Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0
2 : /*
3 : * blk-mq scheduling framework
4 : *
5 : * Copyright (C) 2016 Jens Axboe
6 : */
7 : #include <linux/kernel.h>
8 : #include <linux/module.h>
9 : #include <linux/list_sort.h>
10 :
11 : #include <trace/events/block.h>
12 :
13 : #include "blk.h"
14 : #include "blk-mq.h"
15 : #include "blk-mq-debugfs.h"
16 : #include "blk-mq-sched.h"
17 : #include "blk-wbt.h"
18 :
19 : /*
20 : * Mark a hardware queue as needing a restart.
21 : */
22 0 : void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
23 : {
24 0 : if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
25 : return;
26 :
27 0 : set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
28 : }
29 : EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
30 :
31 0 : void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
32 : {
33 0 : clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
34 :
35 : /*
36 : * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
37 : * in blk_mq_run_hw_queue(). Its pair is the barrier in
38 : * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
39 : * meantime new request added to hctx->dispatch is missed to check in
40 : * blk_mq_run_hw_queue().
41 : */
42 0 : smp_mb();
43 :
44 0 : blk_mq_run_hw_queue(hctx, true);
45 0 : }
46 :
47 0 : static int sched_rq_cmp(void *priv, const struct list_head *a,
48 : const struct list_head *b)
49 : {
50 0 : struct request *rqa = container_of(a, struct request, queuelist);
51 0 : struct request *rqb = container_of(b, struct request, queuelist);
52 :
53 0 : return rqa->mq_hctx > rqb->mq_hctx;
54 : }
55 :
56 0 : static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
57 : {
58 0 : struct blk_mq_hw_ctx *hctx =
59 0 : list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
60 : struct request *rq;
61 0 : LIST_HEAD(hctx_list);
62 0 : unsigned int count = 0;
63 :
64 0 : list_for_each_entry(rq, rq_list, queuelist) {
65 0 : if (rq->mq_hctx != hctx) {
66 0 : list_cut_before(&hctx_list, rq_list, &rq->queuelist);
67 : goto dispatch;
68 : }
69 0 : count++;
70 : }
71 : list_splice_tail_init(rq_list, &hctx_list);
72 :
73 : dispatch:
74 0 : return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
75 : }
76 :
77 : #define BLK_MQ_BUDGET_DELAY 3 /* ms units */
78 :
79 : /*
80 : * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
81 : * its queue by itself in its completion handler, so we don't need to
82 : * restart queue if .get_budget() fails to get the budget.
83 : *
84 : * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
85 : * be run again. This is necessary to avoid starving flushes.
86 : */
87 0 : static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
88 : {
89 0 : struct request_queue *q = hctx->queue;
90 0 : struct elevator_queue *e = q->elevator;
91 0 : bool multi_hctxs = false, run_queue = false;
92 0 : bool dispatched = false, busy = false;
93 : unsigned int max_dispatch;
94 0 : LIST_HEAD(rq_list);
95 0 : int count = 0;
96 :
97 0 : if (hctx->dispatch_busy)
98 : max_dispatch = 1;
99 : else
100 0 : max_dispatch = hctx->queue->nr_requests;
101 :
102 : do {
103 : struct request *rq;
104 : int budget_token;
105 :
106 0 : if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
107 : break;
108 :
109 0 : if (!list_empty_careful(&hctx->dispatch)) {
110 : busy = true;
111 : break;
112 : }
113 :
114 0 : budget_token = blk_mq_get_dispatch_budget(q);
115 0 : if (budget_token < 0)
116 : break;
117 :
118 0 : rq = e->type->ops.dispatch_request(hctx);
119 0 : if (!rq) {
120 : blk_mq_put_dispatch_budget(q, budget_token);
121 : /*
122 : * We're releasing without dispatching. Holding the
123 : * budget could have blocked any "hctx"s with the
124 : * same queue and if we didn't dispatch then there's
125 : * no guarantee anyone will kick the queue. Kick it
126 : * ourselves.
127 : */
128 : run_queue = true;
129 : break;
130 : }
131 :
132 0 : blk_mq_set_rq_budget_token(rq, budget_token);
133 :
134 : /*
135 : * Now this rq owns the budget which has to be released
136 : * if this rq won't be queued to driver via .queue_rq()
137 : * in blk_mq_dispatch_rq_list().
138 : */
139 0 : list_add_tail(&rq->queuelist, &rq_list);
140 0 : count++;
141 0 : if (rq->mq_hctx != hctx)
142 0 : multi_hctxs = true;
143 :
144 : /*
145 : * If we cannot get tag for the request, stop dequeueing
146 : * requests from the IO scheduler. We are unlikely to be able
147 : * to submit them anyway and it creates false impression for
148 : * scheduling heuristics that the device can take more IO.
