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 (!gfpflags_allow_blocking(data->gfp))
 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->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->reserved)
 353                 return __blk_mq_get_tag(data);
 354
 355         return __blk_mq_get_reserved_tag(data);
 356 }
 357
 358 static struct bt_wait_state *bt_wake_ptr(struct blk_mq_bitmap_tags *bt)
 359 {
 360         int i, wake_index;
 361
 362         wake_index = atomic_read(&bt->wake_index);
 363         for (i = 0; i < BT_WAIT_QUEUES; i++) {
 364                 struct bt_wait_state *bs = &bt->bs[wake_index];
 365
 366                 if (waitqueue_active(&bs->wait)) {
 367                         int o = atomic_read(&bt->wake_index);
 368                         if (wake_index != o)
 369                                 atomic_cmpxchg(&bt->wake_index, o, wake_index);
 370
 371                         return bs;
 372                 }
 373
 374                 wake_index = bt_index_inc(wake_index);
 375         }
 376
 377         return NULL;
 378 }
 379
 380 static void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag)
 381 {
 382         const int index = TAG_TO_INDEX(bt, tag);
 383         struct bt_wait_state *bs;
 384         int wait_cnt;
 385
 386         clear_bit(TAG_TO_BIT(bt, tag), &bt->map[index].word);
 387
 388         /* Ensure that the wait list checks occur after clear_bit(). */
 389         smp_mb();
 390
 391         bs = bt_wake_ptr(bt);
 392         if (!bs)
 393                 return;
 394
 395         wait_cnt = atomic_dec_return(&bs->wait_cnt);
 396         if (unlikely(wait_cnt < 0))
 397                 wait_cnt = atomic_inc_return(&bs->wait_cnt);
 398         if (wait_cnt == 0) {
 399                 atomic_add(bt->wake_cnt, &bs->wait_cnt);
 400                 bt_index_atomic_inc(&bt->wake_index);
 401                 wake_up(&bs->wait);
 402         }
 403 }
 404
 405 void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
 406                     unsigned int *last_tag)
 407 {
 408         struct blk_mq_tags *tags = hctx->tags;
 409
 410         if (tag >= tags->nr_reserved_tags) {
 411                 const int real_tag = tag - tags->nr_reserved_tags;
 412
 413                 BUG_ON(real_tag >= tags->nr_tags);
 414                 bt_clear_tag(&tags->bitmap_tags, real_tag);
 415                 if (likely(tags->alloc_policy == BLK_TAG_ALLOC_FIFO))
 416                         *last_tag = real_tag;
 417         } else {
 418                 BUG_ON(tag >= tags->nr_reserved_tags);
 419                 bt_clear_tag(&tags->breserved_tags, tag);
 420         }
 421 }
 422
 423 static void bt_for_each(struct blk_mq_hw_ctx *hctx,
 424                 struct blk_mq_bitmap_tags *bt, unsigned int off,
 425                 busy_iter_fn *fn, void *data, bool reserved)
 426 {
 427         struct request *rq;
 428         int bit, i;
 429
 430         for (i = 0; i < bt->map_nr; i++) {
 431                 struct blk_align_bitmap *bm = &bt->map[i];
 432
 433                 for (bit = find_first_bit(&bm->word, bm->depth);
 434                      bit < bm->depth;
 435                      bit = find_next_bit(&bm->word, bm->depth, bit + 1)) {
 436                         rq = hctx->tags->rqs[off + bit];
 437                         if (rq->q == hctx->queue)
 438                                 fn(hctx, rq, data, reserved);
 439                 }
 440
 441                 off += (1 << bt->bits_per_word);
 442         }
 443 }
 444
 445 static void bt_tags_for_each(struct blk_mq_tags *tags,
 446                 struct blk_mq_bitmap_tags *bt, unsigned int off,
 447                 busy_tag_iter_fn *fn, void *data, bool reserved)
 448 {
 449         struct request *rq;
 450         int bit, i;
 451
 452         if (!tags->rqs)
 453                 return;
 454         for (i = 0; i < bt->map_nr; i++) {
 455                 struct blk_align_bitmap *bm = &bt->map[i];
 456
 457                 for (bit = find_first_bit(&bm->word, bm->depth);
 458                      bit < bm->depth;
 459                      bit = find_next_bit(&bm->word, bm->depth, bit + 1)) {
 460                         rq = tags->rqs[off + bit];
 461                         fn(rq, data, reserved);
 462                 }
 463
 464                 off += (1 << bt->bits_per_word);
 465         }
 466 }
 467
 468 void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags, busy_tag_iter_fn *fn,
 469                 void *priv)
 470 {
 471         if (tags->nr_reserved_tags)
 472                 bt_tags_for_each(tags, &tags->breserved_tags, 0, fn, priv, true);
 473         bt_tags_for_each(tags, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv,
 474                         false);
 475 }
 476 EXPORT_SYMBOL(blk_mq_all_tag_busy_iter);
 477
 478 void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
 479                 void *priv)
 480 {
 481         struct blk_mq_hw_ctx *hctx;
 482         int i;
 483
 484         /*
 485          * Avoid potential races with things like queue removal.
