1 // SPDX-License-Identifier: GPL-2.0
3 * buffered writeback throttling. loosely based on CoDel. We can't drop
4 * packets for IO scheduling, so the logic is something like this:
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.
19 * Copyright (C) 2016 Jens Axboe
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>
30 #include "blk-rq-qos.h"
33 #define CREATE_TRACE_POINTS
34 #include <trace/events/wbt.h>
37 WBT_TRACKED = 1, /* write, tracked for throttling */
38 WBT_READ = 2, /* read */
39 WBT_KSWAPD = 4, /* write, from kswapd */
40 WBT_DISCARD = 8, /* discard */
42 WBT_NR_BITS = 4, /* number of bits */
53 * If current state is WBT_STATE_ON/OFF_DEFAULT, it can be covered to any other
54 * state, if current state is WBT_STATE_ON/OFF_MANUAL, it can only be covered
55 * to WBT_STATE_OFF/ON_MANUAL.
58 WBT_STATE_ON_DEFAULT = 1, /* on by default */
59 WBT_STATE_ON_MANUAL = 2, /* on manually by sysfs */
60 WBT_STATE_OFF_DEFAULT = 3, /* off by default */
61 WBT_STATE_OFF_MANUAL = 4, /* off manually by sysfs */
66 * Settings that govern how we throttle
68 unsigned int wb_background; /* background writeback */
69 unsigned int wb_normal; /* normal writeback */
71 short enable_state; /* WBT_STATE_* */
74 * Number of consecutive periods where we don't have enough
75 * information to make a firm scale up/down decision.
77 unsigned int unknown_cnt;
79 u64 win_nsec; /* default window size */
80 u64 cur_win_nsec; /* current window size */
82 struct blk_stat_callback *cb;
89 unsigned long last_issue; /* last non-throttled issue */
90 unsigned long last_comp; /* last non-throttled comp */
91 unsigned long min_lat_nsec;
93 struct rq_wait rq_wait[WBT_NUM_RWQ];
94 struct rq_depth rq_depth;
97 static inline struct rq_wb *RQWB(struct rq_qos *rqos)
99 return container_of(rqos, struct rq_wb, rqos);
102 static inline void wbt_clear_state(struct request *rq)
107 static inline enum wbt_flags wbt_flags(struct request *rq)
109 return rq->wbt_flags;
112 static inline bool wbt_is_tracked(struct request *rq)
114 return rq->wbt_flags & WBT_TRACKED;
117 static inline bool wbt_is_read(struct request *rq)
119 return rq->wbt_flags & WBT_READ;
124 * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
125 * from here depending on device stats
132 RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL,
135 * Disregard stats, if we don't meet this minimum
137 RWB_MIN_WRITE_SAMPLES = 3,
140 * If we have this number of consecutive windows with not enough
141 * information to scale up or down, scale up.
143 RWB_UNKNOWN_BUMP = 5,
146 static inline bool rwb_enabled(struct rq_wb *rwb)
148 return rwb && rwb->enable_state != WBT_STATE_OFF_DEFAULT &&
152 static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
154 if (rwb_enabled(rwb)) {
155 const unsigned long cur = jiffies;
163 * If a task was rate throttled in balance_dirty_pages() within the last
164 * second or so, use that to indicate a higher cleaning rate.
