block/blk-mq-tag.c

   1 /*
   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
   6  * submitters to sleep.
   7  *
   8  * Uses active queue tracking to support fairer distribution of tags
   9  * between multiple submitters when a shared tag map is used.
  10  *
  11  * Copyright (C) 2013-2014 Jens Axboe
  12  */
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/random.h>
  16
  17 #include <linux/blk-mq.h>
  18 #include "blk.h"
  19 #include "blk-mq.h"
  20 #include "blk-mq-tag.h"
  21
  22 static bool bt_has_free_tags(struct blk_mq_bitmap_tags *bt)
  23 {
  24         int i;
  25
  26         for (i = 0; i < bt->map_nr; i++) {
  27                 struct blk_align_bitmap *bm = &bt->map[i];
  28                 int ret;
  29
  30                 ret = find_first_zero_bit(&bm->word, bm->depth);
  31                 if (ret < bm->depth)
  32                         return true;
  33         }
  34
  35         return false;
  36 }
  37
  38 bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
  39 {
  40         if (!tags)
  41                 return true;
  42
  43         return bt_has_free_tags(&tags->bitmap_tags);
  44 }
  45
  46 static inline int bt_index_inc(int index)
  47 {
  48         return (index + 1) & (BT_WAIT_QUEUES - 1);
  49 }
  50
  51 static inline void bt_index_atomic_inc(atomic_t *index)
  52 {
  53         int old = atomic_read(index);
  54         int new = bt_index_inc(old);
  55         atomic_cmpxchg(index, old, new);
  56 }
  57
  58 /*
  59  * If a previously inactive queue goes active, bump the active user count.
  60  */
  61 bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
  62 {
  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);
  66
  67         return true;
  68 }
  69
  70 /*
  71  * Wakeup all potentially sleeping on tags
  72  */
  73 void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
  74 {
  75         struct blk_mq_bitmap_tags *bt;
  76         int i, wake_index;
  77
  78         /*
  79          * Make sure all changes prior to this are visible from other CPUs.
  80          */
  81         smp_mb();
  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];
  86
  87                 if (waitqueue_active(&bs->wait))
  88                         wake_up(&bs->wait);
  89
  90                 wake_index = bt_index_inc(wake_index);
  91         }
  92
  93         if (include_reserve) {
  94                 bt = &tags->breserved_tags;
  95                 if (waitqueue_active(&bt->bs[0].wait))
  96                         wake_up(&bt->bs[0].wait);
  97         }
  98 }
  99
 100 /*
 101  * If a previously busy queue goes inactive, potential waiters could now
 102  * be allowed to queue. Wake them up and check.
 103  */
 104 void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 105 {
 106         struct blk_mq_tags *tags = hctx->tags;
 107
 108         if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 109                 return;
 110
 111         atomic_dec(&tags->active_queues);
 112
 113         blk_mq_tag_wakeup_all(tags, false);
 114 }
 115
 116 /*
 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.
 119  */
 120 static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 121                                   struct blk_mq_bitmap_tags *bt)
 122 {
 123         unsigned int depth, users;
 124
 125         if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
 126                 return true;
 127         if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 128                 return true;
 129
 130         /*
 131          * Don't try dividing an ant
 132          */
 133         if (bt->depth == 1)
 134                 return true;
 135
 136         users = atomic_read(&hctx->tags->active_queues);
 137         if (!users)
 138                 return true;
 139
 140         /*
 141          * Allow at least some tags
 142          */
 143         depth = max((bt->depth + users - 1) / users, 4U);
 144         return atomic_read(&hctx->nr_active) < depth;
 145 }
 146
 147 static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag,
 148                          bool nowrap)
 149 {
 150         int tag, org_last_tag = last_tag;
 151
 152         while (1) {
 153                 tag = find_next_zero_bit(&bm->word, bm->depth, last_tag);
 154                 if (unlikely(tag >= bm->depth)) {
 155                         /*
 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
 158                          * exhaust the map.
 159                          */
 160                         if (org_last_tag && last_tag && !nowrap) {
 161                                 last_tag = org_last_tag = 0;
 162                                 continue;
 163                         }
 164                         return -1;
 165                 }
 166
 167                 if (!test_and_set_bit(tag, &bm->word))
 168                         break;
 169
 170                 last_tag = tag + 1;
 171                 if (last_tag >= bm->depth - 1)
 172                         last_tag = 0;
 173         }
 174
 175         return tag;
 176 }
 177
 178 #define BT_ALLOC_RR(tags) (tags->alloc_policy == BLK_TAG_ALLOC_RR)
 179
 180 /*
 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.
