1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Tag allocation using scalable bitmaps. Uses active queue tracking to support
4 * fairer distribution of tags between multiple submitters when a shared tag map
5 * is used.
6 *
7 * Copyright (C) 2013-2014 Jens Axboe
8 */
9 #include <linux/kernel.h>
10 #include <linux/module.h>
11
12 #include <linux/delay.h>
13 #include "blk.h"
14 #include "blk-mq.h"
15 #include "blk-mq-sched.h"
16
17 /*
18 * Recalculate wakeup batch when tag is shared by hctx.
19 */
20 static void blk_mq_update_wake_batch(struct blk_mq_tags *tags,
21 unsigned int users)
22 {
23 if (!users)
24 return;
25
26 sbitmap_queue_recalculate_wake_batch(&tags->bitmap_tags,
27 users);
28 sbitmap_queue_recalculate_wake_batch(&tags->breserved_tags,
29 users);
30 }
31
32 /*
33 * If a previously inactive queue goes active, bump the active user count.
34 * We need to do this before try to allocate driver tag, then even if fail
35 * to get tag when first time, the other shared-tag users could reserve
36 * budget for it.
37 */
38 void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
39 {
40 unsigned int users;
41 unsigned long flags;
42 struct blk_mq_tags *tags = hctx->tags;
43
44 /*
45 * calling test_bit() prior to test_and_set_bit() is intentional,
46 * it avoids dirtying the cacheline if the queue is already active.
47 */
48 if (blk_mq_is_shared_tags(hctx->flags)) {
49 struct request_queue *q = hctx->queue;
50
51 if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) ||
52 test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
53 return;
54 } else {
55 if (test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) ||
56 test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
57 return;
58 }
59
60 spin_lock_irqsave(&tags->lock, flags);
61 users = tags->active_queues + 1;
62 WRITE_ONCE(tags->active_queues, users);
63 blk_mq_update_wake_batch(tags, users);
64 spin_unlock_irqrestore(&tags->lock, flags);
65 }
66
67 /*
68 * Wakeup all potentially sleeping on tags
69 */
70 void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
71 {
72 sbitmap_queue_wake_all(&tags->bitmap_tags);
73 if (include_reserve)
74 sbitmap_queue_wake_all(&tags->breserved_tags);
75 }
76
77 /*
78 * If a previously busy queue goes inactive, potential waiters could now
79 * be allowed to queue. Wake them up and check.
80 */
81 void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
82 {
83 struct blk_mq_tags *tags = hctx->tags;
84 unsigned int users;
85
86 if (blk_mq_is_shared_tags(hctx->flags)) {
87 struct request_queue *q = hctx->queue;
88
89 if (!test_and_clear_bit(QUEUE_FLAG_HCTX_ACTIVE,
90 &q->queue_flags))
91 return;
92 } else {
93 if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
94 return;
95 }
96
97 spin_lock_irq(&tags->lock);
98 users = tags->active_queues - 1;
99 WRITE_ONCE(tags->active_queues, users);
100 blk_mq_update_wake_batch(tags, users);
101 spin_unlock_irq(&tags->lock);
102
103 blk_mq_tag_wakeup_all(tags, false);
104 }
105
106 static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
