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Linux/block/blk-mq-tag.c

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  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/blk-mq.h>
 13 #include "blk.h"
 14 #include "blk-mq.h"
 15 #include "blk-mq-tag.h"
 16 
 17 bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
 18 {
 19         if (!tags)
 20                 return true;
 21 
 22         return sbitmap_any_bit_clear(&tags->bitmap_tags.sb);
 23 }
 24 
 25 /*
 26  * If a previously inactive queue goes active, bump the active user count.
 27  * We need to do this before try to allocate driver tag, then even if fail
 28  * to get tag when first time, the other shared-tag users could reserve
 29  * budget for it.
 30  */
 31 bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 32 {
 33         if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
 34             !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 35                 atomic_inc(&hctx->tags->active_queues);
 36 
 37         return true;
 38 }
 39 
 40 /*
 41  * Wakeup all potentially sleeping on tags
 42  */
 43 void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
 44 {
 45         sbitmap_queue_wake_all(&tags->bitmap_tags);
 46         if (include_reserve)
 47                 sbitmap_queue_wake_all(&tags->breserved_tags);
 48 }
 49 
 50 /*
 51  * If a previously busy queue goes inactive, potential waiters could now
 52  * be allowed to queue. Wake them up and check.
 53  */
 54 void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 55 {
 56         struct blk_mq_tags *tags = hctx->tags;
 57 
 58         if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 59                 return;
 60 
 61         atomic_dec(&tags->active_queues);
 62 
 63         blk_mq_tag_wakeup_all(tags, false);
 64 }
 65 
 66 /*
 67  * For shared tag users, we track the number of currently active users
 68  * and attempt to provide a fair share of the tag depth for each of them.
 69  */
 70 static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 71                                   struct sbitmap_queue *bt)
 72 {
 73         unsigned int depth, users;
 74 
 75         if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
 76                 return true;
 77         if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 78                 return true;
 79 
 80         /*
 81          * Don't try dividing an ant
 82          */
 83         if (bt->sb.depth == 1)
 84                 return true;
 85 
 86         users = atomic_read(&hctx->tags->active_queues);
 87         if (!users)
 88                 return true;
 89 
 90         /*
 91          * Allow at least some tags
 92          */
 93         depth = max((bt->sb.depth + users - 1) / users, 4U);
 94         return atomic_read(&hctx->nr_active) < depth;
 95 }
 96 
 97 static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
 98                             struct sbitmap_queue *bt)
 99 {
100         if (!(data->flags & BLK_MQ_REQ_INTERNAL) &&
101             !hctx_may_queue(data->hctx, bt))
102                 return -1;
103         if (data->shallow_depth)
104                 return __sbitmap_queue_get_shallow(bt, data->shallow_depth);
105         else
106                 return __sbitmap_queue_get(bt);
107 }
108 
109 unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
110 {
111         struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
112         struct sbitmap_queue *bt;
113         struct sbq_wait_state *ws;
114         DEFINE_SBQ_WAIT(wait);
115         unsigned int tag_offset;
116         int tag;
117 
118         if (data->flags & BLK_MQ_REQ_RESERVED) {
119                 if (unlikely(!tags->nr_reserved_tags)) {
120                         WARN_ON_ONCE(1);
121                         return BLK_MQ_TAG_FAIL;
122                 }
123                 bt = &tags->breserved_tags;
124                 tag_offset = 0;
125         } else {
126                 bt = &tags->bitmap_tags;
127                 tag_offset = tags->nr_reserved_tags;
128         }
129 
130         tag = __blk_mq_get_tag(data, bt);
131         if (tag != -1)
132                 goto found_tag;
133 
134         if (data->flags & BLK_MQ_REQ_NOWAIT)
135                 return BLK_MQ_TAG_FAIL;
136 
137         ws = bt_wait_ptr(bt, data->hctx);
138         do {
139                 struct sbitmap_queue *bt_prev;
140 
141                 /*
142                  * We're out of tags on this hardware queue, kick any
143                  * pending IO submits before going to sleep waiting for
144                  * some to complete.
145                  */
146                 blk_mq_run_hw_queue(data->hctx, false);
147 
148                 /*
149                  * Retry tag allocation after running the hardware queue,
150                  * as running the queue may also have found completions.
