linux-kernel - [PATCH 5.3 026/197] blk-mq: honor IO scheduler for multiqueue devices

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Message-Id: <20191027203353.126808171@linuxfoundation.org>
Date:   Sun, 27 Oct 2019 21:59:04 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bart Van Assche <bvanassche@....org>,
        Hannes Reinecke <hare@...e.com>,
        Dave Chinner <dchinner@...hat.com>,
        Javier González <javier@...igon.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.3 026/197] blk-mq: honor IO scheduler for multiqueue devices

From: Ming Lei <ming.lei@...hat.com>

[ Upstream commit a12de1d42d74ef3c80e9fb9a2da94daaef747869 ]

If a device is using multiple queues, the IO scheduler may be bypassed.
This may hurt performance for some slow MQ devices, and it also breaks
zoned devices which depend on mq-deadline for respecting the write order
in one zone.

Don't bypass io scheduler if we have one setup.

This patch can double sequential write performance basically on MQ
scsi_debug when mq-deadline is applied.

Cc: Bart Van Assche <bvanassche@....org>
Cc: Hannes Reinecke <hare@...e.com>
Cc: Dave Chinner <dchinner@...hat.com>
Reviewed-by: Javier González <javier@...igon.com>
Reviewed-by: Damien Le Moal <damien.lemoal@....com>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-mq.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a79b9ad1aba18..ed41cde93641c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1998,6 +1998,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		}
 
 		blk_add_rq_to_plug(plug, rq);
+	} else if (q->elevator) {
+		blk_mq_sched_insert_request(rq, false, true, true);
 	} else if (plug && !blk_queue_nomerges(q)) {
 		/*
 		 * We do limited plugging. If the bio can be merged, do that.
@@ -2021,8 +2023,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
 					&cookie);
 		}
-	} else if ((q->nr_hw_queues > 1 && is_sync) || (!q->elevator &&
-			!data.hctx->dispatch_busy)) {
+	} else if ((q->nr_hw_queues > 1 && is_sync) ||
+			!data.hctx->dispatch_busy) {
 		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
 	} else {
 		blk_mq_sched_insert_request(rq, false, true, true);
-- 
2.20.1