 190  */
 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)
 193 {
 194         unsigned int last_tag, org_last_tag;
 195         int index, i, tag;
 196
 197         if (!hctx_may_queue(hctx, bt))
 198                 return -1;
 199
 200         last_tag = org_last_tag = *tag_cache;
 201         index = TAG_TO_INDEX(bt, last_tag);
 202
 203         for (i = 0; i < bt->map_nr; i++) {
 204                 tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag),
 205                                     BT_ALLOC_RR(tags));
 206                 if (tag != -1) {
 207                         tag += (index << bt->bits_per_word);
 208                         goto done;
 209                 }
 210
 211                 /*
 212                  * Jump to next index, and reset the last tag to be the
 213                  * first tag of that index
 214                  */
 215                 index++;
 216                 last_tag = (index << bt->bits_per_word);
 217
 218                 if (index >= bt->map_nr) {
 219                         index = 0;
 220                         last_tag = 0;
 221                 }
 222         }
 223
 224         *tag_cache = 0;
 225         return -1;
 226
 227         /*
 228          * Only update the cache from the allocation path, if we ended
 229          * up using the specific cached tag.
 230          */
 231 done:
 232         if (tag == org_last_tag || unlikely(BT_ALLOC_RR(tags))) {
 233                 last_tag = tag + 1;
 234                 if (last_tag >= bt->depth - 1)
 235                         last_tag = 0;
 236
 237                 *tag_cache = last_tag;
 238         }
 239
 240         return tag;
 241 }
 242
 243 static struct bt_wait_state *bt_wait_ptr(struct blk_mq_bitmap_tags *bt,
 244                                          struct blk_mq_hw_ctx *hctx)
 245 {
 246         struct bt_wait_state *bs;
 247         int wait_index;
 248
 249         if (!hctx)
 250                 return &bt->bs[0];
 251
 252         wait_index = atomic_read(&hctx->wait_index);
 253         bs = &bt->bs[wait_index];
 254         bt_index_atomic_inc(&hctx->wait_index);
 255         return bs;
 256 }
 257
 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)
 262 {
 263         struct bt_wait_state *bs;
 264         DEFINE_WAIT(wait);
 265         int tag;
 266
 267         tag = __bt_get(hctx, bt, last_tag, tags);
 268         if (tag != -1)
 269                 return tag;
 270
 271         if (data->flags & BLK_MQ_REQ_NOWAIT)
 272                 return -1;
 273
 274         bs = bt_wait_ptr(bt, hctx);
 275         do {
 276                 prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
 277
 278                 tag = __bt_get(hctx, bt, last_tag, tags);
 279                 if (tag != -1)
 280                         break;
 281
 282                 /*
 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.
 287                  */
 288                 if (hctx)
 289                         blk_mq_run_hw_queue(hctx, false);
 290
 291                 /*
 292                  * Retry tag allocation after running the hardware queue,
 293                  * as running the queue may also have found completions.
 294                  */
 295                 tag = __bt_get(hctx, bt, last_tag, tags);
 296                 if (tag != -1)
 297                         break;
 298
 299                 blk_mq_put_ctx(data->ctx);
 300
 301                 io_schedule();
 302
 303                 data->ctx = blk_mq_get_ctx(data->q);
 304                 data->hctx = data->q->mq_ops->map_queue(data->q,
 305                                 data->ctx->cpu);
 306                 if (data->flags & BLK_MQ_REQ_RESERVED) {
 307                         bt = &data->hctx->tags->breserved_tags;
 308                 } else {
 309                         last_tag = &data->ctx->last_tag;
 310                         hctx = data->hctx;
 311                         bt = &hctx->tags->bitmap_tags;
 312                 }
 313                 finish_wait(&bs->wait, &wait);
 314                 bs = bt_wait_ptr(bt, hctx);
 315         } while (1);
 316
 317         finish_wait(&bs->wait, &wait);
 318         return tag;
 319 }
 320
 321 static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
 322 {
 323         int tag;
 324
