linux-kernel - Re: Higher than expected disk write(2) latency

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Message-ID: <20080710093109.46db7c40@the-village.bc.nu>
Date:	Thu, 10 Jul 2008 09:31:09 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Martin Sustrik <sustrik@...tmq.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Martin Lucina <mato@...elna.sk>, linux-kernel@...r.kernel.org
Subject: Re: Higher than expected disk write(2) latency

> 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.

Alan
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