Messages in this thread | | | Date | Wed, 9 Dec 2009 20:05:07 +0100 | From | Jens Axboe <> | Subject | Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed |
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On Wed, Dec 09 2009, Jeff Moyer wrote: > Corrado Zoccolo <czoccolo@gmail.com> writes: > > > Hi Jeff, > > On Tue, Dec 8, 2009 at 7:00 PM, Jeff Moyer <jmoyer@redhat.com> wrote: > >> Corrado Zoccolo <czoccolo@gmail.com> writes: > >> > >>> The introduction of ramp-up formula for async queue depths has > >>> slowed down dirty page reclaim, by reducing async write performance. > >>> This patch makes sure the formula kicks in only when sync request > >>> was recently delayed. > >>> @@ -3706,7 +3707,7 @@ static void *cfq_init_queue(struct request_queue *q) > >>> cfqd->cfq_latency = 1; > >>> cfqd->cfq_group_isolation = 0; > >>> cfqd->hw_tag = -1; > >>> - cfqd->last_end_sync_rq = jiffies; > >>> + cfqd->last_delayed_sync = jiffies - HZ; > >> > >> So, umm, what's that about? > > > > Previously, when cfq started, it started in a state where writes were > > completely throttled. Now, we optimistically prefer to start with a > > reasonable max depth (10) > > OK. Can we put a comment in there and change the initialization to > cfq_slice_sync * 10?
Agree, that would be MUCH easier to understand.
-- Jens Axboe
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