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 | void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx) |
23 | { |
24 | if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state)) |
25 | return; |
26 | |
27 | set_bit(nr: BLK_MQ_S_SCHED_RESTART, addr: &hctx->state); |
28 | } |
29 | EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx); |
30 | |
31 | void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx) |
32 | { |
33 | clear_bit(nr: BLK_MQ_S_SCHED_RESTART, addr: &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 | smp_mb(); |
43 | |
44 | blk_mq_run_hw_queue(hctx, async: true); |
45 | } |
46 | |
47 | static int sched_rq_cmp(void *priv, const struct list_head *a, |
48 | const struct list_head *b) |
49 | { |
50 | struct request *rqa = container_of(a, struct request, queuelist); |
51 | struct request *rqb = container_of(b, struct request, queuelist); |
52 | |
53 | return rqa->mq_hctx > rqb->mq_hctx; |
54 | } |
55 | |
56 | static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list) |
57 | { |
58 | struct blk_mq_hw_ctx *hctx = |
59 | list_first_entry(rq_list, struct request, queuelist)->mq_hctx; |
60 | struct request *rq; |
61 | LIST_HEAD(hctx_list); |
62 | unsigned int count = 0; |
63 | |
64 | list_for_each_entry(rq, rq_list, queuelist) { |
65 | if (rq->mq_hctx != hctx) { |
66 | list_cut_before(list: &hctx_list, head: rq_list, entry: &rq->queuelist); |
67 | goto dispatch; |
68 | } |
69 | count++; |
70 | } |
71 | list_splice_tail_init(list: rq_list, head: &hctx_list); |
72 | |
73 | dispatch: |
74 | 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 | static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) |
88 | { |
89 | struct request_queue *q = hctx->queue; |
90 | struct elevator_queue *e = q->elevator; |
91 | bool multi_hctxs = false, run_queue = false; |
92 | bool dispatched = false, busy = false; |
93 | unsigned int max_dispatch; |
94 | LIST_HEAD(rq_list); |
95 | int count = 0; |
96 | |
97 | if (hctx->dispatch_busy) |
98 | max_dispatch = 1; |
99 | else |
100 | max_dispatch = hctx->queue->nr_requests; |
101 | |
102 | do { |
103 | struct request *rq; |
104 | int budget_token; |
105 | |
106 | if (e->type->ops.has_work && !e->type->ops.has_work(hctx)) |
107 | break; |
108 | |
109 | if (!list_empty_careful(head: &hctx->dispatch)) { |
110 | busy = true; |
111 | break; |
112 | } |
113 | |
114 | budget_token = blk_mq_get_dispatch_budget(q); |
115 | if (budget_token < 0) |
116 | break; |
117 | |
118 | rq = e->type->ops.dispatch_request(hctx); |
119 | 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 | blk_mq_set_rq_budget_token(rq, token: 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 | list_add_tail(new: &rq->queuelist, head: &rq_list); |
140 | count++; |
141 | if (rq->mq_hctx != hctx) |
142 | 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 | if (!blk_mq_get_driver_tag(rq)) |
151 | break; |
152 | } while (count < max_dispatch); |
153 | |
154 | if (!count) { |
155 | if (run_queue) |
156 | blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY); |
157 | } 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 | list_sort(NULL, head: &rq_list, cmp: sched_rq_cmp); |
166 | do { |
167 | dispatched |= blk_mq_dispatch_hctx_list(rq_list: &rq_list); |
168 | } while (!list_empty(head: &rq_list)); |
169 | } else { |
170 | dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count); |
171 | } |
172 | |
173 | if (busy) |
174 | return -EAGAIN; |
175 | return !!dispatched; |
176 | } |
177 | |
