empty(&bfqd->dispatch)) {
4658 rq = list_first_entry(&bfqd->dispatch, struct request,
4659 queuelist);
4660 list_del_init(&rq->queuelist);
4661
4662 bfqq = RQ_BFQQ(rq);
4663
4664 if (bfqq) {
4665 /*
4666 * Increment counters here, because this
4667 * dispatch does not follow the standard
4668 * dispatch flow (where counters are
4669 * incremented)
4670 */
4671 bfqq->dispatched++;
4672
4673 goto inc_in_driver_start_rq;
4674 }
4675
4676 /*
4677 * We exploit the bfq_finish_requeue_request hook to
4678 * decrement rq_in_driver, but
4679 * bfq_finish_requeue_request will not be invoked on
4680 * this request. So, to avoid unbalance, just start
4681 * this request, without incrementing rq_in_driver. As
4682 * a negative consequence, rq_in_driver is deceptively
4683 * lower than it should be while this request is in
4684 * service. This may cause bfq_schedule_dispatch to be
4685 * invoked uselessly.
4686 *
4687 * As for implementing an exact solution, the
4688 * bfq_finish_requeue_request hook, if defined, is
4689 * probably invoked also on this request. So, by
4690 * exploiting this hook, we could 1) increment
4691 * rq_in_driver here, and 2) decrement it in
4692 * bfq_finish_requeue_request. Such a solution would
4693 * let the value of the counter be always accurate,
4694 * but it would entail using an extra interface
4695 * function. This cost seems higher than the benefit,
4696 * being the frequency of non-elevator-private
4697 * requests very low.
4698 */
4699 goto start_rq;
4700 }
4701
4702 bfq_log(bfqd, "dispatch requests: %d busy queues",
4703 bfq_tot_busy_queues(bfqd));
4704
4705 if (bfq_tot_busy_queues(bfqd) == 0)
4706 goto exit;
4707
4708 /*
4709 * Force device to serve one request at a time if
4710 * strict_guarantees is true. Forcing this service scheme is
4711 * currently the ONLY way to guarantee that the request
4712 * service order enforced by the scheduler is respected by a
4713 * queueing device. Otherwise the device is free even to make
4714 * some unlucky request wait for as long as the device
4715 * wishes.
4716 *
4717 * Of course, serving one request at a time may cause loss of
4718 * throughput.
4719 */
4720 if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
4721 goto exit;
4722
4723 bfqq = bfq_select_queue(bfqd);
4724 if (!bfqq)
4725 goto exit;
4726
4727 rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
4728
4729 if (rq) {
4730inc_in_driver_start_rq:
4731 bfqd->rq_in_driver++;
4732start_rq:
4733 rq->rq_flags |= RQF_STARTED;
4734 }
4735exit:
4736 return rq;
4737}
4738
4739#ifdef CONFIG_BFQ_CGROUP_DEBUG
4740static void bfq_update_dispatch_stats(struct request_queue *q,
4741 struct request *rq,
4742 struct bfq_queue *in_serv_queue,
4743 bool idle_timer_disabled)
4744{
4745 struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
4746
4747 if (!idle_timer_disabled && !bfqq)
4748 return;
4749
4750 /*
4751 * rq and bfqq are guaranteed to exist until this function
4752 * ends, for the following reasons. First, rq can be
4753 * dispatched to the device, and then can be completed and
4754 * freed, only after this function ends. Second, rq cannot be
4755 * merged (and thus freed because of a merge) any longer,
4756 * because it has already started. Thus rq cannot be freed
4757 * before this function ends, and, since rq has a reference to
4758 * bfqq, the same guarantee holds for bfqq too.
4759 *
4760 * In addition, the following queue lock guarantees that
4761 * bfqq_group(bfqq) exists as well.
4762 */
4763 spin_lock_irq(&q->queue_lock);
4764 if (idle_timer_disabled)
4765 /*
4766 * Since the idle timer has been disabled,
4767 * in_serv_queue contained some request when
4768 * __bfq_dispatch_request was invoked above, which
4769 * implies that rq was picked exactly from
4770 * in_serv_queue. Thus in_serv_queue == bfqq, and is
4771 * therefore guaranteed to exist because of the above
4772 * arguments.
4773 */
4774 bfqg_stats_update_idle_time(bfqq_group(in_serv_queue));
4775 if (bfqq) {
4776 struct bfq_group *bfqg = bfqq_group(bfqq);
4777
4778 bfqg_stats_update_avg_queue_size(bfqg);
4779 bfqg_stats_set_start_empty_time(bfqg);
4780 bfqg_stats_update_io_remove(bfqg, rq->cmd_flags);
4781 }
4782 spin_unlock_irq(&q->queue_lock);
4783}
4784#else
4785static inline void bfq_update_dispatch_stats(struct request_queue *q,
4786 struct request *rq,
4787 struct bfq_queue *in_serv_queue,
4788 bool idle_timer_disabled) {}
4789#endif /* CONFIG_BFQ_CGROUP_DEBUG */
4790
4791static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
4792{
4793 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
4794 struct request *rq;
4795 struct bfq_queue *in_serv_queue;
4796 bool waiting_rq, idle_timer_disabled;
4797
4798 spin_lock_irq(&bfqd->lock);
4799
4800 in_serv_queue = bfqd->in_service_queue;
4801 waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
4802
4803 rq = __bfq_dispatch_request(hctx);
4804
4805 idle_timer_disabled =
4806 waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
4807
4808 spin_unlock_irq(&bfqd->lock);
4809
4810 bfq_update_dispatch_stats(hctx->queue, rq, in_serv_queue,
4811 idle_timer_disabled);
4812
4813 return rq;
4814}
4815
4816/*
4817 * Task holds one reference to the queue, dropped when task exits. Each rq
4818 * in-flight on this queue also holds a reference, dropped when rq is freed.
4819 *
4820 * Scheduler lock must be held here. Recall not to use bfqq after calling
4821 * this function on it.
4822 */
4823void bfq_put_queue(struct bfq_queue *bfqq)
4824{
4825 struct bfq_queue *item;
4826 struct hlist_node *n;
4827 struct bfq_group *bfqg = bfqq_group(bfqq);
4828
4829 if (bfqq->bfqd)
4830 bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d",
4831 bfqq, bfqq->ref);
4832
4833 bfqq->ref--;
4834 if (bfqq->ref)
4835 return;
4836
4837 if (!hlist_unhashed(&bfqq->burst_list_node)) {
4838 hlist_del_init(&bfqq->burst_list_node);
4839 /*
4840 * Decrement also burst size after the removal, if the
4841 * process associated with bfqq is exiting, and thus
4842 * does not contribute to the burst any longer. This
4843 * decrement helps filter out false positives of large
4844 * bursts, when some short-lived process (often due to
4845 * the execution of commands by some service) happens
4846 * to start and exit while a complex application is
4847 * starting, and thus spawning several processes that
4848 * do I/O (and that *must not* be treated as a large
4849 * burst, see comments on bfq_handle_burst).
4850 *
4851 * In particular, the decrement is performed only if:
4852 * 1) bfqq is not a merged queue, because, if it is,
4853 * then this free of bfqq is not triggered by the exit
4854 * of the process bfqq is associated with, but exactly
4855 * by the fact that bfqq has just been merged.
4856 * 2) burst_size is greater than 0, to handle
4857 * unbalanced decrements. Unbalanced decrements may
4858 * happen in te following case: bfqq is inserted into
4859 * the current burst list--without incrementing
4860 * bust_size--because of a split, but the current
4861 * burst list is not the burst list bfqq belonged to
4862 * (see comments on the case of a split in
4863 * bfq_set_request).
4864 */
4865 if (bfqq->bic && bfqq->bfqd->burst_size > 0)
4866 bfqq->bfqd->burst_size--;
4867 }
4868
4869 /*
4870 * bfqq does not exist any longer, so it cannot be woken by
4871 * any other queue, and cannot wake any other queue. Then bfqq
4872 * must be removed from the woken list of its possible waker
4873 * queue, and all queues in the woken list of bfqq must stop
4874 * having a waker queue. Strictly speaking, these updates
4875 * should be performed when bfqq remains with no I/O source
4876 * attached to it, which happens before bfqq gets freed. In
4877 * particular, this happens when the last process associated
4878 * with bfqq exits or gets associated with a different
4879 * queue. However, both events lead to bfqq being freed soon,
4880 * and dangling references would come out only after bfqq gets
4881 * freed. So these updates are done here, as a simple and safe
4882 * way to handle all cases.
4883 */
4884 /* remove bfqq from woken list */
4885 if (!hlist_unhashed(&bfqq->woken_list_node))
4886 hlist_del_init(&bfqq->woken_list_node);
4887
4888 /* reset waker for all queues in woken list */
4889 hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
4890 woken_list_node) {
4891 item->waker_bfqq = NULL;
4892 bfq_clear_bfqq_has_waker(item);
4893 hlist_del_init(&item->woken_list_node);
4894 }
4895
4896 if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq)
4897 bfqq->bfqd->last_completed_rq_bfqq = NULL;
4898
4899 kmem_cache_free(bfq_pool, bfqq);
4900 bfqg_and_blkg_put(bfqg);
4901}
4902
4903static void bfq_put_cooperator(struct bfq_queue *bfqq)
4904{
4905 struct bfq_queue *__bfqq, *next;
4906
4907 /*
4908 * If this queue was scheduled to merge with another queue, be
4909 * sure to drop the reference taken on that queue (and others in
4910 * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
4911 */
4912 __bfqq = bfqq->new_bfqq;
4913 while (__bfqq) {
4914 if (__bfqq == bfqq)
4915 break;
4916 next = __bfqq->new_bfqq;
4917 bfq_put_queue(__bfqq);
4918 __bfqq = next;
4919 }
4920}
4921
4922static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4923{
4924 if (bfqq == bfqd->in_service_queue) {
4925 __bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);
4926 bfq_schedule_dispatch(bfqd);
4927 }
4928
4929 bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
4930
4931 bfq_put_cooperator(bfqq);
4932
4933 bfq_release_process_ref(bfqd, bfqq);
4934}
4935
4936static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
4937{
4938 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
4939 struct bfq_data *bfqd;
4940
4941 if (bfqq)
4942 bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
4943
4944 if (bfqq && bfqd) {
4945 unsigned long flags;
4946
4947 spin_lock_irqsave(&bfqd->lock, flags);
4948 bfqq->bic = NULL;
4949 bfq_exit_bfqq(bfqd, bfqq);
4950 bic_set_bfqq(bic, NULL, is_sync);
4951 spin_unlock_irqrestore(&bfqd->lock, flags);
4952 }
4953}
4954
4955static void bfq_exit_icq(struct io_cq *icq)
4956{
4957 struct bfq_io_cq *bic = icq_to_bic(icq);
4958
4959 bfq_exit_icq_bfqq(bic, true);
4960 bfq_exit_icq_bfqq(bic, false);
4961}
4962
4963/*
4964 * Update the entity prio values; note that the new values will not
4965 * be used until the next (re)activation.
