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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * buffered writeback throttling. loosely based on CoDel. We can't drop
4 * packets for IO scheduling, so the logic is something like this:
5 *
6 * - Monitor latencies in a defined window of time.
7 * - If the minimum latency in the above window exceeds some target, increment
8 * scaling step and scale down queue depth by a factor of 2x. The monitoring
9 * window is then shrunk to 100 / sqrt(scaling step + 1).
10 * - For any window where we don't have solid data on what the latencies
11 * look like, retain status quo.
12 * - If latencies look good, decrement scaling step.
13 * - If we're only doing writes, allow the scaling step to go negative. This
14 * will temporarily boost write performance, snapping back to a stable
15 * scaling step of 0 if reads show up or the heavy writers finish. Unlike
16 * positive scaling steps where we shrink the monitoring window, a negative
17 * scaling step retains the default step==0 window size.
18 *
19 * Copyright (C) 2016 Jens Axboe
20 *
21 */
22#include <linux/kernel.h>
23#include <linux/blk_types.h>
24#include <linux/slab.h>
25#include <linux/backing-dev.h>
26#include <linux/swap.h>
27
28#include "blk-wbt.h"
29#include "blk-rq-qos.h"
30#include "elevator.h"
31
32#define CREATE_TRACE_POINTS
33#include <trace/events/wbt.h>
34
35static inline void wbt_clear_state(struct request *rq)
36{
37 rq->wbt_flags = 0;
38}
39
40static inline enum wbt_flags wbt_flags(struct request *rq)
41{
42 return rq->wbt_flags;
43}
44
45static inline bool wbt_is_tracked(struct request *rq)
46{
47 return rq->wbt_flags & WBT_TRACKED;
48}
49
50static inline bool wbt_is_read(struct request *rq)
51{
52 return rq->wbt_flags & WBT_READ;
53}
54
55enum {
56 /*
57 * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
58 * from here depending on device stats
59 */
60 RWB_DEF_DEPTH = 16,
61
62 /*
63 * 100msec window
64 */
65 RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL,
66
67 /*
68 * Disregard stats, if we don't meet this minimum
69 */
70 RWB_MIN_WRITE_SAMPLES = 3,
71
72 /*
73 * If we have this number of consecutive windows with not enough
74 * information to scale up or down, scale up.
75 */
76 RWB_UNKNOWN_BUMP = 5,
77};
78
79static inline bool rwb_enabled(struct rq_wb *rwb)
80{
81 return rwb && rwb->enable_state != WBT_STATE_OFF_DEFAULT &&
82 rwb->wb_normal != 0;
83}
84
85static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
86{
87 if (rwb_enabled(rwb)) {
88 const unsigned long cur = jiffies;
89
90 if (cur != *var)
91 *var = cur;
92 }
93}
94
95/*
96 * If a task was rate throttled in balance_dirty_pages() within the last
97 * second or so, use that to indicate a higher cleaning rate.
98 */
99static bool wb_recent_wait(struct rq_wb *rwb)
100{
101 struct bdi_writeback *wb = &rwb->rqos.q->disk->bdi->wb;
102
103 return time_before(jiffies, wb->dirty_sleep + HZ);
104}
105
106static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,
107 enum wbt_flags wb_acct)
108{
109 if (wb_acct & WBT_KSWAPD)
110 return &rwb->rq_wait[WBT_RWQ_KSWAPD];
111 else if (wb_acct & WBT_DISCARD)
112 return &rwb->rq_wait[WBT_RWQ_DISCARD];
113
114 return &rwb->rq_wait[WBT_RWQ_BG];
115}
116
117static void rwb_wake_all(struct rq_wb *rwb)
118{
119 int i;
120
121 for (i = 0; i < WBT_NUM_RWQ; i++) {
122 struct rq_wait *rqw = &rwb->rq_wait[i];
123
124 if (wq_has_sleeper(&rqw->wait))
125 wake_up_all(&rqw->wait);
126 }
127}
128
129static void wbt_rqw_done(struct rq_wb *rwb, struct rq_wait *rqw,
130 enum wbt_flags wb_acct)
131{
132 int inflight, limit;
133
134 inflight = atomic_dec_return(&rqw->inflight);
135
136 /*
137 * wbt got disabled with IO in flight. Wake up any potential
138 * waiters, we don't have to do more than that.
139 */
140 if (unlikely(!rwb_enabled(rwb))) {
141 rwb_wake_all(rwb);
142 return;
143 }
144
145 /*
146 * For discards, our limit is always the background. For writes, if
147 * the device does write back caching, drop further down before we
148 * wake people up.
149 */
150 if (wb_acct & WBT_DISCARD)
151 limit = rwb->wb_background;
152 else if (rwb->wc && !wb_recent_wait(rwb))
153 limit = 0;
154 else
155 limit = rwb->wb_normal;
156
157 /*
158 * Don't wake anyone up if we are above the normal limit.
159 */
160 if (inflight && inflight >= limit)
161 return;
162
163 if (wq_has_sleeper(&rqw->wait)) {
164 int diff = limit - inflight;
165
166 if (!inflight || diff >= rwb->wb_background / 2)
167 wake_up_all(&rqw->wait);
168 }
169}
170
171static void __wbt_done(struct rq_qos *rqos, enum wbt_flags wb_acct)
172{
173 struct rq_wb *rwb = RQWB(rqos);
174 struct rq_wait *rqw;
175
176 if (!(wb_acct & WBT_TRACKED))
177 return;
178
179 rqw = get_rq_wait(rwb, wb_acct);
180 wbt_rqw_done(rwb, rqw, wb_acct);
181}
182
183/*
184 * Called on completion of a request. Note that it's also called when
185 * a request is merged, when the request gets freed.
186 */
187static void wbt_done(struct rq_qos *rqos, struct request *rq)
188{
189 struct rq_wb *rwb = RQWB(rqos);
190
191 if (!wbt_is_tracked(rq)) {
192 if (rwb->sync_cookie == rq) {
193 rwb->sync_issue = 0;
194 rwb->sync_cookie = NULL;
195 }
196
197 if (wbt_is_read(rq))
198 wb_timestamp(rwb, &rwb->last_comp);
199 } else {
200 WARN_ON_ONCE(rq == rwb->sync_cookie);
201 __wbt_done(rqos, wbt_flags(rq));
202 }
203 wbt_clear_state(rq);
204}
205
206static inline bool stat_sample_valid(struct blk_rq_stat *stat)
207{
208 /*
209 * We need at least one read sample, and a minimum of
210 * RWB_MIN_WRITE_SAMPLES. We require some write samples to know
211 * that it's writes impacting us, and not just some sole read on
212 * a device that is in a lower power state.
