linux-kernel - Re: specjbb2005 and aim7 regression with 2.6.32-rc kernels

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Date:	Fri, 6 Nov 2009 09:04:18 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: specjbb2005 and aim7 regression with 2.6.32-rc kernels


* Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:

> Comparing with 2.6.31, specjbb2005 and aim7 have some regressions with 
> 2.6.32-rc kernels on core2 machines.
> 
> 1) On 4*4 core tigerton: specjbb2005 has about 5% regression.
> 2) On 2*4 stoakley: aim7 has about 5% regression.
> 
> On Nehalem, specjbb2005 has about 2%~8% improvement instead of 
> regression.
> 
> aim7 has much dependency on schedule patameters, such like 
> sched_latency_ns, sched_min_granularity_ns, and 
> sched_wakeup_granularity_ns. 2.6.32-rc kernel decreases these 
> parameter values. I restore them and retest aim7 on stoakley. aim7 
> regression becomes about 2% and specjbb2005 regression also becomes 
> 2%. But on Nehalem, the improvement shrinks.

Which precise 2.6.32-rc commit have you tested?

Since v2.6.32-rc6 Linus's tree has this one too:

  f685cea: sched: Strengthen buddies and mitigate buddy induced latencies

Which should improve things a bit. For 2.6.33 we have queued up these 
two in -tip:

  a1f84a3: sched: Check for an idle shared cache in select_task_rq_fair()
  1b9508f: sched: Rate-limit newidle

If any of them fixes a performance regression we could still merge them 
into 2.6.32 as well.

	Ingo
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