On Fri, Sep 27, 2019 at 9:25 AM 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
>
I've verified that the issue I saw with zone locking being skipped due
to scheduler bypass is resolved with this patch.
Thanks,
Hans
