Re: perf tools miscellaneous questions

[Victor Jimenez]

On 11/04/2010 09:58 PM, Francis Moreau wrote:
> Francis Moreau<francis.moro@xxxxxxxxx>  writes:
>
> > Francis Moreau<francis.moro@xxxxxxxxx>  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@xxxxxx

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