107 struct sbitmap_queue *bt)
108 {
109 if (!data->q->elevator && !(data->flags & BLK_MQ_REQ_RESERVED) &&
110 !hctx_may_queue(data->hctx, bt))
111 return BLK_MQ_NO_TAG;
112
113 if (data->shallow_depth)
114 return sbitmap_queue_get_shallow(bt, data->shallow_depth);
115 else
116 return __sbitmap_queue_get(bt);
117 }
118
119 unsigned long blk_mq_get_tags(struct blk_mq_alloc_data *data, int nr_tags,
120 unsigned int *offset)
121 {
122 struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
123 struct sbitmap_queue *bt = &tags->bitmap_tags;
124 unsigned long ret;
125
126 if (data->shallow_depth ||data->flags & BLK_MQ_REQ_RESERVED ||
127 data->hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
128 return 0;
129 ret = __sbitmap_queue_get_batch(bt, nr_tags, offset);
130 *offset += tags->nr_reserved_tags;
131 return ret;
132 }
133
134 unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
135 {
136 struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
137 struct sbitmap_queue *bt;
138 struct sbq_wait_state *ws;
139 DEFINE_SBQ_WAIT(wait);
140 unsigned int tag_offset;
141 int tag;
142
143 if (data->flags & BLK_MQ_REQ_RESERVED) {
144 if (unlikely(!tags->nr_reserved_tags)) {
145 WARN_ON_ONCE(1);
146 return BLK_MQ_NO_TAG;
147 }
148 bt = &tags->breserved_tags;
149 tag_offset = 0;
150 } else {
151 bt = &tags->bitmap_tags;
152 tag_offset = tags->nr_reserved_tags;
153 }
154
155 tag = __blk_mq_get_tag(data, bt);
156 if (tag != BLK_MQ_NO_TAG)
157 goto found_tag;
158
159 if (data->flags & BLK_MQ_REQ_NOWAIT)
160 return BLK_MQ_NO_TAG;
161
162 ws = bt_wait_ptr(bt, data->hctx);
163 do {
164 struct sbitmap_queue *bt_prev;
165
166 /*
167 * We're out of tags on this hardware queue, kick any
168 * pending IO submits before going to sleep waiting for
169 * some to complete.
170 */
171 blk_mq_run_hw_queue(data->hctx, false);
172
173 /*
174 * Retry tag allocation after running the hardware queue,
175 * as running the queue may also have found completions.
176 */
177 tag = __blk_mq_get_tag(data, bt);
178 if (tag != BLK_MQ_NO_TAG)
179 break;
180
181 sbitmap_prepare_to_wait(bt, ws, &wait, TASK_UNINTERRUPTIBLE);
182
183 tag = __blk_mq_get_tag(data, bt);
184 if (tag != BLK_MQ_NO_TAG)
185 break;
186
187 bt_prev = bt;
188 io_schedule();
189
190 sbitmap_finish_wait(bt, ws, &wait);
191
192 data->ctx = blk_mq_get_ctx(data->q);
193 data->hctx = blk_mq_map_queue(data->q, data->cmd_flags,
194 data->ctx);
195 tags = blk_mq_tags_from_data(data);
196 if (data->flags & BLK_MQ_REQ_RESERVED)
197 bt = &tags->breserved_tags;
198 else
199 bt = &tags->bitmap_tags;
200
201 /*
202 * If destination hw queue is changed, fake wake up on
203 * previous queue for compensating the wake up miss, so
204 * other allocations on previous queue won't be starved.
205 */
206 if (bt != bt_prev)
207 sbitmap_queue_wake_up(bt_prev, 1);
208
209 ws = bt_wait_ptr(bt, data->hctx);
210 } while (1);
211
212 sbitmap_finish_wait(bt, ws, &wait);
213
214 found_tag:
215 /*
216 * Give up this allocation if the hctx is inactive. The caller will
217 * retry on an active hctx.
