linux-kernel - Re: ext4 performance regression 2.6.27-stable versus 2.6.32 and later

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Date:	Fri, 30 Jul 2010 23:01:36 +0200
From:	Kay Diederichs <kay.diederichs@...-konstanz.de>
To:	Ted Ts'o <tytso@....edu>, linux <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Karsten Schaefer <karsten.schaefer@...-konstanz.de>
Subject: Re: ext4 performance regression 2.6.27-stable versus 2.6.32 and later

Am 30.07.2010 04:20, schrieb Ted Ts'o:
> On Wed, Jul 28, 2010 at 09:51:48PM +0200, Kay Diederichs wrote:
>>
>> When looking at the I/O statistics while the benchmark is running, we
>> see very choppy patterns for 2.6.32, but quite smooth stats for
>> 2.6.27-stable.
>
> Could you try to do two things for me?  Using (preferably from a
> recent e2fsprogs, such as 1.41.11 or 12) run filefrag -v on the files
> created from your 2.6.27 run and your 2.6.32 run?
>
> Secondly can capture blktrace results from 2.6.27 and 2.6.32?  That
> would be very helpful to understand what might be going on.
>
> Either would be helpful; both would be greatly appreciated.
>
> Thanks,
>
> 						- Ted

Ted,

a typical example of filefrag -v output for 2.6.27.48 is

  Filesystem type is: ef53
File size of /mnt/md5/scratch/nfs-test/tmp/xds/frames/h2g28_1_00000.cbf 
is 6229688 (1521 blocks, blocksize 4096)
  ext logical physical expected length flags
    0       0 796160000            1024
    1    1024 826381312 796161023    497 eof

(99 out of 100 files have 2 extents)

whereas for 2.6.32.16 the result is typically
Filesystem type is: ef53
File size of /mnt/md5/scratch/nfs-test/tmp/xds/frames/h2g28_1_00000.cbf 
is 6229688 (1521 blocks, blocksize 4096)
  ext logical physical expected length flags
    0       0 826376200            1521 eof
/mnt/md5/scratch/nfs-test/tmp/xds/frames/h2g28_1_00000.cbf: 1 extent found

(99 out of 100 files have 1 extent)

We'll try the blktrace ASAP and report back.

thanks,

Kay


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