166 static bool wb_recent_wait(struct rq_wb *rwb)
168 struct bdi_writeback *wb = &rwb->rqos.disk->bdi->wb;
170 return time_before(jiffies, wb->dirty_sleep + HZ);
173 static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,
174 enum wbt_flags wb_acct)
176 if (wb_acct & WBT_KSWAPD)
177 return &rwb->rq_wait[WBT_RWQ_KSWAPD];
178 else if (wb_acct & WBT_DISCARD)
179 return &rwb->rq_wait[WBT_RWQ_DISCARD];
181 return &rwb->rq_wait[WBT_RWQ_BG];
184 static void rwb_wake_all(struct rq_wb *rwb)
188 for (i = 0; i < WBT_NUM_RWQ; i++) {
189 struct rq_wait *rqw = &rwb->rq_wait[i];
191 if (wq_has_sleeper(&rqw->wait))
192 wake_up_all(&rqw->wait);
196 static void wbt_rqw_done(struct rq_wb *rwb, struct rq_wait *rqw,
197 enum wbt_flags wb_acct)
201 inflight = atomic_dec_return(&rqw->inflight);
204 * For discards, our limit is always the background. For writes, if
205 * the device does write back caching, drop further down before we
208 if (wb_acct & WBT_DISCARD)
209 limit = rwb->wb_background;
210 else if (rwb->wc && !wb_recent_wait(rwb))
213 limit = rwb->wb_normal;
216 * Don't wake anyone up if we are above the normal limit.
218 if (inflight && inflight >= limit)
221 if (wq_has_sleeper(&rqw->wait)) {
222 int diff = limit - inflight;
224 if (!inflight || diff >= rwb->wb_background / 2)
225 wake_up_all(&rqw->wait);
229 static void __wbt_done(struct rq_qos *rqos, enum wbt_flags wb_acct)
231 struct rq_wb *rwb = RQWB(rqos);
234 if (!(wb_acct & WBT_TRACKED))
237 rqw = get_rq_wait(rwb, wb_acct);
238 wbt_rqw_done(rwb, rqw, wb_acct);
242 * Called on completion of a request. Note that it's also called when
243 * a request is merged, when the request gets freed.
245 static void wbt_done(struct rq_qos *rqos, struct request *rq)
247 struct rq_wb *rwb = RQWB(rqos);
249 if (!wbt_is_tracked(rq)) {
250 if (rwb->sync_cookie == rq) {
252 rwb->sync_cookie = NULL;
256 wb_timestamp(rwb, &rwb->last_comp);
258 WARN_ON_ONCE(rq == rwb->sync_cookie);
259 __wbt_done(rqos, wbt_flags(rq));
264 static inline bool stat_sample_valid(struct blk_rq_stat *stat)
267 * We need at least one read sample, and a minimum of
268 * RWB_MIN_WRITE_SAMPLES. We require some write samples to know
269 * that it's writes impacting us, and not just some sole read on
270 * a device that is in a lower power state.
272 return (stat[READ].nr_samples >= 1 &&
273 stat[WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES);
276 static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
278 u64 now, issue = READ_ONCE(rwb->sync_issue);
280 if (!issue || !rwb->sync_cookie)
283 now = ktime_to_ns(ktime_get());
287 static inline unsigned int wbt_inflight(struct rq_wb *rwb)
289 unsigned int i, ret = 0;
291 for (i = 0; i < WBT_NUM_RWQ; i++)
292 ret += atomic_read(&rwb->rq_wait[i].inflight);
304 static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
306 struct backing_dev_info *bdi = rwb->rqos.disk->bdi;
307 struct rq_depth *rqd = &rwb->rq_depth;
311 * If our stored sync issue exceeds the window size, or it
312 * exceeds our min target AND we haven't logged any entries,
313 * flag the latency as exceeded. wbt works off completion latencies,
314 * but for a flooded device, a single sync IO can take a long time
315 * to complete after being issued. If this time exceeds our
316 * monitoring window AND we didn't see any other completions in that
317 * window, then count that sync IO as a violation of the latency.
319 thislat = rwb_sync_issue_lat(rwb);
320 if (thislat > rwb->cur_win_nsec ||
321 (thislat > rwb->min_lat_nsec && !stat[READ].nr_samples)) {
322 trace_wbt_lat(bdi, thislat);
327 * No read/write mix, if stat isn't valid
329 if (!stat_sample_valid(stat)) {
331 * If we had writes in this stat window and the window is
332 * current, we're only doing writes. If a task recently
333 * waited or still has writes in flights, consider us doing
334 * just writes as well.
