Re: [PATCH 1/2] blk-mq: respect io scheduler

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> On 27 Sep 2019, at 09.24, Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> 
> Now in case of real MQ, io scheduler may be bypassed, and not only this
> way may hurt performance for some slow MQ device, but also break zoned
> device which depends on mq-deadline for respecting the write order in
> one zone.
> 
> So 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@xxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Damien Le Moal <damien.lemoal@xxxxxxx>
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> 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 20a49be536b5..d7aed6518e62 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2003,6 +2003,8 @@ 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.
> @@ -2026,8 +2028,8 @@ 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


Looks good to me. Fixes a couple issues we have seen with zoned devices too.

Reviewed-by: Javier González <javier@xxxxxxxxxxx>

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