Message-ID: <48760BFB.90007@fastmq.com>
Date: Thu, 10 Jul 2008 15:17:47 +0200
From: Martin Sustrik <sustrik@fastmq.com>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: Andrew Morton <akpm@linux-foundation.org>, Martin Lucina <mato@kotelna.sk>,
       linux-kernel@vger.kernel.org
Subject: Re: Higher than expected disk write(2) latency
References: <20080628121131.GA14181@nodbug.moloch.sk>	<20080709222701.8eab4924.akpm@linux-foundation.org>	<4875C45C.2010901@fastmq.com> <20080710093109.46db7c40@the-village.bc.nu>
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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?

Thanks.
Martin
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