151                  */
152                 tag = __blk_mq_get_tag(data, bt);
153                 if (tag != -1)
154                         break;
155 
156                 sbitmap_prepare_to_wait(bt, ws, &wait, TASK_UNINTERRUPTIBLE);
157 
158                 tag = __blk_mq_get_tag(data, bt);
159                 if (tag != -1)
160                         break;
161 
162                 bt_prev = bt;
163                 io_schedule();
164 
165                 sbitmap_finish_wait(bt, ws, &wait);
166 
167                 data->ctx = blk_mq_get_ctx(data->q);
168                 data->hctx = blk_mq_map_queue(data->q, data->cmd_flags,
169                                                 data->ctx);
170                 tags = blk_mq_tags_from_data(data);
171                 if (data->flags & BLK_MQ_REQ_RESERVED)
172                         bt = &tags->breserved_tags;
173                 else
174                         bt = &tags->bitmap_tags;
175 
176                 /*
177                  * If destination hw queue is changed, fake wake up on
178                  * previous queue for compensating the wake up miss, so
179                  * other allocations on previous queue won't be starved.
180                  */
181                 if (bt != bt_prev)
182                         sbitmap_queue_wake_up(bt_prev);
183 
184                 ws = bt_wait_ptr(bt, data->hctx);
185         } while (1);
186 
187         sbitmap_finish_wait(bt, ws, &wait);
188 
189 found_tag:
190         return tag + tag_offset;
191 }
192 
193 void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_tags *tags,
194                     struct blk_mq_ctx *ctx, unsigned int tag)
195 {
196         if (!blk_mq_tag_is_reserved(tags, tag)) {
197                 const int real_tag = tag - tags->nr_reserved_tags;
198 
199                 BUG_ON(real_tag >= tags->nr_tags);
200                 sbitmap_queue_clear(&tags->bitmap_tags, real_tag, ctx->cpu);
201         } else {
202                 BUG_ON(tag >= tags->nr_reserved_tags);
203                 sbitmap_queue_clear(&tags->breserved_tags, tag, ctx->cpu);
204         }
205 }
206 
207 struct bt_iter_data {
208         struct blk_mq_hw_ctx *hctx;
209         busy_iter_fn *fn;
210         void *data;
211         bool reserved;
212 };
213 
214 static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
215 {
216         struct bt_iter_data *iter_data = data;
217         struct blk_mq_hw_ctx *hctx = iter_data->hctx;
218         struct blk_mq_tags *tags = hctx->tags;
219         bool reserved = iter_data->reserved;
220         struct request *rq;
221 
222         if (!reserved)
223                 bitnr += tags->nr_reserved_tags;
224         rq = tags->rqs[bitnr];
225 
226         /*
227          * We can hit rq == NULL here, because the tagging functions
228          * test and set the bit before assigning ->rqs[].
229          */
230         if (rq && rq->q == hctx->queue)
231                 return iter_data->fn(hctx, rq, iter_data->data, reserved);
232         return true;
233 }
234 
235 /**
236  * bt_for_each - iterate over the requests associated with a hardware queue
237  * @hctx:       Hardware queue to examine.
238  * @bt:         sbitmap to examine. This is either the breserved_tags member
239  *              or the bitmap_tags member of struct blk_mq_tags.
240  * @fn:         Pointer to the function that will be called for each request
241  *              associated with @hctx that has been assigned a driver tag.
242  *              @fn will be called as follows: @fn(@hctx, rq, @data, @reserved)
243  *              where rq is a pointer to a request. Return true to continue
244  *              iterating tags, false to stop.
245  * @data:       Will be passed as third argument to @fn.
246  * @reserved:   Indicates whether @bt is the breserved_tags member or the
247  *              bitmap_tags member of struct blk_mq_tags.
248  */
249 static void bt_for_each(struct blk_mq_hw_ctx *hctx, struct sbitmap_queue *bt,
250                         busy_iter_fn *fn, void *data, bool reserved)
251 {
252         struct bt_iter_data iter_data = {
253                 .hctx = hctx,
254                 .fn = fn,
255                 .data = data,
256                 .reserved = reserved,
257         };
258 
259         sbitmap_for_each_set(&bt->sb, bt_iter, &iter_data);
260 }
261 
262 struct bt_tags_iter_data {
263         struct blk_mq_tags *tags;
264         busy_tag_iter_fn *fn;
265         void *data;
266         bool reserved;
267 };
268 
269 static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
270 {
271         struct bt_tags_iter_data *iter_data = data;
272         struct blk_mq_tags *tags = iter_data->tags;
273         bool reserved = iter_data->reserved;
274         struct request *rq;
275 
276         if (!reserved)
277                 bitnr += tags->nr_reserved_tags;
278 
279         /*
280          * We can hit rq == NULL here, because the tagging functions
281          * test and set the bit before assining ->rqs[].
