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86fb5c56cf
This update fixes few issues in bt_get() function: - list_empty(&wait.task_list) check is not protected; - was_empty check is always true which results in *every* thread entering the loop resets bt_wait_state::wait_cnt counter rather than every bt->wake_cnt'th thread; - 'bt_wait_state::wait_cnt' counter update is redundant, since it also gets reset in bt_clear_tag() function; Cc: Christoph Hellwig <hch@infradead.org> Cc: Ming Lei <tom.leiming@gmail.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Alexander Gordeev <agordeev@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
619 lines
14 KiB
C
619 lines
14 KiB
C
/*
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* Fast and scalable bitmap tagging variant. Uses sparser bitmaps spread
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* over multiple cachelines to avoid ping-pong between multiple submitters
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* or submitter and completer. Uses rolling wakeups to avoid falling of
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* the scaling cliff when we run out of tags and have to start putting
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* submitters to sleep.
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*
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* Uses active queue tracking to support fairer distribution of tags
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* between multiple submitters when a shared tag map is used.
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*
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* Copyright (C) 2013-2014 Jens Axboe
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/random.h>
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#include <linux/blk-mq.h>
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#include "blk.h"
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#include "blk-mq.h"
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#include "blk-mq-tag.h"
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static bool bt_has_free_tags(struct blk_mq_bitmap_tags *bt)
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{
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int i;
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for (i = 0; i < bt->map_nr; i++) {
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struct blk_align_bitmap *bm = &bt->map[i];
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int ret;
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ret = find_first_zero_bit(&bm->word, bm->depth);
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if (ret < bm->depth)
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return true;
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}
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return false;
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}
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bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
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{
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if (!tags)
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return true;
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return bt_has_free_tags(&tags->bitmap_tags);
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}
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static inline int bt_index_inc(int index)
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{
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return (index + 1) & (BT_WAIT_QUEUES - 1);
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}
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static inline void bt_index_atomic_inc(atomic_t *index)
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{
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int old = atomic_read(index);
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int new = bt_index_inc(old);
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atomic_cmpxchg(index, old, new);
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}
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/*
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* If a previously inactive queue goes active, bump the active user count.
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*/
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bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
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{
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if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
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!test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
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atomic_inc(&hctx->tags->active_queues);
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return true;
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}
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/*
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* Wakeup all potentially sleeping on normal (non-reserved) tags
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*/
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static void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags)
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{
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struct blk_mq_bitmap_tags *bt;
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int i, wake_index;
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bt = &tags->bitmap_tags;
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wake_index = atomic_read(&bt->wake_index);
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for (i = 0; i < BT_WAIT_QUEUES; i++) {
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struct bt_wait_state *bs = &bt->bs[wake_index];
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if (waitqueue_active(&bs->wait))
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wake_up(&bs->wait);
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wake_index = bt_index_inc(wake_index);
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}
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}
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/*
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* If a previously busy queue goes inactive, potential waiters could now
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* be allowed to queue. Wake them up and check.
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*/
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void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
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{
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struct blk_mq_tags *tags = hctx->tags;
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if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
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return;
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atomic_dec(&tags->active_queues);
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blk_mq_tag_wakeup_all(tags);
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}
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/*
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* For shared tag users, we track the number of currently active users
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* and attempt to provide a fair share of the tag depth for each of them.
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*/
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static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
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struct blk_mq_bitmap_tags *bt)
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{
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unsigned int depth, users;
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if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
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return true;
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if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
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return true;
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/*
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* Don't try dividing an ant
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*/
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if (bt->depth == 1)
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return true;
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users = atomic_read(&hctx->tags->active_queues);
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if (!users)
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return true;
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/*
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* Allow at least some tags
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*/
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depth = max((bt->depth + users - 1) / users, 4U);
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return atomic_read(&hctx->nr_active) < depth;
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}
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static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
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{
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int tag, org_last_tag, end;
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org_last_tag = last_tag;
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end = bm->depth;
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do {
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restart:
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tag = find_next_zero_bit(&bm->word, end, last_tag);
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if (unlikely(tag >= end)) {
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/*
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* We started with an offset, start from 0 to
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* exhaust the map.
