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1/*
2 * Budget Fair Queueing (BFQ) I/O scheduler.
3 *
4 * Based on ideas and code from CFQ:
5 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
6 *
7 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
8 * Paolo Valente <paolo.valente@unimore.it>
9 *
10 * Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
11 * Arianna Avanzini <avanzini@google.com>
12 *
13 * Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
14 *
15 * This program is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU General Public License as
17 * published by the Free Software Foundation; either version 2 of the
18 * License, or (at your option) any later version.
19 *
20 * This program is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * General Public License for more details.
24 *
25 * BFQ is a proportional-share I/O scheduler, with some extra
26 * low-latency capabilities. BFQ also supports full hierarchical
27 * scheduling through cgroups. Next paragraphs provide an introduction
28 * on BFQ inner workings. Details on BFQ benefits, usage and
29 * limitations can be found in Documentation/block/bfq-iosched.txt.
30 *
31 * BFQ is a proportional-share storage-I/O scheduling algorithm based
32 * on the slice-by-slice service scheme of CFQ. But BFQ assigns
33 * budgets, measured in number of sectors, to processes instead of
34 * time slices. The device is not granted to the in-service process
35 * for a given time slice, but until it has exhausted its assigned
36 * budget. This change from the time to the service domain enables BFQ
37 * to distribute the device throughput among processes as desired,
38 * without any distortion due to throughput fluctuations, or to device
39 * internal queueing. BFQ uses an ad hoc internal scheduler, called
40 * B-WF2Q+, to schedule processes according to their budgets. More
41 * precisely, BFQ schedules queues associated with processes. Each
42 * process/queue is assigned a user-configurable weight, and B-WF2Q+
43 * guarantees that each queue receives a fraction of the throughput
44 * proportional to its weight. Thanks to the accurate policy of
45 * B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
46 * processes issuing sequential requests (to boost the throughput),
47 * and yet guarantee a low latency to interactive and soft real-time
48 * applications.
49 *
50 * In particular, to provide these low-latency guarantees, BFQ
51 * explicitly privileges the I/O of two classes of time-sensitive
52 * applications: interactive and soft real-time. This feature enables
53 * BFQ to provide applications in these classes with a very low
54 * latency. Finally, BFQ also features additional heuristics for
55 * preserving both a low latency and a high throughput on NCQ-capable,
56 * rotational or flash-based devices, and to get the job done quickly
57 * for applications consisting in many I/O-bound processes.
58 *
59 * NOTE: if the main or only goal, with a given device, is to achieve
60 * the maximum-possible throughput at all times, then do switch off
61 * all low-latency heuristics for that device, by setting low_latency
62 * to 0.
63 *
64 * BFQ is described in [1], where also a reference to the initial, more
65 * theoretical paper on BFQ can be found. The interested reader can find
66 * in the latter paper full details on the main algorithm, as well as
67 * formulas of the guarantees and formal proofs of all the properties.
68 * With respect to the version of BFQ presented in these papers, this
69 * implementation adds a few more heuristics, such as the one that
70 * guarantees a low latency to soft real-time applications, and a
71 * hierarchical extension based on H-WF2Q+.
72 *
73 * B-WF2Q+ is based on WF2Q+, which is described in [2], together with
74 * H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
75 * with O(log N) complexity derives from the one introduced with EEVDF
76 * in [3].
77 *
78 * [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
79 * Scheduler", Proceedings of the First Workshop on Mobile System
80 * Technologies (MST-2015), May 2015.
81 * http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
82 *
83 * [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
84 * Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
85 * Oct 1997.
86 *
87 * http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
88 *
89 * [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
90 * First: A Flexible and Accurate Mechanism for Proportional Share
91 * Resource Allocation", technical report.
92 *
93 * http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
94 */
95#include <linux/module.h>
96#include <linux/slab.h>
97#include <linux/blkdev.h>
98#include <linux/cgroup.h>
99#include <linux/elevator.h>
100#include <linux/ktime.h>
101#include <linux/rbtree.h>
102#include <linux/ioprio.h>
103#include <linux/sbitmap.h>
104#include <linux/delay.h>
105
106#include "blk.h"
107#include "blk-mq.h"
108#include "blk-mq-tag.h"
109#include "blk-mq-sched.h"
110#include "bfq-iosched.h"
111#include "blk-wbt.h"
112
113#define BFQ_BFQQ_FNS(name) \
114void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
115{ \
116 __set_bit(BFQQF_##name, &(bfqq)->flags); \
117} \
118void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
119{ \
120 __clear_bit(BFQQF_##name, &(bfqq)->flags); \
121} \
122int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
123{ \
124 return test_bit(BFQQF_##name, &(bfqq)->flags); \
125}
126
127BFQ_BFQQ_FNS(just_created);
128BFQ_BFQQ_FNS(busy);
129BFQ_BFQQ_FNS(wait_request);
130BFQ_BFQQ_FNS(non_blocking_wait_rq);
131BFQ_BFQQ_FNS(fifo_expire);
132BFQ_BFQQ_FNS(has_short_ttime);
133BFQ_BFQQ_FNS(sync);
134BFQ_BFQQ_FNS(IO_bound);
135BFQ_BFQQ_FNS(in_large_burst);
136BFQ_BFQQ_FNS(coop);
137BFQ_BFQQ_FNS(split_coop);
138BFQ_BFQQ_FNS(softrt_update);
139#undef BFQ_BFQQ_FNS \
140
141/* Expiration time of sync (0) and async (1) requests, in ns. */
142static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
143
144/* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
145static const int bfq_back_max = 16 * 1024;
146
147/* Penalty of a backwards seek, in number of sectors. */
148static const int bfq_back_penalty = 2;
149
150/* Idling period duration, in ns. */
151static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
152
153/* Minimum number of assigned budgets for which stats are safe to compute. */
154static const int bfq_stats_min_budgets = 194;
155
156/* Default maximum budget values, in sectors and number of requests. */
157static const int bfq_default_max_budget = 16 * 1024;
158
159/*
160 * Async to sync throughput distribution is controlled as follows:
161 * when an async request is served, the entity is charged the number
162 * of sectors of the request, multiplied by the factor below
163 */
164static const int bfq_async_charge_factor = 10;
165
166/* Default timeout values, in jiffies, approximating CFQ defaults. */
167const int bfq_timeout = HZ / 8;
168
169/*
170 * Time limit for merging (see comments in bfq_setup_cooperator). Set
171 * to the slowest value that, in our tests, proved to be effective in
172 * removing false positives, while not causing true positives to miss
173 * queue merging.
174 *
175 * As can be deduced from the low time limit below, queue merging, if
176 * successful, happens at the very beggining of the I/O of the involved
177 * cooperating processes, as a consequence of the arrival of the very
178 * first requests from each cooperator. After that, there is very
179 * little chance to find cooperators.
180 */
181static const unsigned long bfq_merge_time_limit = HZ/10;
182
183static struct kmem_cache *bfq_pool;
184
185/* Below this threshold (in ns), we consider thinktime immediate. */
186#define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
187
188/* hw_tag detection: parallel requests threshold and min samples needed. */
189#define BFQ_HW_QUEUE_THRESHOLD 4
190#define BFQ_HW_QUEUE_SAMPLES 32
191
192#define BFQQ_SEEK_THR (sector_t)(8 * 100)
193#define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
194#define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
195#define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 19)
196
197/* Min number of samples required to perform peak-rate update */
198#define BFQ_RATE_MIN_SAMPLES 32
199/* Min observation time interval required to perform a peak-rate update (ns) */
200#define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
201/* Target observation time interval for a peak-rate update (ns) */
202#define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
203
204/*
205 * Shift used for peak-rate fixed precision calculations.
206 * With
207 * - the current shift: 16 positions
208 * - the current type used to store rate: u32
209 * - the current unit of measure for rate: [sectors/usec], or, more precisely,
210 * [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
211 * the range of rates that can be stored is
212 * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
213 * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
214 * [15, 65G] sectors/sec
215 * Which, assuming a sector size of 512B, corresponds to a range of
216 * [7.5K, 33T] B/sec
217 */
218#define BFQ_RATE_SHIFT 16
219
220/*
221 * By default, BFQ computes the duration of the weight raising for
222 * interactive applications automatically, using the following formula:
223 * duration = (R / r) * T, where r is the peak rate of the device, and
224 * R and T are two reference parameters.
225 * In particular, R is the peak rate of the reference device (see
226 * below), and T is a reference time: given the systems that are
227 * likely to be installed on the reference device according to its
228 * speed class, T is about the maximum time needed, under BFQ and
229 * while reading two files in parallel, to load typical large
230 * applications on these systems (see the comments on
231 * max_service_from_wr below, for more details on how T is obtained).
232 * In practice, the slower/faster the device at hand is, the more/less
233 * it takes to load applications with respect to the reference device.
234 * Accordingly, the longer/shorter BFQ grants weight raising to
235 * interactive applications.
236 *
237 * BFQ uses four different reference pairs (R, T), depending on:
238 * . whether the device is rotational or non-rotational;
239 * . whether the device is slow, such as old or portable HDDs, as well as
240 * SD cards, or fast, such as newer HDDs and SSDs.
241 *
242 * The device's speed class is dynamically (re)detected in
243 * bfq_update_peak_rate() every time the estimated peak rate is updated.
244 *
245 * In the following definitions, R_slow[0]/R_fast[0] and
246 * T_slow[0]/T_fast[0] are the reference values for a slow/fast
247 * rotational device, whereas R_slow[1]/R_fast[1] and
248 * T_slow[1]/T_fast[1] are the reference values for a slow/fast
249 * non-rotational device. Finally, device_speed_thresh are the
250 * thresholds used to switch between speed classes. The reference
251 * rates are not the actual peak rates of the devices used as a
252 * reference, but slightly lower values. The reason for using these
253 * slightly lower values is that the peak-rate estimator tends to
254 * yield slightly lower values than the actual peak rate (it can yield
255 * the actual peak rate only if there is only one process doing I/O,
256 * and the process does sequential I/O).
257 *
258 * Both the reference peak rates and the thresholds are measured in
259 * sectors/usec, left-shifted by BFQ_RATE_SHIFT.
260 */
261static int R_slow[2] = {1000, 10700};
262static int R_fast[2] = {14000, 33000};
263/*
264 * To improve readability, a conversion function is used to initialize the
265 * following arrays, which entails that they can be initialized only in a
266 * function.
267 */
268static int T_slow[2];
269static int T_fast[2];
270static int device_speed_thresh[2];
271
272/*
273 * BFQ uses the above-detailed, time-based weight-raising mechanism to
274 * privilege interactive tasks. This mechanism is vulnerable to the
275 * following false positives: I/O-bound applications that will go on
276 * doing I/O for much longer than the duration of weight
277 * raising. These applications have basically no benefit from being
278 * weight-raised at the beginning of their I/O. On the opposite end,
279 * while being weight-raised, these applications
280 * a) unjustly steal throughput to applications that may actually need
281 * low latency;
282 * b) make BFQ uselessly perform device idling; device idling results
283 * in loss of device throughput with most flash-based storage, and may
284 * increase latencies when used purposelessly.
285 *
286 * BFQ tries to reduce these problems, by adopting the following
287 * countermeasure. To introduce this countermeasure, we need first to
288 * finish explaining how the duration of weight-raising for
289 * interactive tasks is computed.
290 *
291 * For a bfq_queue deemed as interactive, the duration of weight
292 * raising is dynamically adjusted, as a function of the estimated
293 * peak rate of the device, so as to be equal to the time needed to
294 * execute the 'largest' interactive task we benchmarked so far. By
295 * largest task, we mean the task for which each involved process has
296 * to do more I/O than for any of the other tasks we benchmarked. This
297 * reference interactive task is the start-up of LibreOffice Writer,
298 * and in this task each process/bfq_queue needs to have at most ~110K
299 * sectors transferred.
300 *
301 * This last piece of information enables BFQ to reduce the actual
302 * duration of weight-raising for at least one class of I/O-bound
303 * applications: those doing sequential or quasi-sequential I/O. An
304 * example is file copy. In fact, once started, the main I/O-bound
305 * processes of these applications usually consume the above 110K
306 * sectors in much less time than the processes of an application that
307 * is starting, because these I/O-bound processes will greedily devote
308 * almost all their CPU cycles only to their target,
309 * throughput-friendly I/O operations. This is even more true if BFQ
310 * happens to be underestimating the device peak rate, and thus
311 * overestimating the duration of weight raising. But, according to
312 * our measurements, once transferred 110K sectors, these processes
313 * have no right to be weight-raised any longer.
314 *
315 * Basing on the last consideration, BFQ ends weight-raising for a
316 * bfq_queue if the latter happens to have received an amount of
317 * service at least equal to the following constant. The constant is
318 * set to slightly more than 110K, to have a minimum safety margin.
319 *
320 * This early ending of weight-raising reduces the amount of time
321 * during which interactive false positives cause the two problems
322 * described at the beginning of these comments.
323 */
324static const unsigned long max_service_from_wr = 120000;
325
326#define RQ_BIC(rq) icq_to_bic((rq)->elv.priv[0])
327#define RQ_BFQQ(rq) ((rq)->elv.priv[1])
328
329struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
330{
331 return bic->bfqq[is_sync];
332}
333
334void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
335{
336 bic->bfqq[is_sync] = bfqq;
337}
338
339struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
340{
341 return bic->icq.q->elevator->elevator_data;
342}
343
344/**
345 * icq_to_bic - convert iocontext queue structure to bfq_io_cq.
346 * @icq: the iocontext queue.
347 */
348static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
349{
350 /* bic->icq is the first member, %NULL will convert to %NULL */
351 return container_of(icq, struct bfq_io_cq, icq);
352}
353
354/**
355 * bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
356 * @bfqd: the lookup key.
357 * @ioc: the io_context of the process doing I/O.
358 * @q: the request queue.
359 */
360static struct bfq_io_cq *bfq_bic_lookup(struct bfq_data *bfqd,
361 struct io_context *ioc,
362 struct request_queue *q)
363{
364 if (ioc) {
365 unsigned long flags;
366 struct bfq_io_cq *icq;
367
368 spin_lock_irqsave(q->queue_lock, flags);
369 icq = icq_to_bic(ioc_lookup_icq(ioc, q));
370 spin_unlock_irqrestore(q->queue_lock, flags);
371
372 return icq;
373 }
374
375 return NULL;
376}
377
378/*
379 * Scheduler run of queue, if there are requests pending and no one in the
380 * driver that will restart queueing.
381 */
382void bfq_schedule_dispatch(struct bfq_data *bfqd)
383{
384 if (bfqd->queued != 0) {
385 bfq_log(bfqd, "schedule dispatch");
386 blk_mq_run_hw_queues(bfqd->queue, true);
387 }
388}
389
390#define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
391#define bfq_class_rt(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_RT)
392
393#define bfq_sample_valid(samples) ((samples) > 80)
394
395/*
396 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
397 * We choose the request that is closesr to the head right now. Distance
398 * behind the head is penalized and only allowed to a certain extent.
399 */
400static struct request *bfq_choose_req(struct bfq_data *bfqd,
401 struct request *rq1,
402 struct request *rq2,
403 sector_t last)
404{
405 sector_t s1, s2, d1 = 0, d2 = 0;
406 unsigned long back_max;
407#define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
408#define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
409 unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
410
411 if (!rq1 || rq1 == rq2)
412 return rq2;
413 if (!rq2)
414 return rq1;
415
416 if (rq_is_sync(rq1) && !rq_is_sync(rq2))
417 return rq1;
418 else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
419 return rq2;
420 if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
421 return rq1;
422 else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
423 return rq2;
424
425 s1 = blk_rq_pos(rq1);
426 s2 = blk_rq_pos(rq2);
427
428 /*
429 * By definition, 1KiB is 2 sectors.
430 */
431 back_max = bfqd->bfq_back_max * 2;
432
433 /*
434 * Strict one way elevator _except_ in the case where we allow
435 * short backward seeks which are biased as twice the cost of a
436 * similar forward seek.
437 */
438 if (s1 >= last)
439 d1 = s1 - last;
440 else if (s1 + back_max >= last)
441 d1 = (last - s1) * bfqd->bfq_back_penalty;
442 else
443 wrap |= BFQ_RQ1_WRAP;
444
445 if (s2 >= last)
446 d2 = s2 - last;
447 else if (s2 + back_max >= last)
448 d2 = (last - s2) * bfqd->bfq_back_penalty;
449 else
450 wrap |= BFQ_RQ2_WRAP;
451
452 /* Found required data */
453
454 /*
455 * By doing switch() on the bit mask "wrap" we avoid having to
456 * check two variables for all permutations: --> faster!
457 */
458 switch (wrap) {
459 case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
460 if (d1 < d2)
461 return rq1;
462 else if (d2 < d1)
463 return rq2;
464
465 if (s1 >= s2)
466 return rq1;
467 else
468 return rq2;
469
470 case BFQ_RQ2_WRAP:
471 return rq1;
472 case BFQ_RQ1_WRAP:
473 return rq2;
474 case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
475 default:
476 /*
477 * Since both rqs are wrapped,
478 * start with the one that's further behind head
479 * (--> only *one* back seek required),
480 * since back seek takes more time than forward.
481 */
482 if (s1 <= s2)
483 return rq1;
484 else
485 return rq2;
486 }
487}
488
489/*
490 * See the comments on bfq_limit_depth for the purpose of
491 * the depths set in the function.
492 */
493static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
494{
495 bfqd->sb_shift = bt->sb.shift;
496
497 /*
498 * In-word depths if no bfq_queue is being weight-raised:
499 * leaving 25% of tags only for sync reads.
500 *
501 * In next formulas, right-shift the value
502 * (1U<<bfqd->sb_shift), instead of computing directly
503 * (1U<<(bfqd->sb_shift - something)), to be robust against
504 * any possible value of bfqd->sb_shift, without having to
505 * limit 'something'.
506 */
507 /* no more than 50% of tags for async I/O */
508 bfqd->word_depths[0][0] = max((1U<<bfqd->sb_shift)>>1, 1U);
509 /*
510 * no more than 75% of tags for sync writes (25% extra tags
511 * w.r.t. async I/O, to prevent async I/O from starving sync
512 * writes)
513 */
514 bfqd->word_depths[0][1] = max(((1U<<bfqd->sb_shift) * 3)>>2, 1U);
515
516 /*
517 * In-word depths in case some bfq_queue is being weight-
518 * raised: leaving ~63% of tags for sync reads. This is the
519 * highest percentage for which, in our tests, application
520 * start-up times didn't suffer from any regression due to tag
521 * shortage.
522 */
523 /* no more than ~18% of tags for async I/O */
524 bfqd->word_depths[1][0] = max(((1U<<bfqd->sb_shift) * 3)>>4, 1U);
525 /* no more than ~37% of tags for sync writes (~20% extra tags) */
526 bfqd->word_depths[1][1] = max(((1U<<bfqd->sb_shift) * 6)>>4, 1U);
527}
528
529/*
530 * Async I/O can easily starve sync I/O (both sync reads and sync
531 * writes), by consuming all tags. Similarly, storms of sync writes,
532 * such as those that sync(2) may trigger, can starve sync reads.
533 * Limit depths of async I/O and sync writes so as to counter both
534 * problems.
535 */
536static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
537{
538 struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
539 struct bfq_data *bfqd = data->q->elevator->elevator_data;
540 struct sbitmap_queue *bt;
541
542 if (op_is_sync(op) && !op_is_write(op))
543 return;
544
545 if (data->flags & BLK_MQ_REQ_RESERVED) {
546 if (unlikely(!tags->nr_reserved_tags)) {
547 WARN_ON_ONCE(1);
548 return;
549 }
550 bt = &tags->breserved_tags;
551 } else
552 bt = &tags->bitmap_tags;
553
554 if (unlikely(bfqd->sb_shift != bt->sb.shift))
555 bfq_update_depths(bfqd, bt);
556
557 data->shallow_depth =
558 bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)];
559
560 bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
561 __func__, bfqd->wr_busy_queues, op_is_sync(op),
562 data->shallow_depth);
563}
564
565static struct bfq_queue *
566bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
567 sector_t sector, struct rb_node **ret_parent,
568 struct rb_node ***rb_link)
569{
570 struct rb_node **p, *parent;
571 struct bfq_queue *bfqq = NULL;
572
573 parent = NULL;
574 p = &root->rb_node;
575 while (*p) {
576 struct rb_node **n;
577
578 parent = *p;
579 bfqq = rb_entry(parent, struct bfq_queue, pos_node);
580
581 /*
582 * Sort strictly based on sector. Smallest to the left,
583 * largest to the right.
584 */
585 if (sector > blk_rq_pos(bfqq->next_rq))
586 n = &(*p)->rb_right;
587 else if (sector < blk_rq_pos(bfqq->next_rq))
588 n = &(*p)->rb_left;
589 else
590 break;
591 p = n;
592 bfqq = NULL;
593 }
594
595 *ret_parent = parent;
596 if (rb_link)
597 *rb_link = p;
598
599 bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
600 (unsigned long long)sector,
601 bfqq ? bfqq->pid : 0);
602
603 return bfqq;
604}
605
606static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
607{
608 return bfqq->service_from_backlogged > 0 &&
609 time_is_before_jiffies(bfqq->first_IO_time +
610 bfq_merge_time_limit);
611}
612
613void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
614{
615 struct rb_node **p, *parent;
616 struct bfq_queue *__bfqq;
617
618 if (bfqq->pos_root) {
619 rb_erase(&bfqq->pos_node, bfqq->pos_root);
620 bfqq->pos_root = NULL;
621 }
622
623 /*
624 * bfqq cannot be merged any longer (see comments in
625 * bfq_setup_cooperator): no point in adding bfqq into the
626 * position tree.
627 */
628 if (bfq_too_late_for_merging(bfqq))
629 return;
630
631 if (bfq_class_idle(bfqq))
632 return;
633 if (!bfqq->next_rq)
634 return;
635
636 bfqq->pos_root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
637 __bfqq = bfq_rq_pos_tree_lookup(bfqd, bfqq->pos_root,
638 blk_rq_pos(bfqq->next_rq), &parent, &p);
639 if (!__bfqq) {
640 rb_link_node(&bfqq->pos_node, parent, p);
641 rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
642 } else
643 bfqq->pos_root = NULL;
644}
645
646/*
647 * Tell whether there are active queues or groups with differentiated weights.
648 */
649static bool bfq_differentiated_weights(struct bfq_data *bfqd)
650{
651 /*
652 * For weights to differ, at least one of the trees must contain
653 * at least two nodes.
654 */
655 return (!RB_EMPTY_ROOT(&bfqd->queue_weights_tree) &&
656 (bfqd->queue_weights_tree.rb_node->rb_left ||
657 bfqd->queue_weights_tree.rb_node->rb_right)
658#ifdef CONFIG_BFQ_GROUP_IOSCHED
659 ) ||
660 (!RB_EMPTY_ROOT(&bfqd->group_weights_tree) &&
661 (bfqd->group_weights_tree.rb_node->rb_left ||
662 bfqd->group_weights_tree.rb_node->rb_right)
663#endif
664 );
665}
666
667/*
668 * The following function returns true if every queue must receive the
669 * same share of the throughput (this condition is used when deciding
670 * whether idling may be disabled, see the comments in the function
671 * bfq_bfqq_may_idle()).
672 *
673 * Such a scenario occurs when:
674 * 1) all active queues have the same weight,
675 * 2) all active groups at the same level in the groups tree have the same
676 * weight,
677 * 3) all active groups at the same level in the groups tree have the same
678 * number of children.
679 *
680 * Unfortunately, keeping the necessary state for evaluating exactly the
681 * above symmetry conditions would be quite complex and time-consuming.
682 * Therefore this function evaluates, instead, the following stronger
683 * sub-conditions, for which it is much easier to maintain the needed
684 * state:
685 * 1) all active queues have the same weight,
686 * 2) all active groups have the same weight,
687 * 3) all active groups have at most one active child each.
688 * In particular, the last two conditions are always true if hierarchical
689 * support and the cgroups interface are not enabled, thus no state needs
690 * to be maintained in this case.
691 */
692static bool bfq_symmetric_scenario(struct bfq_data *bfqd)
693{
694 return !bfq_differentiated_weights(bfqd);
695}
696
697/*
698 * If the weight-counter tree passed as input contains no counter for
699 * the weight of the input entity, then add that counter; otherwise just
700 * increment the existing counter.
701 *
702 * Note that weight-counter trees contain few nodes in mostly symmetric
703 * scenarios. For example, if all queues have the same weight, then the
704 * weight-counter tree for the queues may contain at most one node.
705 * This holds even if low_latency is on, because weight-raised queues
706 * are not inserted in the tree.
707 * In most scenarios, the rate at which nodes are created/destroyed
708 * should be low too.
709 */
710void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_entity *entity,
711 struct rb_root *root)
712{
713 struct rb_node **new = &(root->rb_node), *parent = NULL;
714
715 /*
716 * Do not insert if the entity is already associated with a
717 * counter, which happens if:
718 * 1) the entity is associated with a queue,
719 * 2) a request arrival has caused the queue to become both
720 * non-weight-raised, and hence change its weight, and
721 * backlogged; in this respect, each of the two events
722 * causes an invocation of this function,
723 * 3) this is the invocation of this function caused by the
724 * second event. This second invocation is actually useless,
725 * and we handle this fact by exiting immediately. More
726 * efficient or clearer solutions might possibly be adopted.
