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SubjectRe: perf tools miscellaneous questions
On 11/04/2010 09:58 PM, Francis Moreau wrote:
> Francis Moreau<francis.moro@gmail.com> writes:
>
>> Francis Moreau<francis.moro@gmail.com> writes:
>>
> [...]
>
>>> How could I know the number of cache level on my cpu ?
>>>
>>> I tried:
>>>
>>> $ perf stat -e cache-misses:u,l1d-loads-misses:u true
>>>
>>> Performance counter stats for 'true':
>>>
>>> 802 cache-misses
>>> 937 L1-dcache-load-misses
>>>
>>> 0.000996578 seconds time elapsed
>>>
>>> $ perf stat -e cache-misses:u,L2-loads-misses:u true
>>>
>>> Performance counter stats for 'true':
>>>
>>> 788 cache-misses
>>> 95 LLC-load-misses
>>>
>>> 0.001025423 seconds time elapsed
>>>
>>> So it looks like you're right: in my case I have this cache
>>> configuration:
>>>
>> oops sorry, I replied too early...
>>
>> so my cache configuration is:
>>
>> L1 -> L2 -> LLC
>>
>> where L2 misses is given by: 'cache-misses' - 'LLC-load-misses'
>>
>> Is that correct ?
>>
>> If so, I found 'cache-misses' term very not intuitive IMHO, probably
>> because I'm not an expert in cpu caches...
> Well thinking more about it, the above is wrong and I'm lost.
>
> If 'cache-misses' is the last level cache misses then how to interpret
> these results ?
>
> $ perf stat -e llc-load-misses:u,llc-store-misses:u true
>
> Performance counter stats for 'true':
>
> 94 LLC-load-misses
> 0 LLC-store-misses
>
> 0.000981840 seconds time elapsed
>
>
> $ perf stat -e cache-misses:u true
>
> Performance counter stats for 'true':
>
> 796 cache-misses
>
> 0.001345136 seconds time elapsed
>
> Here 'cache-misses' value is much more than llc misses one...
>
If you are measuring last level cache misses, I would recommend you to
use a memory intensive application/benchmark instead of /bin/true, as
otherwise there can be a significant variation between two runs.

Victor

--
------------------------------------------------------------------------

Victor Jimenez Perez
Barcelona Supercomputing Center
Centro Nacional de Supercomputacion
WWW: http://www.bsc.es
e-mail: victor.javier@bsc.es

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