218 */
219 if (unlikely(test_bit(BLK_MQ_S_INACTIVE, &data->hctx->state))) {
220 blk_mq_put_tag(tags, data->ctx, tag + tag_offset);
221 return BLK_MQ_NO_TAG;
222 }
223 return tag + tag_offset;
224 }
225
226 void blk_mq_put_tag(struct blk_mq_tags *tags, struct blk_mq_ctx *ctx,
227 unsigned int tag)
228 {
229 if (!blk_mq_tag_is_reserved(tags, tag)) {
230 const int real_tag = tag - tags->nr_reserved_tags;
231
232 BUG_ON(real_tag >= tags->nr_tags);
233 sbitmap_queue_clear(&tags->bitmap_tags, real_tag, ctx->cpu);
234 } else {
235 sbitmap_queue_clear(&tags->breserved_tags, tag, ctx->cpu);
236 }
237 }
238
239 void blk_mq_put_tags(struct blk_mq_tags *tags, int *tag_array, int nr_tags)
240 {
241 sbitmap_queue_clear_batch(&tags->bitmap_tags, tags->nr_reserved_tags,
242 tag_array, nr_tags);
243 }
244
245 struct bt_iter_data {
246 struct blk_mq_hw_ctx *hctx;
247 struct request_queue *q;
248 busy_tag_iter_fn *fn;
249 void *data;
250 bool reserved;
251 };
252
253 static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
254 unsigned int bitnr)
255 {
256 struct request *rq;
257 unsigned long flags;
258
259 spin_lock_irqsave(&tags->lock, flags);
260 rq = tags->rqs[bitnr];
261 if (!rq || rq->tag != bitnr || !req_ref_inc_not_zero(rq))
262 rq = NULL;
263 spin_unlock_irqrestore(&tags->lock, flags);
264 return rq;
265 }
266
267 static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
268 {
269 struct bt_iter_data *iter_data = data;
270 struct blk_mq_hw_ctx *hctx = iter_data->hctx;
271 struct request_queue *q = iter_data->q;
272 struct blk_mq_tag_set *set = q->tag_set;
273 struct blk_mq_tags *tags;
274 struct request *rq;
275 bool ret = true;
276
277 if (blk_mq_is_shared_tags(set->flags))
278 tags = set->shared_tags;
279 else
280 tags = hctx->tags;
281
282 if (!iter_data->reserved)
283 bitnr += tags->nr_reserved_tags;
284 /*
285 * We can hit rq == NULL here, because the tagging functions
286 * test and set the bit before assigning ->rqs[].
287 */
288 rq = blk_mq_find_and_get_req(tags, bitnr);
289 if (!rq)
290 return true;
291
292 if (rq->q == q && (!hctx || rq->mq_hctx == hctx))
293 ret = iter_data->fn(rq, iter_data->data);
294 blk_mq_put_rq_ref(rq);
295 return ret;
296 }
297
298 /**
299 * bt_for_each - iterate over the requests associated with a hardware queue
300 * @hctx: Hardware queue to examine.
301 * @q: Request queue to examine.
302 * @bt: sbitmap to examine. This is either the breserved_tags member
303 * or the bitmap_tags member of struct blk_mq_tags.
304 * @fn: Pointer to the function that will be called for each request
305 * associated with @hctx that has been assigned a driver tag.
306 * @fn will be called as follows: @fn(@hctx, rq, @data, @reserved)
307 * where rq is a pointer to a request. Return true to continue
308 * iterating tags, false to stop.
309 * @data: Will be passed as third argument to @fn.
310 * @reserved: Indicates whether @bt is the breserved_tags member or the
311 * bitmap_tags member of struct blk_mq_tags.
312 */
313 static void bt_for_each(struct blk_mq_hw_ctx *hctx, struct request_queue *q,
314 struct sbitmap_queue *bt, busy_tag_iter_fn *fn,
315 void *data, bool reserved)
316 {
317 struct bt_iter_data iter_data = {
318 .hctx = hctx,
319 .fn = fn,
320 .data = data,
321 .reserved = reserved,
322 .q = q,
323 };
324
325 sbitmap_for_each_set(&bt->sb, bt_iter, &iter_data);
326 }
327
328 struct bt_tags_iter_data {
329 struct blk_mq_tags *tags;
330 busy_tag_iter_fn *fn;
331 void *data;
332 unsigned int flags;
333 };
334
335 #define BT_TAG_ITER_RESERVED (1 << 0)
336 #define BT_TAG_ITER_STARTED (1 << 1)
337 #define BT_TAG_ITER_STATIC_RQS (1 << 2)
338
339 static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
340 {
341 struct bt_tags_iter_data *iter_data = data;
342 struct blk_mq_tags *tags = iter_data->tags;
343 struct request *rq;
344 bool ret = true;
345 bool iter_static_rqs = !!(iter_data->flags & BT_TAG_ITER_STATIC_RQS);
346
347 if (!(iter_data->flags & BT_TAG_ITER_RESERVED))
348 bitnr += tags->nr_reserved_tags;
349
350 /*
351 * We can hit rq == NULL here, because the tagging functions
352 * test and set the bit before assigning ->rqs[].
