linux-kernel - Re: CPU scheduler weirdness?

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Message-ID: <alpine.LNX.2.00.0908191428300.20409@cinke.fazekas.hu>
Date:	Wed, 19 Aug 2009 14:34:45 +0200 (CEST)
From:	Marton Balint <cus@...ekas.hu>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Andreas Mohr <andi@...as.de>, linux-kernel@...r.kernel.org,
	mingo@...e.hu
Subject: Re: CPU scheduler weirdness?



On Wed, 19 Aug 2009, Peter Zijlstra wrote:

> 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?
>

Yes it's in my original post:

http://marc.info/?l=linux-kernel&m=125012584709800&w=2

Regards,
   Marton
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