336 if (stat[WRITE].nr_samples || wb_recent_wait(rwb) ||
338 return LAT_UNKNOWN_WRITES;
343 * If the 'min' latency exceeds our target, step down.
345 if (stat[READ].min > rwb->min_lat_nsec) {
346 trace_wbt_lat(bdi, stat[READ].min);
347 trace_wbt_stat(bdi, stat);
352 trace_wbt_stat(bdi, stat);
357 static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
359 struct backing_dev_info *bdi = rwb->rqos.disk->bdi;
360 struct rq_depth *rqd = &rwb->rq_depth;
362 trace_wbt_step(bdi, msg, rqd->scale_step, rwb->cur_win_nsec,
363 rwb->wb_background, rwb->wb_normal, rqd->max_depth);
366 static void calc_wb_limits(struct rq_wb *rwb)
368 if (rwb->min_lat_nsec == 0) {
369 rwb->wb_normal = rwb->wb_background = 0;
370 } else if (rwb->rq_depth.max_depth <= 2) {
371 rwb->wb_normal = rwb->rq_depth.max_depth;
372 rwb->wb_background = 1;
374 rwb->wb_normal = (rwb->rq_depth.max_depth + 1) / 2;
375 rwb->wb_background = (rwb->rq_depth.max_depth + 3) / 4;
379 static void scale_up(struct rq_wb *rwb)
381 if (!rq_depth_scale_up(&rwb->rq_depth))
384 rwb->unknown_cnt = 0;
386 rwb_trace_step(rwb, tracepoint_string("scale up"));
389 static void scale_down(struct rq_wb *rwb, bool hard_throttle)
391 if (!rq_depth_scale_down(&rwb->rq_depth, hard_throttle))
394 rwb->unknown_cnt = 0;
395 rwb_trace_step(rwb, tracepoint_string("scale down"));
398 static void rwb_arm_timer(struct rq_wb *rwb)
400 struct rq_depth *rqd = &rwb->rq_depth;
402 if (rqd->scale_step > 0) {
404 * We should speed this up, using some variant of a fast
405 * integer inverse square root calculation. Since we only do
406 * this for every window expiration, it's not a huge deal,
409 rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
410 int_sqrt((rqd->scale_step + 1) << 8));
413 * For step < 0, we don't want to increase/decrease the
416 rwb->cur_win_nsec = rwb->win_nsec;
419 blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec);
422 static void wb_timer_fn(struct blk_stat_callback *cb)
424 struct rq_wb *rwb = cb->data;
425 struct rq_depth *rqd = &rwb->rq_depth;
426 unsigned int inflight = wbt_inflight(rwb);
432 status = latency_exceeded(rwb, cb->stat);
434 trace_wbt_timer(rwb->rqos.disk->bdi, status, rqd->scale_step, inflight);
437 * If we exceeded the latency target, step down. If we did not,
438 * step one level up. If we don't know enough to say either exceeded
439 * or ok, then don't do anything.
443 scale_down(rwb, true);
448 case LAT_UNKNOWN_WRITES:
450 * We started a the center step, but don't have a valid
451 * read/write sample, but we do have writes going on.
452 * Allow step to go negative, to increase write perf.
457 if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
460 * We get here when previously scaled reduced depth, and we
461 * currently don't have a valid read/write sample. For that
462 * case, slowly return to center state (step == 0).
