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Date: Thu, 10 Jul 2008 06:18:22 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Martin Sustrik <sustrik@...tmq.com> Cc: Alan Cox <alan@...rguk.ukuu.org.uk>, Martin Lucina <mato@...elna.sk>, linux-kernel@...r.kernel.org Subject: Re: Higher than expected disk write(2) latency On Thu, 10 Jul 2008 15:17:47 +0200 Martin Sustrik <sustrik@...tmq.com> wrote: > Hi Alan, > > >> What we see is that AIO performs rather bad while we are still > >> enqueueing more writes (it misses right position on the disk and has to > >> do superfluous disk revolvings), however, once we stop enqueueing new > >> write request, those already in the queue are processed swiftly. > > > > Which disk scheduler are you using - some of the disk schedulers > > intentionally delay writes to try and get better block merging. > > It's CFQ. Does it delay writes? And if so, what should we use instead? > noop is the simplest scheduler. deadline is the simplest real scheduler, and deadline doesn't have any delaying logic. If CFQ or anticipatory _are_ putting delays into this workload, that'd be a bug. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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