 486          */
 487         if (!percpu_ref_tryget(&q->q_usage_counter))
 488                 return;
 489
 490         queue_for_each_hw_ctx(q, hctx, i) {
 491                 struct blk_mq_tags *tags = hctx->tags;
 492
 493                 /*
 494                  * If not software queues are currently mapped to this
 495                  * hardware queue, there's nothing to check
 496                  */
 497                 if (!blk_mq_hw_queue_mapped(hctx))
 498                         continue;
 499
 500                 if (tags->nr_reserved_tags)
 501                         bt_for_each(hctx, &tags->breserved_tags, 0, fn, priv, true);
 502                 bt_for_each(hctx, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv,
 503                       false);
 504         }
 505         blk_queue_exit(q);
 506 }
 507
 508 static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
 509 {
 510         unsigned int i, used;
 511
 512         for (i = 0, used = 0; i < bt->map_nr; i++) {
 513                 struct blk_align_bitmap *bm = &bt->map[i];
 514
 515                 used += bitmap_weight(&bm->word, bm->depth);
 516         }
 517
 518         return bt->depth - used;
 519 }
 520
 521 static void bt_update_count(struct blk_mq_bitmap_tags *bt,
 522                             unsigned int depth)
 523 {
 524         unsigned int tags_per_word = 1U << bt->bits_per_word;
 525         unsigned int map_depth = depth;
 526
 527         if (depth) {
 528                 int i;
 529
 530                 for (i = 0; i < bt->map_nr; i++) {
 531                         bt->map[i].depth = min(map_depth, tags_per_word);
 532                         map_depth -= bt->map[i].depth;
 533                 }
 534         }
 535
 536         bt->wake_cnt = BT_WAIT_BATCH;
 537         if (bt->wake_cnt > depth / BT_WAIT_QUEUES)
 538                 bt->wake_cnt = max(1U, depth / BT_WAIT_QUEUES);
 539
 540         bt->depth = depth;
 541 }
 542
 543 static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
 544                         int node, bool reserved)
 545 {
 546         int i;
 547
 548         bt->bits_per_word = ilog2(BITS_PER_LONG);
 549
 550         /*
 551          * Depth can be zero for reserved tags, that's not a failure
 552          * condition.
 553          */
 554         if (depth) {
 555                 unsigned int nr, tags_per_word;
 556
 557                 tags_per_word = (1 << bt->bits_per_word);
 558
 559                 /*
 560                  * If the tag space is small, shrink the number of tags
 561                  * per word so we spread over a few cachelines, at least.
 562                  * If less than 4 tags, just forget about it, it's not
 563                  * going to work optimally anyway.
