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Subject: Re: CPU scheduler weirdness?
From: Peter Zijlstra <peterz@infradead.org>
To: Marton Balint <cus@fazekas.hu>
Cc: Andreas Mohr <andi@lisas.de>, linux-kernel@vger.kernel.org, mingo@elte.hu
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Date: Wed, 19 Aug 2009 14:10:34 +0200
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On Wed, 2009-08-19 at 14:01 +0200, Marton Balint wrote:
> On Wed, 19 Aug 2009, Peter Zijlstra wrote:
> > On Tue, 2009-08-18 at 21:49 +0200, Marton Balint wrote:
> >
> >> In the meantime, I was able to create a tiny C program which always
> >> succesfully reproduces the bug. It's basically an endless loop which does
> >> not stop while the process is running on the last CPU core. The program
> >> creates multiple instances of itself, to be able to keep all of the CPU
> >> cores busy. After 1 second, the processes running on other than the last
> >> CPU core die, the processes running on the last CPU core remain stuck
> >> there...
> >>
> >> I tested it on my dual core system, if someone could test it on a quad
> >> core and report back that would probably be useful.
> >>
> >> Usage: ./schedtest <number of CPU cores>
> >>
> >> And don't forget to kill the stuck processes after using the program! :)
> >
> > So what's the bug? Sure one task will stay on the cpu, and because there
> > is no contention it doesn't get migrated, and therefore won't quit,
> > how's that a problem?
> 
> Problem is that more than one processes remain on that CPU core, and none 
> of them get migrated to other (idle) cores. I tested it with my E8400 
> processor and 2.6.31-rc5-git3 kernel.

Only one remains here.. on a c2q running 2.6.31-rc6-tip

Do you have a .config handy?