 325         tag = bt_get(data, &data->hctx->tags->bitmap_tags, data->hctx,
 326                         &data->ctx->last_tag, data->hctx->tags);
 327         if (tag >= 0)
 328                 return tag + data->hctx->tags->nr_reserved_tags;
 329
 330         return BLK_MQ_TAG_FAIL;
 331 }
 332
 333 static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data *data)
 334 {
 335         int tag, zero = 0;
 336
 337         if (unlikely(!data->hctx->tags->nr_reserved_tags)) {
 338                 WARN_ON_ONCE(1);
 339                 return BLK_MQ_TAG_FAIL;
 340         }
 341
 342         tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero,
 343                 data->hctx->tags);
 344         if (tag < 0)
 345                 return BLK_MQ_TAG_FAIL;
 346
 347         return tag;
 348 }
 349
 350 unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 351 {
 352         if (data->flags & BLK_MQ_REQ_RESERVED)
 353                 return __blk_mq_get_reserved_tag(data);
 354         return __blk_mq_get_tag(data);
 355 }
 356
 357 static struct bt_wait_state *bt_wake_ptr(struct blk_mq_bitmap_tags *bt)
 358 {
 359         int i, wake_index;
 360
 361         wake_index = atomic_read(&bt->wake_index);
 362         for (i = 0; i < BT_WAIT_QUEUES; i++) {
 363                 struct bt_wait_state *bs = &bt->bs[wake_index];
 364
 365                 if (waitqueue_active(&bs->wait)) {
 366                         int o = atomic_read(&bt->wake_index);
 367                         if (wake_index != o)
 368                                 atomic_cmpxchg(&bt->wake_index, o, wake_index);
 369
 370                         return bs;
 371                 }
 372
 373                 wake_index = bt_index_inc(wake_index);
 374         }
 375
 376         return NULL;
 377 }
 378
 379 static void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag)
 380 {
 381         const int index = TAG_TO_INDEX(bt, tag);
 382         struct bt_wait_state *bs;
 383         int wait_cnt;
 384
 385         clear_bit(TAG_TO_BIT(bt, tag), &bt->map[index].word);
 386
 387         /* Ensure that the wait list checks occur after clear_bit(). */
 388         smp_mb();
 389
 390         bs = bt_wake_ptr(bt);
 391         if (!bs)
 392                 return;
 393
 394         wait_cnt = atomic_dec_return(&bs->wait_cnt);
 395         if (unlikely(wait_cnt < 0))
 396                 wait_cnt = atomic_inc_return(&bs->wait_cnt);
 397         if (wait_cnt == 0) {
 398                 atomic_add(bt->wake_cnt, &bs->wait_cnt);
 399                 bt_index_atomic_inc(&bt->wake_index);
 400                 wake_up(&bs->wait);
 401         }
 402 }
 403
 404 void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
 405                     unsigned int *last_tag)
 406 {
 407         struct blk_mq_tags *tags = hctx->tags;
 408
 409         if (tag >= tags->nr_reserved_tags) {
 410                 const int real_tag = tag - tags->nr_reserved_tags;
 411
 412                 BUG_ON(real_tag >= tags->nr_tags);
 413                 bt_clear_tag(&tags->bitmap_tags, real_tag);
 414                 if (likely(tags->alloc_policy == BLK_TAG_ALLOC_FIFO))
 415                         *last_tag = real_tag;
 416         } else {
 417                 BUG_ON(tag >= tags->nr_reserved_tags);
 418                 bt_clear_tag(&tags->breserved_tags, tag);
 419         }
 420 }
 421
 422 static void bt_for_each(struct blk_mq_hw_ctx *hctx,
 423                 struct blk_mq_bitmap_tags *bt, unsigned int off,
 424                 busy_iter_fn *fn, void *data, bool reserved)
 425 {
 426         struct request *rq;
 427         int bit, i;
 428
 429         for (i = 0; i < bt->map_nr; i++) {
 430                 struct blk_align_bitmap *bm = &bt->map[i];
 431
 432                 for (bit = find_first_bit(&bm->word, bm->depth);
 433                      bit < bm->depth;
 434                      bit = find_next_bit(&bm->word, bm->depth, bit + 1)) {
 435                         rq = hctx->tags->rqs[off + bit];
 436                         if (rq->q == hctx->queue)
 437                                 fn(hctx, rq, data, reserved);
 438                 }
 439
 440                 off += (1 << bt->bits_per_word);
 441         }
 442 }
 443
 444 static void bt_tags_for_each(struct blk_mq_tags *tags,
 445                 struct blk_mq_bitmap_tags *bt, unsigned int off,
