On Mon, Oct 09, 2017 at 07:24:20PM +0800, Ming Lei wrote:
> When hw queue is busy, we shouldn't take requests from
> scheduler queue any more, otherwise it is difficult to do
> IO merge.
>
> This patch fixes the awful IO performance on some
> SCSI devices(lpfc, qla2xxx, ...) when mq-deadline/kyber
> is used by not taking requests if hw queue is busy.
>
> Reviewed-by: Bart Van Assche <bart.vanassche@xxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Omar Sandoval <osandov@xxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq-sched.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index 4ab69435708c..eca011fdfa0e 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -94,7 +94,7 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
> struct request_queue *q = hctx->queue;
> struct elevator_queue *e = q->elevator;
> const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
> - bool did_work = false;
> + bool do_sched_dispatch = true;
> LIST_HEAD(rq_list);
>
> /* RCU or SRCU read lock is needed before checking quiesced flag */
> @@ -125,18 +125,18 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
> */
> if (!list_empty(&rq_list)) {
> blk_mq_sched_mark_restart_hctx(hctx);
> - did_work = blk_mq_dispatch_rq_list(q, &rq_list);
> + do_sched_dispatch = blk_mq_dispatch_rq_list(q, &rq_list);
> } else if (!has_sched_dispatch) {
> blk_mq_flush_busy_ctxs(hctx, &rq_list);
> blk_mq_dispatch_rq_list(q, &rq_list);
> }
>
> /*
> - * We want to dispatch from the scheduler if we had no work left
> - * on the dispatch list, OR if we did have work but weren't able
> - * to make progress.
> + * We want to dispatch from the scheduler if there was nothing
> + * on the dispatch list or we were able to dispatch from the
> + * dispatch list.
> */
> - if (!did_work && has_sched_dispatch) {
> + if (do_sched_dispatch && has_sched_dispatch) {
> do {
> struct request *rq;
>
> --
> 2.9.5
>
