linux-kernel - Re: [PATCH RFC] [X86] Compile Option Os versus O2 on latest x86 platform

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Message-ID: <20091126094930.GD32275@elte.hu>
Date:	Thu, 26 Nov 2009 10:49:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	ling.ma@...el.com, Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>
Cc:	hpa@...or.com, tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] [X86] Compile Option Os versus O2 on latest x86
 platform


* ling.ma@...el.com <ling.ma@...el.com> wrote:

> Benchmarks:                          improvement 
> volano                                8%
> netperf                               6.7% 
> tbench                                6.45%
> Kbuild                                5.5% (3 time test, average improvement)

that Kbuild result looks suspicious. A kbuild only uses 25% of system 
time, so an 5.5% improvement means that system utilization dropped from 
25% to 19.5%, a 28% improvement in the kernel! That looks rather 
unlikely.

Could you please post before/after 'perf stat --repeat 3' results so 
that we can see the noise level?

Thanks,

	Ingo
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