 446                 busy_tag_iter_fn *fn, void *data, bool reserved)
 447 {
 448         struct request *rq;
 449         int bit, i;
 450
 451         if (!tags->rqs)
 452                 return;
 453         for (i = 0; i < bt->map_nr; i++) {
 454                 struct blk_align_bitmap *bm = &bt->map[i];
 455
 456                 for (bit = find_first_bit(&bm->word, bm->depth);
 457                      bit < bm->depth;
 458                      bit = find_next_bit(&bm->word, bm->depth, bit + 1)) {
 459                         rq = tags->rqs[off + bit];
 460                         fn(rq, data, reserved);
 461                 }
 462
 463                 off += (1 << bt->bits_per_word);
 464         }
 465 }
 466
 467 static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
 468                 busy_tag_iter_fn *fn, void *priv)
 469 {
 470         if (tags->nr_reserved_tags)
 471                 bt_tags_for_each(tags, &tags->breserved_tags, 0, fn, priv, true);
 472         bt_tags_for_each(tags, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv,
 473                         false);
 474 }
 475
 476 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 477                 busy_tag_iter_fn *fn, void *priv)
 478 {
 479         int i;
 480
 481         for (i = 0; i < tagset->nr_hw_queues; i++) {
 482                 if (tagset->tags && tagset->tags[i])
 483                         blk_mq_all_tag_busy_iter(tagset->tags[i], fn, priv);
 484         }
 485 }
 486 EXPORT_SYMBOL(blk_mq_tagset_busy_iter);
 487
 488 void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
 489                 void *priv)
 490 {
 491         struct blk_mq_hw_ctx *hctx;
 492         int i;
 493
 494
 495         queue_for_each_hw_ctx(q, hctx, i) {
 496                 struct blk_mq_tags *tags = hctx->tags;
 497
 498                 /*
 499                  * If not software queues are currently mapped to this
 500                  * hardware queue, there's nothing to check
 501                  */
 502                 if (!blk_mq_hw_queue_mapped(hctx))
 503                         continue;
 504
 505                 if (tags->nr_reserved_tags)
 506                         bt_for_each(hctx, &tags->breserved_tags, 0, fn, priv, true);
 507                 bt_for_each(hctx, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv,
 508                       false);
 509         }
 510
 511 }
 512
 513 static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
 514 {
 515         unsigned int i, used;
 516
 517         for (i = 0, used = 0; i < bt->map_nr; i++) {
 518                 struct blk_align_bitmap *bm = &bt->map[i];
 519
 520                 used += bitmap_weight(&bm->word, bm->depth);
 521         }
 522
 523         return bt->depth - used;
 524 }
 525
 526 static void bt_update_count(struct blk_mq_bitmap_tags *bt,
 527                             unsigned int depth)
 528 {
 529         unsigned int tags_per_word = 1U << bt->bits_per_word;
 530         unsigned int map_depth = depth;
 531
 532         if (depth) {
 533                 int i;
 534
 535                 for (i = 0; i < bt->map_nr; i++) {
 536                         bt->map[i].depth = min(map_depth, tags_per_word);
 537                         map_depth -= bt->map[i].depth;
 538                 }
 539         }
 540
 541         bt->wake_cnt = BT_WAIT_BATCH;
 542         if (bt->wake_cnt > depth / BT_WAIT_QUEUES)
 543                 bt->wake_cnt = max(1U, depth / BT_WAIT_QUEUES);
 544
 545         bt->depth = depth;
 546 }
 547
 548 static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
 549                         int node, bool reserved)
 550 {
 551         int i;
 552
 553         bt->bits_per_word = ilog2(BITS_PER_LONG);
 554
 555         /*
 556          * Depth can be zero for reserved tags, that's not a failure
 557          * condition.
 558          */
 559         if (depth) {
 560                 unsigned int nr, tags_per_word;
 561
 562                 tags_per_word = (1 << bt->bits_per_word);
 563
 564                 /*
 565                  * If the tag space is small, shrink the number of tags
 566                  * per word so we spread over a few cachelines, at least.
 567                  * If less than 4 tags, just forget about it, it's not
 568                  * going to work optimally anyway.