178 | static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) |
179 | { |
180 | unsigned long end = jiffies + HZ; |
181 | int ret; |
182 | |
183 | do { |
184 | ret = __blk_mq_do_dispatch_sched(hctx); |
185 | if (ret != 1) |
186 | break; |
187 | if (need_resched() || time_is_before_jiffies(end)) { |
188 | blk_mq_delay_run_hw_queue(hctx, msecs: 0); |
189 | break; |
190 | } |
191 | } while (1); |
192 | |
193 | 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 | unsigned short idx = ctx->index_hw[hctx->type]; |
200 | |
201 | if (++idx == hctx->nr_ctx) |
202 | idx = 0; |
203 | |
204 | 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 | static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) |
216 | { |
217 | struct request_queue *q = hctx->queue; |
218 | LIST_HEAD(rq_list); |
219 | struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from); |
220 | int ret = 0; |
221 | struct request *rq; |
222 | |
223 | do { |
224 | int budget_token; |
225 | |
226 | if (!list_empty_careful(head: &hctx->dispatch)) { |
227 | ret = -EAGAIN; |
228 | break; |
229 | } |
230 | |
231 | if (!sbitmap_any_bit_set(sb: &hctx->ctx_map)) |
232 | break; |
233 | |
234 | budget_token = blk_mq_get_dispatch_budget(q); |
235 | if (budget_token < 0) |
236 | break; |
237 | |
238 | rq = blk_mq_dequeue_from_ctx(hctx, start: ctx); |
239 | if (!rq) { |
240 | 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 | blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY); |
249 | break; |
250 | } |
251 | |
252 | blk_mq_set_rq_budget_token(rq, token: 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 | list_add(new: &rq->queuelist, head: &rq_list); |
260 | |
261 | /* round robin for fair dispatch */ |
262 | ctx = blk_mq_next_ctx(hctx, ctx: rq->mq_ctx); |
263 | |
264 | } while (blk_mq_dispatch_rq_list(hctx: rq->mq_hctx, &rq_list, 1)); |
265 | |
266 | WRITE_ONCE(hctx->dispatch_from, ctx); |
267 | return ret; |
268 | } |
269 | |
270 | static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) |
271 | { |
272 | bool need_dispatch = false; |
273 | 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 | if (!list_empty_careful(head: &hctx->dispatch)) { |
280 | spin_lock(lock: &hctx->lock); |
281 | if (!list_empty(head: &hctx->dispatch)) |
282 | list_splice_init(list: &hctx->dispatch, head: &rq_list); |
283 | spin_unlock(lock: &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 | if (!list_empty(head: &rq_list)) { |
300 | blk_mq_sched_mark_restart_hctx(hctx); |
301 | if (!blk_mq_dispatch_rq_list(hctx, &rq_list, 0)) |
302 | return 0; |
303 | need_dispatch = true; |
304 | } else { |
305 | need_dispatch = hctx->dispatch_busy; |
306 | } |
307 | |
308 | if (hctx->queue->elevator) |
309 | return blk_mq_do_dispatch_sched(hctx); |
310 | |
311 | /* dequeue request one by one from sw queue if queue is busy */ |
312 | if (need_dispatch) |
313 | return blk_mq_do_dispatch_ctx(hctx); |
314 | blk_mq_flush_busy_ctxs(hctx, list: &rq_list); |
315 | blk_mq_dispatch_rq_list(hctx, &rq_list, 0); |
316 | return 0; |
317 | } |
318 | |
319 | void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) |
320 | { |
321 | struct request_queue *q = hctx->queue; |
322 | |
323 | /* RCU or SRCU read lock is needed before checking quiesced flag */ |
324 | if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))) |
325 | return; |
326 | |
327 | /* |
328 | * A return of -EAGAIN is an indication that hctx->dispatch is not |
329 | * empty and we must run again in order to avoid starving flushes. |
