On Fri, Sep 08, 2017 at 01:54:48PM -0700, Omar Sandoval wrote:
> On Fri, Sep 08, 2017 at 01:48:32PM -0700, Omar Sandoval wrote:
> > On Sat, Sep 02, 2017 at 11:17:16PM +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.vanass...@wdc.com>
> >
> > Jens and I did some testing with xfs/297 and couldn't find any issues,
> > so
> >
> > Reviewed-by: Omar Sandoval <osan...@fb.com>
>
> I take it back, the comment below needs to be updated
>
> > > Signed-off-by: Ming Lei <ming....@redhat.com>
> > > ---
> > > block/blk-mq-sched.c | 6 +++---
> > > 1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> > > index 4ab69435708c..845e5baf8af1 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 */
> > > @@ -125,7 +125,7 @@ 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);
> > > @@ -136,7 +136,7 @@ void blk_mq_sched_dispatch_requests(struct
> > > blk_mq_hw_ctx *hctx)
> > > * on the dispatch list, OR if we did have work but weren't able
> > > * to make progress.
> > > */
>
> This should be updated to say:
>
> 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.
OK, will do it in V5.
--
Ming