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*/
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if (org_last_tag && last_tag) {
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end = last_tag;
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last_tag = 0;
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goto restart;
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}
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return -1;
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}
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last_tag = tag + 1;
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} while (test_and_set_bit_lock(tag, &bm->word));
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return tag;
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}
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/*
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* Straight forward bitmap tag implementation, where each bit is a tag
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* (cleared == free, and set == busy). The small twist is using per-cpu
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* last_tag caches, which blk-mq stores in the blk_mq_ctx software queue
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* contexts. This enables us to drastically limit the space searched,
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* without dirtying an extra shared cacheline like we would if we stored
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* the cache value inside the shared blk_mq_bitmap_tags structure. On top
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* of that, each word of tags is in a separate cacheline. This means that
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* multiple users will tend to stick to different cachelines, at least
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* until the map is exhausted.
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*/
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static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
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unsigned int *tag_cache)
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{
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unsigned int last_tag, org_last_tag;
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int index, i, tag;
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if (!hctx_may_queue(hctx, bt))
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return -1;
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last_tag = org_last_tag = *tag_cache;
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index = TAG_TO_INDEX(bt, last_tag);
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for (i = 0; i < bt->map_nr; i++) {
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tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag));
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if (tag != -1) {
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tag += (index << bt->bits_per_word);
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goto done;
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}
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last_tag = 0;
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if (++index >= bt->map_nr)
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index = 0;
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}
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*tag_cache = 0;
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return -1;
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/*
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* Only update the cache from the allocation path, if we ended
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* up using the specific cached tag.
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*/
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done:
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if (tag == org_last_tag) {
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last_tag = tag + 1;
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if (last_tag >= bt->depth - 1)
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last_tag = 0;
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*tag_cache = last_tag;
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}
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return tag;
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}
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static struct bt_wait_state *bt_wait_ptr(struct blk_mq_bitmap_tags *bt,
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struct blk_mq_hw_ctx *hctx)
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{
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struct bt_wait_state *bs;
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int wait_index;
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if (!hctx)
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return &bt->bs[0];
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wait_index = atomic_read(&hctx->wait_index);
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bs = &bt->bs[wait_index];
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bt_index_atomic_inc(&hctx->wait_index);
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return bs;
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}
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static int bt_get(struct blk_mq_alloc_data *data,
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struct blk_mq_bitmap_tags *bt,
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struct blk_mq_hw_ctx *hctx,
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unsigned int *last_tag)
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{
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struct bt_wait_state *bs;
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DEFINE_WAIT(wait);
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int tag;
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tag = __bt_get(hctx, bt, last_tag);
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if (tag != -1)
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return tag;
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if (!(data->gfp & __GFP_WAIT))
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return -1;
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bs = bt_wait_ptr(bt, hctx);
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do {
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prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
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tag = __bt_get(hctx, bt, last_tag);
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if (tag != -1)
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break;
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blk_mq_put_ctx(data->ctx);
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io_schedule();
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data->ctx = blk_mq_get_ctx(data->q);
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data->hctx = data->q->mq_ops->map_queue(data->q,
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data->ctx->cpu);
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if (data->reserved) {
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bt = &data->hctx->tags->breserved_tags;
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} else {
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last_tag = &data->ctx->last_tag;
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hctx = data->hctx;
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bt = &hctx->tags->bitmap_tags;
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}
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finish_wait(&bs->wait, &wait);
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bs = bt_wait_ptr(bt, hctx);
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} while (1);
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finish_wait(&bs->wait, &wait);
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return tag;
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}
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static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
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{
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int tag;
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tag = bt_get(data, &data->hctx->tags->bitmap_tags, data->hctx,
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&data->ctx->last_tag);
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if (tag >= 0)
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return tag + data->hctx->tags->nr_reserved_tags;
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return BLK_MQ_TAG_FAIL;
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}
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static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data *data)
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{
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int tag, zero = 0;
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if (unlikely(!data->hctx->tags->nr_reserved_tags)) {
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WARN_ON_ONCE(1);
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return BLK_MQ_TAG_FAIL;
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}
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tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero);
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if (tag < 0)
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return BLK_MQ_TAG_FAIL;
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return tag;
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}
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unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
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{
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if (!data->reserved)
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return __blk_mq_get_tag(data);
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return __blk_mq_get_reserved_tag(data);
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}
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static struct bt_wait_state *bt_wake_ptr(struct blk_mq_bitmap_tags *bt)