4966 */
4967static void
4968bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
4969{
4970 struct task_struct *tsk = current;
4971 int ioprio_class;
4972 struct bfq_data *bfqd = bfqq->bfqd;
4973
4974 if (!bfqd)
4975 return;
4976
4977 ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
4978 switch (ioprio_class) {
4979 default:
4980 pr_err("bdi %s: bfq: bad prio class %d\n",
4981 bdi_dev_name(bfqq->bfqd->queue->backing_dev_info),
4982 ioprio_class);
4983 fallthrough;
4984 case IOPRIO_CLASS_NONE:
4985 /*
4986 * No prio set, inherit CPU scheduling settings.
4987 */
4988 bfqq->new_ioprio = task_nice_ioprio(tsk);
4989 bfqq->new_ioprio_class = task_nice_ioclass(tsk);
4990 break;
4991 case IOPRIO_CLASS_RT:
4992 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
4993 bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
4994 break;
4995 case IOPRIO_CLASS_BE:
4996 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
4997 bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
4998 break;
4999 case IOPRIO_CLASS_IDLE:
5000 bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
5001 bfqq->new_ioprio = 7;
5002 break;
5003 }
5004
5005 if (bfqq->new_ioprio >= IOPRIO_BE_NR) {
5006 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
5007 bfqq->new_ioprio);
5008 bfqq->new_ioprio = IOPRIO_BE_NR;
5009 }
5010
5011 bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
5012 bfqq->entity.prio_changed = 1;
5013}
5014
5015static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5016 struct bio *bio, bool is_sync,
5017 struct bfq_io_cq *bic);
5018
5019static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
5020{
5021 struct bfq_data *bfqd = bic_to_bfqd(bic);
5022 struct bfq_queue *bfqq;
5023 int ioprio = bic->icq.ioc->ioprio;
5024
5025 /*
5026 * This condition may trigger on a newly created bic, be sure to
5027 * drop the lock before returning.
5028 */
5029 if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
5030 return;
5031
5032 bic->ioprio = ioprio;
5033
5034 bfqq = bic_to_bfqq(bic, false);
5035 if (bfqq) {
5036 bfq_release_process_ref(bfqd, bfqq);
5037 bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic);
5038 bic_set_bfqq(bic, bfqq, false);
5039 }
5040
5041 bfqq = bic_to_bfqq(bic, true);
5042 if (bfqq)
5043 bfq_set_next_ioprio_data(bfqq, bic);
5044}
5045
5046static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5047 struct bfq_io_cq *bic, pid_t pid, int is_sync)
5048{
5049 RB_CLEAR_NODE(&bfqq->entity.rb_node);
5050 INIT_LIST_HEAD(&bfqq->fifo);
5051 INIT_HLIST_NODE(&bfqq->burst_list_node);
5052 INIT_HLIST_NODE(&bfqq->woken_list_node);
5053 INIT_HLIST_HEAD(&bfqq->woken_list);
5054
5055 bfqq->ref = 0;
5056 bfqq->bfqd = bfqd;
5057
5058 if (bic)
5059 bfq_set_next_ioprio_data(bfqq, bic);
5060
5061 if (is_sync) {
5062 /*
5063 * No need to mark as has_short_ttime if in
5064 * idle_class, because no device idling is performed
5065 * for queues in idle class
5066 */
5067 if (!bfq_class_idle(bfqq))
5068 /* tentatively mark as has_short_ttime */
5069 bfq_mark_bfqq_has_short_ttime(bfqq);
5070 bfq_mark_bfqq_sync(bfqq);
5071 bfq_mark_bfqq_just_created(bfqq);
5072 } else
5073 bfq_clear_bfqq_sync(bfqq);
5074
5075 /* set end request to minus infinity from now */
5076 bfqq->ttime.last_end_request = ktime_get_ns() + 1;
5077
5078 bfq_mark_bfqq_IO_bound(bfqq);
5079
5080 bfqq->pid = pid;
5081
5082 /* Tentative initial value to trade off between thr and lat */
5083 bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
5084 bfqq->budget_timeout = bfq_smallest_from_now();
5085
5086 bfqq->wr_coeff = 1;
5087 bfqq->last_wr_start_finish = jiffies;
5088 bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
5089 bfqq->split_time = bfq_smallest_from_now();
5090
5091 /*
5092 * To not forget the possibly high bandwidth consumed by a
5093 * process/queue in the recent past,
5094 * bfq_bfqq_softrt_next_start() returns a value at least equal
5095 * to the current value of bfqq->soft_rt_next_start (see
5096 * comments on bfq_bfqq_softrt_next_start). Set
5097 * soft_rt_next_start to now, to mean that bfqq has consumed
5098 * no bandwidth so far.
5099 */
5100 bfqq->soft_rt_next_start = jiffies;
5101
5102 /* first request is almost certainly seeky */
5103 bfqq->seek_history = 1;
5104}
5105
5106static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
5107 struct bfq_group *bfqg,
5108 int ioprio_class, int ioprio)
5109{
5110 switch (ioprio_class) {
5111 case IOPRIO_CLASS_RT:
5112 return &bfqg->async_bfqq[0][ioprio];
5113 case IOPRIO_CLASS_NONE:
5114 ioprio = IOPRIO_NORM;
5115 fallthrough;
5116 case IOPRIO_CLASS_BE:
5117 return &bfqg->async_bfqq[1][ioprio];
5118 case IOPRIO_CLASS_IDLE:
5119 return &bfqg->async_idle_bfqq;
5120 default:
5121 return NULL;
5122 }
5123}
5124
5125static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5126 struct bio *bio, bool is_sync,
5127 struct bfq_io_cq *bic)
5128{
5129 const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
5130 const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5131 struct bfq_queue **async_bfqq = NULL;
5132 struct bfq_queue *bfqq;
5133 struct bfq_group *bfqg;
5134
5135 rcu_read_lock();
5136
5137 bfqg = bfq_find_set_group(bfqd, __bio_blkcg(bio));
5138 if (!bfqg) {
5139 bfqq = &bfqd->oom_bfqq;
5140 goto out;
5141 }
5142
5143 if (!is_sync) {
5144 async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
5145 ioprio);
5146 bfqq = *async_bfqq;
5147 if (bfqq)
5148 goto out;
5149 }
5150
5151 bfqq = kmem_cache_alloc_node(bfq_pool,
5152 GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
5153 bfqd->queue->node);
5154
5155 if (bfqq) {
5156 bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
5157 is_sync);
5158 bfq_init_entity(&bfqq->entity, bfqg);
5159 bfq_log_bfqq(bfqd, bfqq, "allocated");
5160 } else {
5161 bfqq = &bfqd->oom_bfqq;
5162 bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
5163 goto out;
5164 }
5165
5166 /*
5167 * Pin the queue now that it's allocated, scheduler exit will
5168 * prune it.
5169 */
5170 if (async_bfqq) {
5171 bfqq->ref++; /*
5172 * Extra group reference, w.r.t. sync
5173 * queue. This extra reference is removed
5174 * only if bfqq->bfqg disappears, to
5175 * guarantee that this queue is not freed
5176 * until its group goes away.
5177 */
5178 bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
5179 bfqq, bfqq->ref);
5180 *async_bfqq = bfqq;
5181 }
5182
5183out:
5184 bfqq->ref++; /* get a process reference to this queue */
5185 bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref);
5186 rcu_read_unlock();
5187 return bfqq;
5188}
5189
5190static void bfq_update_io_thinktime(struct bfq_data *bfqd,
5191 struct bfq_queue *bfqq)
5192{
5193 struct bfq_ttime *ttime = &bfqq->ttime;
5194 u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
5195
5196 elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
5197
5198 ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8;
5199 ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8);
5200 ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
5201 ttime->ttime_samples);
5202}
5203
5204static void
5205bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5206 struct request *rq)
5207{
5208 bfqq->seek_history <<= 1;
5209 bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq);
5210
5211 if (bfqq->wr_coeff > 1 &&
5212 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
5213 BFQQ_TOTALLY_SEEKY(bfqq))
5214 bfq_bfqq_end_wr(bfqq);
5215}
5216
5217static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
5218 struct bfq_queue *bfqq,
5219 struct bfq_io_cq *bic)
5220{
5221 bool has_short_ttime = true, state_changed;
5222
5223 /*
5224 * No need to update has_short_ttime if bfqq is async or in
5225 * idle io prio class, or if bfq_slice_idle is zero, because
5226 * no device idling is performed for bfqq in this case.