727 */
728 if (entity->weight_counter)
729 return;
730
731 while (*new) {
732 struct bfq_weight_counter *__counter = container_of(*new,
733 struct bfq_weight_counter,
734 weights_node);
735 parent = *new;
736
737 if (entity->weight == __counter->weight) {
738 entity->weight_counter = __counter;
739 goto inc_counter;
740 }
741 if (entity->weight < __counter->weight)
742 new = &((*new)->rb_left);
743 else
744 new = &((*new)->rb_right);
745 }
746
747 entity->weight_counter = kzalloc(sizeof(struct bfq_weight_counter),
748 GFP_ATOMIC);
749
750 /*
751 * In the unlucky event of an allocation failure, we just
752 * exit. This will cause the weight of entity to not be
753 * considered in bfq_differentiated_weights, which, in its
754 * turn, causes the scenario to be deemed wrongly symmetric in
755 * case entity's weight would have been the only weight making
756 * the scenario asymmetric. On the bright side, no unbalance
757 * will however occur when entity becomes inactive again (the
758 * invocation of this function is triggered by an activation
759 * of entity). In fact, bfq_weights_tree_remove does nothing
760 * if !entity->weight_counter.
761 */
762 if (unlikely(!entity->weight_counter))
763 return;
764
765 entity->weight_counter->weight = entity->weight;
766 rb_link_node(&entity->weight_counter->weights_node, parent, new);
767 rb_insert_color(&entity->weight_counter->weights_node, root);
768
769inc_counter:
770 entity->weight_counter->num_active++;
771}
772
773/*
774 * Decrement the weight counter associated with the entity, and, if the
775 * counter reaches 0, remove the counter from the tree.
776 * See the comments to the function bfq_weights_tree_add() for considerations
777 * about overhead.
778 */
779void bfq_weights_tree_remove(struct bfq_data *bfqd, struct bfq_entity *entity,
780 struct rb_root *root)
781{
782 if (!entity->weight_counter)
783 return;
784
785 entity->weight_counter->num_active--;
786 if (entity->weight_counter->num_active > 0)
787 goto reset_entity_pointer;
788
789 rb_erase(&entity->weight_counter->weights_node, root);
790 kfree(entity->weight_counter);
791
792reset_entity_pointer:
793 entity->weight_counter = NULL;
794}
795
796/*
797 * Return expired entry, or NULL to just start from scratch in rbtree.
798 */
799static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
800 struct request *last)
801{
802 struct request *rq;
803
804 if (bfq_bfqq_fifo_expire(bfqq))
805 return NULL;
806
807 bfq_mark_bfqq_fifo_expire(bfqq);
808
809 rq = rq_entry_fifo(bfqq->fifo.next);
810
811 if (rq == last || ktime_get_ns() < rq->fifo_time)
812 return NULL;
813
814 bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
815 return rq;
816}
817
818static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
819 struct bfq_queue *bfqq,
820 struct request *last)
821{
822 struct rb_node *rbnext = rb_next(&last->rb_node);
823 struct rb_node *rbprev = rb_prev(&last->rb_node);
824 struct request *next, *prev = NULL;
825
826 /* Follow expired path, else get first next available. */
827 next = bfq_check_fifo(bfqq, last);
828 if (next)
829 return next;
830
831 if (rbprev)
832 prev = rb_entry_rq(rbprev);
833
834 if (rbnext)
835 next = rb_entry_rq(rbnext);
836 else {
837 rbnext = rb_first(&bfqq->sort_list);
838 if (rbnext && rbnext != &last->rb_node)
839 next = rb_entry_rq(rbnext);
840 }
841
842 return bfq_choose_req(bfqd, next, prev, blk_rq_pos(last));
843}
844
845/* see the definition of bfq_async_charge_factor for details */
846static unsigned long bfq_serv_to_charge(struct request *rq,
847 struct bfq_queue *bfqq)
848{
849 if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1)
850 return blk_rq_sectors(rq);
851
852 /*
853 * If there are no weight-raised queues, then amplify service
854 * by just the async charge factor; otherwise amplify service
855 * by twice the async charge factor, to further reduce latency
856 * for weight-raised queues.
857 */
858 if (bfqq->bfqd->wr_busy_queues == 0)
859 return blk_rq_sectors(rq) * bfq_async_charge_factor;
860
861 return blk_rq_sectors(rq) * 2 * bfq_async_charge_factor;
862}
863
864/**
865 * bfq_updated_next_req - update the queue after a new next_rq selection.
866 * @bfqd: the device data the queue belongs to.
867 * @bfqq: the queue to update.
868 *
869 * If the first request of a queue changes we make sure that the queue
870 * has enough budget to serve at least its first request (if the
871 * request has grown). We do this because if the queue has not enough
872 * budget for its first request, it has to go through two dispatch
873 * rounds to actually get it dispatched.
874 */
875static void bfq_updated_next_req(struct bfq_data *bfqd,
876 struct bfq_queue *bfqq)
877{
878 struct bfq_entity *entity = &bfqq->entity;
879 struct request *next_rq = bfqq->next_rq;
880 unsigned long new_budget;
881
882 if (!next_rq)
883 return;
884
885 if (bfqq == bfqd->in_service_queue)
886 /*
887 * In order not to break guarantees, budgets cannot be
888 * changed after an entity has been selected.
889 */
890 return;
891
892 new_budget = max_t(unsigned long, bfqq->max_budget,
893 bfq_serv_to_charge(next_rq, bfqq));
894 if (entity->budget != new_budget) {
895 entity->budget = new_budget;
896 bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
897 new_budget);
898 bfq_requeue_bfqq(bfqd, bfqq, false);
899 }
900}
901
902static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
903{
904 u64 dur;
905
906 if (bfqd->bfq_wr_max_time > 0)
907 return bfqd->bfq_wr_max_time;
908
909 dur = bfqd->RT_prod;
910 do_div(dur, bfqd->peak_rate);
911
912 /*
913 * Limit duration between 3 and 13 seconds. Tests show that
914 * higher values than 13 seconds often yield the opposite of
915 * the desired result, i.e., worsen responsiveness by letting
916 * non-interactive and non-soft-real-time applications
917 * preserve weight raising for a too long time interval.
918 *
919 * On the other end, lower values than 3 seconds make it
920 * difficult for most interactive tasks to complete their jobs
921 * before weight-raising finishes.
922 */
923 if (dur > msecs_to_jiffies(13000))
924 dur = msecs_to_jiffies(13000);
925 else if (dur < msecs_to_jiffies(3000))
926 dur = msecs_to_jiffies(3000);
927
928 return dur;
929}
930
931/* switch back from soft real-time to interactive weight raising */
932static void switch_back_to_interactive_wr(struct bfq_queue *bfqq,
933 struct bfq_data *bfqd)
934{
935 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
936 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
937 bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt;
938}
939
940static void
941bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
942 struct bfq_io_cq *bic, bool bfq_already_existing)
943{
944 unsigned int old_wr_coeff = bfqq->wr_coeff;
945 bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
946
947 if (bic->saved_has_short_ttime)
948 bfq_mark_bfqq_has_short_ttime(bfqq);
949 else
950 bfq_clear_bfqq_has_short_ttime(bfqq);
951
952 if (bic->saved_IO_bound)
953 bfq_mark_bfqq_IO_bound(bfqq);
954 else
955 bfq_clear_bfqq_IO_bound(bfqq);
956
957 bfqq->ttime = bic->saved_ttime;
958 bfqq->wr_coeff = bic->saved_wr_coeff;
959 bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
960 bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
961 bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
962
963 if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
964 time_is_before_jiffies(bfqq->last_wr_start_finish +
965 bfqq->wr_cur_max_time))) {
966 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
967 !bfq_bfqq_in_large_burst(bfqq) &&
968 time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt +
969 bfq_wr_duration(bfqd))) {
970 switch_back_to_interactive_wr(bfqq, bfqd);
971 } else {
972 bfqq->wr_coeff = 1;
973 bfq_log_bfqq(bfqq->bfqd, bfqq,
974 "resume state: switching off wr");
975 }
976 }
977
978 /* make sure weight will be updated, however we got here */
979 bfqq->entity.prio_changed = 1;
980
981 if (likely(!busy))
982 return;
983
984 if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
985 bfqd->wr_busy_queues++;
986 else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
987 bfqd->wr_busy_queues--;
988}
989
990static int bfqq_process_refs(struct bfq_queue *bfqq)
991{
992 return bfqq->ref - bfqq->allocated - bfqq->entity.on_st;
993}
994
995/* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
996static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
997{
998 struct bfq_queue *item;
999 struct hlist_node *n;
1000
1001 hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
1002 hlist_del_init(&item->burst_list_node);
1003 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1004 bfqd->burst_size = 1;
1005 bfqd->burst_parent_entity = bfqq->entity.parent;
1006}
1007
1008/* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
1009static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1010{
1011 /* Increment burst size to take into account also bfqq */
1012 bfqd->burst_size++;
1013
1014 if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
1015 struct bfq_queue *pos, *bfqq_item;
1016 struct hlist_node *n;
1017
1018 /*
1019 * Enough queues have been activated shortly after each
1020 * other to consider this burst as large.
1021 */
1022 bfqd->large_burst = true;
1023
1024 /*
1025 * We can now mark all queues in the burst list as
1026 * belonging to a large burst.
1027 */
1028 hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
1029 burst_list_node)
1030 bfq_mark_bfqq_in_large_burst(bfqq_item);
1031 bfq_mark_bfqq_in_large_burst(bfqq);
1032
1033 /*
1034 * From now on, and until the current burst finishes, any
1035 * new queue being activated shortly after the last queue
1036 * was inserted in the burst can be immediately marked as
1037 * belonging to a large burst. So the burst list is not
1038 * needed any more. Remove it.
1039 */
1040 hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
1041 burst_list_node)
1042 hlist_del_init(&pos->burst_list_node);
1043 } else /*
1044 * Burst not yet large: add bfqq to the burst list. Do
1045 * not increment the ref counter for bfqq, because bfqq
1046 * is removed from the burst list before freeing bfqq
1047 * in put_queue.
1048 */
1049 hlist_add_head(&bfqq->burst_list_node, &bfqd->burst_list);
1050}
1051
1052/*
1053 * If many queues belonging to the same group happen to be created
1054 * shortly after each other, then the processes associated with these
1055 * queues have typically a common goal. In particular, bursts of queue
1056 * creations are usually caused by services or applications that spawn
1057 * many parallel threads/processes. Examples are systemd during boot,
1058 * or git grep. To help these processes get their job done as soon as
1059 * possible, it is usually better to not grant either weight-raising
1060 * or device idling to their queues.
1061 *
1062 * In this comment we describe, firstly, the reasons why this fact
1063 * holds, and, secondly, the next function, which implements the main
1064 * steps needed to properly mark these queues so that they can then be
1065 * treated in a different way.
1066 *
1067 * The above services or applications benefit mostly from a high
1068 * throughput: the quicker the requests of the activated queues are
1069 * cumulatively served, the sooner the target job of these queues gets
1070 * completed. As a consequence, weight-raising any of these queues,
1071 * which also implies idling the device for it, is almost always
1072 * counterproductive. In most cases it just lowers throughput.
1073 *
1074 * On the other hand, a burst of queue creations may be caused also by
1075 * the start of an application that does not consist of a lot of
1076 * parallel I/O-bound threads. In fact, with a complex application,
1077 * several short processes may need to be executed to start-up the
1078 * application. In this respect, to start an application as quickly as
1079 * possible, the best thing to do is in any case to privilege the I/O
1080 * related to the application with respect to all other
1081 * I/O. Therefore, the best strategy to start as quickly as possible
1082 * an application that causes a burst of queue creations is to
1083 * weight-raise all the queues created during the burst. This is the
1084 * exact opposite of the best strategy for the other type of bursts.
1085 *
1086 * In the end, to take the best action for each of the two cases, the
1087 * two types of bursts need to be distinguished. Fortunately, this
1088 * seems relatively easy, by looking at the sizes of the bursts. In
1089 * particular, we found a threshold such that only bursts with a
1090 * larger size than that threshold are apparently caused by
1091 * services or commands such as systemd or git grep. For brevity,
1092 * hereafter we call just 'large' these bursts. BFQ *does not*
1093 * weight-raise queues whose creation occurs in a large burst. In
1094 * addition, for each of these queues BFQ performs or does not perform
1095 * idling depending on which choice boosts the throughput more. The
1096 * exact choice depends on the device and request pattern at
1097 * hand.
1098 *
1099 * Unfortunately, false positives may occur while an interactive task
1100 * is starting (e.g., an application is being started). The
1101 * consequence is that the queues associated with the task do not
1102 * enjoy weight raising as expected. Fortunately these false positives
1103 * are very rare. They typically occur if some service happens to
1104 * start doing I/O exactly when the interactive task starts.
1105 *
1106 * Turning back to the next function, it implements all the steps
1107 * needed to detect the occurrence of a large burst and to properly
1108 * mark all the queues belonging to it (so that they can then be
1109 * treated in a different way). This goal is achieved by maintaining a
1110 * "burst list" that holds, temporarily, the queues that belong to the
1111 * burst in progress. The list is then used to mark these queues as
1112 * belonging to a large burst if the burst does become large. The main
1113 * steps are the following.
1114 *
1115 * . when the very first queue is created, the queue is inserted into the
1116 * list (as it could be the first queue in a possible burst)
1117 *
1118 * . if the current burst has not yet become large, and a queue Q that does
1119 * not yet belong to the burst is activated shortly after the last time
1120 * at which a new queue entered the burst list, then the function appends
1121 * Q to the burst list
1122 *
1123 * . if, as a consequence of the previous step, the burst size reaches
1124 * the large-burst threshold, then
1125 *
1126 * . all the queues in the burst list are marked as belonging to a
1127 * large burst
1128 *
1129 * . the burst list is deleted; in fact, the burst list already served
1130 * its purpose (keeping temporarily track of the queues in a burst,
1131 * so as to be able to mark them as belonging to a large burst in the
1132 * previous sub-step), and now is not needed any more
1133 *
1134 * . the device enters a large-burst mode
1135 *
1136 * . if a queue Q that does not belong to the burst is created while
1137 * the device is in large-burst mode and shortly after the last time
1138 * at which a queue either entered the burst list or was marked as
1139 * belonging to the current large burst, then Q is immediately marked
1140 * as belonging to a large burst.
1141 *
1142 * . if a queue Q that does not belong to the burst is created a while
1143 * later, i.e., not shortly after, than the last time at which a queue
1144 * either entered the burst list or was marked as belonging to the
1145 * current large burst, then the current burst is deemed as finished and:
1146 *
1147 * . the large-burst mode is reset if set
1148 *
1149 * . the burst list is emptied
1150 *
1151 * . Q is inserted in the burst list, as Q may be the first queue
1152 * in a possible new burst (then the burst list contains just Q
1153 * after this step).
1154 */
1155static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1156{
1157 /*
1158 * If bfqq is already in the burst list or is part of a large
1159 * burst, or finally has just been split, then there is
1160 * nothing else to do.
1161 */
1162 if (!hlist_unhashed(&bfqq->burst_list_node) ||
1163 bfq_bfqq_in_large_burst(bfqq) ||
1164 time_is_after_eq_jiffies(bfqq->split_time +
1165 msecs_to_jiffies(10)))
1166 return;
1167
1168 /*
1169 * If bfqq's creation happens late enough, or bfqq belongs to
1170 * a different group than the burst group, then the current
1171 * burst is finished, and related data structures must be
1172 * reset.
1173 *
1174 * In this respect, consider the special case where bfqq is
1175 * the very first queue created after BFQ is selected for this
1176 * device. In this case, last_ins_in_burst and
1177 * burst_parent_entity are not yet significant when we get
1178 * here. But it is easy to verify that, whether or not the
1179 * following condition is true, bfqq will end up being
1180 * inserted into the burst list. In particular the list will
1181 * happen to contain only bfqq. And this is exactly what has
1182 * to happen, as bfqq may be the first queue of the first
1183 * burst.
1184 */
1185 if (time_is_before_jiffies(bfqd->last_ins_in_burst +
1186 bfqd->bfq_burst_interval) ||
1187 bfqq->entity.parent != bfqd->burst_parent_entity) {
1188 bfqd->large_burst = false;
1189 bfq_reset_burst_list(bfqd, bfqq);
1190 goto end;
1191 }
1192
1193 /*
1194 * If we get here, then bfqq is being activated shortly after the
1195 * last queue. So, if the current burst is also large, we can mark
1196 * bfqq as belonging to this large burst immediately.
1197 */
1198 if (bfqd->large_burst) {
1199 bfq_mark_bfqq_in_large_burst(bfqq);
1200 goto end;
1201 }
1202
1203 /*
1204 * If we get here, then a large-burst state has not yet been
1205 * reached, but bfqq is being activated shortly after the last
1206 * queue. Then we add bfqq to the burst.
1207 */
1208 bfq_add_to_burst(bfqd, bfqq);
1209end:
1210 /*
1211 * At this point, bfqq either has been added to the current
1212 * burst or has caused the current burst to terminate and a
1213 * possible new burst to start. In particular, in the second
1214 * case, bfqq has become the first queue in the possible new
1215 * burst. In both cases last_ins_in_burst needs to be moved
1216 * forward.
1217 */
1218 bfqd->last_ins_in_burst = jiffies;
1219}
1220
1221static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1222{
1223 struct bfq_entity *entity = &bfqq->entity;
1224
1225 return entity->budget - entity->service;
1226}
1227
1228/*
1229 * If enough samples have been computed, return the current max budget
1230 * stored in bfqd, which is dynamically updated according to the
1231 * estimated disk peak rate; otherwise return the default max budget
1232 */
1233static int bfq_max_budget(struct bfq_data *bfqd)
1234{
1235 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1236 return bfq_default_max_budget;
1237 else
1238 return bfqd->bfq_max_budget;
1239}
1240
1241/*
1242 * Return min budget, which is a fraction of the current or default
1243 * max budget (trying with 1/32)
1244 */
1245static int bfq_min_budget(struct bfq_data *bfqd)
1246{
1247 if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1248 return bfq_default_max_budget / 32;
1249 else
1250 return bfqd->bfq_max_budget / 32;
1251}
1252
1253/*
1254 * The next function, invoked after the input queue bfqq switches from
1255 * idle to busy, updates the budget of bfqq. The function also tells
1256 * whether the in-service queue should be expired, by returning
1257 * true. The purpose of expiring the in-service queue is to give bfqq
1258 * the chance to possibly preempt the in-service queue, and the reason
1259 * for preempting the in-service queue is to achieve one of the two
1260 * goals below.
1261 *
1262 * 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1263 * expired because it has remained idle. In particular, bfqq may have
1264 * expired for one of the following two reasons:
1265 *
1266 * - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1267 * and did not make it to issue a new request before its last
1268 * request was served;
1269 *
1270 * - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1271 * a new request before the expiration of the idling-time.
1272 *
1273 * Even if bfqq has expired for one of the above reasons, the process
1274 * associated with the queue may be however issuing requests greedily,
1275 * and thus be sensitive to the bandwidth it receives (bfqq may have
1276 * remained idle for other reasons: CPU high load, bfqq not enjoying
1277 * idling, I/O throttling somewhere in the path from the process to
1278 * the I/O scheduler, ...). But if, after every expiration for one of
1279 * the above two reasons, bfqq has to wait for the service of at least
1280 * one full budget of another queue before being served again, then
1281 * bfqq is likely to get a much lower bandwidth or resource time than
1282 * its reserved ones. To address this issue, two countermeasures need
1283 * to be taken.
1284 *
1285 * First, the budget and the timestamps of bfqq need to be updated in
1286 * a special way on bfqq reactivation: they need to be updated as if
1287 * bfqq did not remain idle and did not expire. In fact, if they are
1288 * computed as if bfqq expired and remained idle until reactivation,
1289 * then the process associated with bfqq is treated as if, instead of
1290 * being greedy, it stopped issuing requests when bfqq remained idle,
1291 * and restarts issuing requests only on this reactivation. In other
1292 * words, the scheduler does not help the process recover the "service
1293 * hole" between bfqq expiration and reactivation. As a consequence,
1294 * the process receives a lower bandwidth than its reserved one. In
1295 * contrast, to recover this hole, the budget must be updated as if
1296 * bfqq was not expired at all before this reactivation, i.e., it must
1297 * be set to the value of the remaining budget when bfqq was
1298 * expired. Along the same line, timestamps need to be assigned the
1299 * value they had the last time bfqq was selected for service, i.e.,
1300 * before last expiration. Thus timestamps need to be back-shifted
1301 * with respect to their normal computation (see [1] for more details
1302 * on this tricky aspect).
1303 *
1304 * Secondly, to allow the process to recover the hole, the in-service
1305 * queue must be expired too, to give bfqq the chance to preempt it
1306 * immediately. In fact, if bfqq has to wait for a full budget of the
1307 * in-service queue to be completed, then it may become impossible to
1308 * let the process recover the hole, even if the back-shifted
1309 * timestamps of bfqq are lower than those of the in-service queue. If
1310 * this happens for most or all of the holes, then the process may not
1311 * receive its reserved bandwidth. In this respect, it is worth noting
1312 * that, being the service of outstanding requests unpreemptible, a
1313 * little fraction of the holes may however be unrecoverable, thereby
1314 * causing a little loss of bandwidth.
1315 *
1316 * The last important point is detecting whether bfqq does need this
1317 * bandwidth recovery. In this respect, the next function deems the
1318 * process associated with bfqq greedy, and thus allows it to recover
1319 * the hole, if: 1) the process is waiting for the arrival of a new
1320 * request (which implies that bfqq expired for one of the above two
1321 * reasons), and 2) such a request has arrived soon. The first
1322 * condition is controlled through the flag non_blocking_wait_rq,
1323 * while the second through the flag arrived_in_time. If both
1324 * conditions hold, then the function computes the budget in the
1325 * above-described special way, and signals that the in-service queue
1326 * should be expired. Timestamp back-shifting is done later in
1327 * __bfq_activate_entity.
1328 *
1329 * 2. Reduce latency. Even if timestamps are not backshifted to let
1330 * the process associated with bfqq recover a service hole, bfqq may
1331 * however happen to have, after being (re)activated, a lower finish
1332 * timestamp than the in-service queue. That is, the next budget of
1333 * bfqq may have to be completed before the one of the in-service
1334 * queue. If this is the case, then preempting the in-service queue
1335 * allows this goal to be achieved, apart from the unpreemptible,
1336 * outstanding requests mentioned above.
1337 *
1338 * Unfortunately, regardless of which of the above two goals one wants
1339 * to achieve, service trees need first to be updated to know whether
1340 * the in-service queue must be preempted. To have service trees
1341 * correctly updated, the in-service queue must be expired and
1342 * rescheduled, and bfqq must be scheduled too. This is one of the
1343 * most costly operations (in future versions, the scheduling
1344 * mechanism may be re-designed in such a way to make it possible to
1345 * know whether preemption is needed without needing to update service
1346 * trees). In addition, queue preemptions almost always cause random
1347 * I/O, and thus loss of throughput. Because of these facts, the next
1348 * function adopts the following simple scheme to avoid both costly
1349 * operations and too frequent preemptions: it requests the expiration
1350 * of the in-service queue (unconditionally) only for queues that need
1351 * to recover a hole, or that either are weight-raised or deserve to
1352 * be weight-raised.
1353 */
1354static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1355 struct bfq_queue *bfqq,
1356 bool arrived_in_time,
1357 bool wr_or_deserves_wr)
1358{
1359 struct bfq_entity *entity = &bfqq->entity;
1360
1361 if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) {
1362 /*
1363 * We do not clear the flag non_blocking_wait_rq here, as
1364 * the latter is used in bfq_activate_bfqq to signal
1365 * that timestamps need to be back-shifted (and is
1366 * cleared right after).
1367 */
1368
1369 /*
1370 * In next assignment we rely on that either
1371 * entity->service or entity->budget are not updated
1372 * on expiration if bfqq is empty (see
1373 * __bfq_bfqq_recalc_budget). Thus both quantities
1374 * remain unchanged after such an expiration, and the
1375 * following statement therefore assigns to
1376 * entity->budget the remaining budget on such an
1377 * expiration. For clarity, entity->service is not
1378 * updated on expiration in any case, and, in normal
1379 * operation, is reset only when bfqq is selected for
1380 * service (see bfq_get_next_queue).
1381 */
1382 entity->budget = min_t(unsigned long,
1383 bfq_bfqq_budget_left(bfqq),
1384 bfqq->max_budget);
1385
1386 return true;
1387 }
1388
1389 entity->budget = max_t(unsigned long, bfqq->max_budget,
1390 bfq_serv_to_charge(bfqq->next_rq, bfqq));
1391 bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1392 return wr_or_deserves_wr;
1393}
1394
1395/*
1396 * Return the farthest future time instant according to jiffies
1397 * macros.
1398 */
1399static unsigned long bfq_greatest_from_now(void)
1400{
1401 return jiffies + MAX_JIFFY_OFFSET;
1402}
1403
1404/*
1405 * Return the farthest past time instant according to jiffies
1406 * macros.