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{
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int i, wake_index;
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wake_index = atomic_read(&bt->wake_index);
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for (i = 0; i < BT_WAIT_QUEUES; i++) {
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struct bt_wait_state *bs = &bt->bs[wake_index];
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if (waitqueue_active(&bs->wait)) {
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int o = atomic_read(&bt->wake_index);
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if (wake_index != o)
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atomic_cmpxchg(&bt->wake_index, o, wake_index);
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return bs;
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}
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wake_index = bt_index_inc(wake_index);
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}
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return NULL;
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}
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static void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag)
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{
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const int index = TAG_TO_INDEX(bt, tag);
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struct bt_wait_state *bs;
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int wait_cnt;
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/*
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* The unlock memory barrier need to order access to req in free
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* path and clearing tag bit
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*/
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clear_bit_unlock(TAG_TO_BIT(bt, tag), &bt->map[index].word);
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bs = bt_wake_ptr(bt);
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if (!bs)
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return;
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wait_cnt = atomic_dec_return(&bs->wait_cnt);
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if (wait_cnt == 0) {
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wake:
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atomic_add(bt->wake_cnt, &bs->wait_cnt);
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bt_index_atomic_inc(&bt->wake_index);
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wake_up(&bs->wait);
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} else if (wait_cnt < 0) {
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wait_cnt = atomic_inc_return(&bs->wait_cnt);
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if (!wait_cnt)
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goto wake;
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}
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}
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static void __blk_mq_put_tag(struct blk_mq_tags *tags, unsigned int tag)
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{
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BUG_ON(tag >= tags->nr_tags);
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bt_clear_tag(&tags->bitmap_tags, tag);
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}
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static void __blk_mq_put_reserved_tag(struct blk_mq_tags *tags,
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unsigned int tag)
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{
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BUG_ON(tag >= tags->nr_reserved_tags);
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bt_clear_tag(&tags->breserved_tags, tag);
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}
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void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
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unsigned int *last_tag)
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{
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struct blk_mq_tags *tags = hctx->tags;
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if (tag >= tags->nr_reserved_tags) {
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const int real_tag = tag - tags->nr_reserved_tags;
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__blk_mq_put_tag(tags, real_tag);
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*last_tag = real_tag;
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} else
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__blk_mq_put_reserved_tag(tags, tag);
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}
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static void bt_for_each_free(struct blk_mq_bitmap_tags *bt,
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unsigned long *free_map, unsigned int off)
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{
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int i;
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for (i = 0; i < bt->map_nr; i++) {
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struct blk_align_bitmap *bm = &bt->map[i];
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int bit = 0;
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do {
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bit = find_next_zero_bit(&bm->word, bm->depth, bit);
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if (bit >= bm->depth)
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break;
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__set_bit(bit + off, free_map);
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bit++;
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} while (1);
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off += (1 << bt->bits_per_word);
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}
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}
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void blk_mq_tag_busy_iter(struct blk_mq_tags *tags,
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void (*fn)(void *, unsigned long *), void *data)
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{
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unsigned long *tag_map;
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size_t map_size;
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map_size = ALIGN(tags->nr_tags, BITS_PER_LONG) / BITS_PER_LONG;
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tag_map = kzalloc(map_size * sizeof(unsigned long), GFP_ATOMIC);
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if (!tag_map)
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return;
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bt_for_each_free(&tags->bitmap_tags, tag_map, tags->nr_reserved_tags);
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if (tags->nr_reserved_tags)
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bt_for_each_free(&tags->breserved_tags, tag_map, 0);
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fn(data, tag_map);
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kfree(tag_map);
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}
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EXPORT_SYMBOL(blk_mq_tag_busy_iter);
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static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
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{
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unsigned int i, used;
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for (i = 0, used = 0; i < bt->map_nr; i++) {
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struct blk_align_bitmap *bm = &bt->map[i];
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used += bitmap_weight(&bm->word, bm->depth);
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}
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return bt->depth - used;
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}
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static void bt_update_count(struct blk_mq_bitmap_tags *bt,
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unsigned int depth)
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{
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unsigned int tags_per_word = 1U << bt->bits_per_word;
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unsigned int map_depth = depth;
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if (depth) {
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int i;
|
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|
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for (i = 0; i < bt->map_nr; i++) {
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bt->map[i].depth = min(map_depth, tags_per_word);
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map_depth -= bt->map[i].depth;
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}
|
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}
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|
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bt->wake_cnt = BT_WAIT_BATCH;
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if (bt->wake_cnt > depth / 4)
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bt->wake_cnt = max(1U, depth / 4);
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|
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bt->depth = depth;
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}
|
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|
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static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
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int node, bool reserved)
|
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{
|
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int i;
|
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|
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bt->bits_per_word = ilog2(BITS_PER_LONG);
|
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|
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/*
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* Depth can be zero for reserved tags, that's not a failure
|
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* condition.
