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

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Message-ID: <4B17DD4A.2010305@zytor.com>
Date:	Thu, 03 Dec 2009 07:46:18 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
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

On 12/03/2009 07:31 AM, Ingo Molnar wrote:
> 
> * 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?
> 

Sorry, you're right; cache references and cache misses.  Furthermore,
I'm wrong, I was looking at references *per unit time*, which just show
that roughly the same number was squeezed into a shorter time.

Never mind me... :-/

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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