]>
git.proxmox.com Git - mirror_ubuntu-bionic-kernel.git/blob - block/blk-mq-tag.c
2 * Fast and scalable bitmap tagging variant. Uses sparser bitmaps spread
3 * over multiple cachelines to avoid ping-pong between multiple submitters
4 * or submitter and completer. Uses rolling wakeups to avoid falling of
5 * the scaling cliff when we run out of tags and have to start putting
8 * Uses active queue tracking to support fairer distribution of tags
9 * between multiple submitters when a shared tag map is used.
11 * Copyright (C) 2013-2014 Jens Axboe
13 #include <linux/kernel.h>
14 #include <linux/module.h>
15 #include <linux/random.h>
17 #include <linux/blk-mq.h>
20 #include "blk-mq-tag.h"
22 static bool bt_has_free_tags(struct blk_mq_bitmap_tags
*bt
)
26 for (i
= 0; i
< bt
->map_nr
; i
++) {
27 struct blk_align_bitmap
*bm
= &bt
->map
[i
];
30 ret
= find_first_zero_bit(&bm
->word
, bm
->depth
);
38 bool blk_mq_has_free_tags(struct blk_mq_tags
*tags
)
43 return bt_has_free_tags(&tags
->bitmap_tags
);
46 static inline int bt_index_inc(int index
)
48 return (index
+ 1) & (BT_WAIT_QUEUES
- 1);
51 static inline void bt_index_atomic_inc(atomic_t
*index
)
53 int old
= atomic_read(index
);
54 int new = bt_index_inc(old
);
55 atomic_cmpxchg(index
, old
, new);
59 * If a previously inactive queue goes active, bump the active user count.
61 bool __blk_mq_tag_busy(struct blk_mq_hw_ctx
*hctx
)
63 if (!test_bit(BLK_MQ_S_TAG_ACTIVE
, &hctx
->state
) &&
64 !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE
, &hctx
->state
))
65 atomic_inc(&hctx
->tags
->active_queues
);
71 * Wakeup all potentially sleeping on tags
73 void blk_mq_tag_wakeup_all(struct blk_mq_tags
*tags
, bool include_reserve
)
75 struct blk_mq_bitmap_tags
*bt
;
79 * Make sure all changes prior to this are visible from other CPUs.
82 bt
= &tags
->bitmap_tags
;
83 wake_index
= atomic_read(&bt
->wake_index
);
84 for (i
= 0; i
< BT_WAIT_QUEUES
; i
++) {
85 struct bt_wait_state
*bs
= &bt
->bs
[wake_index
];
87 if (waitqueue_active(&bs
->wait
))
90 wake_index
= bt_index_inc(wake_index
);
93 if (include_reserve
) {
94 bt
= &tags
->breserved_tags
;
95 if (waitqueue_active(&bt
->bs
[0].wait
))
96 wake_up(&bt
->bs
[0].wait
);
101 * If a previously busy queue goes inactive, potential waiters could now
102 * be allowed to queue. Wake them up and check.
104 void __blk_mq_tag_idle(struct blk_mq_hw_ctx
*hctx
)
106 struct blk_mq_tags
*tags
= hctx
->tags
;
108 if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE
, &hctx
->state
))
111 atomic_dec(&tags
->active_queues
);
113 blk_mq_tag_wakeup_all(tags
, false);
117 * For shared tag users, we track the number of currently active users
118 * and attempt to provide a fair share of the tag depth for each of them.
120 static inline bool hctx_may_queue(struct blk_mq_hw_ctx
*hctx
,
121 struct blk_mq_bitmap_tags
*bt
)
123 unsigned int depth
, users
;
125 if (!hctx
|| !(hctx
->flags
& BLK_MQ_F_TAG_SHARED
))
127 if (!test_bit(BLK_MQ_S_TAG_ACTIVE
, &hctx
->state
))
131 * Don't try dividing an ant
136 users
= atomic_read(&hctx
->tags
->active_queues
);
141 * Allow at least some tags
143 depth
= max((bt
->depth
+ users
- 1) / users
, 4U);
144 return atomic_read(&hctx
->nr_active
) < depth
;
147 static int __bt_get_word(struct blk_align_bitmap
*bm
, unsigned int last_tag
,
150 int tag
, org_last_tag
= last_tag
;
153 tag
= find_next_zero_bit(&bm
->word
, bm
->depth
, last_tag
);
154 if (unlikely(tag
>= bm
->depth
)) {
156 * We started with an offset, and we didn't reset the
157 * offset to 0 in a failure case, so start from 0 to
160 if (org_last_tag
&& last_tag
&& !nowrap
) {
161 last_tag
= org_last_tag
= 0;
167 if (!test_and_set_bit(tag
, &bm
->word
))
171 if (last_tag
>= bm
->depth
- 1)
178 #define BT_ALLOC_RR(tags) (tags->alloc_policy == BLK_TAG_ALLOC_RR)
181 * Straight forward bitmap tag implementation, where each bit is a tag
182 * (cleared == free, and set == busy). The small twist is using per-cpu
183 * last_tag caches, which blk-mq stores in the blk_mq_ctx software queue
184 * contexts. This enables us to drastically limit the space searched,
185 * without dirtying an extra shared cacheline like we would if we stored
186 * the cache value inside the shared blk_mq_bitmap_tags structure. On top
187 * of that, each word of tags is in a separate cacheline. This means that
188 * multiple users will tend to stick to different cachelines, at least
189 * until the map is exhausted.