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*/
|
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if (depth) {
|
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unsigned int nr, tags_per_word;
|
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|
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tags_per_word = (1 << bt->bits_per_word);
|
|
|
|
/*
|
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* If the tag space is small, shrink the number of tags
|
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* per word so we spread over a few cachelines, at least.
|
|
* If less than 4 tags, just forget about it, it's not
|
|
* going to work optimally anyway.
|
|
*/
|
|
if (depth >= 4) {
|
|
while (tags_per_word * 4 > depth) {
|
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bt->bits_per_word--;
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tags_per_word = (1 << bt->bits_per_word);
|
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}
|
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}
|
|
|
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nr = ALIGN(depth, tags_per_word) / tags_per_word;
|
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bt->map = kzalloc_node(nr * sizeof(struct blk_align_bitmap),
|
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GFP_KERNEL, node);
|
|
if (!bt->map)
|
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return -ENOMEM;
|
|
|
|
bt->map_nr = nr;
|
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}
|
|
|
|
bt->bs = kzalloc(BT_WAIT_QUEUES * sizeof(*bt->bs), GFP_KERNEL);
|
|
if (!bt->bs) {
|
|
kfree(bt->map);
|
|
return -ENOMEM;
|
|
}
|
|
|
|
bt_update_count(bt, depth);
|
|
|
|
for (i = 0; i < BT_WAIT_QUEUES; i++) {
|
|
init_waitqueue_head(&bt->bs[i].wait);
|
|
atomic_set(&bt->bs[i].wait_cnt, bt->wake_cnt);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
static void bt_free(struct blk_mq_bitmap_tags *bt)
|
|
{
|
|
kfree(bt->map);
|
|
kfree(bt->bs);
|
|
}
|
|
|
|
static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
|
|
int node)
|
|
{
|
|
unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
|
|
|
|
if (bt_alloc(&tags->bitmap_tags, depth, node, false))
|
|
goto enomem;
|
|
if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, node, true))
|
|
goto enomem;
|
|
|
|
return tags;
|
|
enomem:
|
|
bt_free(&tags->bitmap_tags);
|
|
kfree(tags);
|
|
return NULL;
|
|
}
|
|
|
|
struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
|
|
unsigned int reserved_tags, int node)
|
|
{
|
|
struct blk_mq_tags *tags;
|
|
|
|
if (total_tags > BLK_MQ_TAG_MAX) {
|
|
pr_err("blk-mq: tag depth too large\n");
|
|
return NULL;
|
|
}
|
|
|
|
tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
|
|
if (!tags)
|
|
return NULL;
|
|
|
|
tags->nr_tags = total_tags;
|
|
tags->nr_reserved_tags = reserved_tags;
|
|
|
|
return blk_mq_init_bitmap_tags(tags, node);
|
|
}
|
|
|
|
void blk_mq_free_tags(struct blk_mq_tags *tags)
|
|
{
|
|
bt_free(&tags->bitmap_tags);
|
|
bt_free(&tags->breserved_tags);
|
|
kfree(tags);
|
|
}
|
|
|
|
void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *tag)
|
|
{
|
|
unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
|
|
|
|
*tag = prandom_u32() % depth;
|
|
}
|
|
|
|
int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
|
|
{
|
|
tdepth -= tags->nr_reserved_tags;
|
|
if (tdepth > tags->nr_tags)
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* Don't need (or can't) update reserved tags here, they remain
|
|
* static and should never need resizing.
|
|
*/
|
|
bt_update_count(&tags->bitmap_tags, tdepth);
|
|
blk_mq_tag_wakeup_all(tags);
|
|
return 0;
|
|
}
|
|
|
|
ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
|
|
{
|
|
char *orig_page = page;
|
|
unsigned int free, res;
|
|
|
|
if (!tags)
|
|
return 0;
|
|
|
|
page += sprintf(page, "nr_tags=%u, reserved_tags=%u, "
|
|
"bits_per_word=%u\n",
|
|
tags->nr_tags, tags->nr_reserved_tags,
|
|
tags->bitmap_tags.bits_per_word);
|
|
|
|
free = bt_unused_tags(&tags->bitmap_tags);
|
|
res = bt_unused_tags(&tags->breserved_tags);
|
|
|
|
page += sprintf(page, "nr_free=%u, nr_reserved=%u\n", free, res);
|
|
page += sprintf(page, "active_queues=%u\n", atomic_read(&tags->active_queues));
|
|
|
|
return page - orig_page;
|
|
}
|