Messages in this thread | | | Date | Fri, 16 May 2008 17:23:12 +0200 | From | Matthew <> | Subject | Re: performance "regression" in cfq compared to anticipatory, deadline and noop |
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On Fri, May 16, 2008 at 10:57 AM, Jens Axboe <jens.axboe@oracle.com> wrote: > On Fri, May 16 2008, Daniel J Blueman wrote: >> On Fri, May 16, 2008 at 8:57 AM, Jens Axboe <jens.axboe@oracle.com> wrote: >> > On Fri, May 16 2008, Jens Axboe wrote: >> >> On Fri, May 16 2008, Fabio Checconi wrote: >> >> > > From: Jens Axboe <jens.axboe@oracle.com> >> >> > > Date: Fri, May 16, 2008 08:40:03AM +0200 >> >> > > >> >> > ... >> >> > > I think we can improve this further without getting too involved. If a >> >> > > 2nd request is seen in cfq_rq_enqueued(), then DO schedule a dispatch >> >> > > since this likely means that we wont be doing more merges on the first >> >> > > one. >> >> > > >> >> > >> >> > But isn't there the risk that even the second request would be >> >> > dispatched, while it still could have grown? >> >> >> >> Certainly, you'd only want to dispatch the first request. Ideally we'd >> >> just get rid of this logic of 'did empty dispatch round' and only >> >> dispatch requests once merging is done, it's basically the wrong thing >> >> to do to make it visible to the io scheduler so soon. Well of course >> >> even more ideally we'd always get big requests submitted, but >> >> unfortunately many producers aren't that nice. >> >> >> >> The per-process plugging actually solves this nicely, since we do the >> >> merging outside of the io scheduler. Perhaps just not dispatch on a >> >> plugged queue would help a bit. I'm somewhat against this principle of >> >> messing too much with dispatch logic in the schedulers, it'd be nicer to >> >> solve this higher up. >> > >> > Something like this... >> > >> > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c >> > index 5dfb7b9..5ab1a17 100644 >> > --- a/block/cfq-iosched.c >> > +++ b/block/cfq-iosched.c >> > @@ -1775,6 +1775,9 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, >> > >> > cic->last_request_pos = rq->sector + rq->nr_sectors; >> > >> > + if (blk_queue_plugged(cfqd->queue)) >> > + return; >> > + >> > if (cfqq == cfqd->active_queue) { >> > /* >> > * if we are waiting for a request for this queue, let it rip >> > @@ -1784,7 +1787,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, >> > if (cfq_cfqq_wait_request(cfqq)) { >> > cfq_mark_cfqq_must_dispatch(cfqq); >> > del_timer(&cfqd->idle_slice_timer); >> > - blk_start_queueing(cfqd->queue); >> > + cfq_schedule_dispatch(cfqd); >> > } >> > } else if (cfq_should_preempt(cfqd, cfqq, rq)) { >> > /* >> > @@ -1794,7 +1797,7 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, >> > */ >> > cfq_preempt_queue(cfqd, cfqq); >> > cfq_mark_cfqq_must_dispatch(cfqq); >> > - blk_start_queueing(cfqd->queue); >> > + cfq_schedule_dispatch(cfqd); >> > } >> > } >> > >> > @@ -1997,11 +2000,10 @@ static void cfq_kick_queue(struct work_struct *work) >> > struct cfq_data *cfqd = >> > container_of(work, struct cfq_data, unplug_work); >> > struct request_queue *q = cfqd->queue; >> > - unsigned long flags; >> > >> > - spin_lock_irqsave(q->queue_lock, flags); >> > + spin_lock_irq(q->queue_lock); >> > blk_start_queueing(q); >> > - spin_unlock_irqrestore(q->queue_lock, flags); >> > + spin_unlock_irq(q->queue_lock); >> > } >> > >> > /* >> >> Platter speed at 64KB stride, but 16% (101MB/s) less performance at >> 4KB stride - perhaps merging isn't quite right? >> >> Both traces at http://quora.org/blktrace-profiles-3.tar.bz2 ; let me >> know if you'd like me to test Fabio's patch still. > > If you have time, please do test that one as well, thanks :-) > > -- > Jens Axboe > >
thanks for the 2 patches, please keep them coming :)
a short report (due to the time shortage):
I tested both patches this morning and got for both (still) around 52-58 MB/s (/dev/sdd & /dev/sde)
thanks & have a nice weekend :)
Mat
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