213 */
214 return (stat[READ].nr_samples >= 1 &&
215 stat[WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES);
216}
217
218static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
219{
220 u64 now, issue = READ_ONCE(rwb->sync_issue);
221
222 if (!issue || !rwb->sync_cookie)
223 return 0;
224
225 now = ktime_to_ns(ktime_get());
226 return now - issue;
227}
228
229enum {
230 LAT_OK = 1,
231 LAT_UNKNOWN,
232 LAT_UNKNOWN_WRITES,
233 LAT_EXCEEDED,
234};
235
236static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
237{
238 struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;
239 struct rq_depth *rqd = &rwb->rq_depth;
240 u64 thislat;
241
242 /*
243 * If our stored sync issue exceeds the window size, or it
244 * exceeds our min target AND we haven't logged any entries,
245 * flag the latency as exceeded. wbt works off completion latencies,
246 * but for a flooded device, a single sync IO can take a long time
247 * to complete after being issued. If this time exceeds our
248 * monitoring window AND we didn't see any other completions in that
249 * window, then count that sync IO as a violation of the latency.
250 */
251 thislat = rwb_sync_issue_lat(rwb);
252 if (thislat > rwb->cur_win_nsec ||
253 (thislat > rwb->min_lat_nsec && !stat[READ].nr_samples)) {
254 trace_wbt_lat(bdi, thislat);
255 return LAT_EXCEEDED;
256 }
257
258 /*
259 * No read/write mix, if stat isn't valid
260 */
261 if (!stat_sample_valid(stat)) {
262 /*
263 * If we had writes in this stat window and the window is
264 * current, we're only doing writes. If a task recently
265 * waited or still has writes in flights, consider us doing
266 * just writes as well.
267 */
268 if (stat[WRITE].nr_samples || wb_recent_wait(rwb) ||
269 wbt_inflight(rwb))
270 return LAT_UNKNOWN_WRITES;
271 return LAT_UNKNOWN;
272 }
273
274 /*
275 * If the 'min' latency exceeds our target, step down.
276 */
277 if (stat[READ].min > rwb->min_lat_nsec) {
278 trace_wbt_lat(bdi, stat[READ].min);
279 trace_wbt_stat(bdi, stat);
280 return LAT_EXCEEDED;
281 }
282
283 if (rqd->scale_step)
284 trace_wbt_stat(bdi, stat);
285
286 return LAT_OK;
287}
288
289static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
290{
291 struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;
292 struct rq_depth *rqd = &rwb->rq_depth;
293
294 trace_wbt_step(bdi, msg, rqd->scale_step, rwb->cur_win_nsec,
295 rwb->wb_background, rwb->wb_normal, rqd->max_depth);
296}
297
298static void calc_wb_limits(struct rq_wb *rwb)
299{
300 if (rwb->min_lat_nsec == 0) {
301 rwb->wb_normal = rwb->wb_background = 0;
302 } else if (rwb->rq_depth.max_depth <= 2) {
303 rwb->wb_normal = rwb->rq_depth.max_depth;
304 rwb->wb_background = 1;
305 } else {
306 rwb->wb_normal = (rwb->rq_depth.max_depth + 1) / 2;
307 rwb->wb_background = (rwb->rq_depth.max_depth + 3) / 4;
308 }
309}
310
311static void scale_up(struct rq_wb *rwb)
312{
313 if (!rq_depth_scale_up(&rwb->rq_depth))
314 return;
315 calc_wb_limits(rwb);
316 rwb->unknown_cnt = 0;
317 rwb_wake_all(rwb);
318 rwb_trace_step(rwb, tracepoint_string("scale up"));
319}
320
321static void scale_down(struct rq_wb *rwb, bool hard_throttle)
322{
323 if (!rq_depth_scale_down(&rwb->rq_depth, hard_throttle))
324 return;
325 calc_wb_limits(rwb);
326 rwb->unknown_cnt = 0;
327 rwb_trace_step(rwb, tracepoint_string("scale down"));
328}
329
330static void rwb_arm_timer(struct rq_wb *rwb)
331{
332 struct rq_depth *rqd = &rwb->rq_depth;
333
334 if (rqd->scale_step > 0) {
335 /*
336 * We should speed this up, using some variant of a fast
337 * integer inverse square root calculation. Since we only do
338 * this for every window expiration, it's not a huge deal,
339 * though.
340 */
341 rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
342 int_sqrt((rqd->scale_step + 1) << 8));
343 } else {
344 /*
345 * For step < 0, we don't want to increase/decrease the
346 * window size.
347 */
348 rwb->cur_win_nsec = rwb->win_nsec;
349 }
350
351 blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec);
352}
353
354static void wb_timer_fn(struct blk_stat_callback *cb)
355{
356 struct rq_wb *rwb = cb->data;
357 struct rq_depth *rqd = &rwb->rq_depth;
358 unsigned int inflight = wbt_inflight(rwb);
359 int status;
360
361 if (!rwb->rqos.q->disk)
362 return;
363
364 status = latency_exceeded(rwb, cb->stat);
365
366 trace_wbt_timer(rwb->rqos.q->disk->bdi, status, rqd->scale_step,
367 inflight);
368
369 /*
370 * If we exceeded the latency target, step down. If we did not,
371 * step one level up. If we don't know enough to say either exceeded
372 * or ok, then don't do anything.
373 */
374 switch (status) {
375 case LAT_EXCEEDED:
376 scale_down(rwb, true);
377 break;
378 case LAT_OK:
379 scale_up(rwb);
380 break;
381 case LAT_UNKNOWN_WRITES:
382 /*
383 * We started a the center step, but don't have a valid
384 * read/write sample, but we do have writes going on.
385 * Allow step to go negative, to increase write perf.
386 */
387 scale_up(rwb);
388 break;
389 case LAT_UNKNOWN:
390 if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
391 break;
392 /*
393 * We get here when previously scaled reduced depth, and we
394 * currently don't have a valid read/write sample. For that
395 * case, slowly return to center state (step == 0).