191 static int __bt_get(struct blk_mq_hw_ctx
*hctx
, struct blk_mq_bitmap_tags
*bt
,
192 unsigned int *tag_cache
, struct blk_mq_tags
*tags
)
194 unsigned int last_tag
, org_last_tag
;
197 if (!hctx_may_queue(hctx
, bt
))
200 last_tag
= org_last_tag
= *tag_cache
;
201 index
= TAG_TO_INDEX(bt
, last_tag
);
203 for (i
= 0; i
< bt
->map_nr
; i
++) {
204 tag
= __bt_get_word(&bt
->map
[index
], TAG_TO_BIT(bt
, last_tag
),
207 tag
+= (index
<< bt
->bits_per_word
);
212 * Jump to next index, and reset the last tag to be the
213 * first tag of that index
216 last_tag
= (index
<< bt
->bits_per_word
);
218 if (index
>= bt
->map_nr
) {
228 * Only update the cache from the allocation path, if we ended
229 * up using the specific cached tag.
232 if (tag
== org_last_tag
|| unlikely(BT_ALLOC_RR(tags
))) {
234 if (last_tag
>= bt
->depth
- 1)
237 *tag_cache
= last_tag
;
243 static struct bt_wait_state
*bt_wait_ptr(struct blk_mq_bitmap_tags
*bt
,
244 struct blk_mq_hw_ctx
*hctx
)
246 struct bt_wait_state
*bs
;
252 wait_index
= atomic_read(&hctx
->wait_index
);
253 bs
= &bt
->bs
[wait_index
];
254 bt_index_atomic_inc(&hctx
->wait_index
);
258 static int bt_get(struct blk_mq_alloc_data
*data
,
259 struct blk_mq_bitmap_tags
*bt
,
260 struct blk_mq_hw_ctx
*hctx
,
261 unsigned int *last_tag
, struct blk_mq_tags
*tags
)
263 struct bt_wait_state
*bs
;
267 tag
= __bt_get(hctx
, bt
, last_tag
, tags
);
271 if (data
->flags
& BLK_MQ_REQ_NOWAIT
)
274 bs
= bt_wait_ptr(bt
, hctx
);
276 prepare_to_wait(&bs
->wait
, &wait
, TASK_UNINTERRUPTIBLE
);
278 tag
= __bt_get(hctx
, bt
, last_tag
, tags
);
283 * We're out of tags on this hardware queue, kick any
284 * pending IO submits before going to sleep waiting for
285 * some to complete. Note that hctx can be NULL here for
286 * reserved tag allocation.
289 blk_mq_run_hw_queue(hctx
, false);
292 * Retry tag allocation after running the hardware queue,
293 * as running the queue may also have found completions.
