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SubjectRe: [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@zytor.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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