396 */
397 if (rqd->scale_step > 0)
398 scale_up(rwb);
399 else if (rqd->scale_step < 0)
400 scale_down(rwb, false);
401 break;
402 default:
403 break;
404 }
405
406 /*
407 * Re-arm timer, if we have IO in flight
408 */
409 if (rqd->scale_step || inflight)
410 rwb_arm_timer(rwb);
411}
412
413static void wbt_update_limits(struct rq_wb *rwb)
414{
415 struct rq_depth *rqd = &rwb->rq_depth;
416
417 rqd->scale_step = 0;
418 rqd->scaled_max = false;
419
420 rq_depth_calc_max_depth(rqd);
421 calc_wb_limits(rwb);
422
423 rwb_wake_all(rwb);
424}
425
426bool wbt_disabled(struct request_queue *q)
427{
428 struct rq_qos *rqos = wbt_rq_qos(q);
429
430 return !rqos || RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT ||
431 RQWB(rqos)->enable_state == WBT_STATE_OFF_MANUAL;
432}
433
434u64 wbt_get_min_lat(struct request_queue *q)
435{
436 struct rq_qos *rqos = wbt_rq_qos(q);
437 if (!rqos)
438 return 0;
439 return RQWB(rqos)->min_lat_nsec;
440}
441
442void wbt_set_min_lat(struct request_queue *q, u64 val)
443{
444 struct rq_qos *rqos = wbt_rq_qos(q);
445 if (!rqos)
446 return;
447
448 RQWB(rqos)->min_lat_nsec = val;
449 if (val)
450 RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL;
451 else
452 RQWB(rqos)->enable_state = WBT_STATE_OFF_MANUAL;
453
454 wbt_update_limits(RQWB(rqos));
455}
456
457
458static bool close_io(struct rq_wb *rwb)
459{
460 const unsigned long now = jiffies;
461
462 return time_before(now, rwb->last_issue + HZ / 10) ||
463 time_before(now, rwb->last_comp + HZ / 10);
464}
465
466#define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO)
467
468static inline unsigned int get_limit(struct rq_wb *rwb, blk_opf_t opf)
469{
470 unsigned int limit;
471
472 /*
473 * If we got disabled, just return UINT_MAX. This ensures that
474 * we'll properly inc a new IO, and dec+wakeup at the end.
475 */
476 if (!rwb_enabled(rwb))
477 return UINT_MAX;
478
479 if ((opf & REQ_OP_MASK) == REQ_OP_DISCARD)
480 return rwb->wb_background;
481
482 /*
483 * At this point we know it's a buffered write. If this is
484 * kswapd trying to free memory, or REQ_SYNC is set, then
485 * it's WB_SYNC_ALL writeback, and we'll use the max limit for
486 * that. If the write is marked as a background write, then use
487 * the idle limit, or go to normal if we haven't had competing
488 * IO for a bit.
489 */
490 if ((opf & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
491 limit = rwb->rq_depth.max_depth;
492 else if ((opf & REQ_BACKGROUND) || close_io(rwb)) {
493 /*
494 * If less than 100ms since we completed unrelated IO,
495 * limit us to half the depth for background writeback.
496 */
497 limit = rwb->wb_background;
498 } else
499 limit = rwb->wb_normal;
500
501 return limit;
502}
503
504struct wbt_wait_data {
505 struct rq_wb *rwb;
506 enum wbt_flags wb_acct;
507 blk_opf_t opf;
508};
509
510static bool wbt_inflight_cb(struct rq_wait *rqw, void *private_data)
511{
512 struct wbt_wait_data *data = private_data;
513 return rq_wait_inc_below(rqw, get_limit(data->rwb, data->opf));
514}
515
516static void wbt_cleanup_cb(struct rq_wait *rqw, void *private_data)
517{
518 struct wbt_wait_data *data = private_data;
519 wbt_rqw_done(data->rwb, rqw, data->wb_acct);
520}
521
522/*
523 * Block if we will exceed our limit, or if we are currently waiting for
524 * the timer to kick off queuing again.
525 */
526static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
527 blk_opf_t opf)
528{
529 struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);
530 struct wbt_wait_data data = {
531 .rwb = rwb,
532 .wb_acct = wb_acct,
533 .opf = opf,
534 };
535
536 rq_qos_wait(rqw, &data, wbt_inflight_cb, wbt_cleanup_cb);
537}
538
539static inline bool wbt_should_throttle(struct bio *bio)
540{
541 switch (bio_op(bio)) {
542 case REQ_OP_WRITE:
543 /*
544 * Don't throttle WRITE_ODIRECT
545 */
546 if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==
547 (REQ_SYNC | REQ_IDLE))
548 return false;
549 fallthrough;
550 case REQ_OP_DISCARD:
551 return true;
552 default:
553 return false;
554 }
555}
556
557static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio)
558{
559 enum wbt_flags flags = 0;
560
561 if (!rwb_enabled(rwb))
562 return 0;
563
564 if (bio_op(bio) == REQ_OP_READ) {
565 flags = WBT_READ;
566 } else if (wbt_should_throttle(bio)) {
567 if (current_is_kswapd())
568 flags |= WBT_KSWAPD;
569 if (bio_op(bio) == REQ_OP_DISCARD)
570 flags |= WBT_DISCARD;
571 flags |= WBT_TRACKED;
572 }
573 return flags;
574}
575
576static void wbt_cleanup(struct rq_qos *rqos, struct bio *bio)
577{
578 struct rq_wb *rwb = RQWB(rqos);
579 enum wbt_flags flags = bio_to_wbt_flags(rwb, bio);
580 __wbt_done(rqos, flags);
581}
582
583/*
584 * May sleep, if we have exceeded the writeback limits. Caller can pass
585 * in an irq held spinlock, if it holds one when calling this function.
586 * If we do sleep, we'll release and re-grab it.
587 */
588static void wbt_wait(struct rq_qos *rqos, struct bio *bio)
589{
590 struct rq_wb *rwb = RQWB(rqos);
591 enum wbt_flags flags;
592
593 flags = bio_to_wbt_flags(rwb, bio);
594 if (!(flags & WBT_TRACKED)) {
595 if (flags & WBT_READ)
596 wb_timestamp(rwb, &rwb->last_issue);
597 return;
598 }
599
600 __wbt_wait(rwb, flags, bio->bi_opf);
601
602 if (!blk_stat_is_active(rwb->cb))
603 rwb_arm_timer(rwb);
604}
605
606static void wbt_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
607{
608 struct rq_wb *rwb = RQWB(rqos);
609 rq->wbt_flags |= bio_to_wbt_flags(rwb, bio);
610}
611
612static void wbt_issue(struct rq_qos *rqos, struct request *rq)
613{
614 struct rq_wb *rwb = RQWB(rqos);
615
616 if (!rwb_enabled(rwb))
617 return;
618
619 /*
620 * Track sync issue, in case it takes a long time to complete. Allows us
621 * to react quicker, if a sync IO takes a long time to complete. Note
622 * that this is just a hint. The request can go away when it completes,
623 * so it's important we never dereference it. We only use the address to
624 * compare with, which is why we store the sync_issue time locally.