5227 */
5228 if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
5229 bfqd->bfq_slice_idle == 0)
5230 return;
5231
5232 /* Idle window just restored, statistics are meaningless. */
5233 if (time_is_after_eq_jiffies(bfqq->split_time +
5234 bfqd->bfq_wr_min_idle_time))
5235 return;
5236
5237 /* Think time is infinite if no process is linked to
5238 * bfqq. Otherwise check average think time to
5239 * decide whether to mark as has_short_ttime
5240 */
5241 if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
5242 (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
5243 bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle))
5244 has_short_ttime = false;
5245
5246 state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq);
5247
5248 if (has_short_ttime)
5249 bfq_mark_bfqq_has_short_ttime(bfqq);
5250 else
5251 bfq_clear_bfqq_has_short_ttime(bfqq);
5252
5253 /*
5254 * Until the base value for the total service time gets
5255 * finally computed for bfqq, the inject limit does depend on
5256 * the think-time state (short|long). In particular, the limit
5257 * is 0 or 1 if the think time is deemed, respectively, as
5258 * short or long (details in the comments in
5259 * bfq_update_inject_limit()). Accordingly, the next
5260 * instructions reset the inject limit if the think-time state
5261 * has changed and the above base value is still to be
5262 * computed.
5263 *
5264 * However, the reset is performed only if more than 100 ms
5265 * have elapsed since the last update of the inject limit, or
5266 * (inclusive) if the change is from short to long think
5267 * time. The reason for this waiting is as follows.
5268 *
5269 * bfqq may have a long think time because of a
5270 * synchronization with some other queue, i.e., because the
5271 * I/O of some other queue may need to be completed for bfqq
5272 * to receive new I/O. Details in the comments on the choice
5273 * of the queue for injection in bfq_select_queue().
5274 *
5275 * As stressed in those comments, if such a synchronization is
5276 * actually in place, then, without injection on bfqq, the
5277 * blocking I/O cannot happen to served while bfqq is in
5278 * service. As a consequence, if bfqq is granted
5279 * I/O-dispatch-plugging, then bfqq remains empty, and no I/O
5280 * is dispatched, until the idle timeout fires. This is likely
5281 * to result in lower bandwidth and higher latencies for bfqq,
5282 * and in a severe loss of total throughput.
5283 *
5284 * On the opposite end, a non-zero inject limit may allow the
5285 * I/O that blocks bfqq to be executed soon, and therefore
5286 * bfqq to receive new I/O soon.
5287 *
5288 * But, if the blocking gets actually eliminated, then the
5289 * next think-time sample for bfqq may be very low. This in
5290 * turn may cause bfqq's think time to be deemed
5291 * short. Without the 100 ms barrier, this new state change
5292 * would cause the body of the next if to be executed
5293 * immediately. But this would set to 0 the inject
5294 * limit. Without injection, the blocking I/O would cause the
5295 * think time of bfqq to become long again, and therefore the
5296 * inject limit to be raised again, and so on. The only effect
5297 * of such a steady oscillation between the two think-time
5298 * states would be to prevent effective injection on bfqq.
5299 *
5300 * In contrast, if the inject limit is not reset during such a
5301 * long time interval as 100 ms, then the number of short
5302 * think time samples can grow significantly before the reset
5303 * is performed. As a consequence, the think time state can
5304 * become stable before the reset. Therefore there will be no
5305 * state change when the 100 ms elapse, and no reset of the
5306 * inject limit. The inject limit remains steadily equal to 1
5307 * both during and after the 100 ms. So injection can be
5308 * performed at all times, and throughput gets boosted.
5309 *
5310 * An inject limit equal to 1 is however in conflict, in
5311 * general, with the fact that the think time of bfqq is
5312 * short, because injection may be likely to delay bfqq's I/O
5313 * (as explained in the comments in
5314 * bfq_update_inject_limit()). But this does not happen in
5315 * this special case, because bfqq's low think time is due to
5316 * an effective handling of a synchronization, through
5317 * injection. In this special case, bfqq's I/O does not get
5318 * delayed by injection; on the contrary, bfqq's I/O is
5319 * brought forward, because it is not blocked for
5320 * milliseconds.
5321 *
5322 * In addition, serving the blocking I/O much sooner, and much
5323 * more frequently than once per I/O-plugging timeout, makes
5324 * it much quicker to detect a waker queue (the concept of
5325 * waker queue is defined in the comments in
5326 * bfq_add_request()). This makes it possible to start sooner
5327 * to boost throughput more effectively, by injecting the I/O
5328 * of the waker queue unconditionally on every
5329 * bfq_dispatch_request().
5330 *
5331 * One last, important benefit of not resetting the inject
5332 * limit before 100 ms is that, during this time interval, the
5333 * base value for the total service time is likely to get
5334 * finally computed for bfqq, freeing the inject limit from
5335 * its relation with the think time.
5336 */
5337 if (state_changed && bfqq->last_serv_time_ns == 0 &&
5338 (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
5339 msecs_to_jiffies(100)) ||
5340 !has_short_ttime))
5341 bfq_reset_inject_limit(bfqd, bfqq);
5342}
5343
5344/*
5345 * Called when a new fs request (rq) is added to bfqq. Check if there's
5346 * something we should do about it.
5347 */
5348static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5349 struct request *rq)
5350{
5351 if (rq->cmd_flags & REQ_META)
5352 bfqq->meta_pending++;
5353
5354 bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
5355
5356 if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
5357 bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
5358 blk_rq_sectors(rq) < 32;
5359 bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
5360
5361 /*
5362 * There is just this request queued: if
5363 * - the request is small, and
5364 * - we are idling to boost throughput, and
5365 * - the queue is not to be expired,
5366 * then just exit.
5367 *
5368 * In this way, if the device is being idled to wait
5369 * for a new request from the in-service queue, we
5370 * avoid unplugging the device and committing the
5371 * device to serve just a small request. In contrast
5372 * we wait for the block layer to decide when to
5373 * unplug the device: hopefully, new requests will be
5374 * merged to this one quickly, then the device will be
5375 * unplugged and larger requests will be dispatched.
5376 */
5377 if (small_req && idling_boosts_thr_without_issues(bfqd, bfqq) &&
5378 !budget_timeout)
5379 return;
5380
5381 /*
5382 * A large enough request arrived, or idling is being
5383 * performed to preserve service guarantees, or
5384 * finally the queue is to be expired: in all these
5385 * cases disk idling is to be stopped, so clear
5386 * wait_request flag and reset timer.
5387 */
5388 bfq_clear_bfqq_wait_request(bfqq);
5389 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
5390
5391 /*
5392 * The queue is not empty, because a new request just
5393 * arrived. Hence we can safely expire the queue, in
5394 * case of budget timeout, without risking that the
5395 * timestamps of the queue are not updated correctly.
5396 * See [1] for more details.
5397 */
5398 if (budget_timeout)
5399 bfq_bfqq_expire(bfqd, bfqq, false,
5400 BFQQE_BUDGET_TIMEOUT);
5401 }
5402}
5403
5404/* returns true if it causes the idle timer to be disabled */
5405static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
5406{
5407 struct bfq_queue *bfqq = RQ_BFQQ(rq),
5408 *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true);
5409 bool waiting, idle_timer_disabled = false;
5410
5411 if (new_bfqq) {
5412 /*
5413 * Release the request's reference to the old bfqq
5414 * and make sure one is taken to the shared queue.
5415 */
5416 new_bfqq->allocated++;
5417 bfqq->allocated--;
5418 new_bfqq->ref++;
5419 /*
5420 * If the bic associated with the process
5421 * issuing this request still points to bfqq
5422 * (and thus has not been already redirected
5423 * to new_bfqq or even some other bfq_queue),
5424 * then complete the merge and redirect it to
5425 * new_bfqq.
5426 */
5427 if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
5428 bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
5429 bfqq, new_bfqq);
5430
5431 bfq_clear_bfqq_just_created(bfqq);
5432 /*
5433 * rq is about to be enqueued into new_bfqq,
5434 * release rq reference on bfqq
5435 */
5436 bfq_put_queue(bfqq);
5437 rq->elv.priv[1] = new_bfqq;
5438 bfqq = new_bfqq;
5439 }
5440
5441 bfq_update_io_thinktime(bfqd, bfqq);
5442 bfq_update_has_short_ttime(bfqd, bfqq, RQ_BIC(rq));
5443 bfq_update_io_seektime(bfqd, bfqq, rq);
5444
5445 waiting = bfqq && bfq_bfqq_wait_request(bfqq);
5446 bfq_add_request(rq);
5447 idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq);
5448
5449 rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
5450 list_add_tail(&rq->queuelist, &bfqq->fifo);
5451
5452 bfq_rq_enqueued(bfqd, bfqq, rq);
5453
5454 return idle_timer_disabled;
5455}
5456
5457#ifdef CONFIG_BFQ_CGROUP_DEBUG
5458static void bfq_update_insert_stats(struct request_queue *q,
5459 struct bfq_queue *bfqq,
5460 bool idle_timer_disabled,
5461 unsigned int cmd_flags)
5462{
5463 if (!bfqq)
5464 return;
5465
5466 /*
5467 * bfqq still exists, because it can disappear only after
5468 * either it is merged with another queue, or the process it
5469 * is associated with exits. But both actions must be taken by
5470 * the same process currently executing this flow of
5471 * instructions.
5472 *
5473 * In addition, the following queue lock guarantees that
5474 * bfqq_group(bfqq) exists as well.
