Re: 2.6.1 slower than 2.4, smp/scsi/sw-raid/reiserfs
From: Nick Piggin
Date: Tue Feb 03 2004 - 02:20:44 EST
Samium Gromoff wrote:
The machine is a dual P3 450MHz, 512MB, aic7xxx, 2 disk RAID-0 and
ReiserFS. It's a few years old and has always run Linux, most
recently 2.4.24. I decided to try 2.6.1 and the performance is
disappointing.
2.6 has a few performance problems under heavy pageout at present. Nick
Piggin has some patches which largely fix it up.
I`m sorry, but this is misguiding. 2.6 does not have a few performance
problems under heavy pageout.
It`s more like _systematical_ _performance_ _degradation_ increasing with
the pageout rate. The more the box pages out the more 2.6 lags behind 2.4.
Well it is a few problems that cause significant performance
regressions. But nevermind semantics...
What i`m trying to say is that even light paging is affected. And light
paging is warranted when you run, say, KDE on 128M ram.
Go measure the X desktop startup time on a 48M/64M boxen--even light paging
causes 2.6 to be just sloower. Also the vm thrashing point is much much earlier.
Have a look here: http://www.kerneltrap.org/~npiggin/vm/3/
and here: http://www.kerneltrap.org/~npiggin/vm/4/
patches here: http://www.kerneltrap.org/~npiggin/vm/
and I have a couple of things which improve results even more.
True, its only kbuild, but after I do a bit more tuning I'll
focus on other things - I'm hoping most of the improvements
carry over to other cases though.
Tentatively, it looks like 2.6 under very heavy swapping can
actually be significantly improved over 2.4.
Ask Roger Luethi for details.
Andrew is quite well versed in the details :)
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