625 */
626 if (wbt_is_read(rq) && !rwb->sync_issue) {
627 rwb->sync_cookie = rq;
628 rwb->sync_issue = rq->io_start_time_ns;
629 }
630}
631
632static void wbt_requeue(struct rq_qos *rqos, struct request *rq)
633{
634 struct rq_wb *rwb = RQWB(rqos);
635 if (!rwb_enabled(rwb))
636 return;
637 if (rq == rwb->sync_cookie) {
638 rwb->sync_issue = 0;
639 rwb->sync_cookie = NULL;
640 }
641}
642
643void wbt_set_write_cache(struct request_queue *q, bool write_cache_on)
644{
645 struct rq_qos *rqos = wbt_rq_qos(q);
646 if (rqos)
647 RQWB(rqos)->wc = write_cache_on;
648}
649
650/*
651 * Enable wbt if defaults are configured that way
652 */
653void wbt_enable_default(struct request_queue *q)
654{
655 struct rq_qos *rqos;
656 bool disable_flag = q->elevator &&
657 test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags);
658
659 /* Throttling already enabled? */
660 rqos = wbt_rq_qos(q);
661 if (rqos) {
662 if (!disable_flag &&
663 RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
664 RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;
665 return;
666 }
667
668 /* Queue not registered? Maybe shutting down... */
669 if (!blk_queue_registered(q))
670 return;
671
672 if (queue_is_mq(q) && !disable_flag)
673 wbt_init(q);
674}
675EXPORT_SYMBOL_GPL(wbt_enable_default);
676
677u64 wbt_default_latency_nsec(struct request_queue *q)
678{
679 /*
680 * We default to 2msec for non-rotational storage, and 75msec
681 * for rotational storage.
682 */
683 if (blk_queue_nonrot(q))
684 return 2000000ULL;
685 else
686 return 75000000ULL;
687}
688
689static int wbt_data_dir(const struct request *rq)
690{
691 const enum req_op op = req_op(rq);
692
693 if (op == REQ_OP_READ)
694 return READ;
695 else if (op_is_write(op))
696 return WRITE;
697
698 /* don't account */
699 return -1;
700}
701
702static void wbt_queue_depth_changed(struct rq_qos *rqos)
703{
704 RQWB(rqos)->rq_depth.queue_depth = blk_queue_depth(rqos->q);
705 wbt_update_limits(RQWB(rqos));
706}
707
708static void wbt_exit(struct rq_qos *rqos)
709{
710 struct rq_wb *rwb = RQWB(rqos);
711 struct request_queue *q = rqos->q;
712
713 blk_stat_remove_callback(q, rwb->cb);
714 blk_stat_free_callback(rwb->cb);
715 kfree(rwb);
716}
717
718/*
719 * Disable wbt, if enabled by default.
720 */
721void wbt_disable_default(struct request_queue *q)
722{
723 struct rq_qos *rqos = wbt_rq_qos(q);
724 struct rq_wb *rwb;
725 if (!rqos)
726 return;
727 rwb = RQWB(rqos);
728 if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {
729 blk_stat_deactivate(rwb->cb);
730 rwb->enable_state = WBT_STATE_OFF_DEFAULT;
731 }
732}
733EXPORT_SYMBOL_GPL(wbt_disable_default);
734
735#ifdef CONFIG_BLK_DEBUG_FS
736static int wbt_curr_win_nsec_show(void *data, struct seq_file *m)
737{
738 struct rq_qos *rqos = data;
739 struct rq_wb *rwb = RQWB(rqos);
740
741 seq_printf(m, "%llu\n", rwb->cur_win_nsec);
742 return 0;
743}
744
745static int wbt_enabled_show(void *data, struct seq_file *m)
746{
747 struct rq_qos *rqos = data;
748 struct rq_wb *rwb = RQWB(rqos);
749
750 seq_printf(m, "%d\n", rwb->enable_state);
751 return 0;
752}
753
754static int wbt_id_show(void *data, struct seq_file *m)
755{
756 struct rq_qos *rqos = data;
757
758 seq_printf(m, "%u\n", rqos->id);
759 return 0;
760}
761
762static int wbt_inflight_show(void *data, struct seq_file *m)
763{
764 struct rq_qos *rqos = data;
765 struct rq_wb *rwb = RQWB(rqos);
766 int i;
767
768 for (i = 0; i < WBT_NUM_RWQ; i++)
769 seq_printf(m, "%d: inflight %d\n", i,
770 atomic_read(&rwb->rq_wait[i].inflight));
771 return 0;
772}
773
774static int wbt_min_lat_nsec_show(void *data, struct seq_file *m)
775{
776 struct rq_qos *rqos = data;
777 struct rq_wb *rwb = RQWB(rqos);
778
779 seq_printf(m, "%lu\n", rwb->min_lat_nsec);
780 return 0;
781}
782
783static int wbt_unknown_cnt_show(void *data, struct seq_file *m)
784{
785 struct rq_qos *rqos = data;
786 struct rq_wb *rwb = RQWB(rqos);
787
788 seq_printf(m, "%u\n", rwb->unknown_cnt);
789 return 0;
790}
791
792static int wbt_normal_show(void *data, struct seq_file *m)
793{
794 struct rq_qos *rqos = data;
795 struct rq_wb *rwb = RQWB(rqos);
796
797 seq_printf(m, "%u\n", rwb->wb_normal);
798 return 0;
799}
800
801static int wbt_background_show(void *data, struct seq_file *m)
802{
803 struct rq_qos *rqos = data;
804 struct rq_wb *rwb = RQWB(rqos);
805
806 seq_printf(m, "%u\n", rwb->wb_background);
807 return 0;
808}
809
810static const struct blk_mq_debugfs_attr wbt_debugfs_attrs[] = {
811 {"curr_win_nsec", 0400, wbt_curr_win_nsec_show},
812 {"enabled", 0400, wbt_enabled_show},
813 {"id", 0400, wbt_id_show},
814 {"inflight", 0400, wbt_inflight_show},
815 {"min_lat_nsec", 0400, wbt_min_lat_nsec_show},
816 {"unknown_cnt", 0400, wbt_unknown_cnt_show},
817 {"wb_normal", 0400, wbt_normal_show},
818 {"wb_background", 0400, wbt_background_show},
819 {},
820};
821#endif
822
823static struct rq_qos_ops wbt_rqos_ops = {
824 .throttle = wbt_wait,