5475 */
5476 spin_lock_irq(&q->queue_lock);
5477 bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags);
5478 if (idle_timer_disabled)
5479 bfqg_stats_update_idle_time(bfqq_group(bfqq));
5480 spin_unlock_irq(&q->queue_lock);
5481}
5482#else
5483static inline void bfq_update_insert_stats(struct request_queue *q,
5484 struct bfq_queue *bfqq,
5485 bool idle_timer_disabled,
5486 unsigned int cmd_flags) {}
5487#endif /* CONFIG_BFQ_CGROUP_DEBUG */
5488
5489static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
5490 bool at_head)
5491{
5492 struct request_queue *q = hctx->queue;
5493 struct bfq_data *bfqd = q->elevator->elevator_data;
5494 struct bfq_queue *bfqq;
5495 bool idle_timer_disabled = false;
5496 unsigned int cmd_flags;
5497
5498#ifdef CONFIG_BFQ_GROUP_IOSCHED
5499 if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio)
5500 bfqg_stats_update_legacy_io(q, rq);
5501#endif
5502 spin_lock_irq(&bfqd->lock);
5503 if (blk_mq_sched_try_insert_merge(q, rq)) {
5504 spin_unlock_irq(&bfqd->lock);
5505 return;
5506 }
5507
5508 spin_unlock_irq(&bfqd->lock);
5509
5510 blk_mq_sched_request_inserted(rq);
5511
5512 spin_lock_irq(&bfqd->lock);
5513 bfqq = bfq_init_rq(rq);
5514 if (!bfqq || at_head || blk_rq_is_passthrough(rq)) {
5515 if (at_head)
5516 list_add(&rq->queuelist, &bfqd->dispatch);
5517 else
5518 list_add_tail(&rq->queuelist, &bfqd->dispatch);
5519 } else {
5520 idle_timer_disabled = __bfq_insert_request(bfqd, rq);
5521 /*
5522 * Update bfqq, because, if a queue merge has occurred
5523 * in __bfq_insert_request, then rq has been
5524 * redirected into a new queue.
5525 */
5526 bfqq = RQ_BFQQ(rq);
5527
5528 if (rq_mergeable(rq)) {
5529 elv_rqhash_add(q, rq);
5530 if (!q->last_merge)
5531 q->last_merge = rq;
5532 }
5533 }
5534
5535 /*
5536 * Cache cmd_flags before releasing scheduler lock, because rq
5537 * may disappear afterwards (for example, because of a request
5538 * merge).
5539 */
5540 cmd_flags = rq->cmd_flags;
5541
5542 spin_unlock_irq(&bfqd->lock);
5543
5544 bfq_update_insert_stats(q, bfqq, idle_timer_disabled,
5545 cmd_flags);
5546}
5547
5548static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
5549 struct list_head *list, bool at_head)
5550{
5551 while (!list_empty(list)) {
5552 struct request *rq;
5553
5554 rq = list_first_entry(list, struct request, queuelist);
5555 list_del_init(&rq->queuelist);
5556 bfq_insert_request(hctx, rq, at_head);
5557 }
5558}
5559
5560static void bfq_update_hw_tag(struct bfq_data *bfqd)
5561{
5562 struct bfq_queue *bfqq = bfqd->in_service_queue;
5563
5564 bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
5565 bfqd->rq_in_driver);
5566
5567 if (bfqd->hw_tag == 1)
5568 return;
5569
5570 /*
5571 * This sample is valid if the number of outstanding requests
5572 * is large enough to allow a queueing behavior. Note that the
5573 * sum is not exact, as it's not taking into account deactivated
5574 * requests.
5575 */
5576 if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
5577 return;
5578
5579 /*
5580 * If active queue hasn't enough requests and can idle, bfq might not
5581 * dispatch sufficient requests to hardware. Don't zero hw_tag in this
5582 * case
5583 */
5584 if (bfqq && bfq_bfqq_has_short_ttime(bfqq) &&
5585 bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] <
5586 BFQ_HW_QUEUE_THRESHOLD &&
5587 bfqd->rq_in_driver < BFQ_HW_QUEUE_THRESHOLD)
5588 return;
5589
5590 if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
5591 return;
5592
5593 bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
5594 bfqd->max_rq_in_driver = 0;
5595 bfqd->hw_tag_samples = 0;
5596
5597 bfqd->nonrot_with_queueing =
5598 blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag;
5599}
5600
5601static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
5602{
5603 u64 now_ns;
5604 u32 delta_us;
5605
5606 bfq_update_hw_tag(bfqd);
5607
5608 bfqd->rq_in_driver--;
5609 bfqq->dispatched--;
5610
5611 if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
5612 /*
5613 * Set budget_timeout (which we overload to store the
5614 * time at which the queue remains with no backlog and
5615 * no outstanding request; used by the weight-raising
5616 * mechanism).
5617 */
5618 bfqq->budget_timeout = jiffies;
5619
5620 bfq_weights_tree_remove(bfqd, bfqq);
5621 }
5622
5623 now_ns = ktime_get_ns();
5624
5625 bfqq->ttime.last_end_request = now_ns;
5626
5627 /*
5628 * Using us instead of ns, to get a reasonable precision in
5629 * computing rate in next check.
5630 */
5631 delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
5632
5633 /*
5634 * If the request took rather long to complete, and, according
5635 * to the maximum request size recorded, this completion latency
5636 * implies that the request was certainly served at a very low
5637 * rate (less than 1M sectors/sec), then the whole observation
5638 * interval that lasts up to this time instant cannot be a
5639 * valid time interval for computing a new peak rate. Invoke
5640 * bfq_update_rate_reset to have the following three steps
5641 * taken:
5642 * - close the observation interval at the last (previous)
5643 * request dispatch or completion
5644 * - compute rate, if possible, for that observation interval
5645 * - reset to zero samples, which will trigger a proper
5646 * re-initialization of the observation interval on next
5647 * dispatch
5648 */
5649 if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
5650 (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
5651 1UL<<(BFQ_RATE_SHIFT - 10))
5652 bfq_update_rate_reset(bfqd, NULL);
5653 bfqd->last_completion = now_ns;
5654 bfqd->last_completed_rq_bfqq = bfqq;
5655
5656 /*
5657 * If we are waiting to discover whether the request pattern
5658 * of the task associated with the queue is actually
5659 * isochronous, and both requisites for this condition to hold
5660 * are now satisfied, then compute soft_rt_next_start (see the
5661 * comments on the function bfq_bfqq_softrt_next_start()). We
5662 * do not compute soft_rt_next_start if bfqq is in interactive
5663 * weight raising (see the comments in bfq_bfqq_expire() for
5664 * an explanation). We schedule this delayed update when bfqq
5665 * expires, if it still has in-flight requests.
5666 */
5667 if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
5668 RB_EMPTY_ROOT(&bfqq->sort_list) &&
5669 bfqq->wr_coeff != bfqd->bfq_wr_coeff)
5670 bfqq->soft_rt_next_start =
5671 bfq_bfqq_softrt_next_start(bfqd, bfqq);
5672
5673 /*
5674 * If this is the in-service queue, check if it needs to be expired,
5675 * or if we want to idle in case it has no pending requests.
5676 */
5677 if (bfqd->in_service_queue == bfqq) {
5678 if (bfq_bfqq_must_idle(bfqq)) {
5679 if (bfqq->dispatched == 0)
5680 bfq_arm_slice_timer(bfqd);
5681 /*
5682 * If we get here, we do not expire bfqq, even
5683 * if bfqq was in budget timeout or had no
5684 * more requests (as controlled in the next
5685 * conditional instructions). The reason for
5686 * not expiring bfqq is as follows.
5687 *
5688 * Here bfqq->dispatched > 0 holds, but
5689 * bfq_bfqq_must_idle() returned true. This
5690 * implies that, even if no request arrives
5691 * for bfqq before bfqq->dispatched reaches 0,
5692 * bfqq will, however, not be expired on the
5693 * completion event that causes bfqq->dispatch
5694 * to reach zero. In contrast, on this event,
5695 * bfqq will start enjoying device idling
5696 * (I/O-dispatch plugging).
5697 *
5698 * But, if we expired bfqq here, bfqq would
5699 * not have the chance to enjoy device idling
5700 * when bfqq->dispatched finally reaches
5701 * zero. This would expose bfqq to violation
5702 * of its reserved service guarantees.
5703 */
5704 return;
5705 } else if (bfq_may_expire_for_budg_timeout(bfqq))
5706 bfq_bfqq_expire(bfqd, bfqq, false,
5707 BFQQE_BUDGET_TIMEOUT);
5708 else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
5709 (bfqq->dispatched == 0 ||
5710 !bfq_better_to_idle(bfqq)))
5711 bfq_bfqq_expire(bfqd, bfqq, false,
5712 BFQQE_NO_MORE_REQUESTS);
5713 }
5714
5715 if (!bfqd->rq_in_driver)
5716 bfq_schedule_dispatch(bfqd);
5717}
5718
5719static void bfq_finish_requeue_request_body(struct bfq_queue *bfqq)
5720{
5721 bfqq->allocated--;
5722
5723 bfq_put_queue(bfqq);
5724}
5725
5726/*
5727 * The processes associated with bfqq may happen to generate their
5728 * cumulative I/O at a lower rate than the rate at which the device
5729 * could serve the same I/O. This is rather probable, e.g., if only
5730 * one process is associated with bfqq and the device is an SSD. It
5731 * results in bfqq becoming often empty while in service. In this
5732 * respect, if BFQ is allowed to switch to another queue when bfqq
5733 * remains empty, then the device goes on being fed with I/O requests,
5734 * and the throughput is not affected. In contrast, if BFQ is not
5735 * allowed to switch to another queue---because bfqq is sync and
5736 * I/O-dispatch needs to be plugged while bfqq is temporarily
5737 * empty---then, during the service of bfqq, there will be frequent
5738 * "service holes", i.e., time intervals during which bfqq gets empty
5739 * and the device can only consume the I/O already queued in its
5740 * hardware queues. During service holes, the device may even get to
5741 * remaining idle. In the end, during the service of bfqq, the device
5742 * is driven at a lower speed than the one it can reach with the kind
5743 * of I/O flowing through bfqq.
5744 *
5745 * To counter this loss of throughput, BFQ implements a "request
5746 * injection mechanism", which tries to fill the above service holes
5747 * with I/O requests taken from other queues. The hard part in this
5748 * mechanism is finding the right amount of I/O to inject, so as to
5749 * both boost throughput and not break bfqq's bandwidth and latency
5750 * guarantees. In this respect, the mechanism maintains a per-queue
5751 * inject limit, computed as below. While bfqq is empty, the injection
5752 * mechanism dispatches extra I/O requests only until the total number
5753 * of I/O requests in flight---i.e., already dispatched but not yet
5754 * completed---remains lower than this limit.