330 | */ |
331 | if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) { |
332 | if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) |
333 | blk_mq_run_hw_queue(hctx, async: true); |
334 | } |
335 | } |
336 | |
337 | bool blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio, |
338 | unsigned int nr_segs) |
339 | { |
340 | struct elevator_queue *e = q->elevator; |
341 | struct blk_mq_ctx *ctx; |
342 | struct blk_mq_hw_ctx *hctx; |
343 | bool ret = false; |
344 | enum hctx_type type; |
345 | |
346 | if (e && e->type->ops.bio_merge) { |
347 | ret = e->type->ops.bio_merge(q, bio, nr_segs); |
348 | goto out_put; |
349 | } |
350 | |
351 | ctx = blk_mq_get_ctx(q); |
352 | hctx = blk_mq_map_queue(q, opf: bio->bi_opf, ctx); |
353 | type = hctx->type; |
354 | if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) || |
355 | list_empty_careful(head: &ctx->rq_lists[type])) |
356 | goto out_put; |
357 | |
358 | /* default per sw-queue merge */ |
359 | spin_lock(lock: &ctx->lock); |
360 | /* |
361 | * Reverse check our software queue for entries that we could |
362 | * potentially merge with. Currently includes a hand-wavy stop |
363 | * count of 8, to not spend too much time checking for merges. |
364 | */ |
365 | if (blk_bio_list_merge(q, list: &ctx->rq_lists[type], bio, nr_segs)) |
366 | ret = true; |
367 | |
368 | spin_unlock(lock: &ctx->lock); |
369 | out_put: |
370 | return ret; |
371 | } |
372 | |
373 | bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq, |
374 | struct list_head *free) |
375 | { |
376 | return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free); |
377 | } |
378 | EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge); |
379 | |
380 | static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q, |
381 | struct blk_mq_hw_ctx *hctx, |
382 | unsigned int hctx_idx) |
383 | { |
384 | if (blk_mq_is_shared_tags(flags: q->tag_set->flags)) { |
385 | hctx->sched_tags = q->sched_shared_tags; |
386 | return 0; |
387 | } |
388 | |
389 | hctx->sched_tags = blk_mq_alloc_map_and_rqs(set: q->tag_set, hctx_idx, |
390 | depth: q->nr_requests); |
391 | |
392 | if (!hctx->sched_tags) |
393 | return -ENOMEM; |
394 | return 0; |
395 | } |
396 | |
397 | static void blk_mq_exit_sched_shared_tags(struct request_queue *queue) |
398 | { |
399 | blk_mq_free_rq_map(tags: queue->sched_shared_tags); |
400 | queue->sched_shared_tags = NULL; |
401 | } |
402 | |
403 | /* called in queue's release handler, tagset has gone away */ |
404 | static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags) |
405 | { |
406 | struct blk_mq_hw_ctx *hctx; |
407 | unsigned long i; |
408 | |
409 | queue_for_each_hw_ctx(q, hctx, i) { |
410 | if (hctx->sched_tags) { |
411 | if (!blk_mq_is_shared_tags(flags)) |
412 | blk_mq_free_rq_map(tags: hctx->sched_tags); |
413 | hctx->sched_tags = NULL; |
414 | } |
415 | } |
416 | |
417 | if (blk_mq_is_shared_tags(flags)) |
418 | blk_mq_exit_sched_shared_tags(queue: q); |
419 | } |
420 | |
421 | static int blk_mq_init_sched_shared_tags(struct request_queue *queue) |
422 | { |
423 | struct blk_mq_tag_set *set = queue->tag_set; |
424 | |
425 | /* |
426 | * Set initial depth at max so that we don't need to reallocate for |
427 | * updating nr_requests. |
428 | */ |
429 | queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set, |
430 | BLK_MQ_NO_HCTX_IDX, |
431 | MAX_SCHED_RQ); |
432 | if (!queue->sched_shared_tags) |
433 | return -ENOMEM; |
434 | |
435 | blk_mq_tag_update_sched_shared_tags(q: queue); |
