linux-ext4 - Re: [Regression] Filesystem I/O is CPU-bound in rc7 and rc8

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Date:	Fri, 19 Feb 2010 13:22:45 -0800
From:	Mike Fedyk <mfedyk@...efedyk.com>
To:	James Cloos <cloos@...loos.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
	jfs-discussion@...ts.sourceforge.net
Subject: Re: [Regression] Filesystem I/O is CPU-bound in rc7 and rc8

On Sat, Feb 13, 2010 at 7:11 PM, James Cloos <cloos@...loos.com> wrote:
> Sometime between rc6 and rc7 all filesystem I/O started using 100% CPU,
> usually on the order of 60% sys, 40% user.
>
> I've tried this with each of ext4, jfs and btrfs filesystems.  All show
> the same issue.
>

Are you sure you're not running with any of the debugging options
enabled?  I see the same, but I have debugging enabled (rawhide
kernel).

> Using dd(1) to read from the block specials directly works as well and
> as fast as it always has; only reading or writing to mounted filesystems
> is affected.
>
> Box is 32-bit x86, PentiumIII-M; drives are ide using libata.
>
> If the btrfs fs is mounted, the slowdown is enought to trigger the
> hung_task call trace (120s) on the btrfs-transac process.
>
> But the regression is just as apparent when only jfs and ext4 are mounted.
>
> The only filesystems I've found which avoid the regression are tmpfs and
> devtmpfs.
>
> I didn't have time to write up a report when I noticed this in rc7 but
> had to boot back into rc6 for work.
>
> Some of the commits since rc7 looked like they might have addressed this
> regression, but it persists in rc8.
>
> -JimC
> --
> James Cloos <cloos@...loos.com>         OpenPGP: 1024D/ED7DAEA6
> --
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