5755 *
5756 * A first definition comes in handy to introduce the algorithm by
5757 * which the inject limit is computed. We define as first request for
5758 * bfqq, an I/O request for bfqq that arrives while bfqq is in
5759 * service, and causes bfqq to switch from empty to non-empty. The
5760 * algorithm updates the limit as a function of the effect of
5761 * injection on the service times of only the first requests of
5762 * bfqq. The reason for this restriction is that these are the
5763 * requests whose service time is affected most, because they are the
5764 * first to arrive after injection possibly occurred.
5765 *
5766 * To evaluate the effect of injection, the algorithm measures the
5767 * "total service time" of first requests. We define as total service
5768 * time of an I/O request, the time that elapses since when the
5769 * request is enqueued into bfqq, to when it is completed. This
5770 * quantity allows the whole effect of injection to be measured. It is
5771 * easy to see why. Suppose that some requests of other queues are
5772 * actually injected while bfqq is empty, and that a new request R
5773 * then arrives for bfqq. If the device does start to serve all or
5774 * part of the injected requests during the service hole, then,
5775 * because of this extra service, it may delay the next invocation of
5776 * the dispatch hook of BFQ. Then, even after R gets eventually
5777 * dispatched, the device may delay the actual service of R if it is
5778 * still busy serving the extra requests, or if it decides to serve,
5779 * before R, some extra request still present in its queues. As a
5780 * conclusion, the cumulative extra delay caused by injection can be
5781 * easily evaluated by just comparing the total service time of first
5782 * requests with and without injection.
5783 *
5784 * The limit-update algorithm works as follows. On the arrival of a
5785 * first request of bfqq, the algorithm measures the total time of the
5786 * request only if one of the three cases below holds, and, for each
5787 * case, it updates the limit as described below:
5788 *
5789 * (1) If there is no in-flight request. This gives a baseline for the
5790 * total service time of the requests of bfqq. If the baseline has
5791 * not been computed yet, then, after computing it, the limit is
5792 * set to 1, to start boosting throughput, and to prepare the
5793 * ground for the next case. If the baseline has already been
5794 * computed, then it is updated, in case it results to be lower
5795 * than the previous value.
5796 *
5797 * (2) If the limit is higher than 0 and there are in-flight
5798 * requests. By comparing the total service time in this case with
5799 * the above baseline, it is possible to know at which extent the
5800 * current value of the limit is inflating the total service
5801 * time. If the inflation is below a certain threshold, then bfqq
5802 * is assumed to be suffering from no perceivable loss of its
5803 * service guarantees, and the limit is even tentatively
5804 * increased. If the inflation is above the threshold, then the
5805 * limit is decreased. Due to the lack of any hysteresis, this
5806 * logic makes the limit oscillate even in steady workload
5807 * conditions. Yet we opted for it, because it is fast in reaching
5808 * the best value for the limit, as a function of the current I/O
5809 * workload. To reduce oscillations, this step is disabled for a
5810 * short time interval after the limit happens to be decreased.
5811 *
5812 * (3) Periodically, after resetting the limit, to make sure that the
5813 * limit eventually drops in case the workload changes. This is
5814 * needed because, after the limit has gone safely up for a
5815 * certain workload, it is impossible to guess whether the
5816 * baseline total service time may have changed, without measuring
5817 * it again without injection. A more effective version of this
5818 * step might be to just sample the baseline, by interrupting
5819 * injection only once, and then to reset/lower the limit only if
5820 * the total service time with the current limit does happen to be
5821 * too large.
5822 *
5823 * More details on each step are provided in the comments on the
5824 * pieces of code that implement these steps: the branch handling the
5825 * transition from empty to non empty in bfq_add_request(), the branch
5826 * handling injection in bfq_select_queue(), and the function
5827 * bfq_choose_bfqq_for_injection(). These comments also explain some
5828 * exceptions, made by the injection mechanism in some special cases.
5829 */
5830static void bfq_update_inject_limit(struct bfq_data *bfqd,
5831 struct bfq_queue *bfqq)
5832{
5833 u64 tot_time_ns = ktime_get_ns() - bfqd->last_empty_occupied_ns;
5834 unsigned int old_limit = bfqq->inject_limit;
5835
5836 if (bfqq->last_serv_time_ns > 0 && bfqd->rqs_injected) {
5837 u64 threshold = (bfqq->last_serv_time_ns * 3)>>1;
5838
5839 if (tot_time_ns >= threshold && old_limit > 0) {
5840 bfqq->inject_limit--;
5841 bfqq->decrease_time_jif = jiffies;
5842 } else if (tot_time_ns < threshold &&
5843 old_limit <= bfqd->max_rq_in_driver)
5844 bfqq->inject_limit++;
5845 }
5846
5847 /*
5848 * Either we still have to compute the base value for the
5849 * total service time, and there seem to be the right
5850 * conditions to do it, or we can lower the last base value
5851 * computed.
5852 *
5853 * NOTE: (bfqd->rq_in_driver == 1) means that there is no I/O
5854 * request in flight, because this function is in the code
5855 * path that handles the completion of a request of bfqq, and,
5856 * in particular, this function is executed before
5857 * bfqd->rq_in_driver is decremented in such a code path.
5858 */
5859 if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 1) ||
5860 tot_time_ns < bfqq->last_serv_time_ns) {
5861 if (bfqq->last_serv_time_ns == 0) {
5862 /*
5863 * Now we certainly have a base value: make sure we
5864 * start trying injection.
5865 */
5866 bfqq->inject_limit = max_t(unsigned int, 1, old_limit);
5867 }
5868 bfqq->last_serv_time_ns = tot_time_ns;
5869 } else if (!bfqd->rqs_injected && bfqd->rq_in_driver == 1)
5870 /*
5871 * No I/O injected and no request still in service in
5872 * the drive: these are the exact conditions for
5873 * computing the base value of the total service time
5874 * for bfqq. So let's update this value, because it is
5875 * rather variable. For example, it varies if the size
5876 * or the spatial locality of the I/O requests in bfqq
5877 * change.
5878 */
5879 bfqq->last_serv_time_ns = tot_time_ns;
5880
5881
5882 /* update complete, not waiting for any request completion any longer */
5883 bfqd->waited_rq = NULL;
5884 bfqd->rqs_injected = false;
5885}
5886
5887/*
5888 * Handle either a requeue or a finish for rq. The things to do are
5889 * the same in both cases: all references to rq are to be dropped. In
5890 * particular, rq is considered completed from the point of view of
5891 * the scheduler.
5892 */
5893static void bfq_finish_requeue_request(struct request *rq)
5894{
5895 struct bfq_queue *bfqq = RQ_BFQQ(rq);
5896 struct bfq_data *bfqd;
5897
5898 /*
5899 * rq either is not associated with any icq, or is an already
5900 * requeued request that has not (yet) been re-inserted into
5901 * a bfq_queue.
5902 */
5903 if (!rq->elv.icq || !bfqq)
5904 return;
5905
5906 bfqd = bfqq->bfqd;
5907
5908 if (rq->rq_flags & RQF_STARTED)
5909 bfqg_stats_update_completion(bfqq_group(bfqq),
5910 rq->start_time_ns,
5911 rq->io_start_time_ns,
5912 rq->cmd_flags);
5913
5914 if (likely(rq->rq_flags & RQF_STARTED)) {
5915 unsigned long flags;
5916
5917 spin_lock_irqsave(&bfqd->lock, flags);
5918
5919 if (rq == bfqd->waited_rq)
5920 bfq_update_inject_limit(bfqd, bfqq);
5921
5922 bfq_completed_request(bfqq, bfqd);
5923 bfq_finish_requeue_request_body(bfqq);
5924
5925 spin_unlock_irqrestore(&bfqd->lock, flags);
5926 } else {
5927 /*
5928 * Request rq may be still/already in the scheduler,
5929 * in which case we need to remove it (this should
5930 * never happen in case of requeue). And we cannot
5931 * defer such a check and removal, to avoid
5932 * inconsistencies in the time interval from the end
5933 * of this function to the start of the deferred work.
5934 * This situation seems to occur only in process
5935 * context, as a consequence of a merge. In the
5936 * current version of the code, this implies that the
5937 * lock is held.
5938 */
5939
5940 if (!RB_EMPTY_NODE(&rq->rb_node)) {
5941 bfq_remove_request(rq->q, rq);
5942 bfqg_stats_update_io_remove(bfqq_group(bfqq),
5943 rq->cmd_flags);
5944 }
5945 bfq_finish_requeue_request_body(bfqq);
5946 }
5947
5948 /*
5949 * Reset private fields. In case of a requeue, this allows
5950 * this function to correctly do nothing if it is spuriously
5951 * invoked again on this same request (see the check at the
5952 * beginning of the function). Probably, a better general
5953 * design would be to prevent blk-mq from invoking the requeue
5954 * or finish hooks of an elevator, for a request that is not
5955 * referred by that elevator.
5956 *
5957 * Resetting the following fields would break the
5958 * request-insertion logic if rq is re-inserted into a bfq
5959 * internal queue, without a re-preparation. Here we assume
5960 * that re-insertions of requeued requests, without
5961 * re-preparation, can happen only for pass_through or at_head
5962 * requests (which are not re-inserted into bfq internal
5963 * queues).
5964 */
5965 rq->elv.priv[0] = NULL;
5966 rq->elv.priv[1] = NULL;
5967}
5968
5969/*
5970 * Removes the association between the current task and bfqq, assuming
5971 * that bic points to the bfq iocontext of the task.
5972 * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
5973 * was the last process referring to that bfqq.