282          */
283         rq = tags->rqs[bitnr];
284         if (rq && blk_mq_request_started(rq))
285                 return iter_data->fn(rq, iter_data->data, reserved);
286 
287         return true;
288 }
289 
290 /**
291  * bt_tags_for_each - iterate over the requests in a tag map
292  * @tags:       Tag map to iterate over.
293  * @bt:         sbitmap to examine. This is either the breserved_tags member
294  *              or the bitmap_tags member of struct blk_mq_tags.
295  * @fn:         Pointer to the function that will be called for each started
296  *              request. @fn will be called as follows: @fn(rq, @data,
297  *              @reserved) where rq is a pointer to a request. Return true
298  *              to continue iterating tags, false to stop.
299  * @data:       Will be passed as second argument to @fn.
300  * @reserved:   Indicates whether @bt is the breserved_tags member or the
301  *              bitmap_tags member of struct blk_mq_tags.
302  */
303 static void bt_tags_for_each(struct blk_mq_tags *tags, struct sbitmap_queue *bt,
304                              busy_tag_iter_fn *fn, void *data, bool reserved)
305 {
306         struct bt_tags_iter_data iter_data = {
307                 .tags = tags,
308                 .fn = fn,
309                 .data = data,
310                 .reserved = reserved,
311         };
312 
313         if (tags->rqs)
314                 sbitmap_for_each_set(&bt->sb, bt_tags_iter, &iter_data);
315 }
316 
317 /**
318  * blk_mq_all_tag_busy_iter - iterate over all started requests in a tag map
319  * @tags:       Tag map to iterate over.
320  * @fn:         Pointer to the function that will be called for each started
321  *              request. @fn will be called as follows: @fn(rq, @priv,
322  *              reserved) where rq is a pointer to a request. 'reserved'
323  *              indicates whether or not @rq is a reserved request. Return
324  *              true to continue iterating tags, false to stop.
325  * @priv:       Will be passed as second argument to @fn.
326  */
327 static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
328                 busy_tag_iter_fn *fn, void *priv)
329 {
330         if (tags->nr_reserved_tags)
331                 bt_tags_for_each(tags, &tags->breserved_tags, fn, priv, true);
332         bt_tags_for_each(tags, &tags->bitmap_tags, fn, priv, false);
333 }
334 
335 /**
336  * blk_mq_tagset_busy_iter - iterate over all started requests in a tag set
337  * @tagset:     Tag set to iterate over.
338  * @fn:         Pointer to the function that will be called for each started
339  *              request. @fn will be called as follows: @fn(rq, @priv,
340  *              reserved) where rq is a pointer to a request. 'reserved'
341  *              indicates whether or not @rq is a reserved request. Return
342  *              true to continue iterating tags, false to stop.
343  * @priv:       Will be passed as second argument to @fn.
344  */
345 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
346                 busy_tag_iter_fn *fn, void *priv)
347 {
348         int i;
349 
350         for (i = 0; i < tagset->nr_hw_queues; i++) {
351                 if (tagset->tags && tagset->tags[i])
352                         blk_mq_all_tag_busy_iter(tagset->tags[i], fn, priv);
353         }
354 }
355 EXPORT_SYMBOL(blk_mq_tagset_busy_iter);
356 
357 /**
358  * blk_mq_queue_tag_busy_iter - iterate over all requests with a driver tag
359  * @q:          Request queue to examine.
360  * @fn:         Pointer to the function that will be called for each request
361  *              on @q. @fn will be called as follows: @fn(hctx, rq, @priv,
362  *              reserved) where rq is a pointer to a request and hctx points
363  *              to the hardware queue associated with the request. 'reserved'
364  *              indicates whether or not @rq is a reserved request.
365  * @priv:       Will be passed as third argument to @fn.
366  *
367  * Note: if @q->tag_set is shared with other request queues then @fn will be
368  * called for all requests on all queues that share that tag set and not only
369  * for requests associated with @q.
370  */
371 void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
372                 void *priv)
373 {
374         struct blk_mq_hw_ctx *hctx;
375         int i;
376 
377         /*
378          * __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx
379          * while the queue is frozen. So we can use q_usage_counter to avoid
380          * racing with it. __blk_mq_update_nr_hw_queues() uses
381          * synchronize_rcu() to ensure this function left the critical section
382          * below.