295 tag
= __bt_get(hctx
, bt
, last_tag
, tags
);
299 blk_mq_put_ctx(data
->ctx
);
303 data
->ctx
= blk_mq_get_ctx(data
->q
);
304 data
->hctx
= blk_mq_map_queue(data
->q
, data
->ctx
->cpu
);
305 if (data
->flags
& BLK_MQ_REQ_RESERVED
) {
306 bt
= &data
->hctx
->tags
->breserved_tags
;
308 last_tag
= &data
->ctx
->last_tag
;
310 bt
= &hctx
->tags
->bitmap_tags
;
312 finish_wait(&bs
->wait
, &wait
);
313 bs
= bt_wait_ptr(bt
, hctx
);
316 finish_wait(&bs
->wait
, &wait
);
320 static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data
*data
)
324 tag
= bt_get(data
, &data
->hctx
->tags
->bitmap_tags
, data
->hctx
,
325 &data
->ctx
->last_tag
, data
->hctx
->tags
);
327 return tag
+ data
->hctx
->tags
->nr_reserved_tags
;
329 return BLK_MQ_TAG_FAIL
;
332 static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data
*data
)
336 if (unlikely(!data
->hctx
->tags
->nr_reserved_tags
)) {
338 return BLK_MQ_TAG_FAIL
;
341 tag
= bt_get(data
, &data
->hctx
->tags
->breserved_tags
, NULL
, &zero
,
344 return BLK_MQ_TAG_FAIL
;
349 unsigned int blk_mq_get_tag(struct blk_mq_alloc_data
*data
)
351 if (data
->flags
& BLK_MQ_REQ_RESERVED
)
352 return __blk_mq_get_reserved_tag(data
);
353 return __blk_mq_get_tag(data
);
356 static struct bt_wait_state
*bt_wake_ptr(struct blk_mq_bitmap_tags
*bt
)
360 wake_index
= atomic_read(&bt
->wake_index
);
361 for (i
= 0; i
< BT_WAIT_QUEUES
; i
++) {
362 struct bt_wait_state
*bs
= &bt
->bs
[wake_index
];
364 if (waitqueue_active(&bs
->wait
)) {
365 int o
= atomic_read(&bt
->wake_index
);
367 atomic_cmpxchg(&bt
->wake_index
, o
, wake_index
);
372 wake_index
= bt_index_inc(wake_index
);
378 static void bt_clear_tag(struct blk_mq_bitmap_tags
*bt
, unsigned int tag
)
380 const int index
= TAG_TO_INDEX(bt
, tag
);
381 struct bt_wait_state
*bs
;
384 clear_bit(TAG_TO_BIT(bt
, tag
), &bt
->map
[index
].word
);
386 /* Ensure that the wait list checks occur after clear_bit(). */
389 bs
= bt_wake_ptr(bt
);
393 wait_cnt
= atomic_dec_return(&bs
->wait_cnt
);
394 if (unlikely(wait_cnt
< 0))
395 wait_cnt
= atomic_inc_return(&bs
->wait_cnt
);
397 atomic_add(bt
->wake_cnt
, &bs
->wait_cnt
);
398 bt_index_atomic_inc(&bt
->wake_index
);
403 void blk_mq_put_tag(struct blk_mq_hw_ctx
*hctx
, unsigned int tag
,
404 unsigned int *last_tag
)
406 struct blk_mq_tags
*tags
= hctx
->tags
;
408 if (tag
>= tags
->nr_reserved_tags
) {
409 const int real_tag
= tag
- tags
->nr_reserved_tags
;
411 BUG_ON(real_tag
>= tags
->nr_tags
);
412 bt_clear_tag(&tags
->bitmap_tags
, real_tag
);
413 if (likely(tags
->alloc_policy
== BLK_TAG_ALLOC_FIFO
))
414 *last_tag
= real_tag
;
416 BUG_ON(tag
>= tags
->nr_reserved_tags
);
417 bt_clear_tag(&tags
->breserved_tags
, tag
);
421 static void bt_for_each(struct blk_mq_hw_ctx
*hctx
,
422 struct blk_mq_bitmap_tags
*bt
, unsigned int off
,
423 busy_iter_fn
*fn
, void *data
, bool reserved
)
428 for (i
= 0; i
< bt
->map_nr
; i
++) {
429 struct blk_align_bitmap
*bm
= &bt
->map
[i
];
431 for (bit
= find_first_bit(&bm
->word
, bm
->depth
);
433 bit
= find_next_bit(&bm
->word
, bm
->depth
, bit
+ 1)) {
434 rq
= hctx
->tags
->rqs
[off
+ bit
];
435 if (rq
->q
== hctx
->queue
)
436 fn(hctx
, rq
, data
, reserved
);
439 off
+= (1 << bt
->bits_per_word
);
