linux-kernel - Performance degradation with FFSB between 2.6.20 and 2.6.21-rc7

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Message-ID: <462622F8.10107@bull.net>
Date:	Wed, 18 Apr 2007 15:54:00 +0200
From:	Valerie Clement <valerie.clement@...l.net>
To:	ext4 development <linux-ext4@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Performance degradation with FFSB between 2.6.20 and 2.6.21-rc7

Running benchmark tests (FFSB) on an ext4 filesystem, I noticed a 
performance degradation (about 15-20 percent) in sequential write tests 
between 2.6.19-rc6 and 2.6.21-rc4 kernels.

I ran the same tests on ext3 and XFS filesystems and I saw the same 
performance difference between the two kernel versions for these two 
filesystems.

I have also reproduced it between 2.6.20.7 and 2.6.21-rc7.
The FFSB tests run 16 threads, each creating 1GB files. The tests were 
done on the same x86_64 system, with the same kernel configuration and 
on the same scsi device. Below are the throughput values given by FFSB.

   kernel           XFS                ext3
----------
  2.6.20.7        48 MB/sec         44 MB/sec

  2.6.21-rc7      38 MB/sec         37 MB/sec

Did anyone else run across the problem?
Is there a known issue?

    Valérie

(in attachment, my kernel configuration file)

View attachment "config-2.6.21-rc7" of type "text/plain" (35491 bytes)