[mpich-discuss] Why is my quad core slower than cluster

[Burlen Loring]

Hi Gaenato,

In my experience with gnu OpenMP, you have to set thread affinity, 
otherwise the threads all get scheduled to the same core. See this post: 
http://gcc.gnu.org/ml/gcc-help/2008-01/msg00066.html

Burlen

Gaetano Bellanca wrote:
> Hello Gus and list,
>
> I compiled mpich using gcc, no icc. Maybe this could be a good option 
> to try to obtain better performance.
>
> Anyway, maybe I'm wrong as I'm only a (very very basic) user, but I 
> don't think it is a mpich problem.
> Using mpich with n=2, the code speeds up as requested (and I think 
> that 2 different processors are used, looking at htop report). This 
> does not happen with n=4, where I still observed a (really small) 
> speed-up. But with n=6 or n=8, no speed-up is observed!
>
> Again, I tried to compile with parallel and openmp (and to write a 
> very simple code with do loop similar to my original simulator, but 
> without mpi calls, communications, etc ...). I didn't have the 
> expected speed-up also in this case. I'm still investigating .... but 
> ... I really think that multi core are a commercial gadget .... unless 
> you are a very specialist in writing a dedicated code able to take 
> advantage of the specific architecture of the processor.
>
> Hope to be wrong ...
>
> Gaetano
>
> ------------------------------------------------------------------------
> Gaetano Bellanca - Department of Engineering - University of Ferrara 
> Via Saragat, 1 - 44100 - Ferrara - ITALY            
> Voice (VoIP):  +39 0532 974809     Fax:  +39 0532 974870
> mailto:gaetano.bellanca at unife.it
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-- 
Burlen Loring
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x137