linux-kernel - Re: CPU scheduler weirdness?

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Message-Id: <1252045561.7005.7.camel@marge.simson.net>
Date:	Fri, 04 Sep 2009 08:26:01 +0200
From:	Mike Galbraith <efault@....de>
To:	Marton Balint <cus@...ekas.hu>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Andreas Mohr <andi@...as.de>, linux-kernel@...r.kernel.org
Subject: Re: CPU scheduler weirdness?

On Thu, 2009-09-03 at 23:57 +0200, Marton Balint wrote:

> >> In the meantime, I updated my original C program and also created a kernel 
> >> module (schedtest_mod.c) which causes the same scheduling problems as the 
> >> kernel module of my TV card. The kernel module is a skeleton of the 
> >> infrared sensor polling code in cx88-input.c. It uses 
> >> schedule_delayed_work, this seems to cause the problem. The C program 
> >> (schedtest.c) is also updated, it now detects the number of CPU cores, from 
> >> now, what you can set as a command line parameter is the CPU core number, 
> >> on which the schedtest processes will not quit. (previously this was always 
> >> the last core).
> >> 
> >> So to reproduce the bug on a dual core system, compile and insert the 
> >> kernel module (schedtest_mod.c). Then check dmesg, it should contain on 
> >> which CPU core is the delayed_work running. You should use the CPU core id 
> >> of the _other_ CPU core as a command line parameter to the updated 
> >> schedtest program.
> >> 
> >> And by the way, thank you guys for the help so far, hopefully we'll get to 
> >> the bottom of this :)
> >
> > I reproduced the bug with the previously provided kernel module and C program 
> > on a different computer (it's a laptop with a core2 duo P8400 CPU), and also 
> > bisected the bug to this commit:
> >
> > sched: fine-tune SD_MC_INIT:
> > 14800984706bf6936bbec5187f736e928be5c218
> >
> > If I add again the removed SD_BALANCE_NEWIDLE to flags, then everything works 
> > as expected. So what would be the correct fix for this bug? Revert the patch? 
> > Or just add SD_BALANCE_NEWIDLE to flags?

Or, figure out what's going weird with that module loaded.

> Ingo, Peter, could any of you guys have a look at the commit that caused 
> this bug? Is it OK to revert it? Or a fix somewhere else is necessary? I'm 
> pushing this because I hope that this bug will get fixed in the upcoming 
> stable kernel...

Where does your schedtest.c and schedtest_mod.c live?

	-Mike

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