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

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Message-Id: <201002150012.25572.rjw@sisk.pl>
Date:	Mon, 15 Feb 2010 00:12:25 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
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 Sunday 14 February 2010, James Cloos 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.
> 
> 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.

I have created the bug entry at http://bugzilla.kernel.org/show_bug.cgi?id=15306
for your report.

Thanks,
Rafael
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