825 .issue = wbt_issue,
826 .track = wbt_track,
827 .requeue = wbt_requeue,
828 .done = wbt_done,
829 .cleanup = wbt_cleanup,
830 .queue_depth_changed = wbt_queue_depth_changed,
831 .exit = wbt_exit,
832#ifdef CONFIG_BLK_DEBUG_FS
833 .debugfs_attrs = wbt_debugfs_attrs,
834#endif
835};
836
837int wbt_init(struct request_queue *q)
838{
839 struct rq_wb *rwb;
840 int i;
841 int ret;
842
843 rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
844 if (!rwb)
845 return -ENOMEM;
846
847 rwb->cb = blk_stat_alloc_callback(wb_timer_fn, wbt_data_dir, 2, rwb);
848 if (!rwb->cb) {
849 kfree(rwb);
850 return -ENOMEM;
851 }
852
853 for (i = 0; i < WBT_NUM_RWQ; i++)
854 rq_wait_init(&rwb->rq_wait[i]);
855
856 rwb->rqos.id = RQ_QOS_WBT;
857 rwb->rqos.ops = &wbt_rqos_ops;
858 rwb->rqos.q = q;
859 rwb->last_comp = rwb->last_issue = jiffies;
860 rwb->win_nsec = RWB_WINDOW_NSEC;
861 rwb->enable_state = WBT_STATE_ON_DEFAULT;
862 rwb->wc = test_bit(QUEUE_FLAG_WC, &q->queue_flags);
863 rwb->rq_depth.default_depth = RWB_DEF_DEPTH;
864 rwb->min_lat_nsec = wbt_default_latency_nsec(q);
865
866 wbt_queue_depth_changed(&rwb->rqos);
867
868 /*
869 * Assign rwb and add the stats callback.
870 */
871 ret = rq_qos_add(q, &rwb->rqos);
872 if (ret)
873 goto err_free;
874
875 blk_stat_add_callback(q, rwb->cb);
876
877 return 0;
878
879err_free:
880 blk_stat_free_callback(rwb->cb);
881 kfree(rwb);
882 return ret;
883
884}
1/*
2 * buffered writeback throttling. loosely based on CoDel. We can't drop
3 * packets for IO scheduling, so the logic is something like this:
4 *
5 * - Monitor latencies in a defined window of time.
6 * - If the minimum latency in the above window exceeds some target, increment
7 * scaling step and scale down queue depth by a factor of 2x. The monitoring
8 * window is then shrunk to 100 / sqrt(scaling step + 1).
9 * - For any window where we don't have solid data on what the latencies
10 * look like, retain status quo.
11 * - If latencies look good, decrement scaling step.
12 * - If we're only doing writes, allow the scaling step to go negative. This
13 * will temporarily boost write performance, snapping back to a stable
14 * scaling step of 0 if reads show up or the heavy writers finish. Unlike
15 * positive scaling steps where we shrink the monitoring window, a negative
16 * scaling step retains the default step==0 window size.
17 *
18 * Copyright (C) 2016 Jens Axboe
19 *
20 */
21#include <linux/kernel.h>
22#include <linux/blk_types.h>
23#include <linux/slab.h>
24#include <linux/backing-dev.h>
25#include <linux/swap.h>
26
27#include "blk-wbt.h"
28
29#define CREATE_TRACE_POINTS
30#include <trace/events/wbt.h>
31
32enum {
33 /*
34 * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
35 * from here depending on device stats
36 */
37 RWB_DEF_DEPTH = 16,
38
39 /*
40 * 100msec window
41 */
42 RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL,
43
44 /*
45 * Disregard stats, if we don't meet this minimum
46 */
47 RWB_MIN_WRITE_SAMPLES = 3,
48
49 /*
50 * If we have this number of consecutive windows with not enough
51 * information to scale up or down, scale up.
52 */
53 RWB_UNKNOWN_BUMP = 5,
54};
55
56static inline bool rwb_enabled(struct rq_wb *rwb)
57{
58 return rwb && rwb->wb_normal != 0;
59}
60
61/*
62 * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
63 * false if 'v' + 1 would be bigger than 'below'.
64 */
65static bool atomic_inc_below(atomic_t *v, int below)
66{
67 int cur = atomic_read(v);
68
69 for (;;) {
70 int old;
71
72 if (cur >= below)
73 return false;
74 old = atomic_cmpxchg(v, cur, cur + 1);
75 if (old == cur)
76 break;
77 cur = old;
78 }
79
80 return true;
81}
82
83static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
84{
85 if (rwb_enabled(rwb)) {
86 const unsigned long cur = jiffies;
87
88 if (cur != *var)
89 *var = cur;
90 }
91}
92
93/*
94 * If a task was rate throttled in balance_dirty_pages() within the last
95 * second or so, use that to indicate a higher cleaning rate.
96 */
97static bool wb_recent_wait(struct rq_wb *rwb)
98{
99 struct bdi_writeback *wb = &rwb->queue->backing_dev_info.wb;
100
101 return time_before(jiffies, wb->dirty_sleep + HZ);
102}
103
104static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, bool is_kswapd)
105{
106 return &rwb->rq_wait[is_kswapd];
107}
108
109static void rwb_wake_all(struct rq_wb *rwb)
110{
111 int i;
112
113 for (i = 0; i < WBT_NUM_RWQ; i++) {
114 struct rq_wait *rqw = &rwb->rq_wait[i];
115
116 if (waitqueue_active(&rqw->wait))
117 wake_up_all(&rqw->wait);
118 }
119}
120
121void __wbt_done(struct rq_wb *rwb, enum wbt_flags wb_acct)
122{
123 struct rq_wait *rqw;
124 int inflight, limit;
125
126 if (!(wb_acct & WBT_TRACKED))
127 return;
128
129 rqw = get_rq_wait(rwb, wb_acct & WBT_KSWAPD);
130 inflight = atomic_dec_return(&rqw->inflight);
131
132 /*
133 * wbt got disabled with IO in flight. Wake up any potential
134 * waiters, we don't have to do more than that.