1407 */
1408static unsigned long bfq_smallest_from_now(void)
1409{
1410 return jiffies - MAX_JIFFY_OFFSET;
1411}
1412
1413static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1414 struct bfq_queue *bfqq,
1415 unsigned int old_wr_coeff,
1416 bool wr_or_deserves_wr,
1417 bool interactive,
1418 bool in_burst,
1419 bool soft_rt)
1420{
1421 if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1422 /* start a weight-raising period */
1423 if (interactive) {
1424 bfqq->service_from_wr = 0;
1425 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1426 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1427 } else {
1428 /*
1429 * No interactive weight raising in progress
1430 * here: assign minus infinity to
1431 * wr_start_at_switch_to_srt, to make sure
1432 * that, at the end of the soft-real-time
1433 * weight raising periods that is starting
1434 * now, no interactive weight-raising period
1435 * may be wrongly considered as still in
1436 * progress (and thus actually started by
1437 * mistake).
1438 */
1439 bfqq->wr_start_at_switch_to_srt =
1440 bfq_smallest_from_now();
1441 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1442 BFQ_SOFTRT_WEIGHT_FACTOR;
1443 bfqq->wr_cur_max_time =
1444 bfqd->bfq_wr_rt_max_time;
1445 }
1446
1447 /*
1448 * If needed, further reduce budget to make sure it is
1449 * close to bfqq's backlog, so as to reduce the
1450 * scheduling-error component due to a too large
1451 * budget. Do not care about throughput consequences,
1452 * but only about latency. Finally, do not assign a
1453 * too small budget either, to avoid increasing
1454 * latency by causing too frequent expirations.
1455 */
1456 bfqq->entity.budget = min_t(unsigned long,
1457 bfqq->entity.budget,
1458 2 * bfq_min_budget(bfqd));
1459 } else if (old_wr_coeff > 1) {
1460 if (interactive) { /* update wr coeff and duration */
1461 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1462 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1463 } else if (in_burst)
1464 bfqq->wr_coeff = 1;
1465 else if (soft_rt) {
1466 /*
1467 * The application is now or still meeting the
1468 * requirements for being deemed soft rt. We
1469 * can then correctly and safely (re)charge
1470 * the weight-raising duration for the
1471 * application with the weight-raising
1472 * duration for soft rt applications.
1473 *
1474 * In particular, doing this recharge now, i.e.,
1475 * before the weight-raising period for the
1476 * application finishes, reduces the probability
1477 * of the following negative scenario:
1478 * 1) the weight of a soft rt application is
1479 * raised at startup (as for any newly
1480 * created application),
1481 * 2) since the application is not interactive,
1482 * at a certain time weight-raising is
1483 * stopped for the application,
1484 * 3) at that time the application happens to
1485 * still have pending requests, and hence
1486 * is destined to not have a chance to be
1487 * deemed soft rt before these requests are
1488 * completed (see the comments to the
1489 * function bfq_bfqq_softrt_next_start()
1490 * for details on soft rt detection),
1491 * 4) these pending requests experience a high
1492 * latency because the application is not
1493 * weight-raised while they are pending.
1494 */
1495 if (bfqq->wr_cur_max_time !=
1496 bfqd->bfq_wr_rt_max_time) {
1497 bfqq->wr_start_at_switch_to_srt =
1498 bfqq->last_wr_start_finish;
1499
1500 bfqq->wr_cur_max_time =
1501 bfqd->bfq_wr_rt_max_time;
1502 bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1503 BFQ_SOFTRT_WEIGHT_FACTOR;
1504 }
1505 bfqq->last_wr_start_finish = jiffies;
1506 }
1507 }
1508}
1509
1510static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1511 struct bfq_queue *bfqq)
1512{
1513 return bfqq->dispatched == 0 &&
1514 time_is_before_jiffies(
1515 bfqq->budget_timeout +
1516 bfqd->bfq_wr_min_idle_time);
1517}
1518
1519static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1520 struct bfq_queue *bfqq,
1521 int old_wr_coeff,
1522 struct request *rq,
1523 bool *interactive)
1524{
1525 bool soft_rt, in_burst, wr_or_deserves_wr,
1526 bfqq_wants_to_preempt,
1527 idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1528 /*
1529 * See the comments on
1530 * bfq_bfqq_update_budg_for_activation for
1531 * details on the usage of the next variable.
1532 */
1533 arrived_in_time = ktime_get_ns() <=
1534 bfqq->ttime.last_end_request +
1535 bfqd->bfq_slice_idle * 3;
1536
1537
1538 /*
1539 * bfqq deserves to be weight-raised if:
1540 * - it is sync,
1541 * - it does not belong to a large burst,
1542 * - it has been idle for enough time or is soft real-time,
1543 * - is linked to a bfq_io_cq (it is not shared in any sense).
1544 */
1545 in_burst = bfq_bfqq_in_large_burst(bfqq);
1546 soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1547 !in_burst &&
1548 time_is_before_jiffies(bfqq->soft_rt_next_start);
1549 *interactive = !in_burst && idle_for_long_time;
1550 wr_or_deserves_wr = bfqd->low_latency &&
1551 (bfqq->wr_coeff > 1 ||
1552 (bfq_bfqq_sync(bfqq) &&
1553 bfqq->bic && (*interactive || soft_rt)));
1554
1555 /*
1556 * Using the last flag, update budget and check whether bfqq
1557 * may want to preempt the in-service queue.
1558 */
1559 bfqq_wants_to_preempt =
1560 bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1561 arrived_in_time,
1562 wr_or_deserves_wr);
1563
1564 /*
1565 * If bfqq happened to be activated in a burst, but has been
1566 * idle for much more than an interactive queue, then we
1567 * assume that, in the overall I/O initiated in the burst, the
1568 * I/O associated with bfqq is finished. So bfqq does not need
1569 * to be treated as a queue belonging to a burst
1570 * anymore. Accordingly, we reset bfqq's in_large_burst flag
1571 * if set, and remove bfqq from the burst list if it's
1572 * there. We do not decrement burst_size, because the fact
1573 * that bfqq does not need to belong to the burst list any
1574 * more does not invalidate the fact that bfqq was created in
1575 * a burst.
1576 */
1577 if (likely(!bfq_bfqq_just_created(bfqq)) &&
1578 idle_for_long_time &&
1579 time_is_before_jiffies(
1580 bfqq->budget_timeout +
1581 msecs_to_jiffies(10000))) {
1582 hlist_del_init(&bfqq->burst_list_node);
1583 bfq_clear_bfqq_in_large_burst(bfqq);
1584 }
1585
1586 bfq_clear_bfqq_just_created(bfqq);
1587
1588
1589 if (!bfq_bfqq_IO_bound(bfqq)) {
1590 if (arrived_in_time) {
1591 bfqq->requests_within_timer++;
1592 if (bfqq->requests_within_timer >=
1593 bfqd->bfq_requests_within_timer)
1594 bfq_mark_bfqq_IO_bound(bfqq);
1595 } else
1596 bfqq->requests_within_timer = 0;
1597 }
1598
1599 if (bfqd->low_latency) {
1600 if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1601 /* wraparound */
1602 bfqq->split_time =
1603 jiffies - bfqd->bfq_wr_min_idle_time - 1;
1604
1605 if (time_is_before_jiffies(bfqq->split_time +
1606 bfqd->bfq_wr_min_idle_time)) {
1607 bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1608 old_wr_coeff,
1609 wr_or_deserves_wr,
1610 *interactive,
1611 in_burst,
1612 soft_rt);
1613
1614 if (old_wr_coeff != bfqq->wr_coeff)
1615 bfqq->entity.prio_changed = 1;
1616 }
1617 }
1618
1619 bfqq->last_idle_bklogged = jiffies;
1620 bfqq->service_from_backlogged = 0;
1621 bfq_clear_bfqq_softrt_update(bfqq);
1622
1623 bfq_add_bfqq_busy(bfqd, bfqq);
1624
1625 /*
1626 * Expire in-service queue only if preemption may be needed
1627 * for guarantees. In this respect, the function
1628 * next_queue_may_preempt just checks a simple, necessary
1629 * condition, and not a sufficient condition based on
1630 * timestamps. In fact, for the latter condition to be
1631 * evaluated, timestamps would need first to be updated, and
1632 * this operation is quite costly (see the comments on the
1633 * function bfq_bfqq_update_budg_for_activation).
1634 */
1635 if (bfqd->in_service_queue && bfqq_wants_to_preempt &&
1636 bfqd->in_service_queue->wr_coeff < bfqq->wr_coeff &&
1637 next_queue_may_preempt(bfqd))
1638 bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
1639 false, BFQQE_PREEMPTED);
1640}
1641
1642static void bfq_add_request(struct request *rq)
1643{
1644 struct bfq_queue *bfqq = RQ_BFQQ(rq);
1645 struct bfq_data *bfqd = bfqq->bfqd;
1646 struct request *next_rq, *prev;
1647 unsigned int old_wr_coeff = bfqq->wr_coeff;
1648 bool interactive = false;
1649
1650 bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
1651 bfqq->queued[rq_is_sync(rq)]++;
1652 bfqd->queued++;
1653
1654 elv_rb_add(&bfqq->sort_list, rq);
1655
1656 /*
1657 * Check if this request is a better next-serve candidate.
1658 */
1659 prev = bfqq->next_rq;
1660 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, rq, bfqd->last_position);
1661 bfqq->next_rq = next_rq;
1662
1663 /*
1664 * Adjust priority tree position, if next_rq changes.
1665 */
1666 if (prev != bfqq->next_rq)
1667 bfq_pos_tree_add_move(bfqd, bfqq);
1668
1669 if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
1670 bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
1671 rq, &interactive);
1672 else {
1673 if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
1674 time_is_before_jiffies(
1675 bfqq->last_wr_start_finish +
1676 bfqd->bfq_wr_min_inter_arr_async)) {
1677 bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1678 bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1679
1680 bfqd->wr_busy_queues++;
1681 bfqq->entity.prio_changed = 1;
1682 }
1683 if (prev != bfqq->next_rq)
1684 bfq_updated_next_req(bfqd, bfqq);
1685 }
1686
1687 /*
1688 * Assign jiffies to last_wr_start_finish in the following
1689 * cases:
1690 *
1691 * . if bfqq is not going to be weight-raised, because, for
1692 * non weight-raised queues, last_wr_start_finish stores the
1693 * arrival time of the last request; as of now, this piece
1694 * of information is used only for deciding whether to
1695 * weight-raise async queues
1696 *
1697 * . if bfqq is not weight-raised, because, if bfqq is now
1698 * switching to weight-raised, then last_wr_start_finish
1699 * stores the time when weight-raising starts
1700 *
1701 * . if bfqq is interactive, because, regardless of whether
1702 * bfqq is currently weight-raised, the weight-raising
1703 * period must start or restart (this case is considered
1704 * separately because it is not detected by the above
1705 * conditions, if bfqq is already weight-raised)
1706 *
1707 * last_wr_start_finish has to be updated also if bfqq is soft
1708 * real-time, because the weight-raising period is constantly
1709 * restarted on idle-to-busy transitions for these queues, but
1710 * this is already done in bfq_bfqq_handle_idle_busy_switch if
1711 * needed.
1712 */
1713 if (bfqd->low_latency &&
1714 (old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
1715 bfqq->last_wr_start_finish = jiffies;
1716}
1717
1718static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
1719 struct bio *bio,
1720 struct request_queue *q)
1721{
1722 struct bfq_queue *bfqq = bfqd->bio_bfqq;
1723
1724
1725 if (bfqq)
1726 return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
1727
1728 return NULL;
1729}
1730
1731static sector_t get_sdist(sector_t last_pos, struct request *rq)
1732{
1733 if (last_pos)
1734 return abs(blk_rq_pos(rq) - last_pos);
1735
1736 return 0;
1737}
1738
1739#if 0 /* Still not clear if we can do without next two functions */
1740static void bfq_activate_request(struct request_queue *q, struct request *rq)
1741{
1742 struct bfq_data *bfqd = q->elevator->elevator_data;
1743
1744 bfqd->rq_in_driver++;
1745}
1746
1747static void bfq_deactivate_request(struct request_queue *q, struct request *rq)
1748{
1749 struct bfq_data *bfqd = q->elevator->elevator_data;
1750
1751 bfqd->rq_in_driver--;
1752}
1753#endif
1754
1755static void bfq_remove_request(struct request_queue *q,
1756 struct request *rq)
1757{
1758 struct bfq_queue *bfqq = RQ_BFQQ(rq);
1759 struct bfq_data *bfqd = bfqq->bfqd;
1760 const int sync = rq_is_sync(rq);
1761
1762 if (bfqq->next_rq == rq) {
1763 bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, rq);
1764 bfq_updated_next_req(bfqd, bfqq);
1765 }
1766
1767 if (rq->queuelist.prev != &rq->queuelist)
1768 list_del_init(&rq->queuelist);
1769 bfqq->queued[sync]--;
1770 bfqd->queued--;
1771 elv_rb_del(&bfqq->sort_list, rq);
1772
1773 elv_rqhash_del(q, rq);
1774 if (q->last_merge == rq)
1775 q->last_merge = NULL;
1776
1777 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
1778 bfqq->next_rq = NULL;
1779
1780 if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
1781 bfq_del_bfqq_busy(bfqd, bfqq, false);
1782 /*
1783 * bfqq emptied. In normal operation, when
1784 * bfqq is empty, bfqq->entity.service and
1785 * bfqq->entity.budget must contain,
1786 * respectively, the service received and the
1787 * budget used last time bfqq emptied. These
1788 * facts do not hold in this case, as at least
1789 * this last removal occurred while bfqq is
1790 * not in service. To avoid inconsistencies,
1791 * reset both bfqq->entity.service and
1792 * bfqq->entity.budget, if bfqq has still a
1793 * process that may issue I/O requests to it.
1794 */
1795 bfqq->entity.budget = bfqq->entity.service = 0;
1796 }
1797
1798 /*
1799 * Remove queue from request-position tree as it is empty.
1800 */
1801 if (bfqq->pos_root) {
1802 rb_erase(&bfqq->pos_node, bfqq->pos_root);
1803 bfqq->pos_root = NULL;
1804 }
1805 } else {
1806 bfq_pos_tree_add_move(bfqd, bfqq);
1807 }
1808
1809 if (rq->cmd_flags & REQ_META)
1810 bfqq->meta_pending--;
1811
1812}
1813
1814static bool bfq_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
1815{
1816 struct request_queue *q = hctx->queue;
1817 struct bfq_data *bfqd = q->elevator->elevator_data;
1818 struct request *free = NULL;
1819 /*
1820 * bfq_bic_lookup grabs the queue_lock: invoke it now and
1821 * store its return value for later use, to avoid nesting
1822 * queue_lock inside the bfqd->lock. We assume that the bic
1823 * returned by bfq_bic_lookup does not go away before
1824 * bfqd->lock is taken.
1825 */
1826 struct bfq_io_cq *bic = bfq_bic_lookup(bfqd, current->io_context, q);
1827 bool ret;
1828
1829 spin_lock_irq(&bfqd->lock);
1830
1831 if (bic)
1832 bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
1833 else
1834 bfqd->bio_bfqq = NULL;
1835 bfqd->bio_bic = bic;
1836
1837 ret = blk_mq_sched_try_merge(q, bio, &free);
1838
1839 if (free)
1840 blk_mq_free_request(free);
1841 spin_unlock_irq(&bfqd->lock);
1842
1843 return ret;
1844}
1845
1846static int bfq_request_merge(struct request_queue *q, struct request **req,
1847 struct bio *bio)
1848{
1849 struct bfq_data *bfqd = q->elevator->elevator_data;
1850 struct request *__rq;
1851
1852 __rq = bfq_find_rq_fmerge(bfqd, bio, q);
1853 if (__rq && elv_bio_merge_ok(__rq, bio)) {
1854 *req = __rq;
1855 return ELEVATOR_FRONT_MERGE;
1856 }
1857
1858 return ELEVATOR_NO_MERGE;
1859}
1860
1861static void bfq_request_merged(struct request_queue *q, struct request *req,
1862 enum elv_merge type)
1863{
1864 if (type == ELEVATOR_FRONT_MERGE &&
1865 rb_prev(&req->rb_node) &&
1866 blk_rq_pos(req) <
1867 blk_rq_pos(container_of(rb_prev(&req->rb_node),
1868 struct request, rb_node))) {
1869 struct bfq_queue *bfqq = RQ_BFQQ(req);
1870 struct bfq_data *bfqd = bfqq->bfqd;
1871 struct request *prev, *next_rq;
1872
1873 /* Reposition request in its sort_list */
1874 elv_rb_del(&bfqq->sort_list, req);
1875 elv_rb_add(&bfqq->sort_list, req);
1876
1877 /* Choose next request to be served for bfqq */
1878 prev = bfqq->next_rq;
1879 next_rq = bfq_choose_req(bfqd, bfqq->next_rq, req,
1880 bfqd->last_position);
1881 bfqq->next_rq = next_rq;
1882 /*
1883 * If next_rq changes, update both the queue's budget to
1884 * fit the new request and the queue's position in its
1885 * rq_pos_tree.
1886 */
1887 if (prev != bfqq->next_rq) {
1888 bfq_updated_next_req(bfqd, bfqq);
1889 bfq_pos_tree_add_move(bfqd, bfqq);
1890 }
1891 }
1892}
1893
1894static void bfq_requests_merged(struct request_queue *q, struct request *rq,
1895 struct request *next)
1896{
1897 struct bfq_queue *bfqq = RQ_BFQQ(rq), *next_bfqq = RQ_BFQQ(next);
1898
1899 if (!RB_EMPTY_NODE(&rq->rb_node))
1900 goto end;
1901 spin_lock_irq(&bfqq->bfqd->lock);
1902
1903 /*
1904 * If next and rq belong to the same bfq_queue and next is older
1905 * than rq, then reposition rq in the fifo (by substituting next
1906 * with rq). Otherwise, if next and rq belong to different
1907 * bfq_queues, never reposition rq: in fact, we would have to
1908 * reposition it with respect to next's position in its own fifo,
1909 * which would most certainly be too expensive with respect to
1910 * the benefits.
1911 */
1912 if (bfqq == next_bfqq &&
1913 !list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
1914 next->fifo_time < rq->fifo_time) {
1915 list_del_init(&rq->queuelist);
1916 list_replace_init(&next->queuelist, &rq->queuelist);
1917 rq->fifo_time = next->fifo_time;
1918 }
1919
1920 if (bfqq->next_rq == next)
1921 bfqq->next_rq = rq;
1922
1923 bfq_remove_request(q, next);
1924 bfqg_stats_update_io_remove(bfqq_group(bfqq), next->cmd_flags);
1925
1926 spin_unlock_irq(&bfqq->bfqd->lock);
1927end:
1928 bfqg_stats_update_io_merged(bfqq_group(bfqq), next->cmd_flags);
1929}
1930
1931/* Must be called with bfqq != NULL */
1932static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
1933{
1934 if (bfq_bfqq_busy(bfqq))
1935 bfqq->bfqd->wr_busy_queues--;
1936 bfqq->wr_coeff = 1;
1937 bfqq->wr_cur_max_time = 0;
1938 bfqq->last_wr_start_finish = jiffies;
1939 /*
1940 * Trigger a weight change on the next invocation of
1941 * __bfq_entity_update_weight_prio.
1942 */
1943 bfqq->entity.prio_changed = 1;
1944}
1945
1946void bfq_end_wr_async_queues(struct bfq_data *bfqd,
1947 struct bfq_group *bfqg)
1948{
1949 int i, j;
1950
1951 for (i = 0; i < 2; i++)
1952 for (j = 0; j < IOPRIO_BE_NR; j++)
1953 if (bfqg->async_bfqq[i][j])
1954 bfq_bfqq_end_wr(bfqg->async_bfqq[i][j]);
1955 if (bfqg->async_idle_bfqq)
1956 bfq_bfqq_end_wr(bfqg->async_idle_bfqq);
1957}
1958
1959static void bfq_end_wr(struct bfq_data *bfqd)
1960{
1961 struct bfq_queue *bfqq;
1962
1963 spin_lock_irq(&bfqd->lock);
1964
1965 list_for_each_entry(bfqq, &bfqd->active_list, bfqq_list)
1966 bfq_bfqq_end_wr(bfqq);
1967 list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
1968 bfq_bfqq_end_wr(bfqq);
1969 bfq_end_wr_async(bfqd);
1970
1971 spin_unlock_irq(&bfqd->lock);
1972}
1973
1974static sector_t bfq_io_struct_pos(void *io_struct, bool request)
1975{
1976 if (request)
1977 return blk_rq_pos(io_struct);
1978 else
1979 return ((struct bio *)io_struct)->bi_iter.bi_sector;
1980}
1981
1982static int bfq_rq_close_to_sector(void *io_struct, bool request,
1983 sector_t sector)
1984{
1985 return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
1986 BFQQ_CLOSE_THR;
1987}
1988
1989static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
1990 struct bfq_queue *bfqq,
1991 sector_t sector)
1992{
1993 struct rb_root *root = &bfq_bfqq_to_bfqg(bfqq)->rq_pos_tree;
1994 struct rb_node *parent, *node;
1995 struct bfq_queue *__bfqq;
1996
1997 if (RB_EMPTY_ROOT(root))
1998 return NULL;
1999
2000 /*
2001 * First, if we find a request starting at the end of the last
2002 * request, choose it.
2003 */
2004 __bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, &parent, NULL);
2005 if (__bfqq)
2006 return __bfqq;
2007
2008 /*
2009 * If the exact sector wasn't found, the parent of the NULL leaf
2010 * will contain the closest sector (rq_pos_tree sorted by
2011 * next_request position).
2012 */
2013 __bfqq = rb_entry(parent, struct bfq_queue, pos_node);
2014 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2015 return __bfqq;
2016
2017 if (blk_rq_pos(__bfqq->next_rq) < sector)
2018 node = rb_next(&__bfqq->pos_node);
2019 else
2020 node = rb_prev(&__bfqq->pos_node);
2021 if (!node)
2022 return NULL;
2023
2024 __bfqq = rb_entry(node, struct bfq_queue, pos_node);
2025 if (bfq_rq_close_to_sector(__bfqq->next_rq, true, sector))
2026 return __bfqq;
2027
2028 return NULL;
2029}
2030
2031static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
2032 struct bfq_queue *cur_bfqq,
2033 sector_t sector)
2034{
2035 struct bfq_queue *bfqq;
2036
2037 /*
2038 * We shall notice if some of the queues are cooperating,
2039 * e.g., working closely on the same area of the device. In
2040 * that case, we can group them together and: 1) don't waste
2041 * time idling, and 2) serve the union of their requests in
2042 * the best possible order for throughput.
2043 */
2044 bfqq = bfqq_find_close(bfqd, cur_bfqq, sector);
2045 if (!bfqq || bfqq == cur_bfqq)
2046 return NULL;
2047
2048 return bfqq;
2049}
2050
2051static struct bfq_queue *
2052bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2053{
2054 int process_refs, new_process_refs;
2055 struct bfq_queue *__bfqq;
2056
2057 /*
2058 * If there are no process references on the new_bfqq, then it is
2059 * unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
2060 * may have dropped their last reference (not just their last process
2061 * reference).
2062 */
2063 if (!bfqq_process_refs(new_bfqq))
2064 return NULL;
2065
2066 /* Avoid a circular list and skip interim queue merges. */
2067 while ((__bfqq = new_bfqq->new_bfqq)) {
2068 if (__bfqq == bfqq)
2069 return NULL;
2070 new_bfqq = __bfqq;
2071 }
2072
2073 process_refs = bfqq_process_refs(bfqq);
2074 new_process_refs = bfqq_process_refs(new_bfqq);
2075 /*
2076 * If the process for the bfqq has gone away, there is no
2077 * sense in merging the queues.
2078 */
2079 if (process_refs == 0 || new_process_refs == 0)
2080 return NULL;
2081
2082 bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
2083 new_bfqq->pid);
2084
2085 /*
2086 * Merging is just a redirection: the requests of the process
2087 * owning one of the two queues are redirected to the other queue.
2088 * The latter queue, in its turn, is set as shared if this is the
2089 * first time that the requests of some process are redirected to
2090 * it.
2091 *
2092 * We redirect bfqq to new_bfqq and not the opposite, because
2093 * we are in the context of the process owning bfqq, thus we
2094 * have the io_cq of this process. So we can immediately
2095 * configure this io_cq to redirect the requests of the
2096 * process to new_bfqq. In contrast, the io_cq of new_bfqq is
2097 * not available any more (new_bfqq->bic == NULL).
2098 *
2099 * Anyway, even in case new_bfqq coincides with the in-service
2100 * queue, redirecting requests the in-service queue is the
2101 * best option, as we feed the in-service queue with new
2102 * requests close to the last request served and, by doing so,
2103 * are likely to increase the throughput.
2104 */
2105 bfqq->new_bfqq = new_bfqq;
2106 new_bfqq->ref += process_refs;
2107 return new_bfqq;
2108}
2109
2110static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
2111 struct bfq_queue *new_bfqq)
2112{
2113 if (bfq_too_late_for_merging(new_bfqq))
2114 return false;
2115
2116 if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
2117 (bfqq->ioprio_class != new_bfqq->ioprio_class))
2118 return false;
2119
2120 /*
2121 * If either of the queues has already been detected as seeky,
2122 * then merging it with the other queue is unlikely to lead to
2123 * sequential I/O.
