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

[chong tan]

In defend of the designers of the multi-core CPUs, I like to say you are wrong in saying so.  You re given a Jet plane, but prefer to use it as a boat, no wonder it sunk.
 
tan

--- On Mon, 7/14/08, Gaetano Bellanca <gaetano.bellanca at unife.it> wrote:

From: Gaetano Bellanca <gaetano.bellanca at unife.it>
Subject: Re: [mpich-discuss] Why is my quad core slower than cluster
To: mpich-discuss at mcs.anl.gov
Date: Monday, July 14, 2008, 1:39 PM


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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