464 if (rqd->scale_step > 0)
466 else if (rqd->scale_step < 0)
467 scale_down(rwb, false);
474 * Re-arm timer, if we have IO in flight
476 if (rqd->scale_step || inflight)
480 static void wbt_update_limits(struct rq_wb *rwb)
482 struct rq_depth *rqd = &rwb->rq_depth;
485 rqd->scaled_max = false;
487 rq_depth_calc_max_depth(rqd);
493 bool wbt_disabled(struct request_queue *q)
495 struct rq_qos *rqos = wbt_rq_qos(q);
497 return !rqos || RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT ||
498 RQWB(rqos)->enable_state == WBT_STATE_OFF_MANUAL;
501 u64 wbt_get_min_lat(struct request_queue *q)
503 struct rq_qos *rqos = wbt_rq_qos(q);
506 return RQWB(rqos)->min_lat_nsec;
509 void wbt_set_min_lat(struct request_queue *q, u64 val)
511 struct rq_qos *rqos = wbt_rq_qos(q);
515 RQWB(rqos)->min_lat_nsec = val;
517 RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL;
519 RQWB(rqos)->enable_state = WBT_STATE_OFF_MANUAL;
521 wbt_update_limits(RQWB(rqos));
525 static bool close_io(struct rq_wb *rwb)
527 const unsigned long now = jiffies;
529 return time_before(now, rwb->last_issue + HZ / 10) ||
530 time_before(now, rwb->last_comp + HZ / 10);
533 #define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO)
535 static inline unsigned int get_limit(struct rq_wb *rwb, blk_opf_t opf)
539 if ((opf & REQ_OP_MASK) == REQ_OP_DISCARD)
540 return rwb->wb_background;
543 * At this point we know it's a buffered write. If this is
544 * kswapd trying to free memory, or REQ_SYNC is set, then
545 * it's WB_SYNC_ALL writeback, and we'll use the max limit for
546 * that. If the write is marked as a background write, then use
547 * the idle limit, or go to normal if we haven't had competing
550 if ((opf & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
551 limit = rwb->rq_depth.max_depth;
552 else if ((opf & REQ_BACKGROUND) || close_io(rwb)) {
554 * If less than 100ms since we completed unrelated IO,
555 * limit us to half the depth for background writeback.
557 limit = rwb->wb_background;
559 limit = rwb->wb_normal;
564 struct wbt_wait_data {
566 enum wbt_flags wb_acct;
570 static bool wbt_inflight_cb(struct rq_wait *rqw, void *private_data)
572 struct wbt_wait_data *data = private_data;
573 return rq_wait_inc_below(rqw, get_limit(data->rwb, data->opf));
576 static void wbt_cleanup_cb(struct rq_wait *rqw, void *private_data)
578 struct wbt_wait_data *data = private_data;
579 wbt_rqw_done(data->rwb, rqw, data->wb_acct);
583 * Block if we will exceed our limit, or if we are currently waiting for
584 * the timer to kick off queuing again.
586 static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
589 struct rq_wait *rqw = get_rq_wait(rwb, wb_acct);
590 struct wbt_wait_data data = {
596 rq_qos_wait(rqw, &data, wbt_inflight_cb, wbt_cleanup_cb);
599 static inline bool wbt_should_throttle(struct bio *bio)
601 switch (bio_op(bio)) {
604 * Don't throttle WRITE_ODIRECT
606 if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==
607 (REQ_SYNC | REQ_IDLE))
617 static enum wbt_flags bio_to_wbt_flags(struct rq_wb *rwb, struct bio *bio)
619 enum wbt_flags flags = 0;
621 if (!rwb_enabled(rwb))
624 if (bio_op(bio) == REQ_OP_READ) {
626 } else if (wbt_should_throttle(bio)) {
627 if (current_is_kswapd())
629 if (bio_op(bio) == REQ_OP_DISCARD)
630 flags |= WBT_DISCARD;
631 flags |= WBT_TRACKED;
636 static void wbt_cleanup(struct rq_qos *rqos, struct bio *bio)
638 struct rq_wb *rwb = RQWB(rqos);
639 enum wbt_flags flags = bio_to_wbt_flags(rwb, bio);
640 __wbt_done(rqos, flags);
644 * May sleep, if we have exceeded the writeback limits. Caller can pass
645 * in an irq held spinlock, if it holds one when calling this function.
646 * If we do sleep, we'll release and re-grab it.