2124 */
2125 if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
2126 return false;
2127
2128 /*
2129 * Interleaved I/O is known to be done by (some) applications
2130 * only for reads, so it does not make sense to merge async
2131 * queues.
2132 */
2133 if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(new_bfqq))
2134 return false;
2135
2136 return true;
2137}
2138
2139/*
2140 * Attempt to schedule a merge of bfqq with the currently in-service
2141 * queue or with a close queue among the scheduled queues. Return
2142 * NULL if no merge was scheduled, a pointer to the shared bfq_queue
2143 * structure otherwise.
2144 *
2145 * The OOM queue is not allowed to participate to cooperation: in fact, since
2146 * the requests temporarily redirected to the OOM queue could be redirected
2147 * again to dedicated queues at any time, the state needed to correctly
2148 * handle merging with the OOM queue would be quite complex and expensive
2149 * to maintain. Besides, in such a critical condition as an out of memory,
2150 * the benefits of queue merging may be little relevant, or even negligible.
2151 *
2152 * WARNING: queue merging may impair fairness among non-weight raised
2153 * queues, for at least two reasons: 1) the original weight of a
2154 * merged queue may change during the merged state, 2) even being the
2155 * weight the same, a merged queue may be bloated with many more
2156 * requests than the ones produced by its originally-associated
2157 * process.
2158 */
2159static struct bfq_queue *
2160bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2161 void *io_struct, bool request)
2162{
2163 struct bfq_queue *in_service_bfqq, *new_bfqq;
2164
2165 /*
2166 * Prevent bfqq from being merged if it has been created too
2167 * long ago. The idea is that true cooperating processes, and
2168 * thus their associated bfq_queues, are supposed to be
2169 * created shortly after each other. This is the case, e.g.,
2170 * for KVM/QEMU and dump I/O threads. Basing on this
2171 * assumption, the following filtering greatly reduces the
2172 * probability that two non-cooperating processes, which just
2173 * happen to do close I/O for some short time interval, have
2174 * their queues merged by mistake.
2175 */
2176 if (bfq_too_late_for_merging(bfqq))
2177 return NULL;
2178
2179 if (bfqq->new_bfqq)
2180 return bfqq->new_bfqq;
2181
2182 if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
2183 return NULL;
2184
2185 /* If there is only one backlogged queue, don't search. */
2186 if (bfqd->busy_queues == 1)
2187 return NULL;
2188
2189 in_service_bfqq = bfqd->in_service_queue;
2190
2191 if (in_service_bfqq && in_service_bfqq != bfqq &&
2192 likely(in_service_bfqq != &bfqd->oom_bfqq) &&
2193 bfq_rq_close_to_sector(io_struct, request, bfqd->last_position) &&
2194 bfqq->entity.parent == in_service_bfqq->entity.parent &&
2195 bfq_may_be_close_cooperator(bfqq, in_service_bfqq)) {
2196 new_bfqq = bfq_setup_merge(bfqq, in_service_bfqq);
2197 if (new_bfqq)
2198 return new_bfqq;
2199 }
2200 /*
2201 * Check whether there is a cooperator among currently scheduled
2202 * queues. The only thing we need is that the bio/request is not
2203 * NULL, as we need it to establish whether a cooperator exists.
2204 */
2205 new_bfqq = bfq_find_close_cooperator(bfqd, bfqq,
2206 bfq_io_struct_pos(io_struct, request));
2207
2208 if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
2209 bfq_may_be_close_cooperator(bfqq, new_bfqq))
2210 return bfq_setup_merge(bfqq, new_bfqq);
2211
2212 return NULL;
2213}
2214
2215static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
2216{
2217 struct bfq_io_cq *bic = bfqq->bic;
2218
2219 /*
2220 * If !bfqq->bic, the queue is already shared or its requests
2221 * have already been redirected to a shared queue; both idle window
2222 * and weight raising state have already been saved. Do nothing.
2223 */
2224 if (!bic)
2225 return;
2226
2227 bic->saved_ttime = bfqq->ttime;
2228 bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
2229 bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
2230 bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
2231 bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
2232 if (unlikely(bfq_bfqq_just_created(bfqq) &&
2233 !bfq_bfqq_in_large_burst(bfqq) &&
2234 bfqq->bfqd->low_latency)) {
2235 /*
2236 * bfqq being merged right after being created: bfqq
2237 * would have deserved interactive weight raising, but
2238 * did not make it to be set in a weight-raised state,
2239 * because of this early merge. Store directly the
2240 * weight-raising state that would have been assigned
2241 * to bfqq, so that to avoid that bfqq unjustly fails
2242 * to enjoy weight raising if split soon.
2243 */
2244 bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
2245 bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
2246 bic->saved_last_wr_start_finish = jiffies;
2247 } else {
2248 bic->saved_wr_coeff = bfqq->wr_coeff;
2249 bic->saved_wr_start_at_switch_to_srt =
2250 bfqq->wr_start_at_switch_to_srt;
2251 bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
2252 bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
2253 }
2254}
2255
2256static void
2257bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
2258 struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2259{
2260 bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
2261 (unsigned long)new_bfqq->pid);
2262 /* Save weight raising and idle window of the merged queues */
2263 bfq_bfqq_save_state(bfqq);
2264 bfq_bfqq_save_state(new_bfqq);
2265 if (bfq_bfqq_IO_bound(bfqq))
2266 bfq_mark_bfqq_IO_bound(new_bfqq);
2267 bfq_clear_bfqq_IO_bound(bfqq);
2268
2269 /*
2270 * If bfqq is weight-raised, then let new_bfqq inherit
2271 * weight-raising. To reduce false positives, neglect the case
2272 * where bfqq has just been created, but has not yet made it
2273 * to be weight-raised (which may happen because EQM may merge
2274 * bfqq even before bfq_add_request is executed for the first
2275 * time for bfqq). Handling this case would however be very
2276 * easy, thanks to the flag just_created.
2277 */
2278 if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
2279 new_bfqq->wr_coeff = bfqq->wr_coeff;
2280 new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
2281 new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
2282 new_bfqq->wr_start_at_switch_to_srt =
2283 bfqq->wr_start_at_switch_to_srt;
2284 if (bfq_bfqq_busy(new_bfqq))
2285 bfqd->wr_busy_queues++;
2286 new_bfqq->entity.prio_changed = 1;
2287 }
2288
2289 if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
2290 bfqq->wr_coeff = 1;
2291 bfqq->entity.prio_changed = 1;
2292 if (bfq_bfqq_busy(bfqq))
2293 bfqd->wr_busy_queues--;
2294 }
2295
2296 bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
2297 bfqd->wr_busy_queues);
2298
2299 /*
2300 * Merge queues (that is, let bic redirect its requests to new_bfqq)
2301 */
2302 bic_set_bfqq(bic, new_bfqq, 1);
2303 bfq_mark_bfqq_coop(new_bfqq);
2304 /*
2305 * new_bfqq now belongs to at least two bics (it is a shared queue):
2306 * set new_bfqq->bic to NULL. bfqq either:
2307 * - does not belong to any bic any more, and hence bfqq->bic must
2308 * be set to NULL, or
2309 * - is a queue whose owning bics have already been redirected to a
2310 * different queue, hence the queue is destined to not belong to
2311 * any bic soon and bfqq->bic is already NULL (therefore the next
2312 * assignment causes no harm).
2313 */
2314 new_bfqq->bic = NULL;
2315 bfqq->bic = NULL;
2316 /* release process reference to bfqq */
2317 bfq_put_queue(bfqq);
2318}
2319
2320static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
2321 struct bio *bio)
2322{
2323 struct bfq_data *bfqd = q->elevator->elevator_data;
2324 bool is_sync = op_is_sync(bio->bi_opf);
2325 struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
2326
2327 /*
2328 * Disallow merge of a sync bio into an async request.
2329 */
2330 if (is_sync && !rq_is_sync(rq))
2331 return false;
2332
2333 /*
2334 * Lookup the bfqq that this bio will be queued with. Allow
2335 * merge only if rq is queued there.
2336 */
2337 if (!bfqq)
2338 return false;
2339
2340 /*
2341 * We take advantage of this function to perform an early merge
2342 * of the queues of possible cooperating processes.
2343 */
2344 new_bfqq = bfq_setup_cooperator(bfqd, bfqq, bio, false);
2345 if (new_bfqq) {
2346 /*
2347 * bic still points to bfqq, then it has not yet been
2348 * redirected to some other bfq_queue, and a queue
2349 * merge beween bfqq and new_bfqq can be safely
2350 * fulfillled, i.e., bic can be redirected to new_bfqq
2351 * and bfqq can be put.
2352 */
2353 bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
2354 new_bfqq);
2355 /*
2356 * If we get here, bio will be queued into new_queue,
2357 * so use new_bfqq to decide whether bio and rq can be
2358 * merged.
2359 */
2360 bfqq = new_bfqq;
2361
2362 /*
2363 * Change also bqfd->bio_bfqq, as
2364 * bfqd->bio_bic now points to new_bfqq, and
2365 * this function may be invoked again (and then may
2366 * use again bqfd->bio_bfqq).
2367 */
2368 bfqd->bio_bfqq = bfqq;
2369 }
2370
2371 return bfqq == RQ_BFQQ(rq);
2372}
2373
2374/*
2375 * Set the maximum time for the in-service queue to consume its
2376 * budget. This prevents seeky processes from lowering the throughput.
2377 * In practice, a time-slice service scheme is used with seeky
2378 * processes.
2379 */
2380static void bfq_set_budget_timeout(struct bfq_data *bfqd,
2381 struct bfq_queue *bfqq)
2382{
2383 unsigned int timeout_coeff;
2384
2385 if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
2386 timeout_coeff = 1;
2387 else
2388 timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
2389
2390 bfqd->last_budget_start = ktime_get();
2391
2392 bfqq->budget_timeout = jiffies +
2393 bfqd->bfq_timeout * timeout_coeff;
2394}
2395
2396static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
2397 struct bfq_queue *bfqq)
2398{
2399 if (bfqq) {
2400 bfq_clear_bfqq_fifo_expire(bfqq);
2401
2402 bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
2403
2404 if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
2405 bfqq->wr_coeff > 1 &&
2406 bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
2407 time_is_before_jiffies(bfqq->budget_timeout)) {
2408 /*
2409 * For soft real-time queues, move the start
2410 * of the weight-raising period forward by the
2411 * time the queue has not received any
2412 * service. Otherwise, a relatively long
2413 * service delay is likely to cause the
2414 * weight-raising period of the queue to end,
2415 * because of the short duration of the
2416 * weight-raising period of a soft real-time
2417 * queue. It is worth noting that this move
2418 * is not so dangerous for the other queues,
2419 * because soft real-time queues are not
2420 * greedy.
2421 *
2422 * To not add a further variable, we use the
2423 * overloaded field budget_timeout to
2424 * determine for how long the queue has not
2425 * received service, i.e., how much time has
2426 * elapsed since the queue expired. However,
2427 * this is a little imprecise, because
2428 * budget_timeout is set to jiffies if bfqq
2429 * not only expires, but also remains with no
2430 * request.
2431 */
2432 if (time_after(bfqq->budget_timeout,
2433 bfqq->last_wr_start_finish))
2434 bfqq->last_wr_start_finish +=
2435 jiffies - bfqq->budget_timeout;
2436 else
2437 bfqq->last_wr_start_finish = jiffies;
2438 }
2439
2440 bfq_set_budget_timeout(bfqd, bfqq);
2441 bfq_log_bfqq(bfqd, bfqq,
2442 "set_in_service_queue, cur-budget = %d",
2443 bfqq->entity.budget);
2444 }
2445
2446 bfqd->in_service_queue = bfqq;
2447}
2448
2449/*
2450 * Get and set a new queue for service.
2451 */
2452static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
2453{
2454 struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
2455
2456 __bfq_set_in_service_queue(bfqd, bfqq);
2457 return bfqq;
2458}
2459
2460static void bfq_arm_slice_timer(struct bfq_data *bfqd)
2461{
2462 struct bfq_queue *bfqq = bfqd->in_service_queue;
2463 u32 sl;
2464
2465 bfq_mark_bfqq_wait_request(bfqq);
2466
2467 /*
2468 * We don't want to idle for seeks, but we do want to allow
2469 * fair distribution of slice time for a process doing back-to-back
2470 * seeks. So allow a little bit of time for him to submit a new rq.
2471 */
2472 sl = bfqd->bfq_slice_idle;
2473 /*
2474 * Unless the queue is being weight-raised or the scenario is
2475 * asymmetric, grant only minimum idle time if the queue
2476 * is seeky. A long idling is preserved for a weight-raised
2477 * queue, or, more in general, in an asymmetric scenario,
2478 * because a long idling is needed for guaranteeing to a queue
2479 * its reserved share of the throughput (in particular, it is
2480 * needed if the queue has a higher weight than some other
2481 * queue).
2482 */
2483 if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
2484 bfq_symmetric_scenario(bfqd))
2485 sl = min_t(u64, sl, BFQ_MIN_TT);
2486
2487 bfqd->last_idling_start = ktime_get();
2488 hrtimer_start(&bfqd->idle_slice_timer, ns_to_ktime(sl),
2489 HRTIMER_MODE_REL);
2490 bfqg_stats_set_start_idle_time(bfqq_group(bfqq));
2491}
2492
2493/*
2494 * In autotuning mode, max_budget is dynamically recomputed as the
2495 * amount of sectors transferred in timeout at the estimated peak
2496 * rate. This enables BFQ to utilize a full timeslice with a full
2497 * budget, even if the in-service queue is served at peak rate. And
2498 * this maximises throughput with sequential workloads.
2499 */
2500static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
2501{
2502 return (u64)bfqd->peak_rate * USEC_PER_MSEC *
2503 jiffies_to_msecs(bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
2504}
2505
2506/*
2507 * Update parameters related to throughput and responsiveness, as a
2508 * function of the estimated peak rate. See comments on
2509 * bfq_calc_max_budget(), and on T_slow and T_fast arrays.
2510 */
2511static void update_thr_responsiveness_params(struct bfq_data *bfqd)
2512{
2513 int dev_type = blk_queue_nonrot(bfqd->queue);
2514
2515 if (bfqd->bfq_user_max_budget == 0)
2516 bfqd->bfq_max_budget =
2517 bfq_calc_max_budget(bfqd);
2518
2519 if (bfqd->device_speed == BFQ_BFQD_FAST &&
2520 bfqd->peak_rate < device_speed_thresh[dev_type]) {
2521 bfqd->device_speed = BFQ_BFQD_SLOW;
2522 bfqd->RT_prod = R_slow[dev_type] *
2523 T_slow[dev_type];
2524 } else if (bfqd->device_speed == BFQ_BFQD_SLOW &&
2525 bfqd->peak_rate > device_speed_thresh[dev_type]) {
2526 bfqd->device_speed = BFQ_BFQD_FAST;
2527 bfqd->RT_prod = R_fast[dev_type] *
2528 T_fast[dev_type];
2529 }
2530
2531 bfq_log(bfqd,
2532"dev_type %s dev_speed_class = %s (%llu sects/sec), thresh %llu setcs/sec",
2533 dev_type == 0 ? "ROT" : "NONROT",
2534 bfqd->device_speed == BFQ_BFQD_FAST ? "FAST" : "SLOW",
2535 bfqd->device_speed == BFQ_BFQD_FAST ?
2536 (USEC_PER_SEC*(u64)R_fast[dev_type])>>BFQ_RATE_SHIFT :
2537 (USEC_PER_SEC*(u64)R_slow[dev_type])>>BFQ_RATE_SHIFT,
2538 (USEC_PER_SEC*(u64)device_speed_thresh[dev_type])>>
2539 BFQ_RATE_SHIFT);
2540}
2541
2542static void bfq_reset_rate_computation(struct bfq_data *bfqd,
2543 struct request *rq)
2544{
2545 if (rq != NULL) { /* new rq dispatch now, reset accordingly */
2546 bfqd->last_dispatch = bfqd->first_dispatch = ktime_get_ns();
2547 bfqd->peak_rate_samples = 1;
2548 bfqd->sequential_samples = 0;
2549 bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
2550 blk_rq_sectors(rq);
2551 } else /* no new rq dispatched, just reset the number of samples */
2552 bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
2553
2554 bfq_log(bfqd,
2555 "reset_rate_computation at end, sample %u/%u tot_sects %llu",
2556 bfqd->peak_rate_samples, bfqd->sequential_samples,
2557 bfqd->tot_sectors_dispatched);
2558}
2559
2560static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
2561{
2562 u32 rate, weight, divisor;
2563
2564 /*
2565 * For the convergence property to hold (see comments on
2566 * bfq_update_peak_rate()) and for the assessment to be
2567 * reliable, a minimum number of samples must be present, and
2568 * a minimum amount of time must have elapsed. If not so, do
2569 * not compute new rate. Just reset parameters, to get ready
2570 * for a new evaluation attempt.
2571 */
2572 if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
2573 bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
2574 goto reset_computation;
2575
2576 /*
2577 * If a new request completion has occurred after last
2578 * dispatch, then, to approximate the rate at which requests
2579 * have been served by the device, it is more precise to
2580 * extend the observation interval to the last completion.
2581 */
2582 bfqd->delta_from_first =
2583 max_t(u64, bfqd->delta_from_first,
2584 bfqd->last_completion - bfqd->first_dispatch);
2585
2586 /*
2587 * Rate computed in sects/usec, and not sects/nsec, for
2588 * precision issues.
2589 */
2590 rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
2591 div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
2592
2593 /*
2594 * Peak rate not updated if:
2595 * - the percentage of sequential dispatches is below 3/4 of the
2596 * total, and rate is below the current estimated peak rate
2597 * - rate is unreasonably high (> 20M sectors/sec)
2598 */
2599 if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
2600 rate <= bfqd->peak_rate) ||
2601 rate > 20<<BFQ_RATE_SHIFT)
2602 goto reset_computation;
2603
2604 /*
2605 * We have to update the peak rate, at last! To this purpose,
2606 * we use a low-pass filter. We compute the smoothing constant
2607 * of the filter as a function of the 'weight' of the new
2608 * measured rate.
2609 *
2610 * As can be seen in next formulas, we define this weight as a
2611 * quantity proportional to how sequential the workload is,
2612 * and to how long the observation time interval is.
2613 *
2614 * The weight runs from 0 to 8. The maximum value of the
2615 * weight, 8, yields the minimum value for the smoothing
2616 * constant. At this minimum value for the smoothing constant,
2617 * the measured rate contributes for half of the next value of
2618 * the estimated peak rate.
2619 *
2620 * So, the first step is to compute the weight as a function
2621 * of how sequential the workload is. Note that the weight
2622 * cannot reach 9, because bfqd->sequential_samples cannot
2623 * become equal to bfqd->peak_rate_samples, which, in its
2624 * turn, holds true because bfqd->sequential_samples is not
2625 * incremented for the first sample.
2626 */
2627 weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
2628
2629 /*
2630 * Second step: further refine the weight as a function of the
2631 * duration of the observation interval.
2632 */
2633 weight = min_t(u32, 8,
2634 div_u64(weight * bfqd->delta_from_first,
2635 BFQ_RATE_REF_INTERVAL));
2636
2637 /*
2638 * Divisor ranging from 10, for minimum weight, to 2, for
2639 * maximum weight.
2640 */
2641 divisor = 10 - weight;
2642
2643 /*
2644 * Finally, update peak rate:
2645 *
2646 * peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
2647 */
2648 bfqd->peak_rate *= divisor-1;
2649 bfqd->peak_rate /= divisor;
2650 rate /= divisor; /* smoothing constant alpha = 1/divisor */
2651
2652 bfqd->peak_rate += rate;
2653
2654 /*
2655 * For a very slow device, bfqd->peak_rate can reach 0 (see
2656 * the minimum representable values reported in the comments
2657 * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
2658 * divisions by zero where bfqd->peak_rate is used as a
2659 * divisor.
2660 */
2661 bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
2662
2663 update_thr_responsiveness_params(bfqd);
2664
2665reset_computation:
2666 bfq_reset_rate_computation(bfqd, rq);
2667}
2668
2669/*
2670 * Update the read/write peak rate (the main quantity used for
2671 * auto-tuning, see update_thr_responsiveness_params()).
2672 *
2673 * It is not trivial to estimate the peak rate (correctly): because of
2674 * the presence of sw and hw queues between the scheduler and the
2675 * device components that finally serve I/O requests, it is hard to
2676 * say exactly when a given dispatched request is served inside the
2677 * device, and for how long. As a consequence, it is hard to know
2678 * precisely at what rate a given set of requests is actually served
2679 * by the device.
2680 *
2681 * On the opposite end, the dispatch time of any request is trivially
2682 * available, and, from this piece of information, the "dispatch rate"
2683 * of requests can be immediately computed. So, the idea in the next
2684 * function is to use what is known, namely request dispatch times
2685 * (plus, when useful, request completion times), to estimate what is
2686 * unknown, namely in-device request service rate.
2687 *
2688 * The main issue is that, because of the above facts, the rate at
2689 * which a certain set of requests is dispatched over a certain time
2690 * interval can vary greatly with respect to the rate at which the
2691 * same requests are then served. But, since the size of any
2692 * intermediate queue is limited, and the service scheme is lossless
2693 * (no request is silently dropped), the following obvious convergence
2694 * property holds: the number of requests dispatched MUST become
2695 * closer and closer to the number of requests completed as the
2696 * observation interval grows. This is the key property used in
2697 * the next function to estimate the peak service rate as a function
2698 * of the observed dispatch rate. The function assumes to be invoked
2699 * on every request dispatch.
2700 */
2701static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
2702{
2703 u64 now_ns = ktime_get_ns();
2704
2705 if (bfqd->peak_rate_samples == 0) { /* first dispatch */
2706 bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
2707 bfqd->peak_rate_samples);
2708 bfq_reset_rate_computation(bfqd, rq);
2709 goto update_last_values; /* will add one sample */
2710 }
2711
2712 /*
2713 * Device idle for very long: the observation interval lasting
2714 * up to this dispatch cannot be a valid observation interval
2715 * for computing a new peak rate (similarly to the late-
2716 * completion event in bfq_completed_request()). Go to
2717 * update_rate_and_reset to have the following three steps
2718 * taken:
2719 * - close the observation interval at the last (previous)
2720 * request dispatch or completion
2721 * - compute rate, if possible, for that observation interval
2722 * - start a new observation interval with this dispatch
2723 */
2724 if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
2725 bfqd->rq_in_driver == 0)
2726 goto update_rate_and_reset;
2727
2728 /* Update sampling information */
2729 bfqd->peak_rate_samples++;
2730
2731 if ((bfqd->rq_in_driver > 0 ||
2732 now_ns - bfqd->last_completion < BFQ_MIN_TT)
2733 && get_sdist(bfqd->last_position, rq) < BFQQ_SEEK_THR)
2734 bfqd->sequential_samples++;
2735
2736 bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
2737
2738 /* Reset max observed rq size every 32 dispatches */
2739 if (likely(bfqd->peak_rate_samples % 32))
2740 bfqd->last_rq_max_size =
2741 max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
2742 else
2743 bfqd->last_rq_max_size = blk_rq_sectors(rq);
2744
2745 bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
2746
2747 /* Target observation interval not yet reached, go on sampling */
2748 if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
2749 goto update_last_values;
2750
2751update_rate_and_reset:
2752 bfq_update_rate_reset(bfqd, rq);
2753update_last_values:
2754 bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
2755 bfqd->last_dispatch = now_ns;
2756}
2757
2758/*
2759 * Remove request from internal lists.
2760 */
2761static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
2762{
2763 struct bfq_queue *bfqq = RQ_BFQQ(rq);
2764
2765 /*
2766 * For consistency, the next instruction should have been
2767 * executed after removing the request from the queue and
2768 * dispatching it. We execute instead this instruction before
2769 * bfq_remove_request() (and hence introduce a temporary
2770 * inconsistency), for efficiency. In fact, should this
2771 * dispatch occur for a non in-service bfqq, this anticipated
2772 * increment prevents two counters related to bfqq->dispatched
2773 * from risking to be, first, uselessly decremented, and then
2774 * incremented again when the (new) value of bfqq->dispatched
2775 * happens to be taken into account.
2776 */
2777 bfqq->dispatched++;
2778 bfq_update_peak_rate(q->elevator->elevator_data, rq);
2779
2780 bfq_remove_request(q, rq);
2781}
2782
2783static void __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq)
2784{
2785 /*
2786 * If this bfqq is shared between multiple processes, check
2787 * to make sure that those processes are still issuing I/Os
2788 * within the mean seek distance. If not, it may be time to
2789 * break the queues apart again.
2790 */
2791 if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
2792 bfq_mark_bfqq_split_coop(bfqq);
2793
2794 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2795 if (bfqq->dispatched == 0)
2796 /*
2797 * Overloading budget_timeout field to store
2798 * the time at which the queue remains with no
2799 * backlog and no outstanding request; used by
2800 * the weight-raising mechanism.
2801 */
2802 bfqq->budget_timeout = jiffies;
2803
2804 bfq_del_bfqq_busy(bfqd, bfqq, true);
2805 } else {
2806 bfq_requeue_bfqq(bfqd, bfqq, true);
2807 /*
2808 * Resort priority tree of potential close cooperators.