436 | |
437 | return 0; |
438 | } |
439 | |
440 | /* caller must have a reference to @e, will grab another one if successful */ |
441 | int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e) |
442 | { |
443 | unsigned int flags = q->tag_set->flags; |
444 | struct blk_mq_hw_ctx *hctx; |
445 | struct elevator_queue *eq; |
446 | unsigned long i; |
447 | int ret; |
448 | |
449 | /* |
450 | * Default to double of smaller one between hw queue_depth and 128, |
451 | * since we don't split into sync/async like the old code did. |
452 | * Additionally, this is a per-hw queue depth. |
453 | */ |
454 | q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth, |
455 | BLKDEV_DEFAULT_RQ); |
456 | |
457 | if (blk_mq_is_shared_tags(flags)) { |
458 | ret = blk_mq_init_sched_shared_tags(queue: q); |
459 | if (ret) |
460 | return ret; |
461 | } |
462 | |
463 | queue_for_each_hw_ctx(q, hctx, i) { |
464 | ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, hctx_idx: i); |
465 | if (ret) |
466 | goto err_free_map_and_rqs; |
467 | } |
468 | |
469 | ret = e->ops.init_sched(q, e); |
470 | if (ret) |
471 | goto err_free_map_and_rqs; |
472 | |
473 | mutex_lock(&q->debugfs_mutex); |
474 | blk_mq_debugfs_register_sched(q); |
475 | mutex_unlock(lock: &q->debugfs_mutex); |
476 | |
477 | queue_for_each_hw_ctx(q, hctx, i) { |
478 | if (e->ops.init_hctx) { |
479 | ret = e->ops.init_hctx(hctx, i); |
480 | if (ret) { |
481 | eq = q->elevator; |
482 | blk_mq_sched_free_rqs(q); |
483 | blk_mq_exit_sched(q, e: eq); |
484 | kobject_put(kobj: &eq->kobj); |
485 | return ret; |
486 | } |
487 | } |
488 | mutex_lock(&q->debugfs_mutex); |
489 | blk_mq_debugfs_register_sched_hctx(q, hctx); |
490 | mutex_unlock(lock: &q->debugfs_mutex); |
491 | } |
492 | |
493 | return 0; |
494 | |
495 | err_free_map_and_rqs: |
496 | blk_mq_sched_free_rqs(q); |
497 | blk_mq_sched_tags_teardown(q, flags); |
498 | |
499 | q->elevator = NULL; |
500 | return ret; |
501 | } |
502 | |
503 | /* |
504 | * called in either blk_queue_cleanup or elevator_switch, tagset |
505 | * is required for freeing requests |
506 | */ |
507 | void blk_mq_sched_free_rqs(struct request_queue *q) |
508 | { |
509 | struct blk_mq_hw_ctx *hctx; |
510 | unsigned long i; |
511 | |
512 | if (blk_mq_is_shared_tags(flags: q->tag_set->flags)) { |
513 | blk_mq_free_rqs(set: q->tag_set, tags: q->sched_shared_tags, |
514 | BLK_MQ_NO_HCTX_IDX); |
515 | } else { |
516 | queue_for_each_hw_ctx(q, hctx, i) { |
517 | if (hctx->sched_tags) |
518 | blk_mq_free_rqs(set: q->tag_set, |
519 | tags: hctx->sched_tags, hctx_idx: i); |
520 | } |
521 | } |
522 | } |
523 | |
524 | void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e) |
525 | { |
526 | struct blk_mq_hw_ctx *hctx; |
527 | unsigned long i; |
528 | unsigned int flags = 0; |
529 | |
530 | queue_for_each_hw_ctx(q, hctx, i) { |
531 | mutex_lock(&q->debugfs_mutex); |
532 | blk_mq_debugfs_unregister_sched_hctx(hctx); |
533 | mutex_unlock(lock: &q->debugfs_mutex); |
534 | |
535 | if (e->type->ops.exit_hctx && hctx->sched_data) { |
536 | e->type->ops.exit_hctx(hctx, i); |
537 | hctx->sched_data = NULL; |
538 | } |
539 | flags = hctx->flags; |
540 | } |
541 | |
542 | mutex_lock(&q->debugfs_mutex); |
543 | blk_mq_debugfs_unregister_sched(q); |
544 | mutex_unlock(lock: &q->debugfs_mutex); |
545 | |
546 | if (e->type->ops.exit_sched) |
547 | e->type->ops.exit_sched(e); |
548 | blk_mq_sched_tags_teardown(q, flags); |
549 | q->elevator = NULL; |
550 | } |
551 | |