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Subject: Re: hackbench regression with kernel 2.6.32-rc1
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>
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Date: Thu, 29 Oct 2009 08:50:47 +0800
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On Wed, 2009-10-28 at 15:22 +0100, Mike Galbraith wrote:
> On Wed, 2009-10-28 at 17:29 +0800, Zhang, Yanmin wrote:
> > 	-Mike
> > I'm investigating 5% tbench regression on Nehalem machine. perf_counter shows
> > select_task_rq_fair consumes about 5% cpu time with 2.6.32-rc1 while it consumes
> > less than 0.5% with 2.6.31.
> > 
> > Patch c88d5910890 has comments to explain it, but I still can't understand why
> > to add complicated balance logic when selecting task rq.
> > 
> > I will check which section in function select_task_rq_fair consumes so much time.
> 
> Turn off SD_WAKE_BALANCE as it was called in rc1.  See commit 182a85f.
I run testing against 2.6.32-rc1 which already includes the patch.