2809 */
2810 bfq_pos_tree_add_move(bfqd, bfqq);
2811 }
2812
2813 /*
2814 * All in-service entities must have been properly deactivated
2815 * or requeued before executing the next function, which
2816 * resets all in-service entites as no more in service.
2817 */
2818 __bfq_bfqd_reset_in_service(bfqd);
2819}
2820
2821/**
2822 * __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
2823 * @bfqd: device data.
2824 * @bfqq: queue to update.
2825 * @reason: reason for expiration.
2826 *
2827 * Handle the feedback on @bfqq budget at queue expiration.
2828 * See the body for detailed comments.
2829 */
2830static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
2831 struct bfq_queue *bfqq,
2832 enum bfqq_expiration reason)
2833{
2834 struct request *next_rq;
2835 int budget, min_budget;
2836
2837 min_budget = bfq_min_budget(bfqd);
2838
2839 if (bfqq->wr_coeff == 1)
2840 budget = bfqq->max_budget;
2841 else /*
2842 * Use a constant, low budget for weight-raised queues,
2843 * to help achieve a low latency. Keep it slightly higher
2844 * than the minimum possible budget, to cause a little
2845 * bit fewer expirations.
2846 */
2847 budget = 2 * min_budget;
2848
2849 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
2850 bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
2851 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
2852 budget, bfq_min_budget(bfqd));
2853 bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
2854 bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
2855
2856 if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
2857 switch (reason) {
2858 /*
2859 * Caveat: in all the following cases we trade latency
2860 * for throughput.
2861 */
2862 case BFQQE_TOO_IDLE:
2863 /*
2864 * This is the only case where we may reduce
2865 * the budget: if there is no request of the
2866 * process still waiting for completion, then
2867 * we assume (tentatively) that the timer has
2868 * expired because the batch of requests of
2869 * the process could have been served with a
2870 * smaller budget. Hence, betting that
2871 * process will behave in the same way when it
2872 * becomes backlogged again, we reduce its
2873 * next budget. As long as we guess right,
2874 * this budget cut reduces the latency
2875 * experienced by the process.
2876 *
2877 * However, if there are still outstanding
2878 * requests, then the process may have not yet
2879 * issued its next request just because it is
2880 * still waiting for the completion of some of
2881 * the still outstanding ones. So in this
2882 * subcase we do not reduce its budget, on the
2883 * contrary we increase it to possibly boost
2884 * the throughput, as discussed in the
2885 * comments to the BUDGET_TIMEOUT case.
2886 */
2887 if (bfqq->dispatched > 0) /* still outstanding reqs */
2888 budget = min(budget * 2, bfqd->bfq_max_budget);
2889 else {
2890 if (budget > 5 * min_budget)
2891 budget -= 4 * min_budget;
2892 else
2893 budget = min_budget;
2894 }
2895 break;
2896 case BFQQE_BUDGET_TIMEOUT:
2897 /*
2898 * We double the budget here because it gives
2899 * the chance to boost the throughput if this
2900 * is not a seeky process (and has bumped into
2901 * this timeout because of, e.g., ZBR).
2902 */
2903 budget = min(budget * 2, bfqd->bfq_max_budget);
2904 break;
2905 case BFQQE_BUDGET_EXHAUSTED:
2906 /*
2907 * The process still has backlog, and did not
2908 * let either the budget timeout or the disk
2909 * idling timeout expire. Hence it is not
2910 * seeky, has a short thinktime and may be
2911 * happy with a higher budget too. So
2912 * definitely increase the budget of this good
2913 * candidate to boost the disk throughput.
2914 */
2915 budget = min(budget * 4, bfqd->bfq_max_budget);
2916 break;
2917 case BFQQE_NO_MORE_REQUESTS:
2918 /*
2919 * For queues that expire for this reason, it
2920 * is particularly important to keep the
2921 * budget close to the actual service they
2922 * need. Doing so reduces the timestamp
2923 * misalignment problem described in the
2924 * comments in the body of
2925 * __bfq_activate_entity. In fact, suppose
2926 * that a queue systematically expires for
2927 * BFQQE_NO_MORE_REQUESTS and presents a
2928 * new request in time to enjoy timestamp
2929 * back-shifting. The larger the budget of the
2930 * queue is with respect to the service the
2931 * queue actually requests in each service
2932 * slot, the more times the queue can be
2933 * reactivated with the same virtual finish
2934 * time. It follows that, even if this finish
2935 * time is pushed to the system virtual time
2936 * to reduce the consequent timestamp
2937 * misalignment, the queue unjustly enjoys for
2938 * many re-activations a lower finish time
2939 * than all newly activated queues.
2940 *
2941 * The service needed by bfqq is measured
2942 * quite precisely by bfqq->entity.service.
2943 * Since bfqq does not enjoy device idling,
2944 * bfqq->entity.service is equal to the number
2945 * of sectors that the process associated with
2946 * bfqq requested to read/write before waiting
2947 * for request completions, or blocking for
2948 * other reasons.
2949 */
2950 budget = max_t(int, bfqq->entity.service, min_budget);
2951 break;
2952 default:
2953 return;
2954 }
2955 } else if (!bfq_bfqq_sync(bfqq)) {
2956 /*
2957 * Async queues get always the maximum possible
2958 * budget, as for them we do not care about latency
2959 * (in addition, their ability to dispatch is limited
2960 * by the charging factor).
2961 */
2962 budget = bfqd->bfq_max_budget;
2963 }
2964
2965 bfqq->max_budget = budget;
2966
2967 if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
2968 !bfqd->bfq_user_max_budget)
2969 bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
2970
2971 /*
2972 * If there is still backlog, then assign a new budget, making
2973 * sure that it is large enough for the next request. Since
2974 * the finish time of bfqq must be kept in sync with the
2975 * budget, be sure to call __bfq_bfqq_expire() *after* this
2976 * update.
2977 *
2978 * If there is no backlog, then no need to update the budget;
2979 * it will be updated on the arrival of a new request.
2980 */
2981 next_rq = bfqq->next_rq;
2982 if (next_rq)
2983 bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
2984 bfq_serv_to_charge(next_rq, bfqq));
2985
2986 bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
2987 next_rq ? blk_rq_sectors(next_rq) : 0,
2988 bfqq->entity.budget);
2989}
2990
2991/*
2992 * Return true if the process associated with bfqq is "slow". The slow
2993 * flag is used, in addition to the budget timeout, to reduce the
2994 * amount of service provided to seeky processes, and thus reduce
2995 * their chances to lower the throughput. More details in the comments
2996 * on the function bfq_bfqq_expire().
2997 *
2998 * An important observation is in order: as discussed in the comments
2999 * on the function bfq_update_peak_rate(), with devices with internal
3000 * queues, it is hard if ever possible to know when and for how long
3001 * an I/O request is processed by the device (apart from the trivial
3002 * I/O pattern where a new request is dispatched only after the
3003 * previous one has been completed). This makes it hard to evaluate
3004 * the real rate at which the I/O requests of each bfq_queue are
3005 * served. In fact, for an I/O scheduler like BFQ, serving a
3006 * bfq_queue means just dispatching its requests during its service
3007 * slot (i.e., until the budget of the queue is exhausted, or the
3008 * queue remains idle, or, finally, a timeout fires). But, during the
3009 * service slot of a bfq_queue, around 100 ms at most, the device may
3010 * be even still processing requests of bfq_queues served in previous
3011 * service slots. On the opposite end, the requests of the in-service
3012 * bfq_queue may be completed after the service slot of the queue
3013 * finishes.
3014 *
3015 * Anyway, unless more sophisticated solutions are used
3016 * (where possible), the sum of the sizes of the requests dispatched
3017 * during the service slot of a bfq_queue is probably the only
3018 * approximation available for the service received by the bfq_queue
3019 * during its service slot. And this sum is the quantity used in this
3020 * function to evaluate the I/O speed of a process.
3021 */
3022static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3023 bool compensate, enum bfqq_expiration reason,
3024 unsigned long *delta_ms)
3025{
3026 ktime_t delta_ktime;
3027 u32 delta_usecs;
3028 bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
3029
3030 if (!bfq_bfqq_sync(bfqq))
3031 return false;
3032
3033 if (compensate)
3034 delta_ktime = bfqd->last_idling_start;
3035 else
3036 delta_ktime = ktime_get();
3037 delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
3038 delta_usecs = ktime_to_us(delta_ktime);
3039
3040 /* don't use too short time intervals */
3041 if (delta_usecs < 1000) {
3042 if (blk_queue_nonrot(bfqd->queue))
3043 /*
3044 * give same worst-case guarantees as idling
3045 * for seeky
3046 */
3047 *delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
3048 else /* charge at least one seek */
3049 *delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
3050
3051 return slow;
3052 }
3053
3054 *delta_ms = delta_usecs / USEC_PER_MSEC;
3055
3056 /*
3057 * Use only long (> 20ms) intervals to filter out excessive
3058 * spikes in service rate estimation.
3059 */
3060 if (delta_usecs > 20000) {
3061 /*
3062 * Caveat for rotational devices: processes doing I/O
3063 * in the slower disk zones tend to be slow(er) even
3064 * if not seeky. In this respect, the estimated peak
3065 * rate is likely to be an average over the disk
3066 * surface. Accordingly, to not be too harsh with
3067 * unlucky processes, a process is deemed slow only if
3068 * its rate has been lower than half of the estimated
3069 * peak rate.
3070 */
3071 slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
3072 }
3073
3074 bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
3075
3076 return slow;
3077}
3078
3079/*
3080 * To be deemed as soft real-time, an application must meet two
3081 * requirements. First, the application must not require an average
3082 * bandwidth higher than the approximate bandwidth required to playback or
3083 * record a compressed high-definition video.
3084 * The next function is invoked on the completion of the last request of a
3085 * batch, to compute the next-start time instant, soft_rt_next_start, such
3086 * that, if the next request of the application does not arrive before
3087 * soft_rt_next_start, then the above requirement on the bandwidth is met.
3088 *
3089 * The second requirement is that the request pattern of the application is
3090 * isochronous, i.e., that, after issuing a request or a batch of requests,
3091 * the application stops issuing new requests until all its pending requests
3092 * have been completed. After that, the application may issue a new batch,
3093 * and so on.
3094 * For this reason the next function is invoked to compute
3095 * soft_rt_next_start only for applications that meet this requirement,
3096 * whereas soft_rt_next_start is set to infinity for applications that do
3097 * not.
3098 *
3099 * Unfortunately, even a greedy (i.e., I/O-bound) application may
3100 * happen to meet, occasionally or systematically, both the above
3101 * bandwidth and isochrony requirements. This may happen at least in
3102 * the following circumstances. First, if the CPU load is high. The
3103 * application may stop issuing requests while the CPUs are busy
3104 * serving other processes, then restart, then stop again for a while,
3105 * and so on. The other circumstances are related to the storage
3106 * device: the storage device is highly loaded or reaches a low-enough
3107 * throughput with the I/O of the application (e.g., because the I/O
3108 * is random and/or the device is slow). In all these cases, the
3109 * I/O of the application may be simply slowed down enough to meet
3110 * the bandwidth and isochrony requirements. To reduce the probability
3111 * that greedy applications are deemed as soft real-time in these
3112 * corner cases, a further rule is used in the computation of
3113 * soft_rt_next_start: the return value of this function is forced to
3114 * be higher than the maximum between the following two quantities.
3115 *
3116 * (a) Current time plus: (1) the maximum time for which the arrival
3117 * of a request is waited for when a sync queue becomes idle,
3118 * namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We
3119 * postpone for a moment the reason for adding a few extra
3120 * jiffies; we get back to it after next item (b). Lower-bounding
3121 * the return value of this function with the current time plus
3122 * bfqd->bfq_slice_idle tends to filter out greedy applications,
3123 * because the latter issue their next request as soon as possible
3124 * after the last one has been completed. In contrast, a soft
3125 * real-time application spends some time processing data, after a
3126 * batch of its requests has been completed.
3127 *
3128 * (b) Current value of bfqq->soft_rt_next_start. As pointed out
3129 * above, greedy applications may happen to meet both the
3130 * bandwidth and isochrony requirements under heavy CPU or
3131 * storage-device load. In more detail, in these scenarios, these
3132 * applications happen, only for limited time periods, to do I/O
3133 * slowly enough to meet all the requirements described so far,
3134 * including the filtering in above item (a). These slow-speed
3135 * time intervals are usually interspersed between other time
3136 * intervals during which these applications do I/O at a very high
3137 * speed. Fortunately, exactly because of the high speed of the
3138 * I/O in the high-speed intervals, the values returned by this
3139 * function happen to be so high, near the end of any such
3140 * high-speed interval, to be likely to fall *after* the end of
3141 * the low-speed time interval that follows. These high values are
3142 * stored in bfqq->soft_rt_next_start after each invocation of
3143 * this function. As a consequence, if the last value of
3144 * bfqq->soft_rt_next_start is constantly used to lower-bound the
3145 * next value that this function may return, then, from the very
3146 * beginning of a low-speed interval, bfqq->soft_rt_next_start is
3147 * likely to be constantly kept so high that any I/O request
3148 * issued during the low-speed interval is considered as arriving
3149 * to soon for the application to be deemed as soft
3150 * real-time. Then, in the high-speed interval that follows, the
3151 * application will not be deemed as soft real-time, just because
3152 * it will do I/O at a high speed. And so on.
3153 *
3154 * Getting back to the filtering in item (a), in the following two
3155 * cases this filtering might be easily passed by a greedy
3156 * application, if the reference quantity was just
3157 * bfqd->bfq_slice_idle:
3158 * 1) HZ is so low that the duration of a jiffy is comparable to or
3159 * higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
3160 * devices with HZ=100. The time granularity may be so coarse
3161 * that the approximation, in jiffies, of bfqd->bfq_slice_idle
3162 * is rather lower than the exact value.
3163 * 2) jiffies, instead of increasing at a constant rate, may stop increasing
3164 * for a while, then suddenly 'jump' by several units to recover the lost
3165 * increments. This seems to happen, e.g., inside virtual machines.
3166 * To address this issue, in the filtering in (a) we do not use as a
3167 * reference time interval just bfqd->bfq_slice_idle, but
3168 * bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the
3169 * minimum number of jiffies for which the filter seems to be quite
3170 * precise also in embedded systems and KVM/QEMU virtual machines.
3171 */
3172static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
3173 struct bfq_queue *bfqq)
3174{
3175 return max3(bfqq->soft_rt_next_start,
3176 bfqq->last_idle_bklogged +
3177 HZ * bfqq->service_from_backlogged /
3178 bfqd->bfq_wr_max_softrt_rate,
3179 jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
3180}
3181
3182/**
3183 * bfq_bfqq_expire - expire a queue.
3184 * @bfqd: device owning the queue.
3185 * @bfqq: the queue to expire.
3186 * @compensate: if true, compensate for the time spent idling.
3187 * @reason: the reason causing the expiration.
3188 *
3189 * If the process associated with bfqq does slow I/O (e.g., because it
3190 * issues random requests), we charge bfqq with the time it has been
3191 * in service instead of the service it has received (see
3192 * bfq_bfqq_charge_time for details on how this goal is achieved). As
3193 * a consequence, bfqq will typically get higher timestamps upon
3194 * reactivation, and hence it will be rescheduled as if it had
3195 * received more service than what it has actually received. In the
3196 * end, bfqq receives less service in proportion to how slowly its
3197 * associated process consumes its budgets (and hence how seriously it
3198 * tends to lower the throughput). In addition, this time-charging
3199 * strategy guarantees time fairness among slow processes. In
3200 * contrast, if the process associated with bfqq is not slow, we
3201 * charge bfqq exactly with the service it has received.
3202 *
3203 * Charging time to the first type of queues and the exact service to
3204 * the other has the effect of using the WF2Q+ policy to schedule the
3205 * former on a timeslice basis, without violating service domain
3206 * guarantees among the latter.
3207 */
3208void bfq_bfqq_expire(struct bfq_data *bfqd,
3209 struct bfq_queue *bfqq,
3210 bool compensate,
3211 enum bfqq_expiration reason)
3212{
3213 bool slow;
3214 unsigned long delta = 0;
3215 struct bfq_entity *entity = &bfqq->entity;
3216 int ref;
3217
3218 /*
3219 * Check whether the process is slow (see bfq_bfqq_is_slow).
3220 */
3221 slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, reason, &delta);
3222
3223 /*
3224 * As above explained, charge slow (typically seeky) and
3225 * timed-out queues with the time and not the service
3226 * received, to favor sequential workloads.
3227 *
3228 * Processes doing I/O in the slower disk zones will tend to
3229 * be slow(er) even if not seeky. Therefore, since the
3230 * estimated peak rate is actually an average over the disk
3231 * surface, these processes may timeout just for bad luck. To
3232 * avoid punishing them, do not charge time to processes that
3233 * succeeded in consuming at least 2/3 of their budget. This
3234 * allows BFQ to preserve enough elasticity to still perform
3235 * bandwidth, and not time, distribution with little unlucky
3236 * or quasi-sequential processes.
3237 */
3238 if (bfqq->wr_coeff == 1 &&
3239 (slow ||
3240 (reason == BFQQE_BUDGET_TIMEOUT &&
3241 bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
3242 bfq_bfqq_charge_time(bfqd, bfqq, delta);
3243
3244 if (reason == BFQQE_TOO_IDLE &&
3245 entity->service <= 2 * entity->budget / 10)
3246 bfq_clear_bfqq_IO_bound(bfqq);
3247
3248 if (bfqd->low_latency && bfqq->wr_coeff == 1)
3249 bfqq->last_wr_start_finish = jiffies;
3250
3251 if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
3252 RB_EMPTY_ROOT(&bfqq->sort_list)) {
3253 /*
3254 * If we get here, and there are no outstanding
3255 * requests, then the request pattern is isochronous
3256 * (see the comments on the function
3257 * bfq_bfqq_softrt_next_start()). Thus we can compute
3258 * soft_rt_next_start. If, instead, the queue still
3259 * has outstanding requests, then we have to wait for
3260 * the completion of all the outstanding requests to
3261 * discover whether the request pattern is actually
3262 * isochronous.
3263 */
3264 if (bfqq->dispatched == 0)
3265 bfqq->soft_rt_next_start =
3266 bfq_bfqq_softrt_next_start(bfqd, bfqq);
3267 else {
3268 /*
3269 * The application is still waiting for the
3270 * completion of one or more requests:
3271 * prevent it from possibly being incorrectly
3272 * deemed as soft real-time by setting its
3273 * soft_rt_next_start to infinity. In fact,
3274 * without this assignment, the application
3275 * would be incorrectly deemed as soft
3276 * real-time if:
3277 * 1) it issued a new request before the
3278 * completion of all its in-flight
3279 * requests, and
3280 * 2) at that time, its soft_rt_next_start
3281 * happened to be in the past.
3282 */
3283 bfqq->soft_rt_next_start =
3284 bfq_greatest_from_now();
3285 /*
3286 * Schedule an update of soft_rt_next_start to when
3287 * the task may be discovered to be isochronous.
3288 */
3289 bfq_mark_bfqq_softrt_update(bfqq);
3290 }
3291 }
3292
3293 bfq_log_bfqq(bfqd, bfqq,
3294 "expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
3295 slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
3296
3297 /*
3298 * Increase, decrease or leave budget unchanged according to
3299 * reason.
3300 */
3301 __bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
3302 ref = bfqq->ref;
3303 __bfq_bfqq_expire(bfqd, bfqq);
3304
3305 /* mark bfqq as waiting a request only if a bic still points to it */
3306 if (ref > 1 && !bfq_bfqq_busy(bfqq) &&
3307 reason != BFQQE_BUDGET_TIMEOUT &&
3308 reason != BFQQE_BUDGET_EXHAUSTED)
3309 bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
3310}
3311
3312/*
3313 * Budget timeout is not implemented through a dedicated timer, but
3314 * just checked on request arrivals and completions, as well as on
3315 * idle timer expirations.
3316 */
3317static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
3318{
3319 return time_is_before_eq_jiffies(bfqq->budget_timeout);
3320}
3321
3322/*
3323 * If we expire a queue that is actively waiting (i.e., with the
3324 * device idled) for the arrival of a new request, then we may incur
3325 * the timestamp misalignment problem described in the body of the
3326 * function __bfq_activate_entity. Hence we return true only if this
3327 * condition does not hold, or if the queue is slow enough to deserve
3328 * only to be kicked off for preserving a high throughput.
3329 */
3330static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
3331{
3332 bfq_log_bfqq(bfqq->bfqd, bfqq,
3333 "may_budget_timeout: wait_request %d left %d timeout %d",
3334 bfq_bfqq_wait_request(bfqq),
3335 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3,
3336 bfq_bfqq_budget_timeout(bfqq));
3337
3338 return (!bfq_bfqq_wait_request(bfqq) ||
3339 bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3)
3340 &&
3341 bfq_bfqq_budget_timeout(bfqq);
3342}
3343
3344/*
3345 * For a queue that becomes empty, device idling is allowed only if
3346 * this function returns true for the queue. As a consequence, since
3347 * device idling plays a critical role in both throughput boosting and
3348 * service guarantees, the return value of this function plays a
3349 * critical role in both these aspects as well.
3350 *
3351 * In a nutshell, this function returns true only if idling is
3352 * beneficial for throughput or, even if detrimental for throughput,
3353 * idling is however necessary to preserve service guarantees (low
3354 * latency, desired throughput distribution, ...). In particular, on
3355 * NCQ-capable devices, this function tries to return false, so as to
3356 * help keep the drives' internal queues full, whenever this helps the
3357 * device boost the throughput without causing any service-guarantee
3358 * issue.
3359 *
3360 * In more detail, the return value of this function is obtained by,
3361 * first, computing a number of boolean variables that take into
3362 * account throughput and service-guarantee issues, and, then,
3363 * combining these variables in a logical expression. Most of the
3364 * issues taken into account are not trivial. We discuss these issues
3365 * individually while introducing the variables.
3366 */
3367static bool bfq_bfqq_may_idle(struct bfq_queue *bfqq)
3368{
3369 struct bfq_data *bfqd = bfqq->bfqd;
3370 bool rot_without_queueing =
3371 !blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
3372 bfqq_sequential_and_IO_bound,
3373 idling_boosts_thr, idling_boosts_thr_without_issues,
3374 idling_needed_for_service_guarantees,
3375 asymmetric_scenario;
3376
3377 if (bfqd->strict_guarantees)
3378 return true;
3379
3380 /*
3381 * Idling is performed only if slice_idle > 0. In addition, we
3382 * do not idle if
3383 * (a) bfqq is async
3384 * (b) bfqq is in the idle io prio class: in this case we do
3385 * not idle because we want to minimize the bandwidth that
3386 * queues in this class can steal to higher-priority queues
3387 */
3388 if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
3389 bfq_class_idle(bfqq))
3390 return false;
3391
3392 bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
3393 bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
3394
3395 /*
3396 * The next variable takes into account the cases where idling
3397 * boosts the throughput.
3398 *
3399 * The value of the variable is computed considering, first, that
3400 * idling is virtually always beneficial for the throughput if:
3401 * (a) the device is not NCQ-capable and rotational, or
3402 * (b) regardless of the presence of NCQ, the device is rotational and
3403 * the request pattern for bfqq is I/O-bound and sequential, or
3404 * (c) regardless of whether it is rotational, the device is
3405 * not NCQ-capable and the request pattern for bfqq is
3406 * I/O-bound and sequential.
3407 *
3408 * Secondly, and in contrast to the above item (b), idling an
3409 * NCQ-capable flash-based device would not boost the
3410 * throughput even with sequential I/O; rather it would lower
3411 * the throughput in proportion to how fast the device
3412 * is. Accordingly, the next variable is true if any of the
3413 * above conditions (a), (b) or (c) is true, and, in
3414 * particular, happens to be false if bfqd is an NCQ-capable
3415 * flash-based device.
3416 */
3417 idling_boosts_thr = rot_without_queueing ||
3418 ((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
3419 bfqq_sequential_and_IO_bound);
3420
3421 /*
3422 * The value of the next variable,
3423 * idling_boosts_thr_without_issues, is equal to that of
3424 * idling_boosts_thr, unless a special case holds. In this
3425 * special case, described below, idling may cause problems to
3426 * weight-raised queues.
3427 *
3428 * When the request pool is saturated (e.g., in the presence
3429 * of write hogs), if the processes associated with
3430 * non-weight-raised queues ask for requests at a lower rate,
3431 * then processes associated with weight-raised queues have a
3432 * higher probability to get a request from the pool
3433 * immediately (or at least soon) when they need one. Thus
3434 * they have a higher probability to actually get a fraction
3435 * of the device throughput proportional to their high
3436 * weight. This is especially true with NCQ-capable drives,
3437 * which enqueue several requests in advance, and further
3438 * reorder internally-queued requests.
3439 *
3440 * For this reason, we force to false the value of
3441 * idling_boosts_thr_without_issues if there are weight-raised
3442 * busy queues. In this case, and if bfqq is not weight-raised,
3443 * this guarantees that the device is not idled for bfqq (if,
3444 * instead, bfqq is weight-raised, then idling will be
3445 * guaranteed by another variable, see below). Combined with
3446 * the timestamping rules of BFQ (see [1] for details), this
3447 * behavior causes bfqq, and hence any sync non-weight-raised
3448 * queue, to get a lower number of requests served, and thus
3449 * to ask for a lower number of requests from the request
3450 * pool, before the busy weight-raised queues get served
3451 * again. This often mitigates starvation problems in the
3452 * presence of heavy write workloads and NCQ, thereby
3453 * guaranteeing a higher application and system responsiveness
3454 * in these hostile scenarios.