5974 */
5975static struct bfq_queue *
5976bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
5977{
5978 bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
5979
5980 if (bfqq_process_refs(bfqq) == 1) {
5981 bfqq->pid = current->pid;
5982 bfq_clear_bfqq_coop(bfqq);
5983 bfq_clear_bfqq_split_coop(bfqq);
5984 return bfqq;
5985 }
5986
5987 bic_set_bfqq(bic, NULL, 1);
5988
5989 bfq_put_cooperator(bfqq);
5990
5991 bfq_release_process_ref(bfqq->bfqd, bfqq);
5992 return NULL;
5993}
5994
5995static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
5996 struct bfq_io_cq *bic,
5997 struct bio *bio,
5998 bool split, bool is_sync,
5999 bool *new_queue)
6000{
6001 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
6002
6003 if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
6004 return bfqq;
6005
6006 if (new_queue)
6007 *new_queue = true;
6008
6009 if (bfqq)
6010 bfq_put_queue(bfqq);
6011 bfqq = bfq_get_queue(bfqd, bio, is_sync, bic);
6012
6013 bic_set_bfqq(bic, bfqq, is_sync);
6014 if (split && is_sync) {
6015 if ((bic->was_in_burst_list && bfqd->large_burst) ||
6016 bic->saved_in_large_burst)
6017 bfq_mark_bfqq_in_large_burst(bfqq);
6018 else {
6019 bfq_clear_bfqq_in_large_burst(bfqq);
6020 if (bic->was_in_burst_list)
6021 /*
6022 * If bfqq was in the current
6023 * burst list before being
6024 * merged, then we have to add
6025 * it back. And we do not need
6026 * to increase burst_size, as
6027 * we did not decrement
6028 * burst_size when we removed
6029 * bfqq from the burst list as
6030 * a consequence of a merge
6031 * (see comments in
6032 * bfq_put_queue). In this
6033 * respect, it would be rather
6034 * costly to know whether the
6035 * current burst list is still
6036 * the same burst list from
6037 * which bfqq was removed on
6038 * the merge. To avoid this
6039 * cost, if bfqq was in a
6040 * burst list, then we add
6041 * bfqq to the current burst
6042 * list without any further
6043 * check. This can cause
6044 * inappropriate insertions,
6045 * but rarely enough to not
6046 * harm the detection of large
6047 * bursts significantly.
6048 */
6049 hlist_add_head(&bfqq->burst_list_node,
6050 &bfqd->burst_list);
6051 }
6052 bfqq->split_time = jiffies;
6053 }
6054
6055 return bfqq;
6056}
6057
6058/*
6059 * Only reset private fields. The actual request preparation will be
6060 * performed by bfq_init_rq, when rq is either inserted or merged. See
6061 * comments on bfq_init_rq for the reason behind this delayed
6062 * preparation.
6063 */
6064static void bfq_prepare_request(struct request *rq)
6065{
6066 /*
6067 * Regardless of whether we have an icq attached, we have to
6068 * clear the scheduler pointers, as they might point to
6069 * previously allocated bic/bfqq structs.
6070 */
6071 rq->elv.priv[0] = rq->elv.priv[1] = NULL;
6072}
6073
6074/*
6075 * If needed, init rq, allocate bfq data structures associated with
6076 * rq, and increment reference counters in the destination bfq_queue
6077 * for rq. Return the destination bfq_queue for rq, or NULL is rq is
6078 * not associated with any bfq_queue.
6079 *
6080 * This function is invoked by the functions that perform rq insertion
6081 * or merging. One may have expected the above preparation operations
6082 * to be performed in bfq_prepare_request, and not delayed to when rq
6083 * is inserted or merged. The rationale behind this delayed
6084 * preparation is that, after the prepare_request hook is invoked for
6085 * rq, rq may still be transformed into a request with no icq, i.e., a
6086 * request not associated with any queue. No bfq hook is invoked to
6087 * signal this transformation. As a consequence, should these
6088 * preparation operations be performed when the prepare_request hook
6089 * is invoked, and should rq be transformed one moment later, bfq
6090 * would end up in an inconsistent state, because it would have
6091 * incremented some queue counters for an rq destined to
6092 * transformation, without any chance to correctly lower these
6093 * counters back. In contrast, no transformation can still happen for
6094 * rq after rq has been inserted or merged. So, it is safe to execute
6095 * these preparation operations when rq is finally inserted or merged.
6096 */
6097static struct bfq_queue *bfq_init_rq(struct request *rq)
6098{
6099 struct request_queue *q = rq->q;
6100 struct bio *bio = rq->bio;
6101 struct bfq_data *bfqd = q->elevator->elevator_data;
6102 struct bfq_io_cq *bic;
6103 const int is_sync = rq_is_sync(rq);
6104 struct bfq_queue *bfqq;
6105 bool new_queue = false;
6106 bool bfqq_already_existing = false, split = false;
6107
6108 if (unlikely(!rq->elv.icq))
6109 return NULL;
6110
6111 /*
6112 * Assuming that elv.priv[1] is set only if everything is set
6113 * for this rq. This holds true, because this function is
6114 * invoked only for insertion or merging, and, after such
6115 * events, a request cannot be manipulated any longer before
6116 * being removed from bfq.
6117 */
6118 if (rq->elv.priv[1])
6119 return rq->elv.priv[1];
6120
6121 bic = icq_to_bic(rq->elv.icq);
6122
6123 bfq_check_ioprio_change(bic, bio);
6124
6125 bfq_bic_update_cgroup(bic, bio);
6126
6127 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
6128 &new_queue);
6129
6130 if (likely(!new_queue)) {
6131 /* If the queue was seeky for too long, break it apart. */
6132 if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) {
6133 bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq");
6134
6135 /* Update bic before losing reference to bfqq */
6136 if (bfq_bfqq_in_large_burst(bfqq))
6137 bic->saved_in_large_burst = true;
6138
6139 bfqq = bfq_split_bfqq(bic, bfqq);
6140 split = true;
6141
6142 if (!bfqq)
6143 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
6144 true, is_sync,
6145 NULL);
6146 else
6147 bfqq_already_existing = true;
6148 }
6149 }
6150
6151 bfqq->allocated++;
6152 bfqq->ref++;
6153 bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
6154 rq, bfqq, bfqq->ref);
6155
6156 rq->elv.priv[0] = bic;
6157 rq->elv.priv[1] = bfqq;
6158
6159 /*
6160 * If a bfq_queue has only one process reference, it is owned
6161 * by only this bic: we can then set bfqq->bic = bic. in
6162 * addition, if the queue has also just been split, we have to
6163 * resume its state.
6164 */
6165 if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
6166 bfqq->bic = bic;
6167 if (split) {
6168 /*
6169 * The queue has just been split from a shared
6170 * queue: restore the idle window and the
6171 * possible weight raising period.
6172 */
6173 bfq_bfqq_resume_state(bfqq, bfqd, bic,
6174 bfqq_already_existing);
6175 }
6176 }
6177
6178 /*
6179 * Consider bfqq as possibly belonging to a burst of newly
6180 * created queues only if:
6181 * 1) A burst is actually happening (bfqd->burst_size > 0)
6182 * or
6183 * 2) There is no other active queue. In fact, if, in
6184 * contrast, there are active queues not belonging to the
6185 * possible burst bfqq may belong to, then there is no gain
6186 * in considering bfqq as belonging to a burst, and
6187 * therefore in not weight-raising bfqq. See comments on
6188 * bfq_handle_burst().
6189 *
6190 * This filtering also helps eliminating false positives,
6191 * occurring when bfqq does not belong to an actual large
6192 * burst, but some background task (e.g., a service) happens
6193 * to trigger the creation of new queues very close to when
6194 * bfqq and its possible companion queues are created. See
6195 * comments on bfq_handle_burst() for further details also on
6196 * this issue.
6197 */
6198 if (unlikely(bfq_bfqq_just_created(bfqq) &&
6199 (bfqd->burst_size > 0 ||
6200 bfq_tot_busy_queues(bfqd) == 0)))
6201 bfq_handle_burst(bfqd, bfqq);
6202
6203 return bfqq;
6204}
6205
6206static void
6207bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq)
6208{
6209 enum bfqq_expiration reason;
6210 unsigned long flags;
6211
6212 spin_lock_irqsave(&bfqd->lock, flags);
6213
6214 /*
6215 * Considering that bfqq may be in race, we should firstly check
6216 * whether bfqq is in service before doing something on it. If
6217 * the bfqq in race is not in service, it has already been expired
6218 * through __bfq_bfqq_expire func and its wait_request flags has
6219 * been cleared in __bfq_bfqd_reset_in_service func.
6220 */
6221 if (bfqq != bfqd->in_service_queue) {
6222 spin_unlock_irqrestore(&bfqd->lock, flags);
6223 return;
6224 }
6225
6226 bfq_clear_bfqq_wait_request(bfqq);
6227
6228 if (bfq_bfqq_budget_timeout(bfqq))
6229 /*
6230 * Also here the queue can be safely expired
6231 * for budget timeout without wasting
6232 * guarantees
6233 */
6234 reason = BFQQE_BUDGET_TIMEOUT;
6235 else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
6236 /*
6237 * The queue may not be empty upon timer expiration,
6238 * because we may not disable the timer when the
6239 * first request of the in-service queue arrives
6240 * during disk idling.
6241 */
6242 reason = BFQQE_TOO_IDLE;
6243 else
6244 goto schedule_dispatch;
6245
6246 bfq_bfqq_expire(bfqd, bfqq, true, reason);
6247
6248schedule_dispatch:
6249 spin_unlock_irqrestore(&bfqd->lock, flags);
6250 bfq_schedule_dispatch(bfqd);
6251}
6252
6253/*
6254 * Handler of the expiration of the timer running if the in-service queue
6255 * is idling inside its time slice.
