linux-kernel - Re: FW: sched_setaffinity not working with kernel 2.6.32.15

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Message-ID: <1277277558.1875.745.camel@laptop>
Date:	Wed, 23 Jun 2010 09:19:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Αλέξανδρος Παπαδογιαννάκης <psxlover@...mail.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: FW: sched_setaffinity not working with kernel 2.6.32.15

On Tue, 2010-06-22 at 17:16 -0700, Andrew Morton wrote:
> On Sun, 20 Jun 2010 22:10:18 +0300
> ____________________ ______________________________  <psxlover@...mail.com> wrote:
> 
> > 
> > From: psxlover@...mail.com
> > To: mingo@...e.hu; peterz@...radead.org
> > Subject:
> >  sched_setaffinity not working with kernel 2.6.32.15
> > Date: Sun, 20 
> > Jun 2010 17:14:12 +0300
> 
> I assume from this that you initially sent the email privately to
> Peter&Ingo, then forwarded it to the list without cc'ing Peter&Ingo. 
> So if they're already responded to the inital email, I'm wasting my
> time.  Ho hum.

My private copy seems to have gone missing..

> > ...
> 
> That's a great bug report - fully bisected and it includes a testcase. 
> Thanks.
> 
> However I think your testcase is buggy.  You have main() racing against
> print_affinity().  If a sub-thread runs print_affinity() before main()
> has run set_threadaffinity(), print_affinity() will obviously print
> main()'s affinity.
> 
> Between 2.6.18 and 2.6.35-rc3 the timing changed a bit - in the later
> kernel the sub-threads are running before main() is able to change
> their affinity.  In the earlier kernel the sub-threads run first.
> 
> In both kernels, all CPU consumption is on CPU 0 as desired.
> 
> Re-enabling the sleep(1) in threadCode() fixes the print_affinity()
> output, confirming that it's a userspace race.

Andrew is right, your program is buggy. 
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