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block: Remove redundant plug in __submit_bio()

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The patch removes the automatic plug/unplug operations from __submit_bio()
that were added to cache nsecs time when no explicit plug is used.

The plug mechanism is most effective when batching multiple I/O
operations together. Creating a plug for every bio submission
provides minimal benefit while adding function call overhead and
stack usage for every I/O operation.

Below is performance comparison with the latest upstream kernel.

Iotype  qd nj  rmix  mpstat busy  mpstat busy without plug
Randrw  1  20  100       53%                 24%
Randrw  1  40  100       70%                 24%
Randrw  1  20  70        40%                 24%
Randrw  1  40  70        60%                 26%
Randrw  1  20  0         14%                 6%
Randrw  1  40  0         20%                 7%

Fixes: 060406c61c ("block: add plug while submitting IO")
Signed-off-by: Wen Xiong <wenxiong@linux.ibm.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260616143121.878021-1-wenxiong@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Wen Xiong
2026-06-16 10:31:21 -04:00
committed by Jens Axboe
parent 4f919141be
commit 9cbbac29d7
1 changed files with 0 additions and 7 deletions
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7
block/blk-core.c
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@@ -669,11 +669,6 @@ static inline blk_status_t blk_check_zone_append(struct request_queue *q,
static void __submit_bio(struct bio *bio)
{
/* If plug is not used, add new plug here to cache nsecs time. */
struct blk_plug plug;
blk_start_plug(&plug);
if (!bdev_test_flag(bio->bi_bdev, BD_HAS_SUBMIT_BIO)) {
blk_mq_submit_bio(bio);
} else if (likely(bio_queue_enter(bio) == 0)) {
@@ -686,8 +681,6 @@ static void __submit_bio(struct bio *bio)
disk->fops->submit_bio(bio);
blk_queue_exit(disk->queue);
}
blk_finish_plug(&plug);
}
/*