135 */
136 if (unlikely(!rwb_enabled(rwb))) {
137 rwb_wake_all(rwb);
138 return;
139 }
140
141 /*
142 * If the device does write back caching, drop further down
143 * before we wake people up.
144 */
145 if (rwb->wc && !wb_recent_wait(rwb))
146 limit = 0;
147 else
148 limit = rwb->wb_normal;
149
150 /*
151 * Don't wake anyone up if we are above the normal limit.
152 */
153 if (inflight && inflight >= limit)
154 return;
155
156 if (waitqueue_active(&rqw->wait)) {
157 int diff = limit - inflight;
158
159 if (!inflight || diff >= rwb->wb_background / 2)
160 wake_up_all(&rqw->wait);
161 }
162}
163
164/*
165 * Called on completion of a request. Note that it's also called when
166 * a request is merged, when the request gets freed.
167 */
168void wbt_done(struct rq_wb *rwb, struct blk_issue_stat *stat)
169{
170 if (!rwb)
171 return;
172
173 if (!wbt_is_tracked(stat)) {
174 if (rwb->sync_cookie == stat) {
175 rwb->sync_issue = 0;
176 rwb->sync_cookie = NULL;
177 }
178
179 if (wbt_is_read(stat))
180 wb_timestamp(rwb, &rwb->last_comp);
181 wbt_clear_state(stat);
182 } else {
183 WARN_ON_ONCE(stat == rwb->sync_cookie);
184 __wbt_done(rwb, wbt_stat_to_mask(stat));
185 wbt_clear_state(stat);
186 }
187}
188
189/*
190 * Return true, if we can't increase the depth further by scaling
191 */
192static bool calc_wb_limits(struct rq_wb *rwb)
193{
194 unsigned int depth;
195 bool ret = false;
196
197 if (!rwb->min_lat_nsec) {
198 rwb->wb_max = rwb->wb_normal = rwb->wb_background = 0;
199 return false;
200 }
201
202 /*
203 * For QD=1 devices, this is a special case. It's important for those
204 * to have one request ready when one completes, so force a depth of
205 * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
206 * since the device can't have more than that in flight. If we're
207 * scaling down, then keep a setting of 1/1/1.
208 */
209 if (rwb->queue_depth == 1) {
210 if (rwb->scale_step > 0)
211 rwb->wb_max = rwb->wb_normal = 1;
212 else {
213 rwb->wb_max = rwb->wb_normal = 2;
214 ret = true;
215 }
216 rwb->wb_background = 1;
217 } else {
218 /*
219 * scale_step == 0 is our default state. If we have suffered
220 * latency spikes, step will be > 0, and we shrink the
221 * allowed write depths. If step is < 0, we're only doing
222 * writes, and we allow a temporarily higher depth to
223 * increase performance.
224 */
225 depth = min_t(unsigned int, RWB_DEF_DEPTH, rwb->queue_depth);
226 if (rwb->scale_step > 0)
227 depth = 1 + ((depth - 1) >> min(31, rwb->scale_step));
228 else if (rwb->scale_step < 0) {
229 unsigned int maxd = 3 * rwb->queue_depth / 4;
230
231 depth = 1 + ((depth - 1) << -rwb->scale_step);
232 if (depth > maxd) {
233 depth = maxd;
234 ret = true;
235 }
236 }
237
238 /*
239 * Set our max/normal/bg queue depths based on how far
240 * we have scaled down (->scale_step).
241 */
242 rwb->wb_max = depth;
243 rwb->wb_normal = (rwb->wb_max + 1) / 2;
244 rwb->wb_background = (rwb->wb_max + 3) / 4;
245 }
246
247 return ret;
248}
249
250static inline bool stat_sample_valid(struct blk_rq_stat *stat)
251{
252 /*
253 * We need at least one read sample, and a minimum of
254 * RWB_MIN_WRITE_SAMPLES. We require some write samples to know
255 * that it's writes impacting us, and not just some sole read on
256 * a device that is in a lower power state.
257 */
258 return stat[BLK_STAT_READ].nr_samples >= 1 &&
259 stat[BLK_STAT_WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES;
260}
261
262static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
263{
264 u64 now, issue = ACCESS_ONCE(rwb->sync_issue);
265
266 if (!issue || !rwb->sync_cookie)
267 return 0;
268
269 now = ktime_to_ns(ktime_get());
270 return now - issue;
271}
272
273enum {
274 LAT_OK = 1,
275 LAT_UNKNOWN,
276 LAT_UNKNOWN_WRITES,
277 LAT_EXCEEDED,
278};
279
280static int __latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
281{
282 struct backing_dev_info *bdi = &rwb->queue->backing_dev_info;
283 u64 thislat;
284
285 /*
286 * If our stored sync issue exceeds the window size, or it
287 * exceeds our min target AND we haven't logged any entries,
288 * flag the latency as exceeded. wbt works off completion latencies,
289 * but for a flooded device, a single sync IO can take a long time
290 * to complete after being issued. If this time exceeds our
291 * monitoring window AND we didn't see any other completions in that
292 * window, then count that sync IO as a violation of the latency.
293 */
294 thislat = rwb_sync_issue_lat(rwb);
295 if (thislat > rwb->cur_win_nsec ||
296 (thislat > rwb->min_lat_nsec && !stat[BLK_STAT_READ].nr_samples)) {
297 trace_wbt_lat(bdi, thislat);
298 return LAT_EXCEEDED;
299 }
300
301 /*
302 * No read/write mix, if stat isn't valid
303 */
304 if (!stat_sample_valid(stat)) {
305 /*
306 * If we had writes in this stat window and the window is
307 * current, we're only doing writes. If a task recently
308 * waited or still has writes in flights, consider us doing
309 * just writes as well.
310 */
311 if ((stat[BLK_STAT_WRITE].nr_samples && blk_stat_is_current(stat)) ||
312 wb_recent_wait(rwb) || wbt_inflight(rwb))
313 return LAT_UNKNOWN_WRITES;
314 return LAT_UNKNOWN;
315 }
316
317 /*
318 * If the 'min' latency exceeds our target, step down.
