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)