3455 */
3456 idling_boosts_thr_without_issues = idling_boosts_thr &&
3457 bfqd->wr_busy_queues == 0;
3458
3459 /*
3460 * There is then a case where idling must be performed not
3461 * for throughput concerns, but to preserve service
3462 * guarantees.
3463 *
3464 * To introduce this case, we can note that allowing the drive
3465 * to enqueue more than one request at a time, and hence
3466 * delegating de facto final scheduling decisions to the
3467 * drive's internal scheduler, entails loss of control on the
3468 * actual request service order. In particular, the critical
3469 * situation is when requests from different processes happen
3470 * to be present, at the same time, in the internal queue(s)
3471 * of the drive. In such a situation, the drive, by deciding
3472 * the service order of the internally-queued requests, does
3473 * determine also the actual throughput distribution among
3474 * these processes. But the drive typically has no notion or
3475 * concern about per-process throughput distribution, and
3476 * makes its decisions only on a per-request basis. Therefore,
3477 * the service distribution enforced by the drive's internal
3478 * scheduler is likely to coincide with the desired
3479 * device-throughput distribution only in a completely
3480 * symmetric scenario where:
3481 * (i) each of these processes must get the same throughput as
3482 * the others;
3483 * (ii) all these processes have the same I/O pattern
3484 (either sequential or random).
3485 * In fact, in such a scenario, the drive will tend to treat
3486 * the requests of each of these processes in about the same
3487 * way as the requests of the others, and thus to provide
3488 * each of these processes with about the same throughput
3489 * (which is exactly the desired throughput distribution). In
3490 * contrast, in any asymmetric scenario, device idling is
3491 * certainly needed to guarantee that bfqq receives its
3492 * assigned fraction of the device throughput (see [1] for
3493 * details).
3494 *
3495 * We address this issue by controlling, actually, only the
3496 * symmetry sub-condition (i), i.e., provided that
3497 * sub-condition (i) holds, idling is not performed,
3498 * regardless of whether sub-condition (ii) holds. In other
3499 * words, only if sub-condition (i) holds, then idling is
3500 * allowed, and the device tends to be prevented from queueing
3501 * many requests, possibly of several processes. The reason
3502 * for not controlling also sub-condition (ii) is that we
3503 * exploit preemption to preserve guarantees in case of
3504 * symmetric scenarios, even if (ii) does not hold, as
3505 * explained in the next two paragraphs.
3506 *
3507 * Even if a queue, say Q, is expired when it remains idle, Q
3508 * can still preempt the new in-service queue if the next
3509 * request of Q arrives soon (see the comments on
3510 * bfq_bfqq_update_budg_for_activation). If all queues and
3511 * groups have the same weight, this form of preemption,
3512 * combined with the hole-recovery heuristic described in the
3513 * comments on function bfq_bfqq_update_budg_for_activation,
3514 * are enough to preserve a correct bandwidth distribution in
3515 * the mid term, even without idling. In fact, even if not
3516 * idling allows the internal queues of the device to contain
3517 * many requests, and thus to reorder requests, we can rather
3518 * safely assume that the internal scheduler still preserves a
3519 * minimum of mid-term fairness. The motivation for using
3520 * preemption instead of idling is that, by not idling,
3521 * service guarantees are preserved without minimally
3522 * sacrificing throughput. In other words, both a high
3523 * throughput and its desired distribution are obtained.
3524 *
3525 * More precisely, this preemption-based, idleless approach
3526 * provides fairness in terms of IOPS, and not sectors per
3527 * second. This can be seen with a simple example. Suppose
3528 * that there are two queues with the same weight, but that
3529 * the first queue receives requests of 8 sectors, while the
3530 * second queue receives requests of 1024 sectors. In
3531 * addition, suppose that each of the two queues contains at
3532 * most one request at a time, which implies that each queue
3533 * always remains idle after it is served. Finally, after
3534 * remaining idle, each queue receives very quickly a new
3535 * request. It follows that the two queues are served
3536 * alternatively, preempting each other if needed. This
3537 * implies that, although both queues have the same weight,
3538 * the queue with large requests receives a service that is
3539 * 1024/8 times as high as the service received by the other
3540 * queue.
3541 *
3542 * On the other hand, device idling is performed, and thus
3543 * pure sector-domain guarantees are provided, for the
3544 * following queues, which are likely to need stronger
3545 * throughput guarantees: weight-raised queues, and queues
3546 * with a higher weight than other queues. When such queues
3547 * are active, sub-condition (i) is false, which triggers
3548 * device idling.
3549 *
3550 * According to the above considerations, the next variable is
3551 * true (only) if sub-condition (i) holds. To compute the
3552 * value of this variable, we not only use the return value of
3553 * the function bfq_symmetric_scenario(), but also check
3554 * whether bfqq is being weight-raised, because
3555 * bfq_symmetric_scenario() does not take into account also
3556 * weight-raised queues (see comments on
3557 * bfq_weights_tree_add()).
3558 *
3559 * As a side note, it is worth considering that the above
3560 * device-idling countermeasures may however fail in the
3561 * following unlucky scenario: if idling is (correctly)
3562 * disabled in a time period during which all symmetry
3563 * sub-conditions hold, and hence the device is allowed to
3564 * enqueue many requests, but at some later point in time some
3565 * sub-condition stops to hold, then it may become impossible
3566 * to let requests be served in the desired order until all
3567 * the requests already queued in the device have been served.
3568 */
3569 asymmetric_scenario = bfqq->wr_coeff > 1 ||
3570 !bfq_symmetric_scenario(bfqd);
3571
3572 /*
3573 * Finally, there is a case where maximizing throughput is the
3574 * best choice even if it may cause unfairness toward
3575 * bfqq. Such a case is when bfqq became active in a burst of
3576 * queue activations. Queues that became active during a large
3577 * burst benefit only from throughput, as discussed in the
3578 * comments on bfq_handle_burst. Thus, if bfqq became active
3579 * in a burst and not idling the device maximizes throughput,
3580 * then the device must no be idled, because not idling the
3581 * device provides bfqq and all other queues in the burst with
3582 * maximum benefit. Combining this and the above case, we can
3583 * now establish when idling is actually needed to preserve
3584 * service guarantees.
3585 */
3586 idling_needed_for_service_guarantees =
3587 asymmetric_scenario && !bfq_bfqq_in_large_burst(bfqq);
3588
3589 /*
3590 * We have now all the components we need to compute the
3591 * return value of the function, which is true only if idling
3592 * either boosts the throughput (without issues), or is
3593 * necessary to preserve service guarantees.
3594 */
3595 return idling_boosts_thr_without_issues ||
3596 idling_needed_for_service_guarantees;
3597}
3598
3599/*
3600 * If the in-service queue is empty but the function bfq_bfqq_may_idle
3601 * returns true, then:
3602 * 1) the queue must remain in service and cannot be expired, and
3603 * 2) the device must be idled to wait for the possible arrival of a new
3604 * request for the queue.
3605 * See the comments on the function bfq_bfqq_may_idle for the reasons
3606 * why performing device idling is the best choice to boost the throughput
3607 * and preserve service guarantees when bfq_bfqq_may_idle itself
3608 * returns true.
3609 */
3610static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
3611{
3612 return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_bfqq_may_idle(bfqq);
3613}
3614
3615/*
3616 * Select a queue for service. If we have a current queue in service,
3617 * check whether to continue servicing it, or retrieve and set a new one.
3618 */
3619static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
3620{
3621 struct bfq_queue *bfqq;
3622 struct request *next_rq;
3623 enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
3624
3625 bfqq = bfqd->in_service_queue;
3626 if (!bfqq)
3627 goto new_queue;
3628
3629 bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
3630
3631 if (bfq_may_expire_for_budg_timeout(bfqq) &&
3632 !bfq_bfqq_wait_request(bfqq) &&
3633 !bfq_bfqq_must_idle(bfqq))
3634 goto expire;
3635
3636check_queue:
3637 /*
3638 * This loop is rarely executed more than once. Even when it
3639 * happens, it is much more convenient to re-execute this loop
3640 * than to return NULL and trigger a new dispatch to get a
3641 * request served.
3642 */
3643 next_rq = bfqq->next_rq;
3644 /*
3645 * If bfqq has requests queued and it has enough budget left to
3646 * serve them, keep the queue, otherwise expire it.
3647 */
3648 if (next_rq) {
3649 if (bfq_serv_to_charge(next_rq, bfqq) >
3650 bfq_bfqq_budget_left(bfqq)) {
3651 /*
3652 * Expire the queue for budget exhaustion,
3653 * which makes sure that the next budget is
3654 * enough to serve the next request, even if
3655 * it comes from the fifo expired path.
3656 */
3657 reason = BFQQE_BUDGET_EXHAUSTED;
3658 goto expire;
3659 } else {
3660 /*
3661 * The idle timer may be pending because we may
3662 * not disable disk idling even when a new request
3663 * arrives.
3664 */
3665 if (bfq_bfqq_wait_request(bfqq)) {
3666 /*
3667 * If we get here: 1) at least a new request
3668 * has arrived but we have not disabled the
3669 * timer because the request was too small,
3670 * 2) then the block layer has unplugged
3671 * the device, causing the dispatch to be
3672 * invoked.
3673 *
3674 * Since the device is unplugged, now the
3675 * requests are probably large enough to
3676 * provide a reasonable throughput.
3677 * So we disable idling.
3678 */
3679 bfq_clear_bfqq_wait_request(bfqq);
3680 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
3681 }
3682 goto keep_queue;
3683 }
3684 }
3685
3686 /*
3687 * No requests pending. However, if the in-service queue is idling
3688 * for a new request, or has requests waiting for a completion and
3689 * may idle after their completion, then keep it anyway.
3690 */
3691 if (bfq_bfqq_wait_request(bfqq) ||
3692 (bfqq->dispatched != 0 && bfq_bfqq_may_idle(bfqq))) {
3693 bfqq = NULL;
3694 goto keep_queue;
3695 }
3696
3697 reason = BFQQE_NO_MORE_REQUESTS;
3698expire:
3699 bfq_bfqq_expire(bfqd, bfqq, false, reason);
3700new_queue:
3701 bfqq = bfq_set_in_service_queue(bfqd);
3702 if (bfqq) {
3703 bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
3704 goto check_queue;
3705 }
3706keep_queue:
3707 if (bfqq)
3708 bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
3709 else
3710 bfq_log(bfqd, "select_queue: no queue returned");
3711
3712 return bfqq;
3713}
3714
3715static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
3716{
3717 struct bfq_entity *entity = &bfqq->entity;
3718
3719 if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
3720 bfq_log_bfqq(bfqd, bfqq,
3721 "raising period dur %u/%u msec, old coeff %u, w %d(%d)",
3722 jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
3723 jiffies_to_msecs(bfqq->wr_cur_max_time),
3724 bfqq->wr_coeff,
3725 bfqq->entity.weight, bfqq->entity.orig_weight);
3726
3727 if (entity->prio_changed)
3728 bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
3729
3730 /*
3731 * If the queue was activated in a burst, or too much
3732 * time has elapsed from the beginning of this
3733 * weight-raising period, then end weight raising.
3734 */
3735 if (bfq_bfqq_in_large_burst(bfqq))
3736 bfq_bfqq_end_wr(bfqq);
3737 else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
3738 bfqq->wr_cur_max_time)) {
3739 if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
3740 time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
3741 bfq_wr_duration(bfqd)))
3742 bfq_bfqq_end_wr(bfqq);
3743 else {
3744 switch_back_to_interactive_wr(bfqq, bfqd);
3745 bfqq->entity.prio_changed = 1;
3746 }
3747 }
3748 if (bfqq->wr_coeff > 1 &&
3749 bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time &&
3750 bfqq->service_from_wr > max_service_from_wr) {
3751 /* see comments on max_service_from_wr */
3752 bfq_bfqq_end_wr(bfqq);
3753 }
3754 }
3755 /*
3756 * To improve latency (for this or other queues), immediately
3757 * update weight both if it must be raised and if it must be
3758 * lowered. Since, entity may be on some active tree here, and
3759 * might have a pending change of its ioprio class, invoke
3760 * next function with the last parameter unset (see the
3761 * comments on the function).
3762 */
3763 if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
3764 __bfq_entity_update_weight_prio(bfq_entity_service_tree(entity),
3765 entity, false);
3766}
3767
3768/*
3769 * Dispatch next request from bfqq.
3770 */
3771static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
3772 struct bfq_queue *bfqq)
3773{
3774 struct request *rq = bfqq->next_rq;
3775 unsigned long service_to_charge;
3776
3777 service_to_charge = bfq_serv_to_charge(rq, bfqq);
3778
3779 bfq_bfqq_served(bfqq, service_to_charge);
3780
3781 bfq_dispatch_remove(bfqd->queue, rq);
3782
3783 /*
3784 * If weight raising has to terminate for bfqq, then next
3785 * function causes an immediate update of bfqq's weight,
3786 * without waiting for next activation. As a consequence, on
3787 * expiration, bfqq will be timestamped as if has never been
3788 * weight-raised during this service slot, even if it has
3789 * received part or even most of the service as a
3790 * weight-raised queue. This inflates bfqq's timestamps, which
3791 * is beneficial, as bfqq is then more willing to leave the
3792 * device immediately to possible other weight-raised queues.
3793 */
3794 bfq_update_wr_data(bfqd, bfqq);
3795
3796 /*
3797 * Expire bfqq, pretending that its budget expired, if bfqq
3798 * belongs to CLASS_IDLE and other queues are waiting for
3799 * service.
3800 */
3801 if (bfqd->busy_queues > 1 && bfq_class_idle(bfqq))
3802 goto expire;
3803
3804 return rq;
3805
3806expire:
3807 bfq_bfqq_expire(bfqd, bfqq, false, BFQQE_BUDGET_EXHAUSTED);
3808 return rq;
3809}
3810
3811static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
3812{
3813 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
3814
3815 /*
3816 * Avoiding lock: a race on bfqd->busy_queues should cause at
3817 * most a call to dispatch for nothing
3818 */
3819 return !list_empty_careful(&bfqd->dispatch) ||
3820 bfqd->busy_queues > 0;
3821}
3822
3823static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
3824{
3825 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
3826 struct request *rq = NULL;
3827 struct bfq_queue *bfqq = NULL;
3828
3829 if (!list_empty(&bfqd->dispatch)) {
3830 rq = list_first_entry(&bfqd->dispatch, struct request,
3831 queuelist);
3832 list_del_init(&rq->queuelist);
3833
3834 bfqq = RQ_BFQQ(rq);
3835
3836 if (bfqq) {
3837 /*
3838 * Increment counters here, because this
3839 * dispatch does not follow the standard
3840 * dispatch flow (where counters are
3841 * incremented)
3842 */
3843 bfqq->dispatched++;
3844
3845 goto inc_in_driver_start_rq;
3846 }
3847
3848 /*
3849 * We exploit the bfq_finish_requeue_request hook to
3850 * decrement rq_in_driver, but
3851 * bfq_finish_requeue_request will not be invoked on
3852 * this request. So, to avoid unbalance, just start
3853 * this request, without incrementing rq_in_driver. As
3854 * a negative consequence, rq_in_driver is deceptively
3855 * lower than it should be while this request is in
3856 * service. This may cause bfq_schedule_dispatch to be
3857 * invoked uselessly.
3858 *
3859 * As for implementing an exact solution, the
3860 * bfq_finish_requeue_request hook, if defined, is
3861 * probably invoked also on this request. So, by
3862 * exploiting this hook, we could 1) increment
3863 * rq_in_driver here, and 2) decrement it in
3864 * bfq_finish_requeue_request. Such a solution would
3865 * let the value of the counter be always accurate,
3866 * but it would entail using an extra interface
3867 * function. This cost seems higher than the benefit,
3868 * being the frequency of non-elevator-private
3869 * requests very low.
3870 */
3871 goto start_rq;
3872 }
3873
3874 bfq_log(bfqd, "dispatch requests: %d busy queues", bfqd->busy_queues);
3875
3876 if (bfqd->busy_queues == 0)
3877 goto exit;
3878
3879 /*
3880 * Force device to serve one request at a time if
3881 * strict_guarantees is true. Forcing this service scheme is
3882 * currently the ONLY way to guarantee that the request
3883 * service order enforced by the scheduler is respected by a
3884 * queueing device. Otherwise the device is free even to make
3885 * some unlucky request wait for as long as the device
3886 * wishes.
3887 *
3888 * Of course, serving one request at at time may cause loss of
3889 * throughput.
3890 */
3891 if (bfqd->strict_guarantees && bfqd->rq_in_driver > 0)
3892 goto exit;
3893
3894 bfqq = bfq_select_queue(bfqd);
3895 if (!bfqq)
3896 goto exit;
3897
3898 rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
3899
3900 if (rq) {
3901inc_in_driver_start_rq:
3902 bfqd->rq_in_driver++;
3903start_rq:
3904 rq->rq_flags |= RQF_STARTED;
3905 }
3906exit:
3907 return rq;
3908}
3909
3910#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
3911static void bfq_update_dispatch_stats(struct request_queue *q,
3912 struct request *rq,
3913 struct bfq_queue *in_serv_queue,
3914 bool idle_timer_disabled)
3915{
3916 struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
3917
3918 if (!idle_timer_disabled && !bfqq)
3919 return;
3920
3921 /*
3922 * rq and bfqq are guaranteed to exist until this function
3923 * ends, for the following reasons. First, rq can be
3924 * dispatched to the device, and then can be completed and
3925 * freed, only after this function ends. Second, rq cannot be
3926 * merged (and thus freed because of a merge) any longer,
3927 * because it has already started. Thus rq cannot be freed
3928 * before this function ends, and, since rq has a reference to
3929 * bfqq, the same guarantee holds for bfqq too.
3930 *
3931 * In addition, the following queue lock guarantees that
3932 * bfqq_group(bfqq) exists as well.
3933 */
3934 spin_lock_irq(q->queue_lock);
3935 if (idle_timer_disabled)
3936 /*
3937 * Since the idle timer has been disabled,
3938 * in_serv_queue contained some request when
3939 * __bfq_dispatch_request was invoked above, which
3940 * implies that rq was picked exactly from
3941 * in_serv_queue. Thus in_serv_queue == bfqq, and is
3942 * therefore guaranteed to exist because of the above
3943 * arguments.
3944 */
3945 bfqg_stats_update_idle_time(bfqq_group(in_serv_queue));
3946 if (bfqq) {
3947 struct bfq_group *bfqg = bfqq_group(bfqq);
3948
3949 bfqg_stats_update_avg_queue_size(bfqg);
3950 bfqg_stats_set_start_empty_time(bfqg);
3951 bfqg_stats_update_io_remove(bfqg, rq->cmd_flags);
3952 }
3953 spin_unlock_irq(q->queue_lock);
3954}
3955#else
3956static inline void bfq_update_dispatch_stats(struct request_queue *q,
3957 struct request *rq,
3958 struct bfq_queue *in_serv_queue,
3959 bool idle_timer_disabled) {}
3960#endif
3961
3962static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
3963{
3964 struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
3965 struct request *rq;
3966 struct bfq_queue *in_serv_queue;
3967 bool waiting_rq, idle_timer_disabled;
3968
3969 spin_lock_irq(&bfqd->lock);
3970
3971 in_serv_queue = bfqd->in_service_queue;
3972 waiting_rq = in_serv_queue && bfq_bfqq_wait_request(in_serv_queue);
3973
3974 rq = __bfq_dispatch_request(hctx);
3975
3976 idle_timer_disabled =
3977 waiting_rq && !bfq_bfqq_wait_request(in_serv_queue);
3978
3979 spin_unlock_irq(&bfqd->lock);
3980
3981 bfq_update_dispatch_stats(hctx->queue, rq, in_serv_queue,
3982 idle_timer_disabled);
3983
3984 return rq;
3985}
3986
3987/*
3988 * Task holds one reference to the queue, dropped when task exits. Each rq
3989 * in-flight on this queue also holds a reference, dropped when rq is freed.
3990 *
3991 * Scheduler lock must be held here. Recall not to use bfqq after calling
3992 * this function on it.
3993 */
3994void bfq_put_queue(struct bfq_queue *bfqq)
3995{
3996#ifdef CONFIG_BFQ_GROUP_IOSCHED
3997 struct bfq_group *bfqg = bfqq_group(bfqq);
3998#endif
3999
4000 if (bfqq->bfqd)
4001 bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d",
4002 bfqq, bfqq->ref);
4003
4004 bfqq->ref--;
4005 if (bfqq->ref)
4006 return;
4007
4008 if (!hlist_unhashed(&bfqq->burst_list_node)) {
4009 hlist_del_init(&bfqq->burst_list_node);
4010 /*
4011 * Decrement also burst size after the removal, if the
4012 * process associated with bfqq is exiting, and thus
4013 * does not contribute to the burst any longer. This
4014 * decrement helps filter out false positives of large
4015 * bursts, when some short-lived process (often due to
4016 * the execution of commands by some service) happens
4017 * to start and exit while a complex application is
4018 * starting, and thus spawning several processes that
4019 * do I/O (and that *must not* be treated as a large
4020 * burst, see comments on bfq_handle_burst).
4021 *
4022 * In particular, the decrement is performed only if:
4023 * 1) bfqq is not a merged queue, because, if it is,
4024 * then this free of bfqq is not triggered by the exit
4025 * of the process bfqq is associated with, but exactly
4026 * by the fact that bfqq has just been merged.
4027 * 2) burst_size is greater than 0, to handle
4028 * unbalanced decrements. Unbalanced decrements may
4029 * happen in te following case: bfqq is inserted into
4030 * the current burst list--without incrementing
4031 * bust_size--because of a split, but the current
4032 * burst list is not the burst list bfqq belonged to
4033 * (see comments on the case of a split in
4034 * bfq_set_request).
4035 */
4036 if (bfqq->bic && bfqq->bfqd->burst_size > 0)
4037 bfqq->bfqd->burst_size--;
4038 }
4039
4040 kmem_cache_free(bfq_pool, bfqq);
4041#ifdef CONFIG_BFQ_GROUP_IOSCHED
4042 bfqg_and_blkg_put(bfqg);
4043#endif
4044}
4045
4046static void bfq_put_cooperator(struct bfq_queue *bfqq)
4047{
4048 struct bfq_queue *__bfqq, *next;
4049
4050 /*
4051 * If this queue was scheduled to merge with another queue, be
4052 * sure to drop the reference taken on that queue (and others in
4053 * the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
4054 */
4055 __bfqq = bfqq->new_bfqq;
4056 while (__bfqq) {
4057 if (__bfqq == bfqq)
4058 break;
4059 next = __bfqq->new_bfqq;
4060 bfq_put_queue(__bfqq);
4061 __bfqq = next;
4062 }
4063}
4064
4065static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
4066{
4067 if (bfqq == bfqd->in_service_queue) {
4068 __bfq_bfqq_expire(bfqd, bfqq);
4069 bfq_schedule_dispatch(bfqd);
4070 }
4071
4072 bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
4073
4074 bfq_put_cooperator(bfqq);
4075
4076 bfq_put_queue(bfqq); /* release process reference */
4077}
4078
4079static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
4080{
4081 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
4082 struct bfq_data *bfqd;
4083
4084 if (bfqq)
4085 bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
4086
4087 if (bfqq && bfqd) {
4088 unsigned long flags;
4089
4090 spin_lock_irqsave(&bfqd->lock, flags);
4091 bfq_exit_bfqq(bfqd, bfqq);
4092 bic_set_bfqq(bic, NULL, is_sync);
4093 spin_unlock_irqrestore(&bfqd->lock, flags);
4094 }
4095}
4096
4097static void bfq_exit_icq(struct io_cq *icq)
4098{
4099 struct bfq_io_cq *bic = icq_to_bic(icq);
4100
4101 bfq_exit_icq_bfqq(bic, true);
4102 bfq_exit_icq_bfqq(bic, false);
4103}
4104
4105/*
4106 * Update the entity prio values; note that the new values will not
4107 * be used until the next (re)activation.
4108 */
4109static void
4110bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
4111{
4112 struct task_struct *tsk = current;
4113 int ioprio_class;
4114 struct bfq_data *bfqd = bfqq->bfqd;
4115
4116 if (!bfqd)
4117 return;
4118
4119 ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
4120 switch (ioprio_class) {
4121 default:
4122 dev_err(bfqq->bfqd->queue->backing_dev_info->dev,
4123 "bfq: bad prio class %d\n", ioprio_class);
4124 /* fall through */
4125 case IOPRIO_CLASS_NONE:
4126 /*
4127 * No prio set, inherit CPU scheduling settings.