149 : */
150 0 : if (!blk_mq_get_driver_tag(rq))
151 : break;
152 0 : } while (count < max_dispatch);
153 :
154 0 : if (!count) {
155 0 : if (run_queue)
156 0 : blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
157 0 : } else if (multi_hctxs) {
158 : /*
159 : * Requests from different hctx may be dequeued from some
160 : * schedulers, such as bfq and deadline.
161 : *
162 : * Sort the requests in the list according to their hctx,
163 : * dispatch batching requests from same hctx at a time.
164 : */
165 0 : list_sort(NULL, &rq_list, sched_rq_cmp);
166 : do {
167 0 : dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
168 0 : } while (!list_empty(&rq_list));
169 : } else {
170 0 : dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
171 : }
172 :
173 0 : if (busy)
174 : return -EAGAIN;
175 0 : return !!dispatched;
176 : }
177 :
178 0 : static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
179 : {
180 0 : unsigned long end = jiffies + HZ;
181 : int ret;
182 :
183 : do {
184 0 : ret = __blk_mq_do_dispatch_sched(hctx);
185 0 : if (ret != 1)
186 : break;
187 0 : if (need_resched() || time_is_before_jiffies(end)) {
188 0 : blk_mq_delay_run_hw_queue(hctx, 0);
189 0 : break;
190 : }
191 : } while (1);
192 :
193 0 : return ret;
194 : }
195 :
196 : static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
197 : struct blk_mq_ctx *ctx)
198 : {
199 0 : unsigned short idx = ctx->index_hw[hctx->type];
200 :
201 0 : if (++idx == hctx->nr_ctx)
202 0 : idx = 0;
203 :
204 0 : return hctx->ctxs[idx];
205 : }
206 :
207 : /*
208 : * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
209 : * its queue by itself in its completion handler, so we don't need to
210 : * restart queue if .get_budget() fails to get the budget.
211 : *
212 : * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
213 : * be run again. This is necessary to avoid starving flushes.
214 : */
215 0 : static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
216 : {
217 0 : struct request_queue *q = hctx->queue;
218 0 : LIST_HEAD(rq_list);
219 0 : struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
220 0 : int ret = 0;
221 : struct request *rq;
222 :
223 : do {
224 : int budget_token;
225 :
226 0 : if (!list_empty_careful(&hctx->dispatch)) {
227 : ret = -EAGAIN;
228 : break;
229 : }
230 :
231 0 : if (!sbitmap_any_bit_set(&hctx->ctx_map))
232 : break;
233 :
234 0 : budget_token = blk_mq_get_dispatch_budget(q);
235 0 : if (budget_token < 0)
236 : break;
237 :
238 0 : rq = blk_mq_dequeue_from_ctx(hctx, ctx);
239 0 : if (!rq) {
240 0 : blk_mq_put_dispatch_budget(q, budget_token);
241 : /*
242 : * We're releasing without dispatching. Holding the
243 : * budget could have blocked any "hctx"s with the
244 : * same queue and if we didn't dispatch then there's
245 : * no guarantee anyone will kick the queue. Kick it
246 : * ourselves.
247 : */
248 0 : blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
249 0 : break;
250 : }
251 :
252 0 : blk_mq_set_rq_budget_token(rq, budget_token);
253 :
254 : /*
255 : * Now this rq owns the budget which has to be released
256 : * if this rq won't be queued to driver via .queue_rq()
257 : * in blk_mq_dispatch_rq_list().
258 : */
259 0 : list_add(&rq->queuelist, &rq_list);
260 :
261 : /* round robin for fair dispatch */
262 0 : ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
263 :
264 0 : } while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));
265 :
266 0 : WRITE_ONCE(hctx->dispatch_from, ctx);
267 0 : return ret;
268 : }
269 :
270 0 : static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
271 : {
272 0 : bool need_dispatch = false;
273 0 : LIST_HEAD(rq_list);
274 :
275 : /*
276 : * If we have previous entries on our dispatch list, grab them first for
277 : * more fair dispatch.
278 : */
279 0 : if (!list_empty_careful(&hctx->dispatch)) {
280 0 : spin_lock(&hctx->lock);
281 0 : if (!list_empty(&hctx->dispatch))
282 0 : list_splice_init(&hctx->dispatch, &rq_list);
283 0 : spin_unlock(&hctx->lock);
284 : }
285 :
286 : /*
287 : * Only ask the scheduler for requests, if we didn't have residual
288 : * requests from the dispatch list. This is to avoid the case where
289 : * we only ever dispatch a fraction of the requests available because
290 : * of low device queue depth. Once we pull requests out of the IO
291 : * scheduler, we can no longer merge or sort them. So it's best to
292 : * leave them there for as long as we can. Mark the hw queue as
293 : * needing a restart in that case.