443 static void bt_tags_for_each(struct blk_mq_tags
*tags
,
444 struct blk_mq_bitmap_tags
*bt
, unsigned int off
,
445 busy_tag_iter_fn
*fn
, void *data
, bool reserved
)
452 for (i
= 0; i
< bt
->map_nr
; i
++) {
453 struct blk_align_bitmap
*bm
= &bt
->map
[i
];
455 for (bit
= find_first_bit(&bm
->word
, bm
->depth
);
457 bit
= find_next_bit(&bm
->word
, bm
->depth
, bit
+ 1)) {
458 rq
= tags
->rqs
[off
+ bit
];
459 fn(rq
, data
, reserved
);
462 off
+= (1 << bt
->bits_per_word
);
466 static void blk_mq_all_tag_busy_iter(struct blk_mq_tags
*tags
,
467 busy_tag_iter_fn
*fn
, void *priv
)
469 if (tags
->nr_reserved_tags
)
470 bt_tags_for_each(tags
, &tags
->breserved_tags
, 0, fn
, priv
, true);
471 bt_tags_for_each(tags
, &tags
->bitmap_tags
, tags
->nr_reserved_tags
, fn
, priv
,
475 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set
*tagset
,
476 busy_tag_iter_fn
*fn
, void *priv
)
480 for (i
= 0; i
< tagset
->nr_hw_queues
; i
++) {
481 if (tagset
->tags
&& tagset
->tags
[i
])
482 blk_mq_all_tag_busy_iter(tagset
->tags
[i
], fn
, priv
);
485 EXPORT_SYMBOL(blk_mq_tagset_busy_iter
);
487 int blk_mq_reinit_tagset(struct blk_mq_tag_set
*set
)
491 if (!set
->ops
->reinit_request
)
494 for (i
= 0; i
< set
->nr_hw_queues
; i
++) {
495 struct blk_mq_tags
*tags
= set
->tags
[i
];
497 for (j
= 0; j
< tags
->nr_tags
; j
++) {
501 ret
= set
->ops
->reinit_request(set
->driver_data
,
511 EXPORT_SYMBOL_GPL(blk_mq_reinit_tagset
);
513 void blk_mq_queue_tag_busy_iter(struct request_queue
*q
, busy_iter_fn
*fn
,
516 struct blk_mq_hw_ctx
*hctx
;
520 queue_for_each_hw_ctx(q
, hctx
, i
) {
521 struct blk_mq_tags
*tags
= hctx
->tags
;
524 * If not software queues are currently mapped to this
525 * hardware queue, there's nothing to check
527 if (!blk_mq_hw_queue_mapped(hctx
))
530 if (tags
->nr_reserved_tags
)
531 bt_for_each(hctx
, &tags
->breserved_tags
, 0, fn
, priv
, true);
532 bt_for_each(hctx
, &tags
->bitmap_tags
, tags
->nr_reserved_tags
, fn
, priv
,
538 static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags
*bt
)
540 unsigned int i
, used
;
542 for (i
= 0, used
= 0; i
< bt
->map_nr
; i
++) {
543 struct blk_align_bitmap
*bm
= &bt
->map
[i
];
545 used
+= bitmap_weight(&bm
->word
, bm
->depth
);
548 return bt
->depth
- used
;
551 static void bt_update_count(struct blk_mq_bitmap_tags
*bt
,
554 unsigned int tags_per_word
= 1U << bt
->bits_per_word
;
555 unsigned int map_depth
= depth
;
560 for (i
= 0; i
< bt
->map_nr
; i
++) {
561 bt
->map
[i
].depth
= min(map_depth
, tags_per_word
);
562 map_depth
-= bt
->map
[i
].depth
;
566 bt
->wake_cnt
= BT_WAIT_BATCH
;
567 if (bt
->wake_cnt
> depth
/ BT_WAIT_QUEUES
)
568 bt
->wake_cnt
= max(1U, depth
/ BT_WAIT_QUEUES
);
573 static int bt_alloc(struct blk_mq_bitmap_tags
*bt
, unsigned int depth
,
574 int node
, bool reserved
)
578 bt
->bits_per_word
= ilog2(BITS_PER_LONG
);
581 * Depth can be zero for reserved tags, that's not a failure
585 unsigned int nr
, tags_per_word
;
587 tags_per_word
= (1 << bt
->bits_per_word
);
590 * If the tag space is small, shrink the number of tags
591 * per word so we spread over a few cachelines, at least.
592 * If less than 4 tags, just forget about it, it's not
593 * going to work optimally anyway.
