From: Ming Lei <ming.lei@redhat.com>
Date: Fri, 27 Sep 2019 15:24:30 +0800
Subject: blk-mq: honor IO scheduler for multiqueue devices
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Git-commit: a12de1d42d74ef3c80e9fb9a2da94daaef747869
Patch-mainline: v5.4-rc2
References: bsc#1165478

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@acm.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Javier González <javier@javigon.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Martin Wilck <mwilck@suse.com>
---
 block/blk-mq.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1926,6 +1926,9 @@ static blk_qc_t blk_mq_make_request(stru
 		}
 
 		list_add_tail(&rq->queuelist, &plug->mq_list);
+	} else if (q->elevator) {
+		blk_mq_put_ctx(data.ctx);
+		blk_mq_sched_insert_request(rq, false, true, true);
 	} else if (plug && !blk_queue_nomerges(q)) {
 
 		/*
@@ -1949,8 +1952,8 @@ static blk_qc_t blk_mq_make_request(stru
 			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_put_ctx(data.ctx);
 		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
 	} else {