6256 */
6257static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
6258{
6259 struct bfq_data *bfqd = container_of(timer, struct bfq_data,
6260 idle_slice_timer);
6261 struct bfq_queue *bfqq = bfqd->in_service_queue;
6262
6263 /*
6264 * Theoretical race here: the in-service queue can be NULL or
6265 * different from the queue that was idling if a new request
6266 * arrives for the current queue and there is a full dispatch
6267 * cycle that changes the in-service queue. This can hardly
6268 * happen, but in the worst case we just expire a queue too
6269 * early.
6270 */
6271 if (bfqq)
6272 bfq_idle_slice_timer_body(bfqd, bfqq);
6273
6274 return HRTIMER_NORESTART;
6275}
6276
6277static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
6278 struct bfq_queue **bfqq_ptr)
6279{
6280 struct bfq_queue *bfqq = *bfqq_ptr;
6281
6282 bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
6283 if (bfqq) {
6284 bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
6285
6286 bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
6287 bfqq, bfqq->ref);
6288 bfq_put_queue(bfqq);
6289 *bfqq_ptr = NULL;
6290 }
6291}
6292
6293/*
6294 * Release all the bfqg references to its async queues. If we are
6295 * deallocating the group these queues may still contain requests, so
6296 * we reparent them to the root cgroup (i.e., the only one that will
6297 * exist for sure until all the requests on a device are gone).
6298 */
6299void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
6300{
6301 int i, j;
6302
6303 for (i = 0; i < 2; i++)
6304 for (j = 0; j < IOPRIO_BE_NR; j++)
6305 __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
6306
6307 __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
6308}
6309
6310/*
6311 * See the comments on bfq_limit_depth for the purpose of
6312 * the depths set in the function. Return minimum shallow depth we'll use.
6313 */
6314static unsigned int bfq_update_depths(struct bfq_data *bfqd,
6315 struct sbitmap_queue *bt)
6316{
6317 unsigned int i, j, min_shallow = UINT_MAX;
6318
6319 /*
6320 * In-word depths if no bfq_queue is being weight-raised:
6321 * leaving 25% of tags only for sync reads.
6322 *
6323 * In next formulas, right-shift the value
6324 * (1U<<bt->sb.shift), instead of computing directly
6325 * (1U<<(bt->sb.shift - something)), to be robust against
6326 * any possible value of bt->sb.shift, without having to
6327 * limit 'something'.
6328 */
6329 /* no more than 50% of tags for async I/O */
6330 bfqd->word_depths[0][0] = max((1U << bt->sb.shift) >> 1, 1U);
6331 /*
6332 * no more than 75% of tags for sync writes (25% extra tags
6333 * w.r.t. async I/O, to prevent async I/O from starving sync
6334 * writes)
6335 */
6336 bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 3) >> 2, 1U);
6337
6338 /*
6339 * In-word depths in case some bfq_queue is being weight-
6340 * raised: leaving ~63% of tags for sync reads. This is the
6341 * highest percentage for which, in our tests, application
6342 * start-up times didn't suffer from any regression due to tag
6343 * shortage.
6344 */
6345 /* no more than ~18% of tags for async I/O */
6346 bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U);
6347 /* no more than ~37% of tags for sync writes (~20% extra tags) */
6348 bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U);
6349
6350 for (i = 0; i < 2; i++)
6351 for (j = 0; j < 2; j++)
6352 min_shallow = min(min_shallow, bfqd->word_depths[i][j]);
6353
6354 return min_shallow;
6355}
6356
6357static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx)
6358{
6359 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
6360 struct blk_mq_tags *tags = hctx->sched_tags;
6361 unsigned int min_shallow;
6362
6363 min_shallow = bfq_update_depths(bfqd, &tags->bitmap_tags);
6364 sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, min_shallow);
6365}
6366
6367static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
6368{
6369 bfq_depth_updated(hctx);
6370 return 0;
6371}
6372
6373static void bfq_exit_queue(struct elevator_queue *e)
6374{
6375 struct bfq_data *bfqd = e->elevator_data;
6376 struct bfq_queue *bfqq, *n;
6377
6378 hrtimer_cancel(&bfqd->idle_slice_timer);
6379
6380 spin_lock_irq(&bfqd->lock);
6381 list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
6382 bfq_deactivate_bfqq(bfqd, bfqq, false, false);
6383 spin_unlock_irq(&bfqd->lock);
6384
6385 hrtimer_cancel(&bfqd->idle_slice_timer);
6386
6387 /* release oom-queue reference to root group */
6388 bfqg_and_blkg_put(bfqd->root_group);
6389
6390#ifdef CONFIG_BFQ_GROUP_IOSCHED
6391 blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
6392#else
6393 spin_lock_irq(&bfqd->lock);
6394 bfq_put_async_queues(bfqd, bfqd->root_group);
6395 kfree(bfqd->root_group);
6396 spin_unlock_irq(&bfqd->lock);
6397#endif
6398
6399 kfree(bfqd);
6400}
6401
6402static void bfq_init_root_group(struct bfq_group *root_group,
6403 struct bfq_data *bfqd)
6404{
6405 int i;
6406
6407#ifdef CONFIG_BFQ_GROUP_IOSCHED
6408 root_group->entity.parent = NULL;
6409 root_group->my_entity = NULL;
6410 root_group->bfqd = bfqd;
6411#endif
6412 root_group->rq_pos_tree = RB_ROOT;
6413 for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
6414 root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
6415 root_group->sched_data.bfq_class_idle_last_service = jiffies;
6416}
6417
6418static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
6419{
6420 struct bfq_data *bfqd;
6421 struct elevator_queue *eq;
6422
6423 eq = elevator_alloc(q, e);
6424 if (!eq)
6425 return -ENOMEM;
6426
6427 bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
6428 if (!bfqd) {
6429 kobject_put(&eq->kobj);
6430 return -ENOMEM;
6431 }
6432 eq->elevator_data = bfqd;
6433
6434 spin_lock_irq(&q->queue_lock);
6435 q->elevator = eq;
6436 spin_unlock_irq(&q->queue_lock);
6437
6438 /*
6439 * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
6440 * Grab a permanent reference to it, so that the normal code flow
6441 * will not attempt to free it.
6442 */
6443 bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
6444 bfqd->oom_bfqq.ref++;
6445 bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
6446 bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
6447 bfqd->oom_bfqq.entity.new_weight =
6448 bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
6449
6450 /* oom_bfqq does not participate to bursts */
6451 bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
6452
6453 /*
6454 * Trigger weight initialization, according to ioprio, at the
6455 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
6456 * class won't be changed any more.
6457 */
6458 bfqd->oom_bfqq.entity.prio_changed = 1;
6459
6460 bfqd->queue = q;
6461
6462 INIT_LIST_HEAD(&bfqd->dispatch);
6463
6464 hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
6465 HRTIMER_MODE_REL);
6466 bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
6467
6468 bfqd->queue_weights_tree = RB_ROOT_CACHED;
6469 bfqd->num_groups_with_pending_reqs = 0;
6470
6471 INIT_LIST_HEAD(&bfqd->active_list);
6472 INIT_LIST_HEAD(&bfqd->idle_list);
6473 INIT_HLIST_HEAD(&bfqd->burst_list);
6474
6475 bfqd->hw_tag = -1;
6476 bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue);
6477
6478 bfqd->bfq_max_budget = bfq_default_max_budget;
6479
6480 bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
6481 bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
6482 bfqd->bfq_back_max = bfq_back_max;
6483 bfqd->bfq_back_penalty = bfq_back_penalty;
6484 bfqd->bfq_slice_idle = bfq_slice_idle;
6485 bfqd->bfq_timeout = bfq_timeout;
6486
6487 bfqd->bfq_requests_within_timer = 120;
6488
6489 bfqd->bfq_large_burst_thresh = 8;
6490 bfqd->bfq_burst_interval = msecs_to_jiffies(180);
6491
6492 bfqd->low_latency = true;
6493
6494 /*
6495 * Trade-off between responsiveness and fairness.
6496 */
6497 bfqd->bfq_wr_coeff = 30;
6498 bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
6499 bfqd->bfq_wr_max_time = 0;
6500 bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
6501 bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
6502 bfqd->bfq_wr_max_softrt_rate = 7000; /*
6503 * Approximate rate required
6504 * to playback or record a
6505 * high-definition compressed
6506 * video.
6507 */
6508 bfqd->wr_busy_queues = 0;
6509
6510 /*
6511 * Begin by assuming, optimistically, that the device peak
6512 * rate is equal to 2/3 of the highest reference rate.
6513 */
6514 bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] *
6515 ref_wr_duration[blk_queue_nonrot(bfqd->queue)];
6516 bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
6517
6518 spin_lock_init(&bfqd->lock);
6519
6520 /*
6521 * The invocation of the next bfq_create_group_hierarchy
6522 * function is the head of a chain of function calls
6523 * (bfq_create_group_hierarchy->blkcg_activate_policy->
6524 * blk_mq_freeze_queue) that may lead to the invocation of the
6525 * has_work hook function. For this reason,
6526 * bfq_create_group_hierarchy is invoked only after all
6527 * scheduler data has been initialized, apart from the fields
6528 * that can be initialized only after invoking
6529 * bfq_create_group_hierarchy. This, in particular, enables
6530 * has_work to correctly return false. Of course, to avoid
6531 * other inconsistencies, the blk-mq stack must then refrain
6532 * from invoking further scheduler hooks before this init
6533 * function is finished.