294 : *
295 : * We want to dispatch from the scheduler if there was nothing
296 : * on the dispatch list or we were able to dispatch from the
297 : * dispatch list.
298 : */
299 0 : if (!list_empty(&rq_list)) {
300 0 : blk_mq_sched_mark_restart_hctx(hctx);
301 0 : if (!blk_mq_dispatch_rq_list(hctx, &rq_list, 0))
302 : return 0;
303 : need_dispatch = true;
304 : } else {
305 0 : need_dispatch = hctx->dispatch_busy;
306 : }
307 :
308 0 : if (hctx->queue->elevator)
309 0 : return blk_mq_do_dispatch_sched(hctx);
310 :
311 : /* dequeue request one by one from sw queue if queue is busy */
312 0 : if (need_dispatch)
313 0 : return blk_mq_do_dispatch_ctx(hctx);
314 0 : blk_mq_flush_busy_ctxs(hctx, &rq_list);
315 0 : blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
316 0 : return 0;
317 : }
318 :
319 0 : void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
320 : {
321 0 : struct request_queue *q = hctx->queue;
322 :
323 : /* RCU or SRCU read lock is needed before checking quiesced flag */
324 0 : if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
325 : return;
326 :
327 0 : hctx->run++;
328 :
329 : /*
330 : * A return of -EAGAIN is an indication that hctx->dispatch is not
331 : * empty and we must run again in order to avoid starving flushes.
332 : */
333 0 : if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
334 0 : if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
335 0 : blk_mq_run_hw_queue(hctx, true);
336 : }
337 : }
338 :
339 0 : bool blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
340 : unsigned int nr_segs)
341 : {
342 0 : struct elevator_queue *e = q->elevator;
343 : struct blk_mq_ctx *ctx;
344 : struct blk_mq_hw_ctx *hctx;
345 0 : bool ret = false;
346 : enum hctx_type type;
347 :
348 0 : if (e && e->type->ops.bio_merge) {
349 0 : ret = e->type->ops.bio_merge(q, bio, nr_segs);
350 0 : goto out_put;
351 : }
352 :
353 0 : ctx = blk_mq_get_ctx(q);
354 0 : hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
355 0 : type = hctx->type;
356 0 : if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
357 0 : list_empty_careful(&ctx->rq_lists[type]))
358 : goto out_put;
359 :
360 : /* default per sw-queue merge */
361 0 : spin_lock(&ctx->lock);
362 : /*
363 : * Reverse check our software queue for entries that we could
364 : * potentially merge with. Currently includes a hand-wavy stop
365 : * count of 8, to not spend too much time checking for merges.
366 : */
367 0 : if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs))
368 0 : ret = true;
369 :
370 0 : spin_unlock(&ctx->lock);
371 : out_put:
372 0 : return ret;
373 : }
374 :
375 0 : bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq,
376 : struct list_head *free)
377 : {
378 0 : return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
379 : }
380 : EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
381 :
382 0 : static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q,
383 : struct blk_mq_hw_ctx *hctx,
384 : unsigned int hctx_idx)
385 : {
386 0 : if (blk_mq_is_shared_tags(q->tag_set->flags)) {
387 0 : hctx->sched_tags = q->sched_shared_tags;
388 : return 0;
389 : }
390 :
391 0 : hctx->sched_tags = blk_mq_alloc_map_and_rqs(q->tag_set, hctx_idx,
392 0 : q->nr_requests);
393 :
394 0 : if (!hctx->sched_tags)
395 : return -ENOMEM;
396 : return 0;
397 : }
398 :
399 : static void blk_mq_exit_sched_shared_tags(struct request_queue *queue)
400 : {
401 0 : blk_mq_free_rq_map(queue->sched_shared_tags);
402 0 : queue->sched_shared_tags = NULL;
403 : }
404 :
405 : /* called in queue's release handler, tagset has gone away */
406 0 : static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags)
407 : {
408 : struct blk_mq_hw_ctx *hctx;
409 : unsigned long i;
410 :
411 0 : queue_for_each_hw_ctx(q, hctx, i) {
412 0 : if (hctx->sched_tags) {
413 0 : if (!blk_mq_is_shared_tags(flags))
414 0 : blk_mq_free_rq_map(hctx->sched_tags);
415 0 : hctx->sched_tags = NULL;
416 : }
417 : }
418 :
419 0 : if (blk_mq_is_shared_tags(flags))
420 0 : blk_mq_exit_sched_shared_tags(q);
421 0 : }
422 :
423 0 : static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
424 : {
425 0 : struct blk_mq_tag_set *set = queue->tag_set;
426 :
427 : /*
428 : * Set initial depth at max so that we don't need to reallocate for
429 : * updating nr_requests.