353 */
354 if (iter_static_rqs)
355 rq = tags->static_rqs[bitnr];
356 else
357 rq = blk_mq_find_and_get_req(tags, bitnr);
358 if (!rq)
359 return true;
360
361 if (!(iter_data->flags & BT_TAG_ITER_STARTED) ||
362 blk_mq_request_started(rq))
363 ret = iter_data->fn(rq, iter_data->data);
364 if (!iter_static_rqs)
365 blk_mq_put_rq_ref(rq);
366 return ret;
367 }
368
369 /**
370 * bt_tags_for_each - iterate over the requests in a tag map
371 * @tags: Tag map to iterate over.
372 * @bt: sbitmap to examine. This is either the breserved_tags member
373 * or the bitmap_tags member of struct blk_mq_tags.
374 * @fn: Pointer to the function that will be called for each started
375 * request. @fn will be called as follows: @fn(rq, @data,
376 * @reserved) where rq is a pointer to a request. Return true
377 * to continue iterating tags, false to stop.
378 * @data: Will be passed as second argument to @fn.
379 * @flags: BT_TAG_ITER_*
380 */
381 static void bt_tags_for_each(struct blk_mq_tags *tags, struct sbitmap_queue *bt,
382 busy_tag_iter_fn *fn, void *data, unsigned int flags)
383 {
384 struct bt_tags_iter_data iter_data = {
385 .tags = tags,
386 .fn = fn,
387 .data = data,
388 .flags = flags,
389 };
390
391 if (tags->rqs)
392 sbitmap_for_each_set(&bt->sb, bt_tags_iter, &iter_data);
393 }
394
395 static void __blk_mq_all_tag_iter(struct blk_mq_tags *tags,
396 busy_tag_iter_fn *fn, void *priv, unsigned int flags)
397 {
398 WARN_ON_ONCE(flags & BT_TAG_ITER_RESERVED);
399
400 if (tags->nr_reserved_tags)
401 bt_tags_for_each(tags, &tags->breserved_tags, fn, priv,
402 flags | BT_TAG_ITER_RESERVED);
403 bt_tags_for_each(tags, &tags->bitmap_tags, fn, priv, flags);
404 }
405
406 /**
407 * blk_mq_all_tag_iter - iterate over all requests in a tag map
408 * @tags: Tag map to iterate over.
409 * @fn: Pointer to the function that will be called for each
410 * request. @fn will be called as follows: @fn(rq, @priv,
411 * reserved) where rq is a pointer to a request. 'reserved'
412 * indicates whether or not @rq is a reserved request. Return
413 * true to continue iterating tags, false to stop.
414 * @priv: Will be passed as second argument to @fn.
415 *
416 * Caller has to pass the tag map from which requests are allocated.
417 */
418 void blk_mq_all_tag_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
419 void *priv)
420 {
421 __blk_mq_all_tag_iter(tags, fn, priv, BT_TAG_ITER_STATIC_RQS);
422 }
423
424 /**
425 * blk_mq_tagset_busy_iter - iterate over all started requests in a tag set
426 * @tagset: Tag set to iterate over.
427 * @fn: Pointer to the function that will be called for each started
428 * request. @fn will be called as follows: @fn(rq, @priv,
429 * reserved) where rq is a pointer to a request. 'reserved'
430 * indicates whether or not @rq is a reserved request. Return
431 * true to continue iterating tags, false to stop.
432 * @priv: Will be passed as second argument to @fn.
433 *
434 * We grab one request reference before calling @fn and release it after
435 * @fn returns.
436 */
437 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
438 busy_tag_iter_fn *fn, void *priv)
439 {
440 unsigned int flags = tagset->flags;
441 int i, nr_tags;
442
443 nr_tags = blk_mq_is_shared_tags(flags) ? 1 : tagset->nr_hw_queues;
444
445 for (i = 0; i < nr_tags; i++) {
446 if (tagset->tags && tagset->tags[i])
447 __blk_mq_all_tag_iter(tagset->tags[i], fn, priv,
448 BT_TAG_ITER_STARTED);
449 }
450 }
451 EXPORT_SYMBOL(blk_mq_tagset_busy_iter);
452
453 static bool blk_mq_tagset_count_completed_rqs(struct request *rq, void *data)
454 {
455 unsigned *count = data;
456
457 if (blk_mq_request_completed(rq))
458 (*count)++;
459 return true;
460 }
461
462 /**
463 * blk_mq_tagset_wait_completed_request - Wait until all scheduled request
464 * completions have finished.
