Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920

Bruce Simpson bms at incunabulum.net
Mon Apr 12 09:49:16 UTC 2010


On 04/12/10 05:12, Maho NAKATA wrote:
> *Abstract*
> I compared the peak performance of FreeBSD 8.0/amd64 and Ubuntu 9.10 amd64 using dgemm
> (a linear algebra routine, matrix-matrix multiplication).
> I obtained only 70% of theoretical peak performance on FreeBSD 8/amd64 and
> almost 95% on Ubuntu 9.10 /amd64. I'm really disappointed.
>    

So, where's the profiling to discover why this is the case?

Also I'm not clear on what constitutes 'theoretical peak performance' 
here or how it is being calculated. So figures like these come across as 
unscientific.

I'm sure this is something which can be resolved if someone sits down, 
profiles the app, and makes the necessary adjustments (e.g. 
pthread_setaffinity_np()) to configure CPU affinity, if the lack of it 
is pessimizing your friend's app.

The PMC framework is rapidly maturing, and you can use KCacheGrind with 
it to visualize context switch overhead.

But I think it's expecting a bit much to post informal results to 
-stable, in an expectation of something other thaninformal suggestions 
of what may help someone's maths-intensive application.

If there are performance issues, then reproducible results are needed, 
as well as some basic profiling effort of the system elements involved, 
before people could say anything either way, or offer further help.

cheers,
BMS


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