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

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Message-Id: <20100622171622.fc9d04c1.akpm@linux-foundation.org>
Date:	Tue, 22 Jun 2010 17:16:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Αλέξανδρος Παπαδογιαννάκης <psxlover@...mail.com>
Cc:	<linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: FW: sched_setaffinity not working with kernel 2.6.32.15

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.

> ...

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.

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