465 * @tagset: Tag set to drain completed request
466 *
467 * Note: This function has to be run after all IO queues are shutdown
468 */
469 void blk_mq_tagset_wait_completed_request(struct blk_mq_tag_set *tagset)
470 {
471 while (true) {
472 unsigned count = 0;
473
474 blk_mq_tagset_busy_iter(tagset,
475 blk_mq_tagset_count_completed_rqs, &count);
476 if (!count)
477 break;
478 msleep(5);
479 }
480 }
481 EXPORT_SYMBOL(blk_mq_tagset_wait_completed_request);
482
483 /**
484 * blk_mq_queue_tag_busy_iter - iterate over all requests with a driver tag
485 * @q: Request queue to examine.
486 * @fn: Pointer to the function that will be called for each request
487 * on @q. @fn will be called as follows: @fn(hctx, rq, @priv,
488 * reserved) where rq is a pointer to a request and hctx points
489 * to the hardware queue associated with the request. 'reserved'
490 * indicates whether or not @rq is a reserved request.
491 * @priv: Will be passed as third argument to @fn.
492 *
493 * Note: if @q->tag_set is shared with other request queues then @fn will be
494 * called for all requests on all queues that share that tag set and not only
495 * for requests associated with @q.
496 */
497 void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_tag_iter_fn *fn,
498 void *priv)
499 {
500 /*
501 * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and hctx_table
502 * while the queue is frozen. So we can use q_usage_counter to avoid
503 * racing with it.
504 */
505 if (!percpu_ref_tryget(&q->q_usage_counter))
506 return;
507
508 if (blk_mq_is_shared_tags(q->tag_set->flags)) {
509 struct blk_mq_tags *tags = q->tag_set->shared_tags;
510 struct sbitmap_queue *bresv = &tags->breserved_tags;
511 struct sbitmap_queue *btags = &tags->bitmap_tags;
512
513 if (tags->nr_reserved_tags)
514 bt_for_each(NULL, q, bresv, fn, priv, true);
515 bt_for_each(NULL, q, btags, fn, priv, false);
516 } else {
517 struct blk_mq_hw_ctx *hctx;
518 unsigned long i;
519
520 queue_for_each_hw_ctx(q, hctx, i) {
521 struct blk_mq_tags *tags = hctx->tags;
522 struct sbitmap_queue *bresv = &tags->breserved_tags;
523 struct sbitmap_queue *btags = &tags->bitmap_tags;
524
525 /*
526 * If no software queues are currently mapped to this
527 * hardware queue, there's nothing to check
528 */
529 if (!blk_mq_hw_queue_mapped(hctx))
530 continue;
531
532 if (tags->nr_reserved_tags)
533 bt_for_each(hctx, q, bresv, fn, priv, true);
534 bt_for_each(hctx, q, btags, fn, priv, false);
535 }
536 }
537 blk_queue_exit(q);
538 }
539
540 static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
541 bool round_robin, int node)
542 {
543 return sbitmap_queue_init_node(bt, depth, -1, round_robin, GFP_KERNEL,
544 node);
545 }
546
547 int blk_mq_init_bitmaps(struct sbitmap_queue *bitmap_tags,
548 struct sbitmap_queue *breserved_tags,
549 unsigned int queue_depth, unsigned int reserved,
550 int node, int alloc_policy)
551 {
552 unsigned int depth = queue_depth - reserved;
553 bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
554
555 if (bt_alloc(bitmap_tags, depth, round_robin, node))
556 return -ENOMEM;
557 if (bt_alloc(breserved_tags, reserved, round_robin, node))
558 goto free_bitmap_tags;
559
560 return 0;
561
562 free_bitmap_tags:
563 sbitmap_queue_free(bitmap_tags);
564 return -ENOMEM;
565 }
566
567 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