648 static void wbt_wait(struct rq_qos *rqos, struct bio *bio)
650 struct rq_wb *rwb = RQWB(rqos);
651 enum wbt_flags flags;
653 flags = bio_to_wbt_flags(rwb, bio);
654 if (!(flags & WBT_TRACKED)) {
655 if (flags & WBT_READ)
656 wb_timestamp(rwb, &rwb->last_issue);
660 __wbt_wait(rwb, flags, bio->bi_opf);
662 if (!blk_stat_is_active(rwb->cb))
666 static void wbt_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
668 struct rq_wb *rwb = RQWB(rqos);
669 rq->wbt_flags |= bio_to_wbt_flags(rwb, bio);
672 static void wbt_issue(struct rq_qos *rqos, struct request *rq)
674 struct rq_wb *rwb = RQWB(rqos);
676 if (!rwb_enabled(rwb))
680 * Track sync issue, in case it takes a long time to complete. Allows us
681 * to react quicker, if a sync IO takes a long time to complete. Note
682 * that this is just a hint. The request can go away when it completes,
683 * so it's important we never dereference it. We only use the address to
684 * compare with, which is why we store the sync_issue time locally.
686 if (wbt_is_read(rq) && !rwb->sync_issue) {
687 rwb->sync_cookie = rq;
688 rwb->sync_issue = rq->io_start_time_ns;
692 static void wbt_requeue(struct rq_qos *rqos, struct request *rq)
694 struct rq_wb *rwb = RQWB(rqos);
695 if (!rwb_enabled(rwb))
697 if (rq == rwb->sync_cookie) {
699 rwb->sync_cookie = NULL;
703 void wbt_set_write_cache(struct request_queue *q, bool write_cache_on)
705 struct rq_qos *rqos = wbt_rq_qos(q);
707 RQWB(rqos)->wc = write_cache_on;
711 * Enable wbt if defaults are configured that way
713 void wbt_enable_default(struct gendisk *disk)
715 struct request_queue *q = disk->queue;
717 bool disable_flag = q->elevator &&
718 test_bit(ELEVATOR_FLAG_DISABLE_WBT, &q->elevator->flags);
720 /* Throttling already enabled? */
721 rqos = wbt_rq_qos(q);
724 RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)
725 RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;
729 /* Queue not registered? Maybe shutting down... */
730 if (!blk_queue_registered(q))
733 if (queue_is_mq(q) && !disable_flag)
736 EXPORT_SYMBOL_GPL(wbt_enable_default);
738 u64 wbt_default_latency_nsec(struct request_queue *q)
741 * We default to 2msec for non-rotational storage, and 75msec
742 * for rotational storage.
744 if (blk_queue_nonrot(q))
750 static int wbt_data_dir(const struct request *rq)
752 const enum req_op op = req_op(rq);
754 if (op == REQ_OP_READ)
756 else if (op_is_write(op))
763 static void wbt_queue_depth_changed(struct rq_qos *rqos)
765 RQWB(rqos)->rq_depth.queue_depth = blk_queue_depth(rqos->disk->queue);
766 wbt_update_limits(RQWB(rqos));
769 static void wbt_exit(struct rq_qos *rqos)
771 struct rq_wb *rwb = RQWB(rqos);
773 blk_stat_remove_callback(rqos->disk->queue, rwb->cb);
774 blk_stat_free_callback(rwb->cb);
779 * Disable wbt, if enabled by default.
