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

[Gaetano Bellanca]

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


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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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