596 while (tags_per_word
* 4 > depth
) {
598 tags_per_word
= (1 << bt
->bits_per_word
);
602 nr
= ALIGN(depth
, tags_per_word
) / tags_per_word
;
603 bt
->map
= kzalloc_node(nr
* sizeof(struct blk_align_bitmap
),
611 bt
->bs
= kzalloc(BT_WAIT_QUEUES
* sizeof(*bt
->bs
), GFP_KERNEL
);
618 bt_update_count(bt
, depth
);
620 for (i
= 0; i
< BT_WAIT_QUEUES
; i
++) {
621 init_waitqueue_head(&bt
->bs
[i
].wait
);
622 atomic_set(&bt
->bs
[i
].wait_cnt
, bt
->wake_cnt
);
628 static void bt_free(struct blk_mq_bitmap_tags
*bt
)
634 static struct blk_mq_tags
*blk_mq_init_bitmap_tags(struct blk_mq_tags
*tags
,
635 int node
, int alloc_policy
)
637 unsigned int depth
= tags
->nr_tags
- tags
->nr_reserved_tags
;
639 tags
->alloc_policy
= alloc_policy
;
641 if (bt_alloc(&tags
->bitmap_tags
, depth
, node
, false))
643 if (bt_alloc(&tags
->breserved_tags
, tags
->nr_reserved_tags
, node
, true))
648 bt_free(&tags
->bitmap_tags
);
653 struct blk_mq_tags
*blk_mq_init_tags(unsigned int total_tags
,
654 unsigned int reserved_tags
,
655 int node
, int alloc_policy
)
657 struct blk_mq_tags
*tags
;
659 if (total_tags
> BLK_MQ_TAG_MAX
) {
660 pr_err("blk-mq: tag depth too large\n");
664 tags
= kzalloc_node(sizeof(*tags
), GFP_KERNEL
, node
);
668 if (!zalloc_cpumask_var(&tags
->cpumask
, GFP_KERNEL
)) {
673 tags
->nr_tags
= total_tags
;
674 tags
->nr_reserved_tags
= reserved_tags
;
676 return blk_mq_init_bitmap_tags(tags
, node
, alloc_policy
);
679 void blk_mq_free_tags(struct blk_mq_tags
*tags
)
681 bt_free(&tags
->bitmap_tags
);
682 bt_free(&tags
->breserved_tags
);
683 free_cpumask_var(tags
->cpumask
);
687 void blk_mq_tag_init_last_tag(struct blk_mq_tags
*tags
, unsigned int *tag
)
689 unsigned int depth
= tags
->nr_tags
- tags
->nr_reserved_tags
;
691 *tag
= prandom_u32() % depth
;
694 int blk_mq_tag_update_depth(struct blk_mq_tags
*tags
, unsigned int tdepth
)
696 tdepth
-= tags
->nr_reserved_tags
;
697 if (tdepth
> tags
->nr_tags
)
701 * Don't need (or can't) update reserved tags here, they remain
702 * static and should never need resizing.
704 bt_update_count(&tags
->bitmap_tags
, tdepth
);
705 blk_mq_tag_wakeup_all(tags
, false);
710 * blk_mq_unique_tag() - return a tag that is unique queue-wide
711 * @rq: request for which to compute a unique tag
713 * The tag field in struct request is unique per hardware queue but not over
714 * all hardware queues. Hence this function that returns a tag with the
715 * hardware context index in the upper bits and the per hardware queue tag in
718 * Note: When called for a request that is queued on a non-multiqueue request
719 * queue, the hardware context index is set to zero.
721 u32
blk_mq_unique_tag(struct request
*rq
)
723 struct request_queue
*q
= rq
->q
;
724 struct blk_mq_hw_ctx
*hctx
;
728 hctx
= blk_mq_map_queue(q
, rq
->mq_ctx
->cpu
);
729 hwq
= hctx
->queue_num
;
732 return (hwq
<< BLK_MQ_UNIQUE_TAG_BITS
) |
733 (rq
->tag
& BLK_MQ_UNIQUE_TAG_MASK
);
735 EXPORT_SYMBOL(blk_mq_unique_tag
);
737 ssize_t
blk_mq_tag_sysfs_show(struct blk_mq_tags
*tags
, char *page
)
739 char *orig_page
= page
;
740 unsigned int free
, res
;
745 page
+= sprintf(page
, "nr_tags=%u, reserved_tags=%u, "
746 "bits_per_word=%u\n",
747 tags
->nr_tags
, tags
->nr_reserved_tags
,
748 tags
->bitmap_tags
.bits_per_word
);
750 free
= bt_unused_tags(&tags
->bitmap_tags
);
751 res
= bt_unused_tags(&tags
->breserved_tags
);
753 page
+= sprintf(page
, "nr_free=%u, nr_reserved=%u\n", free
, res
);
754 page
+= sprintf(page
, "active_queues=%u\n", atomic_read(&tags
->active_queues
));
756 return page
- orig_page
;