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

[Gaetano Bellanca]

Hi,

maybe I reached my goal; I wanted to be a little polemic to see if, 
someone who knows more things about that, can give us a clear answer. 
I tested a multicore machine with a commercial software, and I noted 
that some speed-up can be obtained (not as good as expected, but much 
more than I have)... :)

The problem is that I didn't  find any clear answer  on the 
references I was able to find.
I looked on the network to have some suggestions, but I confess that 
I didn't find anything really effective.
I tried the options indicated in the OpenMP manual; I'm not a 
computer scientist, but a simple user, and using them I was unable to 
have any increase in the speed-up.

Things where totally different with mpi: in few days, attending a 
good school, and also using a very good materials available on the 
network,, it has been very easy to see the results of my effort. 
Maybe this problems is more difficult; maybe I'm unable to find the 
good references. Maybe I don't have the capability. In any case, it 
seems I'm not the only one with these problems.

Please, if someone have some clear references, share them with the 
community (I'm asking references, not the solutions! We are not 
expecting something falling from the sky ... in case, we will buy a 
commercial software :)  ).

Gaetano


At 23.06 14/07/2008, you wrote:


>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>mailto:gaetano.bellanca at unife.it
>
>----------


----------
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

----------
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/mpich-discuss/attachments/20080715/377048a4/attachment.htm>