568 unsigned int reserved_tags,
569 int node, int alloc_policy)
570 {
571 struct blk_mq_tags *tags;
572
573 if (total_tags > BLK_MQ_TAG_MAX) {
574 pr_err("blk-mq: tag depth too large\n");
575 return NULL;
576 }
577
578 tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
579 if (!tags)
580 return NULL;
581
582 tags->nr_tags = total_tags;
583 tags->nr_reserved_tags = reserved_tags;
584 spin_lock_init(&tags->lock);
585
586 if (blk_mq_init_bitmaps(&tags->bitmap_tags, &tags->breserved_tags,
587 total_tags, reserved_tags, node,
588 alloc_policy) < 0) {
589 kfree(tags);
590 return NULL;
591 }
592 return tags;
593 }
594
595 void blk_mq_free_tags(struct blk_mq_tags *tags)
596 {
597 sbitmap_queue_free(&tags->bitmap_tags);
598 sbitmap_queue_free(&tags->breserved_tags);
599 kfree(tags);
600 }
601
602 int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx,
603 struct blk_mq_tags **tagsptr, unsigned int tdepth,
604 bool can_grow)
605 {
606 struct blk_mq_tags *tags = *tagsptr;
607
608 if (tdepth <= tags->nr_reserved_tags)
609 return -EINVAL;
610
611 /*
612 * If we are allowed to grow beyond the original size, allocate
613 * a new set of tags before freeing the old one.
614 */
615 if (tdepth > tags->nr_tags) {
616 struct blk_mq_tag_set *set = hctx->queue->tag_set;
617 struct blk_mq_tags *new;
618
619 if (!can_grow)
620 return -EINVAL;
621
622 /*
623 * We need some sort of upper limit, set it high enough that
624 * no valid use cases should require more.
625 */
626 if (tdepth > MAX_SCHED_RQ)
627 return -EINVAL;
628
629 /*
630 * Only the sbitmap needs resizing since we allocated the max
631 * initially.
632 */
633 if (blk_mq_is_shared_tags(set->flags))
634 return 0;
635
636 new = blk_mq_alloc_map_and_rqs(set, hctx->queue_num, tdepth);
637 if (!new)
638 return -ENOMEM;
639
640 blk_mq_free_map_and_rqs(set, *tagsptr, hctx->queue_num);
641 *tagsptr = new;
642 } else {
643 /*
644 * Don't need (or can't) update reserved tags here, they
645 * remain static and should never need resizing.
646 */
647 sbitmap_queue_resize(&tags->bitmap_tags,
648 tdepth - tags->nr_reserved_tags);
649 }
650
651 return 0;
652 }
653
654 void blk_mq_tag_resize_shared_tags(struct blk_mq_tag_set *set, unsigned int size)
655 {
656 struct blk_mq_tags *tags = set->shared_tags;
657
658 sbitmap_queue_resize(&tags->bitmap_tags, size - set->reserved_tags);
659 }
660
661 void blk_mq_tag_update_sched_shared_tags(struct request_queue *q)
662 {
663 sbitmap_queue_resize(&q->sched_shared_tags->bitmap_tags,
664 q->nr_requests - q->tag_set->reserved_tags);
665 }
666
667 /**
668 * blk_mq_unique_tag() - return a tag that is unique queue-wide
669 * @rq: request for which to compute a unique tag
670 *
671 * The tag field in struct request is unique per hardware queue but not over
672 * all hardware queues. Hence this function that returns a tag with the
673 * hardware context index in the upper bits and the per hardware queue tag in
674 * the lower bits.
675 *
676 * Note: When called for a request that is queued on a non-multiqueue request
677 * queue, the hardware context index is set to zero.
678 */
679 u32 blk_mq_unique_tag(struct request *rq)
680 {
681 return (rq->mq_hctx->queue_num << BLK_MQ_UNIQUE_TAG_BITS) |
682 (rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
683 }
684 EXPORT_SYMBOL(blk_mq_unique_tag);
685
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