linux-kernel - Re: perf tools miscellaneous questions

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Date:	Thu, 04 Nov 2010 21:58:32 +0100
From:	Francis Moreau <francis.moro@...il.com>
To:	Reid Kleckner <reid.kleckner@...il.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	linux-perf-users@...r.kernel.org
Subject: Re: perf tools miscellaneous questions

Francis Moreau <francis.moro@...il.com> writes:

> Francis Moreau <francis.moro@...il.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...

-- 
Francis
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