Hard disk performance differences between Gutsy kernel 2.6.22-6.13 and kernel from git tree

Krzysztof Lichota krzysiek at lichota.net
Sat Jun 16 12:59:11 UTC 2007

Hello kernel guys!
I am working on prefetching Google Summer of Code project for Ubuntu
(mentored by Tollef Fog Heen) and I am using Gutsy kernel as base for my

I have started from measuring OpenOffice cold startup time and I have
run into hard to explain difference in startup time between precompiled
kernel which comes with Gutsy (2.6.22-6.13-generic) and the kernel I
have compiled from Ubuntu kernel git tree hosted at
http://kernel.ubuntu.com/git (the ubuntu/ubuntu-gutsy.git tree).

On standard kernel, OpenOffice cold startup is about 14 seconds. On
custom compiled kernel it is between 9 seconds (when testing manually)
and 11 seconds (when testing automatically). 9 seconds is even less than
startup time when using drop_caches to purge cache (~11 seconds).
But even 11 seconds is much less than 14 seconds measured on standard

I have also performed measurements of hdparm -T and hdparm -t on these 2
kernel versions and Ubuntu kernel is better in hdparm -T test (it has
about 7 MB/s better throughput) but is much worse in hdparm -t test (it
starts slower and it takes more time to achieve full throughput).

Jan Kara and me have looked through diff between these 2 versions but
could not find any change which would justify such behaviour.

If you have any suspicions what would cause such change, please let me
If the kernel in git tree is supposed to be released as next Gutsy
kernel update (I assume so), this might also affect all Gutsy users.

The results of my tests are described at:
There is also description of configuration used for kernel compilation
and machine hardware description.

The issues are discussed in this e-mail thread:

The diff between sources is attached to the following e-mail message:

If you are interested in prefetching project, the home page is:

	Krzysztof Lichota

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