Date: Wed, 9 Jun 2004 16:25:48 -0700
From: Andrew Morton <akpm@osdl.org>
To: Clint Byrum <cbyrum@spamaps.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.6 vm/elevator loading down disks where 2.4 does not
Message-Id: <20040609162548.63d69b78.akpm@osdl.org>
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Clint Byrum <cbyrum@spamaps.org> wrote:
>
> When we upgraded one of our production boxes (details below) to 2.6.6,
> we noticed an immediate loss of 5 - 15 percent efficiency. While these
> boxes usually had less than 0.5% variation through out the day, this box
> was consistently doing 10% fewer searches than the others.
> 
> Upon investigation, we saw that the 2.6 box was reading from the disk
> about 5 times as much as 2.4. Iin 2.4 we can almost completely saturate
> the CPUs; they'll get to 90% of the real CPU's, and 15% of the virtual
> CPUs. With 2.6, they never get above 60/10 because they are in io-wait
> state constantly (which, under 2.4, is reported as idle IIRC).

Possibly a memory zone problem.  Could you try booting with "mem=896m" on
the kernel command line, see how that affects things?
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