 564                  */
 565                 if (depth >= 4) {
 566                         while (tags_per_word * 4 > depth) {
 567                                 bt->bits_per_word--;
 568                                 tags_per_word = (1 << bt->bits_per_word);
 569                         }
 570                 }
 571
 572                 nr = ALIGN(depth, tags_per_word) / tags_per_word;
 573                 bt->map = kzalloc_node(nr * sizeof(struct blk_align_bitmap),
 574                                                 GFP_KERNEL, node);
 575                 if (!bt->map)
 576                         return -ENOMEM;
 577
 578                 bt->map_nr = nr;
 579         }
 580
 581         bt->bs = kzalloc(BT_WAIT_QUEUES * sizeof(*bt->bs), GFP_KERNEL);
 582         if (!bt->bs) {
 583                 kfree(bt->map);
 584                 bt->map = NULL;
 585                 return -ENOMEM;
 586         }
 587
 588         bt_update_count(bt, depth);
 589
 590         for (i = 0; i < BT_WAIT_QUEUES; i++) {
 591                 init_waitqueue_head(&bt->bs[i].wait);
 592                 atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);
 593         }
 594
 595         return 0;
 596 }
 597
 598 static void bt_free(struct blk_mq_bitmap_tags *bt)
 599 {
 600         kfree(bt->map);
 601         kfree(bt->bs);
 602 }
 603
 604 static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
 605                                                    int node, int alloc_policy)
 606 {
 607         unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
 608
 609         tags->alloc_policy = alloc_policy;
 610
 611         if (bt_alloc(&tags->bitmap_tags, depth, node, false))
 612                 goto enomem;
 613         if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, node, true))
 614                 goto enomem;
 615
 616         return tags;
 617 enomem:
 618         bt_free(&tags->bitmap_tags);
 619         kfree(tags);
 620         return NULL;
 621 }
 622
 623 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 624                                      unsigned int reserved_tags,
 625                                      int node, int alloc_policy)
 626 {
 627         struct blk_mq_tags *tags;
 628
 629         if (total_tags > BLK_MQ_TAG_MAX) {
 630                 pr_err("blk-mq: tag depth too large\n");
 631                 return NULL;
 632         }
 633
 634         tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
 635         if (!tags)
 636                 return NULL;
 637
 638         if (!zalloc_cpumask_var(&tags->cpumask, GFP_KERNEL)) {
 639                 kfree(tags);
 640                 return NULL;
 641         }
 642
 643         tags->nr_tags = total_tags;
 644         tags->nr_reserved_tags = reserved_tags;
 645
 646         return blk_mq_init_bitmap_tags(tags, node, alloc_policy);
 647 }
 648
 649 void blk_mq_free_tags(struct blk_mq_tags *tags)
 650 {
 651         bt_free(&tags->bitmap_tags);
 652         bt_free(&tags->breserved_tags);
 653         free_cpumask_var(tags->cpumask);
 654         kfree(tags);
 655 }
 656
 657 void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *tag)
 658 {
 659         unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
 660
 661         *tag = prandom_u32() % depth;
 662 }
 663
 664 int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
 665 {
 666         tdepth -= tags->nr_reserved_tags;
 667         if (tdepth > tags->nr_tags)
 668                 return -EINVAL;
 669
 670         /*
 671          * Don't need (or can't) update reserved tags here, they remain
 672          * static and should never need resizing.
 673          */
 674         bt_update_count(&tags->bitmap_tags, tdepth);
 675         blk_mq_tag_wakeup_all(tags, false);
 676         return 0;
 677 }
 678
 679 /**
 680  * blk_mq_unique_tag() - return a tag that is unique queue-wide
 681  * @rq: request for which to compute a unique tag
 682  *
 683  * The tag field in struct request is unique per hardware queue but not over
 684  * all hardware queues. Hence this function that returns a tag with the
 685  * hardware context index in the upper bits and the per hardware queue tag in
 686  * the lower bits.
 687  *
 688  * Note: When called for a request that is queued on a non-multiqueue request
 689  * queue, the hardware context index is set to zero.
 690  */
 691 u32 blk_mq_unique_tag(struct request *rq)
 692 {
 693         struct request_queue *q = rq->q;
 694         struct blk_mq_hw_ctx *hctx;
 695         int hwq = 0;
 696
 697         if (q->mq_ops) {
 698                 hctx = q->mq_ops->map_queue(q, rq->mq_ctx->cpu);
 699                 hwq = hctx->queue_num;
 700         }
 701
 702         return (hwq << BLK_MQ_UNIQUE_TAG_BITS) |
 703                 (rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
 704 }
 705 EXPORT_SYMBOL(blk_mq_unique_tag);
 706
 707 ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
 708 {
 709         char *orig_page = page;
 710         unsigned int free, res;
 711
 712         if (!tags)
 713                 return 0;
 714
 715         page += sprintf(page, "nr_tags=%u, reserved_tags=%u, "
 716                         "bits_per_word=%u\n",
 717                         tags->nr_tags, tags->nr_reserved_tags,
 718                         tags->bitmap_tags.bits_per_word);
 719
 720         free = bt_unused_tags(&tags->bitmap_tags);
 721         res = bt_unused_tags(&tags->breserved_tags);
 722
 723         page += sprintf(page, "nr_free=%u, nr_reserved=%u\n", free, res);
 724         page += sprintf(page, "active_queues=%u\n", atomic_read(&tags->active_queues));
 725
 726         return page - orig_page;
 727 }