781 void wbt_disable_default(struct gendisk *disk)
783 struct rq_qos *rqos = wbt_rq_qos(disk->queue);
788 if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {
789 blk_stat_deactivate(rwb->cb);
790 rwb->enable_state = WBT_STATE_OFF_DEFAULT;
793 EXPORT_SYMBOL_GPL(wbt_disable_default);
795 #ifdef CONFIG_BLK_DEBUG_FS
796 static int wbt_curr_win_nsec_show(void *data, struct seq_file *m)
798 struct rq_qos *rqos = data;
799 struct rq_wb *rwb = RQWB(rqos);
801 seq_printf(m, "%llu\n", rwb->cur_win_nsec);
805 static int wbt_enabled_show(void *data, struct seq_file *m)
807 struct rq_qos *rqos = data;
808 struct rq_wb *rwb = RQWB(rqos);
810 seq_printf(m, "%d\n", rwb->enable_state);
814 static int wbt_id_show(void *data, struct seq_file *m)
816 struct rq_qos *rqos = data;
818 seq_printf(m, "%u\n", rqos->id);
822 static int wbt_inflight_show(void *data, struct seq_file *m)
824 struct rq_qos *rqos = data;
825 struct rq_wb *rwb = RQWB(rqos);
828 for (i = 0; i < WBT_NUM_RWQ; i++)
829 seq_printf(m, "%d: inflight %d\n", i,
830 atomic_read(&rwb->rq_wait[i].inflight));
834 static int wbt_min_lat_nsec_show(void *data, struct seq_file *m)
836 struct rq_qos *rqos = data;
837 struct rq_wb *rwb = RQWB(rqos);
839 seq_printf(m, "%lu\n", rwb->min_lat_nsec);
843 static int wbt_unknown_cnt_show(void *data, struct seq_file *m)
845 struct rq_qos *rqos = data;
846 struct rq_wb *rwb = RQWB(rqos);
848 seq_printf(m, "%u\n", rwb->unknown_cnt);
852 static int wbt_normal_show(void *data, struct seq_file *m)
854 struct rq_qos *rqos = data;
855 struct rq_wb *rwb = RQWB(rqos);
857 seq_printf(m, "%u\n", rwb->wb_normal);
861 static int wbt_background_show(void *data, struct seq_file *m)
863 struct rq_qos *rqos = data;
864 struct rq_wb *rwb = RQWB(rqos);
866 seq_printf(m, "%u\n", rwb->wb_background);
870 static const struct blk_mq_debugfs_attr wbt_debugfs_attrs[] = {
871 {"curr_win_nsec", 0400, wbt_curr_win_nsec_show},
872 {"enabled", 0400, wbt_enabled_show},
873 {"id", 0400, wbt_id_show},
874 {"inflight", 0400, wbt_inflight_show},
875 {"min_lat_nsec", 0400, wbt_min_lat_nsec_show},
876 {"unknown_cnt", 0400, wbt_unknown_cnt_show},
877 {"wb_normal", 0400, wbt_normal_show},
878 {"wb_background", 0400, wbt_background_show},
883 static const struct rq_qos_ops wbt_rqos_ops = {
884 .throttle = wbt_wait,
887 .requeue = wbt_requeue,
889 .cleanup = wbt_cleanup,
890 .queue_depth_changed = wbt_queue_depth_changed,
892 #ifdef CONFIG_BLK_DEBUG_FS
893 .debugfs_attrs = wbt_debugfs_attrs,
897 int wbt_init(struct gendisk *disk)
899 struct request_queue *q = disk->queue;
904 rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
908 rwb->cb = blk_stat_alloc_callback(wb_timer_fn, wbt_data_dir, 2, rwb);
914 for (i = 0; i < WBT_NUM_RWQ; i++)
915 rq_wait_init(&rwb->rq_wait[i]);
917 rwb->last_comp = rwb->last_issue = jiffies;
918 rwb->win_nsec = RWB_WINDOW_NSEC;
919 rwb->enable_state = WBT_STATE_ON_DEFAULT;
920 rwb->wc = test_bit(QUEUE_FLAG_WC, &q->queue_flags);
921 rwb->rq_depth.default_depth = RWB_DEF_DEPTH;
922 rwb->min_lat_nsec = wbt_default_latency_nsec(q);
923 rwb->rq_depth.queue_depth = blk_queue_depth(q);
924 wbt_update_limits(rwb);
927 * Assign rwb and add the stats callback.
929 mutex_lock(&q->rq_qos_mutex);
930 ret = rq_qos_add(&rwb->rqos, disk, RQ_QOS_WBT, &wbt_rqos_ops);
931 mutex_unlock(&q->rq_qos_mutex);
935 blk_stat_add_callback(q, rwb->cb);
940 blk_stat_free_callback(rwb->cb);