319 */
320 if (stat[BLK_STAT_READ].min > rwb->min_lat_nsec) {
321 trace_wbt_lat(bdi, stat[BLK_STAT_READ].min);
322 trace_wbt_stat(bdi, stat);
323 return LAT_EXCEEDED;
324 }
325
326 if (rwb->scale_step)
327 trace_wbt_stat(bdi, stat);
328
329 return LAT_OK;
330}
331
332static int latency_exceeded(struct rq_wb *rwb)
333{
334 struct blk_rq_stat stat[2];
335
336 blk_queue_stat_get(rwb->queue, stat);
337 return __latency_exceeded(rwb, stat);
338}
339
340static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
341{
342 struct backing_dev_info *bdi = &rwb->queue->backing_dev_info;
343
344 trace_wbt_step(bdi, msg, rwb->scale_step, rwb->cur_win_nsec,
345 rwb->wb_background, rwb->wb_normal, rwb->wb_max);
346}
347
348static void scale_up(struct rq_wb *rwb)
349{
350 /*
351 * Hit max in previous round, stop here
352 */
353 if (rwb->scaled_max)
354 return;
355
356 rwb->scale_step--;
357 rwb->unknown_cnt = 0;
358 blk_stat_clear(rwb->queue);
359
360 rwb->scaled_max = calc_wb_limits(rwb);
361
362 rwb_wake_all(rwb);
363
364 rwb_trace_step(rwb, "step up");
365}
366
367/*
368 * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
369 * had a latency violation.
370 */
371static void scale_down(struct rq_wb *rwb, bool hard_throttle)
372{
373 /*
374 * Stop scaling down when we've hit the limit. This also prevents
375 * ->scale_step from going to crazy values, if the device can't
376 * keep up.
377 */
378 if (rwb->wb_max == 1)
379 return;
380
381 if (rwb->scale_step < 0 && hard_throttle)
382 rwb->scale_step = 0;
383 else
384 rwb->scale_step++;
385
386 rwb->scaled_max = false;
387 rwb->unknown_cnt = 0;
388 blk_stat_clear(rwb->queue);
389 calc_wb_limits(rwb);
390 rwb_trace_step(rwb, "step down");
391}
392
393static void rwb_arm_timer(struct rq_wb *rwb)
394{
395 unsigned long expires;
396
397 if (rwb->scale_step > 0) {
398 /*
399 * We should speed this up, using some variant of a fast
400 * integer inverse square root calculation. Since we only do
401 * this for every window expiration, it's not a huge deal,
402 * though.
403 */
404 rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
405 int_sqrt((rwb->scale_step + 1) << 8));
406 } else {
407 /*
408 * For step < 0, we don't want to increase/decrease the
409 * window size.
410 */
411 rwb->cur_win_nsec = rwb->win_nsec;
412 }
413
414 expires = jiffies + nsecs_to_jiffies(rwb->cur_win_nsec);
415 mod_timer(&rwb->window_timer, expires);
416}
417
418static void wb_timer_fn(unsigned long data)
419{
420 struct rq_wb *rwb = (struct rq_wb *) data;
421 unsigned int inflight = wbt_inflight(rwb);
422 int status;
423
424 status = latency_exceeded(rwb);
425
426 trace_wbt_timer(&rwb->queue->backing_dev_info, status, rwb->scale_step,
427 inflight);
428
429 /*
430 * If we exceeded the latency target, step down. If we did not,
431 * step one level up. If we don't know enough to say either exceeded
432 * or ok, then don't do anything.
433 */
434 switch (status) {
435 case LAT_EXCEEDED:
436 scale_down(rwb, true);
437 break;
438 case LAT_OK:
439 scale_up(rwb);
440 break;
441 case LAT_UNKNOWN_WRITES:
442 /*
443 * We started a the center step, but don't have a valid
444 * read/write sample, but we do have writes going on.
445 * Allow step to go negative, to increase write perf.
446 */
447 scale_up(rwb);
448 break;
449 case LAT_UNKNOWN:
450 if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
451 break;
452 /*
453 * We get here when previously scaled reduced depth, and we
454 * currently don't have a valid read/write sample. For that
455 * case, slowly return to center state (step == 0).
456 */
457 if (rwb->scale_step > 0)
458 scale_up(rwb);
459 else if (rwb->scale_step < 0)
460 scale_down(rwb, false);
461 break;
462 default:
463 break;
464 }
465
466 /*
467 * Re-arm timer, if we have IO in flight
468 */
469 if (rwb->scale_step || inflight)
470 rwb_arm_timer(rwb);
471}
472
473void wbt_update_limits(struct rq_wb *rwb)
474{
475 rwb->scale_step = 0;
476 rwb->scaled_max = false;
477 calc_wb_limits(rwb);
478
479 rwb_wake_all(rwb);
480}
481
482static bool close_io(struct rq_wb *rwb)
483{
484 const unsigned long now = jiffies;
485
486 return time_before(now, rwb->last_issue + HZ / 10) ||
487 time_before(now, rwb->last_comp + HZ / 10);
488}
489
490#define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO)
491
492static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
493{
494 unsigned int limit;
495
496 /*
497 * At this point we know it's a buffered write. If this is
498 * kswapd trying to free memory, or REQ_SYNC is set, set, then
499 * it's WB_SYNC_ALL writeback, and we'll use the max limit for
500 * that. If the write is marked as a background write, then use
501 * the idle limit, or go to normal if we haven't had competing
502 * IO for a bit.
503 */
504 if ((rw & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
505 limit = rwb->wb_max;
506 else if ((rw & REQ_BACKGROUND) || close_io(rwb)) {
507 /*
508 * If less than 100ms since we completed unrelated IO,
509 * limit us to half the depth for background writeback.
510 */
511 limit = rwb->wb_background;
512 } else
513 limit = rwb->wb_normal;
514
515 return limit;
516}
517
518static inline bool may_queue(struct rq_wb *rwb, struct rq_wait *rqw,
519 wait_queue_t *wait, unsigned long rw)
520{
521 /*
522 * inc it here even if disabled, since we'll dec it at completion.
523 * this only happens if the task was sleeping in __wbt_wait(),
524 * and someone turned it off at the same time.
525 */
526 if (!rwb_enabled(rwb)) {
527 atomic_inc(&rqw->inflight);
528 return true;
529 }
530
531 /*
532 * If the waitqueue is already active and we are not the next
533 * in line to be woken up, wait for our turn.
534 */
535 if (waitqueue_active(&rqw->wait) &&
536 rqw->wait.task_list.next != &wait->task_list)
537 return false;
538
539 return atomic_inc_below(&rqw->inflight, get_limit(rwb, rw));
540}
541
542/*
543 * Block if we will exceed our limit, or if we are currently waiting for
544 * the timer to kick off queuing again.