4128 */
4129 bfqq->new_ioprio = task_nice_ioprio(tsk);
4130 bfqq->new_ioprio_class = task_nice_ioclass(tsk);
4131 break;
4132 case IOPRIO_CLASS_RT:
4133 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
4134 bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
4135 break;
4136 case IOPRIO_CLASS_BE:
4137 bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
4138 bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
4139 break;
4140 case IOPRIO_CLASS_IDLE:
4141 bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
4142 bfqq->new_ioprio = 7;
4143 break;
4144 }
4145
4146 if (bfqq->new_ioprio >= IOPRIO_BE_NR) {
4147 pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
4148 bfqq->new_ioprio);
4149 bfqq->new_ioprio = IOPRIO_BE_NR;
4150 }
4151
4152 bfqq->entity.new_weight = bfq_ioprio_to_weight(bfqq->new_ioprio);
4153 bfqq->entity.prio_changed = 1;
4154}
4155
4156static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
4157 struct bio *bio, bool is_sync,
4158 struct bfq_io_cq *bic);
4159
4160static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
4161{
4162 struct bfq_data *bfqd = bic_to_bfqd(bic);
4163 struct bfq_queue *bfqq;
4164 int ioprio = bic->icq.ioc->ioprio;
4165
4166 /*
4167 * This condition may trigger on a newly created bic, be sure to
4168 * drop the lock before returning.
4169 */
4170 if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
4171 return;
4172
4173 bic->ioprio = ioprio;
4174
4175 bfqq = bic_to_bfqq(bic, false);
4176 if (bfqq) {
4177 /* release process reference on this queue */
4178 bfq_put_queue(bfqq);
4179 bfqq = bfq_get_queue(bfqd, bio, BLK_RW_ASYNC, bic);
4180 bic_set_bfqq(bic, bfqq, false);
4181 }
4182
4183 bfqq = bic_to_bfqq(bic, true);
4184 if (bfqq)
4185 bfq_set_next_ioprio_data(bfqq, bic);
4186}
4187
4188static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4189 struct bfq_io_cq *bic, pid_t pid, int is_sync)
4190{
4191 RB_CLEAR_NODE(&bfqq->entity.rb_node);
4192 INIT_LIST_HEAD(&bfqq->fifo);
4193 INIT_HLIST_NODE(&bfqq->burst_list_node);
4194
4195 bfqq->ref = 0;
4196 bfqq->bfqd = bfqd;
4197
4198 if (bic)
4199 bfq_set_next_ioprio_data(bfqq, bic);
4200
4201 if (is_sync) {
4202 /*
4203 * No need to mark as has_short_ttime if in
4204 * idle_class, because no device idling is performed
4205 * for queues in idle class
4206 */
4207 if (!bfq_class_idle(bfqq))
4208 /* tentatively mark as has_short_ttime */
4209 bfq_mark_bfqq_has_short_ttime(bfqq);
4210 bfq_mark_bfqq_sync(bfqq);
4211 bfq_mark_bfqq_just_created(bfqq);
4212 } else
4213 bfq_clear_bfqq_sync(bfqq);
4214
4215 /* set end request to minus infinity from now */
4216 bfqq->ttime.last_end_request = ktime_get_ns() + 1;
4217
4218 bfq_mark_bfqq_IO_bound(bfqq);
4219
4220 bfqq->pid = pid;
4221
4222 /* Tentative initial value to trade off between thr and lat */
4223 bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
4224 bfqq->budget_timeout = bfq_smallest_from_now();
4225
4226 bfqq->wr_coeff = 1;
4227 bfqq->last_wr_start_finish = jiffies;
4228 bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
4229 bfqq->split_time = bfq_smallest_from_now();
4230
4231 /*
4232 * To not forget the possibly high bandwidth consumed by a
4233 * process/queue in the recent past,
4234 * bfq_bfqq_softrt_next_start() returns a value at least equal
4235 * to the current value of bfqq->soft_rt_next_start (see
4236 * comments on bfq_bfqq_softrt_next_start). Set
4237 * soft_rt_next_start to now, to mean that bfqq has consumed
4238 * no bandwidth so far.
4239 */
4240 bfqq->soft_rt_next_start = jiffies;
4241
4242 /* first request is almost certainly seeky */
4243 bfqq->seek_history = 1;
4244}
4245
4246static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
4247 struct bfq_group *bfqg,
4248 int ioprio_class, int ioprio)
4249{
4250 switch (ioprio_class) {
4251 case IOPRIO_CLASS_RT:
4252 return &bfqg->async_bfqq[0][ioprio];
4253 case IOPRIO_CLASS_NONE:
4254 ioprio = IOPRIO_NORM;
4255 /* fall through */
4256 case IOPRIO_CLASS_BE:
4257 return &bfqg->async_bfqq[1][ioprio];
4258 case IOPRIO_CLASS_IDLE:
4259 return &bfqg->async_idle_bfqq;
4260 default:
4261 return NULL;
4262 }
4263}
4264
4265static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
4266 struct bio *bio, bool is_sync,
4267 struct bfq_io_cq *bic)
4268{
4269 const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
4270 const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
4271 struct bfq_queue **async_bfqq = NULL;
4272 struct bfq_queue *bfqq;
4273 struct bfq_group *bfqg;
4274
4275 rcu_read_lock();
4276
4277 bfqg = bfq_find_set_group(bfqd, bio_blkcg(bio));
4278 if (!bfqg) {
4279 bfqq = &bfqd->oom_bfqq;
4280 goto out;
4281 }
4282
4283 if (!is_sync) {
4284 async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
4285 ioprio);
4286 bfqq = *async_bfqq;
4287 if (bfqq)
4288 goto out;
4289 }
4290
4291 bfqq = kmem_cache_alloc_node(bfq_pool,
4292 GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
4293 bfqd->queue->node);
4294
4295 if (bfqq) {
4296 bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
4297 is_sync);
4298 bfq_init_entity(&bfqq->entity, bfqg);
4299 bfq_log_bfqq(bfqd, bfqq, "allocated");
4300 } else {
4301 bfqq = &bfqd->oom_bfqq;
4302 bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
4303 goto out;
4304 }
4305
4306 /*
4307 * Pin the queue now that it's allocated, scheduler exit will
4308 * prune it.
4309 */
4310 if (async_bfqq) {
4311 bfqq->ref++; /*
4312 * Extra group reference, w.r.t. sync
4313 * queue. This extra reference is removed
4314 * only if bfqq->bfqg disappears, to
4315 * guarantee that this queue is not freed
4316 * until its group goes away.
4317 */
4318 bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
4319 bfqq, bfqq->ref);
4320 *async_bfqq = bfqq;
4321 }
4322
4323out:
4324 bfqq->ref++; /* get a process reference to this queue */
4325 bfq_log_bfqq(bfqd, bfqq, "get_queue, at end: %p, %d", bfqq, bfqq->ref);
4326 rcu_read_unlock();
4327 return bfqq;
4328}
4329
4330static void bfq_update_io_thinktime(struct bfq_data *bfqd,
4331 struct bfq_queue *bfqq)
4332{
4333 struct bfq_ttime *ttime = &bfqq->ttime;
4334 u64 elapsed = ktime_get_ns() - bfqq->ttime.last_end_request;
4335
4336 elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
4337
4338 ttime->ttime_samples = (7*bfqq->ttime.ttime_samples + 256) / 8;
4339 ttime->ttime_total = div_u64(7*ttime->ttime_total + 256*elapsed, 8);
4340 ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
4341 ttime->ttime_samples);
4342}
4343
4344static void
4345bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4346 struct request *rq)
4347{
4348 bfqq->seek_history <<= 1;
4349 bfqq->seek_history |=
4350 get_sdist(bfqq->last_request_pos, rq) > BFQQ_SEEK_THR &&
4351 (!blk_queue_nonrot(bfqd->queue) ||
4352 blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT);
4353}
4354
4355static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
4356 struct bfq_queue *bfqq,
4357 struct bfq_io_cq *bic)
4358{
4359 bool has_short_ttime = true;
4360
4361 /*
4362 * No need to update has_short_ttime if bfqq is async or in
4363 * idle io prio class, or if bfq_slice_idle is zero, because
4364 * no device idling is performed for bfqq in this case.
4365 */
4366 if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
4367 bfqd->bfq_slice_idle == 0)
4368 return;
4369
4370 /* Idle window just restored, statistics are meaningless. */
4371 if (time_is_after_eq_jiffies(bfqq->split_time +
4372 bfqd->bfq_wr_min_idle_time))
4373 return;
4374
4375 /* Think time is infinite if no process is linked to
4376 * bfqq. Otherwise check average think time to
4377 * decide whether to mark as has_short_ttime
4378 */
4379 if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
4380 (bfq_sample_valid(bfqq->ttime.ttime_samples) &&
4381 bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle))
4382 has_short_ttime = false;
4383
4384 bfq_log_bfqq(bfqd, bfqq, "update_has_short_ttime: has_short_ttime %d",
4385 has_short_ttime);
4386
4387 if (has_short_ttime)
4388 bfq_mark_bfqq_has_short_ttime(bfqq);
4389 else
4390 bfq_clear_bfqq_has_short_ttime(bfqq);
4391}
4392
4393/*
4394 * Called when a new fs request (rq) is added to bfqq. Check if there's
4395 * something we should do about it.
4396 */
4397static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4398 struct request *rq)
4399{
4400 struct bfq_io_cq *bic = RQ_BIC(rq);
4401
4402 if (rq->cmd_flags & REQ_META)
4403 bfqq->meta_pending++;
4404
4405 bfq_update_io_thinktime(bfqd, bfqq);
4406 bfq_update_has_short_ttime(bfqd, bfqq, bic);
4407 bfq_update_io_seektime(bfqd, bfqq, rq);
4408
4409 bfq_log_bfqq(bfqd, bfqq,
4410 "rq_enqueued: has_short_ttime=%d (seeky %d)",
4411 bfq_bfqq_has_short_ttime(bfqq), BFQQ_SEEKY(bfqq));
4412
4413 bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
4414
4415 if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
4416 bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
4417 blk_rq_sectors(rq) < 32;
4418 bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
4419
4420 /*
4421 * There is just this request queued: if the request
4422 * is small and the queue is not to be expired, then
4423 * just exit.
4424 *
4425 * In this way, if the device is being idled to wait
4426 * for a new request from the in-service queue, we
4427 * avoid unplugging the device and committing the
4428 * device to serve just a small request. On the
4429 * contrary, we wait for the block layer to decide
4430 * when to unplug the device: hopefully, new requests
4431 * will be merged to this one quickly, then the device
4432 * will be unplugged and larger requests will be
4433 * dispatched.
4434 */
4435 if (small_req && !budget_timeout)
4436 return;
4437
4438 /*
4439 * A large enough request arrived, or the queue is to
4440 * be expired: in both cases disk idling is to be
4441 * stopped, so clear wait_request flag and reset
4442 * timer.
4443 */
4444 bfq_clear_bfqq_wait_request(bfqq);
4445 hrtimer_try_to_cancel(&bfqd->idle_slice_timer);
4446
4447 /*
4448 * The queue is not empty, because a new request just
4449 * arrived. Hence we can safely expire the queue, in
4450 * case of budget timeout, without risking that the
4451 * timestamps of the queue are not updated correctly.
4452 * See [1] for more details.
4453 */
4454 if (budget_timeout)
4455 bfq_bfqq_expire(bfqd, bfqq, false,
4456 BFQQE_BUDGET_TIMEOUT);
4457 }
4458}
4459
4460/* returns true if it causes the idle timer to be disabled */
4461static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
4462{
4463 struct bfq_queue *bfqq = RQ_BFQQ(rq),
4464 *new_bfqq = bfq_setup_cooperator(bfqd, bfqq, rq, true);
4465 bool waiting, idle_timer_disabled = false;
4466
4467 if (new_bfqq) {
4468 if (bic_to_bfqq(RQ_BIC(rq), 1) != bfqq)
4469 new_bfqq = bic_to_bfqq(RQ_BIC(rq), 1);
4470 /*
4471 * Release the request's reference to the old bfqq
4472 * and make sure one is taken to the shared queue.
4473 */
4474 new_bfqq->allocated++;
4475 bfqq->allocated--;
4476 new_bfqq->ref++;
4477 /*
4478 * If the bic associated with the process
4479 * issuing this request still points to bfqq
4480 * (and thus has not been already redirected
4481 * to new_bfqq or even some other bfq_queue),
4482 * then complete the merge and redirect it to
4483 * new_bfqq.
4484 */
4485 if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
4486 bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
4487 bfqq, new_bfqq);
4488
4489 bfq_clear_bfqq_just_created(bfqq);
4490 /*
4491 * rq is about to be enqueued into new_bfqq,
4492 * release rq reference on bfqq
4493 */
4494 bfq_put_queue(bfqq);
4495 rq->elv.priv[1] = new_bfqq;
4496 bfqq = new_bfqq;
4497 }
4498
4499 waiting = bfqq && bfq_bfqq_wait_request(bfqq);
4500 bfq_add_request(rq);
4501 idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq);
4502
4503 rq->fifo_time = ktime_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
4504 list_add_tail(&rq->queuelist, &bfqq->fifo);
4505
4506 bfq_rq_enqueued(bfqd, bfqq, rq);
4507
4508 return idle_timer_disabled;
4509}
4510
4511#if defined(CONFIG_BFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
4512static void bfq_update_insert_stats(struct request_queue *q,
4513 struct bfq_queue *bfqq,
4514 bool idle_timer_disabled,
4515 unsigned int cmd_flags)
4516{
4517 if (!bfqq)
4518 return;
4519
4520 /*
4521 * bfqq still exists, because it can disappear only after
4522 * either it is merged with another queue, or the process it
4523 * is associated with exits. But both actions must be taken by
4524 * the same process currently executing this flow of
4525 * instructions.
4526 *
4527 * In addition, the following queue lock guarantees that
4528 * bfqq_group(bfqq) exists as well.
4529 */
4530 spin_lock_irq(q->queue_lock);
4531 bfqg_stats_update_io_add(bfqq_group(bfqq), bfqq, cmd_flags);
4532 if (idle_timer_disabled)
4533 bfqg_stats_update_idle_time(bfqq_group(bfqq));
4534 spin_unlock_irq(q->queue_lock);
4535}
4536#else
4537static inline void bfq_update_insert_stats(struct request_queue *q,
4538 struct bfq_queue *bfqq,
4539 bool idle_timer_disabled,
4540 unsigned int cmd_flags) {}
4541#endif
4542
4543static void bfq_prepare_request(struct request *rq, struct bio *bio);
4544
4545static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
4546 bool at_head)
4547{
4548 struct request_queue *q = hctx->queue;
4549 struct bfq_data *bfqd = q->elevator->elevator_data;
4550 struct bfq_queue *bfqq = RQ_BFQQ(rq);
4551 bool idle_timer_disabled = false;
4552 unsigned int cmd_flags;
4553
4554 spin_lock_irq(&bfqd->lock);
4555 if (blk_mq_sched_try_insert_merge(q, rq)) {
4556 spin_unlock_irq(&bfqd->lock);
4557 return;
4558 }
4559
4560 spin_unlock_irq(&bfqd->lock);
4561
4562 blk_mq_sched_request_inserted(rq);
4563
4564 spin_lock_irq(&bfqd->lock);
4565 if (at_head || blk_rq_is_passthrough(rq)) {
4566 if (at_head)
4567 list_add(&rq->queuelist, &bfqd->dispatch);
4568 else
4569 list_add_tail(&rq->queuelist, &bfqd->dispatch);
4570 } else {
4571 if (WARN_ON_ONCE(!bfqq)) {
4572 /*
4573 * This should never happen. Most likely rq is
4574 * a requeued regular request, being
4575 * re-inserted without being first
4576 * re-prepared. Do a prepare, to avoid
4577 * failure.
4578 */
4579 bfq_prepare_request(rq, rq->bio);
4580 bfqq = RQ_BFQQ(rq);
4581 }
4582
4583 idle_timer_disabled = __bfq_insert_request(bfqd, rq);
4584 /*
4585 * Update bfqq, because, if a queue merge has occurred
4586 * in __bfq_insert_request, then rq has been
4587 * redirected into a new queue.
4588 */
4589 bfqq = RQ_BFQQ(rq);
4590
4591 if (rq_mergeable(rq)) {
4592 elv_rqhash_add(q, rq);
4593 if (!q->last_merge)
4594 q->last_merge = rq;
4595 }
4596 }
4597
4598 /*
4599 * Cache cmd_flags before releasing scheduler lock, because rq
4600 * may disappear afterwards (for example, because of a request
4601 * merge).
4602 */
4603 cmd_flags = rq->cmd_flags;
4604
4605 spin_unlock_irq(&bfqd->lock);
4606
4607 bfq_update_insert_stats(q, bfqq, idle_timer_disabled,
4608 cmd_flags);
4609}
4610
4611static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
4612 struct list_head *list, bool at_head)
4613{
4614 while (!list_empty(list)) {
4615 struct request *rq;
4616
4617 rq = list_first_entry(list, struct request, queuelist);
4618 list_del_init(&rq->queuelist);
4619 bfq_insert_request(hctx, rq, at_head);
4620 }
4621}
4622
4623static void bfq_update_hw_tag(struct bfq_data *bfqd)
4624{
4625 bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
4626 bfqd->rq_in_driver);
4627
4628 if (bfqd->hw_tag == 1)
4629 return;
4630
4631 /*
4632 * This sample is valid if the number of outstanding requests
4633 * is large enough to allow a queueing behavior. Note that the
4634 * sum is not exact, as it's not taking into account deactivated
4635 * requests.
4636 */
4637 if (bfqd->rq_in_driver + bfqd->queued < BFQ_HW_QUEUE_THRESHOLD)
4638 return;
4639
4640 if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
4641 return;
4642
4643 bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
4644 bfqd->max_rq_in_driver = 0;
4645 bfqd->hw_tag_samples = 0;
4646}
4647
4648static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
4649{
4650 u64 now_ns;
4651 u32 delta_us;
4652
4653 bfq_update_hw_tag(bfqd);
4654
4655 bfqd->rq_in_driver--;
4656 bfqq->dispatched--;
4657
4658 if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
4659 /*
4660 * Set budget_timeout (which we overload to store the
4661 * time at which the queue remains with no backlog and
4662 * no outstanding request; used by the weight-raising
4663 * mechanism).
4664 */
4665 bfqq->budget_timeout = jiffies;
4666
4667 bfq_weights_tree_remove(bfqd, &bfqq->entity,
4668 &bfqd->queue_weights_tree);
4669 }
4670
4671 now_ns = ktime_get_ns();
4672
4673 bfqq->ttime.last_end_request = now_ns;
4674
4675 /*
4676 * Using us instead of ns, to get a reasonable precision in
4677 * computing rate in next check.
4678 */
4679 delta_us = div_u64(now_ns - bfqd->last_completion, NSEC_PER_USEC);
4680
4681 /*
4682 * If the request took rather long to complete, and, according
4683 * to the maximum request size recorded, this completion latency
4684 * implies that the request was certainly served at a very low
4685 * rate (less than 1M sectors/sec), then the whole observation
4686 * interval that lasts up to this time instant cannot be a
4687 * valid time interval for computing a new peak rate. Invoke
4688 * bfq_update_rate_reset to have the following three steps
4689 * taken:
4690 * - close the observation interval at the last (previous)
4691 * request dispatch or completion
4692 * - compute rate, if possible, for that observation interval
4693 * - reset to zero samples, which will trigger a proper
4694 * re-initialization of the observation interval on next
4695 * dispatch
4696 */
4697 if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
4698 (bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
4699 1UL<<(BFQ_RATE_SHIFT - 10))
4700 bfq_update_rate_reset(bfqd, NULL);
4701 bfqd->last_completion = now_ns;
4702
4703 /*
4704 * If we are waiting to discover whether the request pattern
4705 * of the task associated with the queue is actually
4706 * isochronous, and both requisites for this condition to hold
4707 * are now satisfied, then compute soft_rt_next_start (see the
4708 * comments on the function bfq_bfqq_softrt_next_start()). We
4709 * schedule this delayed check when bfqq expires, if it still
4710 * has in-flight requests.
4711 */
4712 if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
4713 RB_EMPTY_ROOT(&bfqq->sort_list))
4714 bfqq->soft_rt_next_start =
4715 bfq_bfqq_softrt_next_start(bfqd, bfqq);
4716
4717 /*
4718 * If this is the in-service queue, check if it needs to be expired,
4719 * or if we want to idle in case it has no pending requests.
4720 */
4721 if (bfqd->in_service_queue == bfqq) {
4722 if (bfqq->dispatched == 0 && bfq_bfqq_must_idle(bfqq)) {
4723 bfq_arm_slice_timer(bfqd);
4724 return;
4725 } else if (bfq_may_expire_for_budg_timeout(bfqq))
4726 bfq_bfqq_expire(bfqd, bfqq, false,
4727 BFQQE_BUDGET_TIMEOUT);
4728 else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
4729 (bfqq->dispatched == 0 ||
4730 !bfq_bfqq_may_idle(bfqq)))
4731 bfq_bfqq_expire(bfqd, bfqq, false,
4732 BFQQE_NO_MORE_REQUESTS);
4733 }
4734
4735 if (!bfqd->rq_in_driver)
4736 bfq_schedule_dispatch(bfqd);
4737}
4738
4739static void bfq_finish_requeue_request_body(struct bfq_queue *bfqq)
4740{
4741 bfqq->allocated--;
4742
4743 bfq_put_queue(bfqq);
4744}
4745
4746/*
4747 * Handle either a requeue or a finish for rq. The things to do are
4748 * the same in both cases: all references to rq are to be dropped. In
4749 * particular, rq is considered completed from the point of view of
4750 * the scheduler.
4751 */
4752static void bfq_finish_requeue_request(struct request *rq)
4753{
4754 struct bfq_queue *bfqq = RQ_BFQQ(rq);
4755 struct bfq_data *bfqd;
4756
4757 /*
4758 * Requeue and finish hooks are invoked in blk-mq without
4759 * checking whether the involved request is actually still
4760 * referenced in the scheduler. To handle this fact, the
4761 * following two checks make this function exit in case of
4762 * spurious invocations, for which there is nothing to do.
4763 *
4764 * First, check whether rq has nothing to do with an elevator.
4765 */
4766 if (unlikely(!(rq->rq_flags & RQF_ELVPRIV)))
4767 return;
4768
4769 /*
4770 * rq either is not associated with any icq, or is an already
4771 * requeued request that has not (yet) been re-inserted into
4772 * a bfq_queue.
4773 */
4774 if (!rq->elv.icq || !bfqq)
4775 return;
4776
4777 bfqd = bfqq->bfqd;
4778
4779 if (rq->rq_flags & RQF_STARTED)
4780 bfqg_stats_update_completion(bfqq_group(bfqq),
4781 rq_start_time_ns(rq),
4782 rq_io_start_time_ns(rq),
4783 rq->cmd_flags);
4784
4785 if (likely(rq->rq_flags & RQF_STARTED)) {
4786 unsigned long flags;
4787
4788 spin_lock_irqsave(&bfqd->lock, flags);
4789
4790 bfq_completed_request(bfqq, bfqd);
4791 bfq_finish_requeue_request_body(bfqq);
4792
4793 spin_unlock_irqrestore(&bfqd->lock, flags);
4794 } else {
4795 /*
4796 * Request rq may be still/already in the scheduler,
4797 * in which case we need to remove it (this should
4798 * never happen in case of requeue). And we cannot
4799 * defer such a check and removal, to avoid
4800 * inconsistencies in the time interval from the end
4801 * of this function to the start of the deferred work.
4802 * This situation seems to occur only in process
4803 * context, as a consequence of a merge. In the
4804 * current version of the code, this implies that the
4805 * lock is held.
4806 */
4807
4808 if (!RB_EMPTY_NODE(&rq->rb_node)) {
4809 bfq_remove_request(rq->q, rq);
4810 bfqg_stats_update_io_remove(bfqq_group(bfqq),
4811 rq->cmd_flags);
4812 }
4813 bfq_finish_requeue_request_body(bfqq);
4814 }
4815
4816 /*
4817 * Reset private fields. In case of a requeue, this allows
4818 * this function to correctly do nothing if it is spuriously
4819 * invoked again on this same request (see the check at the
4820 * beginning of the function). Probably, a better general
4821 * design would be to prevent blk-mq from invoking the requeue
4822 * or finish hooks of an elevator, for a request that is not
4823 * referred by that elevator.
4824 *
4825 * Resetting the following fields would break the
4826 * request-insertion logic if rq is re-inserted into a bfq
4827 * internal queue, without a re-preparation. Here we assume
4828 * that re-insertions of requeued requests, without
4829 * re-preparation, can happen only for pass_through or at_head
4830 * requests (which are not re-inserted into bfq internal
4831 * queues).
4832 */
4833 rq->elv.priv[0] = NULL;
4834 rq->elv.priv[1] = NULL;
4835}
4836
4837/*
4838 * Returns NULL if a new bfqq should be allocated, or the old bfqq if this
4839 * was the last process referring to that bfqq.
