linux-kernel - Re: 2.6.22.2-cfs-v19.1 stops honouring nice 3 after some hours

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Message-Id: <200708200954.34812.mgd@technosis.de>
Date:	Mon, 20 Aug 2007 09:54:22 +0200
From:	Michael Gerdau <mgd@...hnosis.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.22.2-cfs-v19.1 stops honouring nice 3 after some hours

> > I played a bit with renicing my (mostly) CPU bound jobs and found
> > somewhat strange behaviour.
> > 
> > I'm on 2.6.22.2-cfs-v19.1 -- I can't boot into 2.6.23-rc3 as part of
> > my daily work because my NVIDIA driver doesn't yet work with it though
> > I could try to do some X-less testing if need be.
> 
> Please do try, a lot has changed since v19.1.

Meanwhile I've done some testing on 2.6.23-rc3.

The good news is that the strange behaviour w/r to nice I had seen on
2.6.22.3-cfs-v19.1 is no longer there.

Long running CPU bound jobs at different nice levels do indeed progress
(roughly) according to the %CPU figures as reported by top now.

However what I find somewhat unexpected is the IMO huge variation
in %CPU as observed even with 'top -d 60'. I've attached a log showing
5 CPU bound tasks observed for an our with 'top -b -d 60 -n 60'.

Jobs 5897, 5928 and 5977 do perform essentially the same tasks.
Jobs 17085 and 21492 do perform essentially the same task but differ
from the other 3 task.

I would have expected Jobs 5897 and 5928 to differ by at most one
percent point when measured for 60 seconds.

Best,
Michael
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