Commit 03f26d8f authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
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blk-mq: plug request for shared sbitmap 



In case of shared sbitmap, request won't be held in plug list any more
sine commit 32bc15af ("blk-mq: Facilitate a shared sbitmap per
tagset"), this way makes request merge from flush plug list & batching
submission not possible, so cause performance regression.

Yanhui reports performance regression when running sequential IO
test(libaio, 16 jobs, 8 depth for each job) in VM, and the VM disk
is emulated with image stored on xfs/megaraid_sas.

Fix the issue by recovering original behavior to allow to hold request
in plug list.

Cc: Yanhui Ma <yama@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: kashyap.desai@broadcom.com
Fixes: 32bc15af ("blk-mq: Facilitate a shared sbitmap per tagset")
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210514022052.1047665-1-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 6bdf2fbc

block/blk-mq.c

+3 −2
Original line number Diff line number Diff line
@@ -2232,8 +2232,9 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio) 
		/* Bypass scheduler for flush requests */

		blk_insert_flush(rq);

		blk_mq_run_hw_queue(data.hctx, true);

	} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs ||

				!blk_queue_nonrot(q))) {

	} else if (plug && (q->nr_hw_queues == 1 ||

		   blk_mq_is_sbitmap_shared(rq->mq_hctx->flags) ||

		   q->mq_ops->commit_rqs || !blk_queue_nonrot(q))) {

		/*

		 * Use plugging if we have a ->commit_rqs() hook as well, as

		 * we know the driver uses bd->last in a smart fashion.