4840 */
4841static struct bfq_queue *
4842bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
4843{
4844 bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
4845
4846 if (bfqq_process_refs(bfqq) == 1) {
4847 bfqq->pid = current->pid;
4848 bfq_clear_bfqq_coop(bfqq);
4849 bfq_clear_bfqq_split_coop(bfqq);
4850 return bfqq;
4851 }
4852
4853 bic_set_bfqq(bic, NULL, 1);
4854
4855 bfq_put_cooperator(bfqq);
4856
4857 bfq_put_queue(bfqq);
4858 return NULL;
4859}
4860
4861static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
4862 struct bfq_io_cq *bic,
4863 struct bio *bio,
4864 bool split, bool is_sync,
4865 bool *new_queue)
4866{
4867 struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
4868
4869 if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
4870 return bfqq;
4871
4872 if (new_queue)
4873 *new_queue = true;
4874
4875 if (bfqq)
4876 bfq_put_queue(bfqq);
4877 bfqq = bfq_get_queue(bfqd, bio, is_sync, bic);
4878
4879 bic_set_bfqq(bic, bfqq, is_sync);
4880 if (split && is_sync) {
4881 if ((bic->was_in_burst_list && bfqd->large_burst) ||
4882 bic->saved_in_large_burst)
4883 bfq_mark_bfqq_in_large_burst(bfqq);
4884 else {
4885 bfq_clear_bfqq_in_large_burst(bfqq);
4886 if (bic->was_in_burst_list)
4887 /*
4888 * If bfqq was in the current
4889 * burst list before being
4890 * merged, then we have to add
4891 * it back. And we do not need
4892 * to increase burst_size, as
4893 * we did not decrement
4894 * burst_size when we removed
4895 * bfqq from the burst list as
4896 * a consequence of a merge
4897 * (see comments in
4898 * bfq_put_queue). In this
4899 * respect, it would be rather
4900 * costly to know whether the
4901 * current burst list is still
4902 * the same burst list from
4903 * which bfqq was removed on
4904 * the merge. To avoid this
4905 * cost, if bfqq was in a
4906 * burst list, then we add
4907 * bfqq to the current burst
4908 * list without any further
4909 * check. This can cause
4910 * inappropriate insertions,
4911 * but rarely enough to not
4912 * harm the detection of large
4913 * bursts significantly.
4914 */
4915 hlist_add_head(&bfqq->burst_list_node,
4916 &bfqd->burst_list);
4917 }
4918 bfqq->split_time = jiffies;
4919 }
4920
4921 return bfqq;
4922}
4923
4924/*
4925 * Allocate bfq data structures associated with this request.
4926 */
4927static void bfq_prepare_request(struct request *rq, struct bio *bio)
4928{
4929 struct request_queue *q = rq->q;
4930 struct bfq_data *bfqd = q->elevator->elevator_data;
4931 struct bfq_io_cq *bic;
4932 const int is_sync = rq_is_sync(rq);
4933 struct bfq_queue *bfqq;
4934 bool new_queue = false;
4935 bool bfqq_already_existing = false, split = false;
4936
4937 /*
4938 * Even if we don't have an icq attached, we should still clear
4939 * the scheduler pointers, as they might point to previously
4940 * allocated bic/bfqq structs.
4941 */
4942 if (!rq->elv.icq) {
4943 rq->elv.priv[0] = rq->elv.priv[1] = NULL;
4944 return;
4945 }
4946
4947 bic = icq_to_bic(rq->elv.icq);
4948
4949 spin_lock_irq(&bfqd->lock);
4950
4951 bfq_check_ioprio_change(bic, bio);
4952
4953 bfq_bic_update_cgroup(bic, bio);
4954
4955 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, false, is_sync,
4956 &new_queue);
4957
4958 if (likely(!new_queue)) {
4959 /* If the queue was seeky for too long, break it apart. */
4960 if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq)) {
4961 bfq_log_bfqq(bfqd, bfqq, "breaking apart bfqq");
4962
4963 /* Update bic before losing reference to bfqq */
4964 if (bfq_bfqq_in_large_burst(bfqq))
4965 bic->saved_in_large_burst = true;
4966
4967 bfqq = bfq_split_bfqq(bic, bfqq);
4968 split = true;
4969
4970 if (!bfqq)
4971 bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
4972 true, is_sync,
4973 NULL);
4974 else
4975 bfqq_already_existing = true;
4976 }
4977 }
4978
4979 bfqq->allocated++;
4980 bfqq->ref++;
4981 bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
4982 rq, bfqq, bfqq->ref);
4983
4984 rq->elv.priv[0] = bic;
4985 rq->elv.priv[1] = bfqq;
4986
4987 /*
4988 * If a bfq_queue has only one process reference, it is owned
4989 * by only this bic: we can then set bfqq->bic = bic. in
4990 * addition, if the queue has also just been split, we have to
4991 * resume its state.
4992 */
4993 if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
4994 bfqq->bic = bic;
4995 if (split) {
4996 /*
4997 * The queue has just been split from a shared
4998 * queue: restore the idle window and the
4999 * possible weight raising period.
5000 */
5001 bfq_bfqq_resume_state(bfqq, bfqd, bic,
5002 bfqq_already_existing);
5003 }
5004 }
5005
5006 if (unlikely(bfq_bfqq_just_created(bfqq)))
5007 bfq_handle_burst(bfqd, bfqq);
5008
5009 spin_unlock_irq(&bfqd->lock);
5010}
5011
5012static void bfq_idle_slice_timer_body(struct bfq_queue *bfqq)
5013{
5014 struct bfq_data *bfqd = bfqq->bfqd;
5015 enum bfqq_expiration reason;
5016 unsigned long flags;
5017
5018 spin_lock_irqsave(&bfqd->lock, flags);
5019 bfq_clear_bfqq_wait_request(bfqq);
5020
5021 if (bfqq != bfqd->in_service_queue) {
5022 spin_unlock_irqrestore(&bfqd->lock, flags);
5023 return;
5024 }
5025
5026 if (bfq_bfqq_budget_timeout(bfqq))
5027 /*
5028 * Also here the queue can be safely expired
5029 * for budget timeout without wasting
5030 * guarantees
5031 */
5032 reason = BFQQE_BUDGET_TIMEOUT;
5033 else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
5034 /*
5035 * The queue may not be empty upon timer expiration,
5036 * because we may not disable the timer when the
5037 * first request of the in-service queue arrives
5038 * during disk idling.
5039 */
5040 reason = BFQQE_TOO_IDLE;
5041 else
5042 goto schedule_dispatch;
5043
5044 bfq_bfqq_expire(bfqd, bfqq, true, reason);
5045
5046schedule_dispatch:
5047 spin_unlock_irqrestore(&bfqd->lock, flags);
5048 bfq_schedule_dispatch(bfqd);
5049}
5050
5051/*
5052 * Handler of the expiration of the timer running if the in-service queue
5053 * is idling inside its time slice.
5054 */
5055static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
5056{
5057 struct bfq_data *bfqd = container_of(timer, struct bfq_data,
5058 idle_slice_timer);
5059 struct bfq_queue *bfqq = bfqd->in_service_queue;
5060
5061 /*
5062 * Theoretical race here: the in-service queue can be NULL or
5063 * different from the queue that was idling if a new request
5064 * arrives for the current queue and there is a full dispatch
5065 * cycle that changes the in-service queue. This can hardly
5066 * happen, but in the worst case we just expire a queue too
5067 * early.
5068 */
5069 if (bfqq)
5070 bfq_idle_slice_timer_body(bfqq);
5071
5072 return HRTIMER_NORESTART;
5073}
5074
5075static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
5076 struct bfq_queue **bfqq_ptr)
5077{
5078 struct bfq_queue *bfqq = *bfqq_ptr;
5079
5080 bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
5081 if (bfqq) {
5082 bfq_bfqq_move(bfqd, bfqq, bfqd->root_group);
5083
5084 bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
5085 bfqq, bfqq->ref);
5086 bfq_put_queue(bfqq);
5087 *bfqq_ptr = NULL;
5088 }
5089}
5090
5091/*
5092 * Release all the bfqg references to its async queues. If we are
5093 * deallocating the group these queues may still contain requests, so
5094 * we reparent them to the root cgroup (i.e., the only one that will
5095 * exist for sure until all the requests on a device are gone).
5096 */
5097void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
5098{
5099 int i, j;
5100
5101 for (i = 0; i < 2; i++)
5102 for (j = 0; j < IOPRIO_BE_NR; j++)
5103 __bfq_put_async_bfqq(bfqd, &bfqg->async_bfqq[i][j]);
5104
5105 __bfq_put_async_bfqq(bfqd, &bfqg->async_idle_bfqq);
5106}
5107
5108static void bfq_exit_queue(struct elevator_queue *e)
5109{
5110 struct bfq_data *bfqd = e->elevator_data;
5111 struct bfq_queue *bfqq, *n;
5112
5113 hrtimer_cancel(&bfqd->idle_slice_timer);
5114
5115 spin_lock_irq(&bfqd->lock);
5116 list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
5117 bfq_deactivate_bfqq(bfqd, bfqq, false, false);
5118 spin_unlock_irq(&bfqd->lock);
5119
5120 hrtimer_cancel(&bfqd->idle_slice_timer);
5121
5122#ifdef CONFIG_BFQ_GROUP_IOSCHED
5123 /* release oom-queue reference to root group */
5124 bfqg_and_blkg_put(bfqd->root_group);
5125
5126 blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
5127#else
5128 spin_lock_irq(&bfqd->lock);
5129 bfq_put_async_queues(bfqd, bfqd->root_group);
5130 kfree(bfqd->root_group);
5131 spin_unlock_irq(&bfqd->lock);
5132#endif
5133
5134 kfree(bfqd);
5135}
5136
5137static void bfq_init_root_group(struct bfq_group *root_group,
5138 struct bfq_data *bfqd)
5139{
5140 int i;
5141
5142#ifdef CONFIG_BFQ_GROUP_IOSCHED
5143 root_group->entity.parent = NULL;
5144 root_group->my_entity = NULL;
5145 root_group->bfqd = bfqd;
5146#endif
5147 root_group->rq_pos_tree = RB_ROOT;
5148 for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
5149 root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
5150 root_group->sched_data.bfq_class_idle_last_service = jiffies;
5151}
5152
5153static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
5154{
5155 struct bfq_data *bfqd;
5156 struct elevator_queue *eq;
5157
5158 eq = elevator_alloc(q, e);
5159 if (!eq)
5160 return -ENOMEM;
5161
5162 bfqd = kzalloc_node(sizeof(*bfqd), GFP_KERNEL, q->node);
5163 if (!bfqd) {
5164 kobject_put(&eq->kobj);
5165 return -ENOMEM;
5166 }
5167 eq->elevator_data = bfqd;
5168
5169 spin_lock_irq(q->queue_lock);
5170 q->elevator = eq;
5171 spin_unlock_irq(q->queue_lock);
5172
5173 /*
5174 * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
5175 * Grab a permanent reference to it, so that the normal code flow
5176 * will not attempt to free it.
5177 */
5178 bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
5179 bfqd->oom_bfqq.ref++;
5180 bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
5181 bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
5182 bfqd->oom_bfqq.entity.new_weight =
5183 bfq_ioprio_to_weight(bfqd->oom_bfqq.new_ioprio);
5184
5185 /* oom_bfqq does not participate to bursts */
5186 bfq_clear_bfqq_just_created(&bfqd->oom_bfqq);
5187
5188 /*
5189 * Trigger weight initialization, according to ioprio, at the
5190 * oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
5191 * class won't be changed any more.
5192 */
5193 bfqd->oom_bfqq.entity.prio_changed = 1;
5194
5195 bfqd->queue = q;
5196
5197 INIT_LIST_HEAD(&bfqd->dispatch);
5198
5199 hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
5200 HRTIMER_MODE_REL);
5201 bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
5202
5203 bfqd->queue_weights_tree = RB_ROOT;
5204 bfqd->group_weights_tree = RB_ROOT;
5205
5206 INIT_LIST_HEAD(&bfqd->active_list);
5207 INIT_LIST_HEAD(&bfqd->idle_list);
5208 INIT_HLIST_HEAD(&bfqd->burst_list);
5209
5210 bfqd->hw_tag = -1;
5211
5212 bfqd->bfq_max_budget = bfq_default_max_budget;
5213
5214 bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
5215 bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
5216 bfqd->bfq_back_max = bfq_back_max;
5217 bfqd->bfq_back_penalty = bfq_back_penalty;
5218 bfqd->bfq_slice_idle = bfq_slice_idle;
5219 bfqd->bfq_timeout = bfq_timeout;
5220
5221 bfqd->bfq_requests_within_timer = 120;
5222
5223 bfqd->bfq_large_burst_thresh = 8;
5224 bfqd->bfq_burst_interval = msecs_to_jiffies(180);
5225
5226 bfqd->low_latency = true;
5227
5228 /*
5229 * Trade-off between responsiveness and fairness.
5230 */
5231 bfqd->bfq_wr_coeff = 30;
5232 bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(300);
5233 bfqd->bfq_wr_max_time = 0;
5234 bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(2000);
5235 bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(500);
5236 bfqd->bfq_wr_max_softrt_rate = 7000; /*
5237 * Approximate rate required
5238 * to playback or record a
5239 * high-definition compressed
5240 * video.
5241 */
5242 bfqd->wr_busy_queues = 0;
5243
5244 /*
5245 * Begin by assuming, optimistically, that the device is a
5246 * high-speed one, and that its peak rate is equal to 2/3 of
5247 * the highest reference rate.
5248 */
5249 bfqd->RT_prod = R_fast[blk_queue_nonrot(bfqd->queue)] *
5250 T_fast[blk_queue_nonrot(bfqd->queue)];
5251 bfqd->peak_rate = R_fast[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
5252 bfqd->device_speed = BFQ_BFQD_FAST;
5253
5254 spin_lock_init(&bfqd->lock);
5255
5256 /*
5257 * The invocation of the next bfq_create_group_hierarchy
5258 * function is the head of a chain of function calls
5259 * (bfq_create_group_hierarchy->blkcg_activate_policy->
5260 * blk_mq_freeze_queue) that may lead to the invocation of the
5261 * has_work hook function. For this reason,
5262 * bfq_create_group_hierarchy is invoked only after all
5263 * scheduler data has been initialized, apart from the fields
5264 * that can be initialized only after invoking
5265 * bfq_create_group_hierarchy. This, in particular, enables
5266 * has_work to correctly return false. Of course, to avoid
5267 * other inconsistencies, the blk-mq stack must then refrain
5268 * from invoking further scheduler hooks before this init
5269 * function is finished.
5270 */
5271 bfqd->root_group = bfq_create_group_hierarchy(bfqd, q->node);
5272 if (!bfqd->root_group)
5273 goto out_free;
5274 bfq_init_root_group(bfqd->root_group, bfqd);
5275 bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);
5276
5277 wbt_disable_default(q);
5278 return 0;
5279
5280out_free:
5281 kfree(bfqd);
5282 kobject_put(&eq->kobj);
5283 return -ENOMEM;
5284}
5285
5286static void bfq_slab_kill(void)
5287{
5288 kmem_cache_destroy(bfq_pool);
5289}
5290
5291static int __init bfq_slab_setup(void)
5292{
5293 bfq_pool = KMEM_CACHE(bfq_queue, 0);
5294 if (!bfq_pool)
5295 return -ENOMEM;
5296 return 0;
5297}
5298
5299static ssize_t bfq_var_show(unsigned int var, char *page)
5300{
5301 return sprintf(page, "%u\n", var);
5302}
5303
5304static int bfq_var_store(unsigned long *var, const char *page)
5305{
5306 unsigned long new_val;
5307 int ret = kstrtoul(page, 10, &new_val);
5308
5309 if (ret)
5310 return ret;
5311 *var = new_val;
5312 return 0;
5313}
5314
5315#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
5316static ssize_t __FUNC(struct elevator_queue *e, char *page) \
5317{ \
5318 struct bfq_data *bfqd = e->elevator_data; \
5319 u64 __data = __VAR; \
5320 if (__CONV == 1) \
5321 __data = jiffies_to_msecs(__data); \
5322 else if (__CONV == 2) \
5323 __data = div_u64(__data, NSEC_PER_MSEC); \
5324 return bfq_var_show(__data, (page)); \
5325}
5326SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
5327SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
5328SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
5329SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
5330SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
5331SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
5332SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
5333SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
5334SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
5335#undef SHOW_FUNCTION
5336
5337#define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
5338static ssize_t __FUNC(struct elevator_queue *e, char *page) \
5339{ \
5340 struct bfq_data *bfqd = e->elevator_data; \
5341 u64 __data = __VAR; \
5342 __data = div_u64(__data, NSEC_PER_USEC); \
5343 return bfq_var_show(__data, (page)); \
5344}
5345USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
5346#undef USEC_SHOW_FUNCTION
5347
5348#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
5349static ssize_t \
5350__FUNC(struct elevator_queue *e, const char *page, size_t count) \
5351{ \
5352 struct bfq_data *bfqd = e->elevator_data; \
5353 unsigned long __data, __min = (MIN), __max = (MAX); \
5354 int ret; \
5355 \
5356 ret = bfq_var_store(&__data, (page)); \
5357 if (ret) \
5358 return ret; \
5359 if (__data < __min) \
5360 __data = __min; \
5361 else if (__data > __max) \
5362 __data = __max; \
5363 if (__CONV == 1) \
5364 *(__PTR) = msecs_to_jiffies(__data); \
5365 else if (__CONV == 2) \
5366 *(__PTR) = (u64)__data * NSEC_PER_MSEC; \
5367 else \
5368 *(__PTR) = __data; \
5369 return count; \
5370}
5371STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
5372 INT_MAX, 2);
5373STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
5374 INT_MAX, 2);
5375STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
5376STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
5377 INT_MAX, 0);
5378STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
5379#undef STORE_FUNCTION
5380
5381#define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
5382static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
5383{ \
5384 struct bfq_data *bfqd = e->elevator_data; \
5385 unsigned long __data, __min = (MIN), __max = (MAX); \
5386 int ret; \
5387 \
5388 ret = bfq_var_store(&__data, (page)); \
5389 if (ret) \
5390 return ret; \
5391 if (__data < __min) \
5392 __data = __min; \
5393 else if (__data > __max) \
5394 __data = __max; \
5395 *(__PTR) = (u64)__data * NSEC_PER_USEC; \
5396 return count; \
5397}
5398USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
5399 UINT_MAX);
5400#undef USEC_STORE_FUNCTION
5401
5402static ssize_t bfq_max_budget_store(struct elevator_queue *e,
5403 const char *page, size_t count)
5404{
5405 struct bfq_data *bfqd = e->elevator_data;
5406 unsigned long __data;
5407 int ret;
5408
5409 ret = bfq_var_store(&__data, (page));
5410 if (ret)
5411 return ret;
5412
5413 if (__data == 0)
5414 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
5415 else {
5416 if (__data > INT_MAX)
5417 __data = INT_MAX;
5418 bfqd->bfq_max_budget = __data;
5419 }
5420
5421 bfqd->bfq_user_max_budget = __data;
5422
5423 return count;
5424}
5425
5426/*
5427 * Leaving this name to preserve name compatibility with cfq
5428 * parameters, but this timeout is used for both sync and async.
5429 */
5430static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
5431 const char *page, size_t count)
5432{
5433 struct bfq_data *bfqd = e->elevator_data;
5434 unsigned long __data;
5435 int ret;
5436
5437 ret = bfq_var_store(&__data, (page));
5438 if (ret)
5439 return ret;
5440
5441 if (__data < 1)
5442 __data = 1;
5443 else if (__data > INT_MAX)
5444 __data = INT_MAX;
5445
5446 bfqd->bfq_timeout = msecs_to_jiffies(__data);
5447 if (bfqd->bfq_user_max_budget == 0)
5448 bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
5449
5450 return count;
5451}
5452
5453static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
5454 const char *page, size_t count)
5455{
5456 struct bfq_data *bfqd = e->elevator_data;
5457 unsigned long __data;
5458 int ret;
5459
5460 ret = bfq_var_store(&__data, (page));
5461 if (ret)
5462 return ret;
5463
5464 if (__data > 1)
5465 __data = 1;
5466 if (!bfqd->strict_guarantees && __data == 1
5467 && bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
5468 bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
5469
5470 bfqd->strict_guarantees = __data;
5471
5472 return count;
5473}
5474
5475static ssize_t bfq_low_latency_store(struct elevator_queue *e,
5476 const char *page, size_t count)
5477{
5478 struct bfq_data *bfqd = e->elevator_data;
5479 unsigned long __data;
5480 int ret;
5481
5482 ret = bfq_var_store(&__data, (page));
5483 if (ret)
5484 return ret;
5485
5486 if (__data > 1)
5487 __data = 1;
5488 if (__data == 0 && bfqd->low_latency != 0)
5489 bfq_end_wr(bfqd);
5490 bfqd->low_latency = __data;
5491
5492 return count;
5493}
5494
5495#define BFQ_ATTR(name) \
5496 __ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
5497
5498static struct elv_fs_entry bfq_attrs[] = {
5499 BFQ_ATTR(fifo_expire_sync),
5500 BFQ_ATTR(fifo_expire_async),
5501 BFQ_ATTR(back_seek_max),
5502 BFQ_ATTR(back_seek_penalty),
5503 BFQ_ATTR(slice_idle),
5504 BFQ_ATTR(slice_idle_us),
5505 BFQ_ATTR(max_budget),
5506 BFQ_ATTR(timeout_sync),
5507 BFQ_ATTR(strict_guarantees),
5508 BFQ_ATTR(low_latency),
5509 __ATTR_NULL
5510};
5511
5512static struct elevator_type iosched_bfq_mq = {
5513 .ops.mq = {
5514 .limit_depth = bfq_limit_depth,
5515 .prepare_request = bfq_prepare_request,
5516 .requeue_request = bfq_finish_requeue_request,
5517 .finish_request = bfq_finish_requeue_request,
5518 .exit_icq = bfq_exit_icq,
5519 .insert_requests = bfq_insert_requests,
5520 .dispatch_request = bfq_dispatch_request,
5521 .next_request = elv_rb_latter_request,
5522 .former_request = elv_rb_former_request,
5523 .allow_merge = bfq_allow_bio_merge,
5524 .bio_merge = bfq_bio_merge,
5525 .request_merge = bfq_request_merge,
5526 .requests_merged = bfq_requests_merged,
5527 .request_merged = bfq_request_merged,
5528 .has_work = bfq_has_work,
5529 .init_sched = bfq_init_queue,
5530 .exit_sched = bfq_exit_queue,
5531 },
5532
5533 .uses_mq = true,
5534 .icq_size = sizeof(struct bfq_io_cq),
5535 .icq_align = __alignof__(struct bfq_io_cq),
5536 .elevator_attrs = bfq_attrs,
5537 .elevator_name = "bfq",
5538 .elevator_owner = THIS_MODULE,
5539};
5540MODULE_ALIAS("bfq-iosched");
5541
5542static int __init bfq_init(void)
5543{
5544 int ret;
5545
5546#ifdef CONFIG_BFQ_GROUP_IOSCHED
5547 ret = blkcg_policy_register(&blkcg_policy_bfq);
5548 if (ret)
5549 return ret;
5550#endif
5551
5552 ret = -ENOMEM;
5553 if (bfq_slab_setup())
5554 goto err_pol_unreg;
5555
5556 /*
5557 * Times to load large popular applications for the typical
5558 * systems installed on the reference devices (see the
5559 * comments before the definitions of the next two
5560 * arrays). Actually, we use slightly slower values, as the
5561 * estimated peak rate tends to be smaller than the actual
5562 * peak rate. The reason for this last fact is that estimates
5563 * are computed over much shorter time intervals than the long
5564 * intervals typically used for benchmarking. Why? First, to
5565 * adapt more quickly to variations. Second, because an I/O
5566 * scheduler cannot rely on a peak-rate-evaluation workload to
5567 * be run for a long time.
5568 */
5569 T_slow[0] = msecs_to_jiffies(3500); /* actually 4 sec */
5570 T_slow[1] = msecs_to_jiffies(6000); /* actually 6.5 sec */
5571 T_fast[0] = msecs_to_jiffies(7000); /* actually 8 sec */
5572 T_fast[1] = msecs_to_jiffies(2500); /* actually 3 sec */
5573
5574 /*
5575 * Thresholds that determine the switch between speed classes
5576 * (see the comments before the definition of the array
5577 * device_speed_thresh). These thresholds are biased towards
5578 * transitions to the fast class. This is safer than the
5579 * opposite bias. In fact, a wrong transition to the slow
5580 * class results in short weight-raising periods, because the
5581 * speed of the device then tends to be higher that the
5582 * reference peak rate. On the opposite end, a wrong
5583 * transition to the fast class tends to increase
5584 * weight-raising periods, because of the opposite reason.
5585 */
5586 device_speed_thresh[0] = (4 * R_slow[0]) / 3;
5587 device_speed_thresh[1] = (4 * R_slow[1]) / 3;
5588
5589 ret = elv_register(&iosched_bfq_mq);
5590 if (ret)
5591 goto slab_kill;
5592
5593 return 0;
5594
5595slab_kill:
5596 bfq_slab_kill();
5597err_pol_unreg:
5598#ifdef CONFIG_BFQ_GROUP_IOSCHED
5599 blkcg_policy_unregister(&blkcg_policy_bfq);
5600#endif
5601 return ret;
5602}
5603
5604static void __exit bfq_exit(void)
5605{
5606 elv_unregister(&iosched_bfq_mq);
5607#ifdef CONFIG_BFQ_GROUP_IOSCHED
5608 blkcg_policy_unregister(&blkcg_policy_bfq);
5609#endif
5610 bfq_slab_kill();
5611}
5612
5613module_init(bfq_init);
5614module_exit(bfq_exit);
5615
5616MODULE_AUTHOR("Paolo Valente");
5617MODULE_LICENSE("GPL");
5618MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");