545 */
546static void __wbt_wait(struct rq_wb *rwb, unsigned long rw, spinlock_t *lock)
547 __releases(lock)
548 __acquires(lock)
549{
550 struct rq_wait *rqw = get_rq_wait(rwb, current_is_kswapd());
551 DEFINE_WAIT(wait);
552
553 if (may_queue(rwb, rqw, &wait, rw))
554 return;
555
556 do {
557 prepare_to_wait_exclusive(&rqw->wait, &wait,
558 TASK_UNINTERRUPTIBLE);
559
560 if (may_queue(rwb, rqw, &wait, rw))
561 break;
562
563 if (lock) {
564 spin_unlock_irq(lock);
565 io_schedule();
566 spin_lock_irq(lock);
567 } else
568 io_schedule();
569 } while (1);
570
571 finish_wait(&rqw->wait, &wait);
572}
573
574static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
575{
576 const int op = bio_op(bio);
577
578 /*
579 * If not a WRITE, do nothing
580 */
581 if (op != REQ_OP_WRITE)
582 return false;
583
584 /*
585 * Don't throttle WRITE_ODIRECT
586 */
587 if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE))
588 return false;
589
590 return true;
591}
592
593/*
594 * Returns true if the IO request should be accounted, false if not.
595 * May sleep, if we have exceeded the writeback limits. Caller can pass
596 * in an irq held spinlock, if it holds one when calling this function.
597 * If we do sleep, we'll release and re-grab it.
598 */
599enum wbt_flags wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock)
600{
601 unsigned int ret = 0;
602
603 if (!rwb_enabled(rwb))
604 return 0;
605
606 if (bio_op(bio) == REQ_OP_READ)
607 ret = WBT_READ;
608
609 if (!wbt_should_throttle(rwb, bio)) {
610 if (ret & WBT_READ)
611 wb_timestamp(rwb, &rwb->last_issue);
612 return ret;
613 }
614
615 __wbt_wait(rwb, bio->bi_opf, lock);
616
617 if (!timer_pending(&rwb->window_timer))
618 rwb_arm_timer(rwb);
619
620 if (current_is_kswapd())
621 ret |= WBT_KSWAPD;
622
623 return ret | WBT_TRACKED;
624}
625
626void wbt_issue(struct rq_wb *rwb, struct blk_issue_stat *stat)
627{
628 if (!rwb_enabled(rwb))
629 return;
630
631 /*
632 * Track sync issue, in case it takes a long time to complete. Allows
633 * us to react quicker, if a sync IO takes a long time to complete.
634 * Note that this is just a hint. 'stat' can go away when the
635 * request completes, so it's important we never dereference it. We
636 * only use the address to compare with, which is why we store the
637 * sync_issue time locally.
638 */
639 if (wbt_is_read(stat) && !rwb->sync_issue) {
640 rwb->sync_cookie = stat;
641 rwb->sync_issue = blk_stat_time(stat);
642 }
643}
644
645void wbt_requeue(struct rq_wb *rwb, struct blk_issue_stat *stat)
646{
647 if (!rwb_enabled(rwb))
648 return;
649 if (stat == rwb->sync_cookie) {
650 rwb->sync_issue = 0;
651 rwb->sync_cookie = NULL;
652 }
653}
654
655void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth)
656{
657 if (rwb) {
658 rwb->queue_depth = depth;
659 wbt_update_limits(rwb);
660 }
661}
662
663void wbt_set_write_cache(struct rq_wb *rwb, bool write_cache_on)
664{
665 if (rwb)
666 rwb->wc = write_cache_on;
667}
668
669 /*
670 * Disable wbt, if enabled by default. Only called from CFQ, if we have
671 * cgroups enabled
672 */
673void wbt_disable_default(struct request_queue *q)
674{
675 struct rq_wb *rwb = q->rq_wb;
676
677 if (rwb && rwb->enable_state == WBT_STATE_ON_DEFAULT) {
678 del_timer_sync(&rwb->window_timer);
679 rwb->win_nsec = rwb->min_lat_nsec = 0;
680 wbt_update_limits(rwb);
681 }
682}
683EXPORT_SYMBOL_GPL(wbt_disable_default);
684
685u64 wbt_default_latency_nsec(struct request_queue *q)
686{
687 /*
688 * We default to 2msec for non-rotational storage, and 75msec
689 * for rotational storage.
690 */
691 if (blk_queue_nonrot(q))
692 return 2000000ULL;
693 else
694 return 75000000ULL;
695}
696
697int wbt_init(struct request_queue *q)
698{
699 struct rq_wb *rwb;
700 int i;
701
702 /*
703 * For now, we depend on the stats window being larger than
704 * our monitoring window. Ensure that this isn't inadvertently
705 * violated.
706 */
707 BUILD_BUG_ON(RWB_WINDOW_NSEC > BLK_STAT_NSEC);
708 BUILD_BUG_ON(WBT_NR_BITS > BLK_STAT_RES_BITS);
709
710 rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
711 if (!rwb)
712 return -ENOMEM;
713
714 for (i = 0; i < WBT_NUM_RWQ; i++) {
715 atomic_set(&rwb->rq_wait[i].inflight, 0);
716 init_waitqueue_head(&rwb->rq_wait[i].wait);
717 }
718
719 setup_timer(&rwb->window_timer, wb_timer_fn, (unsigned long) rwb);
720 rwb->wc = 1;
721 rwb->queue_depth = RWB_DEF_DEPTH;
722 rwb->last_comp = rwb->last_issue = jiffies;
723 rwb->queue = q;
724 rwb->win_nsec = RWB_WINDOW_NSEC;
725 rwb->enable_state = WBT_STATE_ON_DEFAULT;
726 wbt_update_limits(rwb);
727
728 /*
729 * Assign rwb, and turn on stats tracking for this queue
730 */
731 q->rq_wb = rwb;
732 blk_stat_enable(q);
733
734 rwb->min_lat_nsec = wbt_default_latency_nsec(q);
735
736 wbt_set_queue_depth(rwb, blk_queue_depth(q));
737 wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));
738
739 return 0;
740}
741
742void wbt_exit(struct request_queue *q)
743{
744 struct rq_wb *rwb = q->rq_wb;
745
746 if (rwb) {
747 del_timer_sync(&rwb->window_timer);
748 q->rq_wb = NULL;
749 kfree(rwb);
750 }
751}