430 : */
431 0 : queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set,
432 : BLK_MQ_NO_HCTX_IDX,
433 : MAX_SCHED_RQ);
434 0 : if (!queue->sched_shared_tags)
435 : return -ENOMEM;
436 :
437 0 : blk_mq_tag_update_sched_shared_tags(queue);
438 :
439 0 : return 0;
440 : }
441 :
442 : /* caller must have a reference to @e, will grab another one if successful */
443 0 : int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
444 : {
445 0 : unsigned int flags = q->tag_set->flags;
446 : struct blk_mq_hw_ctx *hctx;
447 : struct elevator_queue *eq;
448 : unsigned long i;
449 : int ret;
450 :
451 : /*
452 : * Default to double of smaller one between hw queue_depth and 128,
453 : * since we don't split into sync/async like the old code did.
454 : * Additionally, this is a per-hw queue depth.
455 : */
456 0 : q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
457 : BLKDEV_DEFAULT_RQ);
458 :
459 0 : if (blk_mq_is_shared_tags(flags)) {
460 0 : ret = blk_mq_init_sched_shared_tags(q);
461 0 : if (ret)
462 : return ret;
463 : }
464 :
465 0 : queue_for_each_hw_ctx(q, hctx, i) {
466 0 : ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, i);
467 0 : if (ret)
468 : goto err_free_map_and_rqs;
469 : }
470 :
471 0 : ret = e->ops.init_sched(q, e);
472 0 : if (ret)
473 : goto err_free_map_and_rqs;
474 :
475 0 : mutex_lock(&q->debugfs_mutex);
476 0 : blk_mq_debugfs_register_sched(q);
477 0 : mutex_unlock(&q->debugfs_mutex);
478 :
479 0 : queue_for_each_hw_ctx(q, hctx, i) {
480 0 : if (e->ops.init_hctx) {
481 0 : ret = e->ops.init_hctx(hctx, i);
482 0 : if (ret) {
483 0 : eq = q->elevator;
484 0 : blk_mq_sched_free_rqs(q);
485 0 : blk_mq_exit_sched(q, eq);
486 0 : kobject_put(&eq->kobj);
487 0 : return ret;
488 : }
489 : }
490 0 : mutex_lock(&q->debugfs_mutex);
491 0 : blk_mq_debugfs_register_sched_hctx(q, hctx);
492 0 : mutex_unlock(&q->debugfs_mutex);
493 : }
494 :
495 : return 0;
496 :
497 : err_free_map_and_rqs:
498 0 : blk_mq_sched_free_rqs(q);
499 0 : blk_mq_sched_tags_teardown(q, flags);
500 :
501 0 : q->elevator = NULL;
502 0 : return ret;
503 : }
504 :
505 : /*
506 : * called in either blk_queue_cleanup or elevator_switch, tagset
507 : * is required for freeing requests
508 : */
509 0 : void blk_mq_sched_free_rqs(struct request_queue *q)
510 : {
511 : struct blk_mq_hw_ctx *hctx;
512 : unsigned long i;
513 :
514 0 : if (blk_mq_is_shared_tags(q->tag_set->flags)) {
515 0 : blk_mq_free_rqs(q->tag_set, q->sched_shared_tags,
516 : BLK_MQ_NO_HCTX_IDX);
517 : } else {
518 0 : queue_for_each_hw_ctx(q, hctx, i) {
519 0 : if (hctx->sched_tags)
520 0 : blk_mq_free_rqs(q->tag_set,
521 : hctx->sched_tags, i);
522 : }
523 : }
524 0 : }
525 :
526 0 : void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
527 : {
528 : struct blk_mq_hw_ctx *hctx;
529 : unsigned long i;
530 0 : unsigned int flags = 0;
531 :
532 0 : queue_for_each_hw_ctx(q, hctx, i) {
533 0 : mutex_lock(&q->debugfs_mutex);
534 0 : blk_mq_debugfs_unregister_sched_hctx(hctx);
535 0 : mutex_unlock(&q->debugfs_mutex);
536 :
537 0 : if (e->type->ops.exit_hctx && hctx->sched_data) {
538 0 : e->type->ops.exit_hctx(hctx, i);
539 0 : hctx->sched_data = NULL;
540 : }
541 0 : flags = hctx->flags;
542 : }
543 :
544 0 : mutex_lock(&q->debugfs_mutex);
545 0 : blk_mq_debugfs_unregister_sched(q);
546 0 : mutex_unlock(&q->debugfs_mutex);
547 :
548 0 : if (e->type->ops.exit_sched)
549 0 : e->type->ops.exit_sched(e);
550 0 : blk_mq_sched_tags_teardown(q, flags);
551 0 : q->elevator = NULL;
552 0 : }
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