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

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Date:	Thu, 3 Dec 2009 16:31:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Ma, Ling" <ling.ma@...el.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] [X86] Compile Option Os versus O2 on latest x86
 platform


* H. Peter Anvin <hpa@...or.com> wrote:

> On 12/03/2009 07:03 AM, Ma, Ling wrote:
> >> a key question is.. how much more memory do you have free due to -Os?
> >> (because memory is cache is performance on a system level as well)
> > The kernel code size from Os is 12M, that from O2 is 14M.
> >> and how much less icache pressure is there?
> > From perf stat report, cache reference(unified cache) from O2 is almost the same with Os.
> 
> The icache pressure was substantially higher (by ~10%) in the reports 
> that I saw.

hm, icache numbers are not included in perf stat runs by default. Are 
there some icache numbers i missed perhaps?

	Ingo
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