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Subject: Re: [PATCH 0/3][RFC] Improve load balancing when tasks have large
 weight differential
From: Mike Galbraith <efault@gmx.de>
To: Nikhil Rao <ncrao@google.com>
Cc: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
        Venkatesh Pallipadi <venki@google.com>, linux-kernel@vger.kernel.org
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Date: Fri, 08 Oct 2010 09:22:23 +0200
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On Wed, 2010-10-06 at 01:23 -0700, Nikhil Rao wrote:
> On Sun, Oct 3, 2010 at 8:08 PM, Mike Galbraith <efault@gmx.de> wrote:
> > On Wed, 2010-09-29 at 12:32 -0700, Nikhil Rao wrote:
> >> The closest I have is a quad-core dual-socket machine (MC, CPU
> >> domains). And I'm having trouble reproducing it on that machine as
> >> well :-( I ran 5 soaker threads (one of them niced to -15) for a few
> >> hours and didn't see the problem. Can you please give me some trace
> >> data & schedstats to work with?
> >
> > Booting with isolcpus or offlining the excess should help.
> >
> 
> Sorry for the late reply. Booting with isolcpus did the trick, thanks.
> 
> ... and now to dig into why this is happening.

I was poking it (again) yesterday, and it's kind of annoying.  I can't
call this behavior black/white broken.  It's freeing up a cache for a
very high priority task, which is kinda nice, but SMP nice is costing
25% of my box's processor power in this case too.  Hrmph.

	-Mike