6534 */
6535 bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
6536 if (!bfqd->root_group)
6537 goto out_free;
6538 bfq_init_root_group(bfqd->root_group, bfqd);
6539 bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
6540
6541 wbt_disable_default(q);
6542 return 0;
6543
6544out_free:
6545 kfree(bfqd);
6546 kobject_put(&eq->kobj);
6547 return -ENOMEM;
6548}
6549
6550static void bfq_slab_kill(void)
6551{
6552 kmem_cache_destroy(bfq_pool);
6553}
6554
6555static int __init bfq_slab_setup(void)
6556{
6557 bfq_pool = KMEM_CACHE(bfq_queue, 0);
6558 if (!bfq_pool)
6559 return -ENOMEM;
6560 return 0;
6561}
6562
6563static ssize_t bfq_var_show(unsigned int var, char *page)
6564{
6565 return sprintf(page, "%u\n", var);
6566}
6567
6568static int bfq_var_store(unsigned long *var, const char *page)
6569{
6570 unsigned long new_val;
6571 int ret = kstrtoul(page, 10, &new_val);
6572
6573 if (ret)
6574 return ret;
6575 *var = new_val;
6576 return 0;
6577}
6578
6579#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
6580static ssize_t __FUNC(struct elevator_queue *e, char *page) \
6581{ \
6582 struct bfq_data *bfqd = e->elevator_data; \
6583 u64 __data = __VAR; \
6584 if (__CONV == 1) \
6585 __data = jiffies_to_msecs(__data); \
6586 else if (__CONV == 2) \
6587 __data = div_u64(__data, NSEC_PER_MSEC); \
6588 return bfq_var_show(__data, (page)); \
6589}
6590SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
6591SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
6592SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
6593SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
6594SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
6595SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
6596SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
6597SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
6598SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
6599#undef SHOW_FUNCTION
6600
6601#define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
6602static ssize_t __FUNC(struct elevator_queue *e, char *page) \
6603{ \
6604 struct bfq_data *bfqd = e->elevator_data; \
6605 u64 __data = __VAR; \
6606 __data = div_u64(__data, NSEC_PER_USEC); \
6607 return bfq_var_show(__data, (page)); \
6608}
6609USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
6610#undef USEC_SHOW_FUNCTION
6611
6612#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
6613static ssize_t \
6614__FUNC(struct elevator_queue *e, const char *page, size_t count) \
6615{ \
6616 struct bfq_data *bfqd = e->elevator_data; \
6617 unsigned long __data, __min = (MIN), __max = (MAX); \
6618 int ret; \
6619 \
6620 ret = bfq_var_store(&__data, (page)); \
6621 if (ret) \
6622 return ret; \
6623 if (__data < __min) \
6624 __data = __min; \
6625 else if (__data > __max) \
6626 __data = __max; \
6627 if (__CONV == 1) \
6628 *(__PTR) = msecs_to_jiffies(__data); \
6629 else if (__CONV == 2) \
6630 *(__PTR) = (u64)__data * NSEC_PER_MSEC; \
6631 else \
6632 *(__PTR) = __data; \
6633 return count; \
6634}
6635STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
6636 INT_MAX, 2);
6637STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
6638 INT_MAX, 2);
6639STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
6640STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
6641 INT_MAX, 0);
6642STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
6643#undef STORE_FUNCTION
6644
6645#define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
6646static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
6647{ \
6648 struct bfq_data *bfqd = e->elevator_data; \
6649 unsigned long __data, __min = (MIN), __max = (MAX); \
6650 int ret; \
6651 \
6652 ret = bfq_var_store(&__data, (page)); \
6653 if (ret) \
6654 return ret; \
6655 if (__data < __min) \
6656 __data = __min; \
6657 else if (__data > __max) \
6658 __data = __max; \
6659 *(__PTR) = (u64)__data * NSEC_PER_USEC; \
6660 return count; \
6661}
6662USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
6663 UINT_MAX);
6664#undef USEC_STORE_FUNCTION
6665
6666static ssize_t bfq_max_budget_store(struct elevator_queue *e,
6667 const char *page, size_t count)
6668{
6669 struct bfq_data *bfqd = e->elevator_data;
6670 unsigned long __data;
6671 int ret;
6672
6673 ret = bfq_var_store(&__data, (page));
6674 if (ret)
6675 return ret;
6676
6677 if (__data == 0)
6678 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
6679 else {
6680 if (__data > INT_MAX)
6681 __data = INT_MAX;
6682 bfqd->bfq_max_budget = __data;
6683 }
6684
6685 bfqd->bfq_user_max_budget = __data;
6686
6687 return count;
6688}
6689
6690/*
6691 * Leaving this name to preserve name compatibility with cfq
6692 * parameters, but this timeout is used for both sync and async.
6693 */
6694static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
6695 const char *page, size_t count)
6696{
6697 struct bfq_data *bfqd = e->elevator_data;
6698 unsigned long __data;
6699 int ret;
6700
6701 ret = bfq_var_store(&__data, (page));
6702 if (ret)
6703 return ret;
6704
6705 if (__data < 1)
6706 __data = 1;
6707 else if (__data > INT_MAX)
6708 __data = INT_MAX;
6709
6710 bfqd->bfq_timeout = msecs_to_jiffies(__data);
6711 if (bfqd->bfq_user_max_budget == 0)
6712 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
6713
6714 return count;
6715}
6716
6717static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
6718 const char *page, size_t count)
6719{
6720 struct bfq_data *bfqd = e->elevator_data;
6721 unsigned long __data;
6722 int ret;
6723
6724 ret = bfq_var_store(&__data, (page));
6725 if (ret)
6726 return ret;
6727
6728 if (__data > 1)
6729 __data = 1;
6730 if (!bfqd->strict_guarantees && __data == 1
6731 && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
6732 bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
6733
6734 bfqd->strict_guarantees = __data;
6735
6736 return count;
6737}
6738
6739static ssize_t bfq_low_latency_store(struct elevator_queue *e,
6740 const char *page, size_t count)
6741{
6742 struct bfq_data *bfqd = e->elevator_data;
6743 unsigned long __data;
6744 int ret;
6745
6746 ret = bfq_var_store(&__data, (page));
6747 if (ret)
6748 return ret;
6749
6750 if (__data > 1)
6751 __data = 1;
6752 if (__data == 0 && bfqd->low_latency != 0)
6753 bfq_end_wr(bfqd);
6754 bfqd->low_latency = __data;
6755
6756 return count;
6757}
6758
6759#define BFQ_ATTR(name) \
6760 __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
6761
6762static struct elv_fs_entry bfq_attrs[] = {
6763 BFQ_ATTR(fifo_expire_sync),
6764 BFQ_ATTR(fifo_expire_async),
6765 BFQ_ATTR(back_seek_max),
6766 BFQ_ATTR(back_seek_penalty),
6767 BFQ_ATTR(slice_idle),
6768 BFQ_ATTR(slice_idle_us),
6769 BFQ_ATTR(max_budget),
6770 BFQ_ATTR(timeout_sync),
6771 BFQ_ATTR(strict_guarantees),
6772 BFQ_ATTR(low_latency),
6773 __ATTR_NULL
6774};
6775
6776static struct elevator_type iosched_bfq_mq = {
6777 .ops = {
6778 .limit_depth = bfq_limit_depth,
6779 .prepare_request = bfq_prepare_request,
6780 .requeue_request = bfq_finish_requeue_request,
6781 .finish_request = bfq_finish_requeue_request,
6782 .exit_icq = bfq_exit_icq,
6783 .insert_requests = bfq_insert_requests,
6784 .dispatch_request = bfq_dispatch_request,
6785 .next_request = elv_rb_latter_request,
6786 .former_request = elv_rb_former_request,
6787 .allow_merge = bfq_allow_bio_merge,
6788 .bio_merge = bfq_bio_merge,
6789 .request_merge = bfq_request_merge,
6790 .requests_merged = bfq_requests_merged,
6791 .request_merged = bfq_request_merged,
6792 .has_work = bfq_has_work,
6793 .depth_updated = bfq_depth_updated,
6794 .init_hctx = bfq_init_hctx,
6795 .init_sched = bfq_init_queue,
6796 .exit_sched = bfq_exit_queue,
6797 },
6798
6799 .icq_size = sizeof(struct bfq_io_cq),
6800 .icq_align = __alignof__(struct bfq_io_cq),
6801 .elevator_attrs = bfq_attrs,
6802 .elevator_name = "bfq",
6803 .elevator_owner = THIS_MODULE,
6804};
6805MODULE_ALIAS("bfq-iosched");
6806
6807static int __init bfq_init(void)
6808{
6809 int ret;
6810
6811#ifdef CONFIG_BFQ_GROUP_IOSCHED
6812 ret = blkcg_policy_register(&blkcg_policy_bfq);
6813 if (ret)
6814 return ret;
6815#endif
6816
6817 ret = -ENOMEM;
6818 if (bfq_slab_setup())
6819 goto err_pol_unreg;
6820
6821 /*
6822 * Times to load large popular applications for the typical
6823 * systems installed on the reference devices (see the
6824 * comments before the definition of the next
6825 * array). Actually, we use slightly lower values, as the
6826 * estimated peak rate tends to be smaller than the actual
6827 * peak rate. The reason for this last fact is that estimates
6828 * are computed over much shorter time intervals than the long
6829 * intervals typically used for benchmarking. Why? First, to
6830 * adapt more quickly to variations. Second, because an I/O
6831 * scheduler cannot rely on a peak-rate-evaluation workload to
6832 * be run for a long time.
6833 */
6834 ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */
6835 ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */
6836
6837 ret = elv_register(&iosched_bfq_mq);
6838 if (ret)
6839 goto slab_kill;
6840
6841 return 0;
6842
6843slab_kill:
6844 bfq_slab_kill();
6845err_pol_unreg:
6846#ifdef CONFIG_BFQ_GROUP_IOSCHED
6847 blkcg_policy_unregister(&blkcg_policy_bfq);
6848#endif
6849 return ret;
6850}
6851
6852static void __exit bfq_exit(void)
6853{
6854 elv_unregister(&iosched_bfq_mq);
6855#ifdef CONFIG_BFQ_GROUP_IOSCHED
6856 blkcg_policy_unregister(&blkcg_policy_bfq);
6857#endif
6858 bfq_slab_kill();
6859}
6860
6861module_init(bfq_init);
6862module_exit(bfq_exit);
6863
6864MODULE_AUTHOR("Paolo Valente");
6865MODULE_LICENSE("GPL");
6866MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");