 569                  */
 570                 if (depth >= 4) {
 571                         while (tags_per_word * 4 > depth) {
 572                                 bt->bits_per_word--;
 573                                 tags_per_word = (1 << bt->bits_per_word);
 574                         }
 575                 }
 576
 577                 nr = ALIGN(depth, tags_per_word) / tags_per_word;
 578                 bt->map = kzalloc_node(nr * sizeof(struct blk_align_bitmap),
 579                                                 GFP_KERNEL, node);
 580                 if (!bt->map)
 581                         return -ENOMEM;
 582
 583                 bt->map_nr = nr;
 584         }
 585
 586         bt->bs = kzalloc(BT_WAIT_QUEUES * sizeof(*bt->bs), GFP_KERNEL);
 587         if (!bt->bs) {
 588                 kfree(bt->map);
 589                 bt->map = NULL;
 590                 return -ENOMEM;
 591         }
 592
 593         bt_update_count(bt, depth);
 594
 595         for (i = 0; i < BT_WAIT_QUEUES; i++) {
 596                 init_waitqueue_head(&bt->bs[i].wait);
 597                 atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);
 598         }
 599
 600         return 0;
 601 }
 602
 603 static void bt_free(struct blk_mq_bitmap_tags *bt)
 604 {
 605         kfree(bt->map);
 606         kfree(bt->bs);
 607 }
 608
 609 static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
 610                                                    int node, int alloc_policy)
 611 {
 612         unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
 613
 614         tags->alloc_policy = alloc_policy;
 615
 616         if (bt_alloc(&tags->bitmap_tags, depth, node, false))
 617                 goto enomem;
 618         if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, node, true))
 619                 goto enomem;
 620
 621         return tags;
 622 enomem:
 623         bt_free(&tags->bitmap_tags);
 624         kfree(tags);
 625         return NULL;
 626 }
 627
 628 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 629                                      unsigned int reserved_tags,
 630                                      int node, int alloc_policy)
 631 {
 632         struct blk_mq_tags *tags;
 633
 634         if (total_tags > BLK_MQ_TAG_MAX) {
 635                 pr_err("blk-mq: tag depth too large\n");
 636                 return NULL;
 637         }
 638
 639         tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
 640         if (!tags)
 641                 return NULL;
 642
 643         if (!zalloc_cpumask_var(&tags->cpumask, GFP_KERNEL)) {
 644                 kfree(tags);
 645                 return NULL;
 646         }
 647
 648         tags->nr_tags = total_tags;
 649         tags->nr_reserved_tags = reserved_tags;
 650
 651         return blk_mq_init_bitmap_tags(tags, node, alloc_policy);
 652 }
 653
 654 void blk_mq_free_tags(struct blk_mq_tags *tags)
 655 {
 656         bt_free(&tags->bitmap_tags);
 657         bt_free(&tags->breserved_tags);
 658         free_cpumask_var(tags->cpumask);
 659         kfree(tags);
 660 }
 661
 662 void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *tag)
 663 {
 664         unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
 665
 666         *tag = prandom_u32() % depth;
 667 }
 668
 669 int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
 670 {
 671         tdepth -= tags->nr_reserved_tags;
 672         if (tdepth > tags->nr_tags)
 673                 return -EINVAL;
 674
 675         /*
 676          * Don't need (or can't) update reserved tags here, they remain
 677          * static and should never need resizing.
 678          */
 679         bt_update_count(&tags->bitmap_tags, tdepth);
 680         blk_mq_tag_wakeup_all(tags, false);
 681         return 0;
 682 }
 683
 684 /**
 685  * blk_mq_unique_tag() - return a tag that is unique queue-wide
 686  * @rq: request for which to compute a unique tag
 687  *
 688  * The tag field in struct request is unique per hardware queue but not over
 689  * all hardware queues. Hence this function that returns a tag with the
 690  * hardware context index in the upper bits and the per hardware queue tag in
 691  * the lower bits.
 692  *
 693  * Note: When called for a request that is queued on a non-multiqueue request
 694  * queue, the hardware context index is set to zero.
 695  */
 696 u32 blk_mq_unique_tag(struct request *rq)
 697 {
 698         struct request_queue *q = rq->q;
 699         struct blk_mq_hw_ctx *hctx;
 700         int hwq = 0;
 701
 702         if (q->mq_ops) {
 703                 hctx = q->mq_ops->map_queue(q, rq->mq_ctx->cpu);
 704                 hwq = hctx->queue_num;
 705         }
 706
 707         return (hwq << BLK_MQ_UNIQUE_TAG_BITS) |
 708                 (rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
 709 }
 710 EXPORT_SYMBOL(blk_mq_unique_tag);
 711
 712 ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
 713 {
 714         char *orig_page = page;
 715         unsigned int free, res;
 716
 717         if (!tags)
 718                 return 0;
 719
 720         page += sprintf(page, "nr_tags=%u, reserved_tags=%u, "
 721                         "bits_per_word=%u\n",
 722                         tags->nr_tags, tags->nr_reserved_tags,
 723                         tags->bitmap_tags.bits_per_word);
 724
 725         free = bt_unused_tags(&tags->bitmap_tags);
 726         res = bt_unused_tags(&tags->breserved_tags);
 727
 728         page += sprintf(page, "nr_free=%u, nr_reserved=%u\n", free, res);
 729         page += sprintf(page, "active_queues=%u\n", atomic_read(&tags->active_queues));
 730
 731         return page - orig_page;
 732 }