383          */
384         if (!percpu_ref_tryget(&q->q_usage_counter))
385                 return;
386 
387         queue_for_each_hw_ctx(q, hctx, i) {
388                 struct blk_mq_tags *tags = hctx->tags;
389 
390                 /*
391                  * If no software queues are currently mapped to this
392                  * hardware queue, there's nothing to check
393                  */
394                 if (!blk_mq_hw_queue_mapped(hctx))
395                         continue;
396 
397                 if (tags->nr_reserved_tags)
398                         bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
399                 bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
400         }
401         blk_queue_exit(q);
402 }
403 
404 static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
405                     bool round_robin, int node)
406 {
407         return sbitmap_queue_init_node(bt, depth, -1, round_robin, GFP_KERNEL,
408                                        node);
409 }
410 
411 static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
412                                                    int node, int alloc_policy)
413 {
414         unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
415         bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
416 
417         if (bt_alloc(&tags->bitmap_tags, depth, round_robin, node))
418                 goto free_tags;
419         if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, round_robin,
420                      node))
421                 goto free_bitmap_tags;
422 
423         return tags;
424 free_bitmap_tags:
425         sbitmap_queue_free(&tags->bitmap_tags);
426 free_tags:
427         kfree(tags);
428         return NULL;
429 }
430 
431 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
432                                      unsigned int reserved_tags,
433                                      int node, int alloc_policy)
434 {
435         struct blk_mq_tags *tags;
436 
437         if (total_tags > BLK_MQ_TAG_MAX) {
438                 pr_err("blk-mq: tag depth too large\n");
439                 return NULL;
440         }
441 
442         tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
443         if (!tags)
444                 return NULL;
445 
446         tags->nr_tags = total_tags;
447         tags->nr_reserved_tags = reserved_tags;
448 
449         return blk_mq_init_bitmap_tags(tags, node, alloc_policy);
450 }
451 
452 void blk_mq_free_tags(struct blk_mq_tags *tags)
453 {
454         sbitmap_queue_free(&tags->bitmap_tags);
455         sbitmap_queue_free(&tags->breserved_tags);
456         kfree(tags);
457 }
458 
459 int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx,
460                             struct blk_mq_tags **tagsptr, unsigned int tdepth,
461                             bool can_grow)
462 {
463         struct blk_mq_tags *tags = *tagsptr;
464 
465         if (tdepth <= tags->nr_reserved_tags)
466                 return -EINVAL;
467 
468         /*
469          * If we are allowed to grow beyond the original size, allocate
470          * a new set of tags before freeing the old one.
471          */
472         if (tdepth > tags->nr_tags) {
473                 struct blk_mq_tag_set *set = hctx->queue->tag_set;
474                 struct blk_mq_tags *new;
475                 bool ret;
476 
477                 if (!can_grow)
478                         return -EINVAL;
479 
480                 /*
481                  * We need some sort of upper limit, set it high enough that
482                  * no valid use cases should require more.
483                  */
484                 if (tdepth > 16 * BLKDEV_MAX_RQ)
485                         return -EINVAL;
486 
487                 new = blk_mq_alloc_rq_map(set, hctx->queue_num, tdepth,
488                                 tags->nr_reserved_tags);
489                 if (!new)
490                         return -ENOMEM;
491                 ret = blk_mq_alloc_rqs(set, new, hctx->queue_num, tdepth);
492                 if (ret) {
493                         blk_mq_free_rq_map(new);
494                         return -ENOMEM;
495                 }
496 
497                 blk_mq_free_rqs(set, *tagsptr, hctx->queue_num);
498                 blk_mq_free_rq_map(*tagsptr);
499                 *tagsptr = new;
500         } else {
501                 /*
502                  * Don't need (or can't) update reserved tags here, they
503                  * remain static and should never need resizing.
504                  */
505                 sbitmap_queue_resize(&tags->bitmap_tags,
506                                 tdepth - tags->nr_reserved_tags);
507         }
508 
509         return 0;
510 }
511 
512 /**
513  * blk_mq_unique_tag() - return a tag that is unique queue-wide
514  * @rq: request for which to compute a unique tag
515  *
516  * The tag field in struct request is unique per hardware queue but not over
517  * all hardware queues. Hence this function that returns a tag with the
518  * hardware context index in the upper bits and the per hardware queue tag in
519  * the lower bits.
520  *
521  * Note: When called for a request that is queued on a non-multiqueue request
522  * queue, the hardware context index is set to zero.
523  */
524 u32 blk_mq_unique_tag(struct request *rq)
525 {
526         return (rq->mq_hctx->queue_num << BLK_MQ_UNIQUE_TAG_BITS) |
527                 (rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
528 }
529 EXPORT_SYMBOL(blk_mq_unique_tag);
530 

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