linux-kernel - Re: Performance regression in 2.6.22-git1 (new sched code?)

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Date:	Tue, 10 Jul 2007 23:09:45 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Martin Bligh <mbligh@...igh.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andy Whitcroft <apw@...dowen.org>
Subject: Re: Performance regression in 2.6.22-git1 (new sched code?)


* Martin Bligh <mbligh@...igh.org> wrote:

> ~ 1% on 4-way x86_64
> 
> http://test.kernel.org/perf/kernbench.elm3b6.png
> 
> ~ 4% on 16-way NUMA-Q (i386)
> 
> http://test.kernel.org/perf/kernbench.moe.png
> 
> ~ 1.5% on 4-way i386
> 
> http://test.kernel.org/perf/kernbench.elm3b132.png

thx! I'll check this tomorrow, meanwhile here are a few quick ideas.

1) does reverting this patch improve performance:

   commit 9c4801cebc2add1fe514bc8eb201b16372eee11a
   Author: Ingo Molnar <mingo@...e.hu>
   Date:   Mon Jul 9 18:52:01 2007 +0200

       sched: more agressive idle balancing

2) does changing CONFIG_HZ=250 to CONFIG_HZ=100 improve the numbers? 
   CFS has some internal tuning that depends on HZ - a higher HZ is a 
   sign that the user wants more finegrained scheduling. So for maximum 
   server throughput, use CONFIG_HZ=100.

3) could you turn off CONFIG_SCHED_DEBUG? The cost is small but perhaps 
   measurable.

(these 3 suggestions could be tested together - they should have 
cumulative effects.)

	Ingo
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