[mpich-discuss] core 2 quad and other multiple core processors

[chong tan]

Ari,
Are you a student ? Anyway, I like to point you to the answer of your problem:
mpiexec -help
 
or  look at your mpich2 packge, under www/www1, there is a mpiexec.html
 
it is easier to give your the answer, but getting you to look for the answer is better.
 
 
stan

--- On Wed, 7/2/08, Ariovaldo de Souza Junior <ariovaldojunior at gmail.com> wrote:

From: Ariovaldo de Souza Junior <ariovaldojunior at gmail.com>
Subject: [mpich-discuss] core 2 quad and other multiple core processors
To: mpich-discuss at mcs.anl.gov
Date: Wednesday, July 2, 2008, 1:15 PM


Hello everybody!

I'm really a newbie on clustering, so I have some, let's say, stupid questions. When I'm starting a job like this "mpiexec -l -n 6 ./cpi" in my small cluster of (until now) 6 core 2 quad machines, I'm sending 1 process to each node, right? Assuming that I'm correct, each process will utilize only 1 core of each node? and how to make 1 process run utilizing the whole processing capacity of the processor, the 4 cores? is there a way to do this? or I'll always utilize just one processor for each process? if I change this submission to "mpiexec -l -n 24 ./cpi" then the same process will run 24 times, 4 times per node (maybe simultaneously) and one process per core, right?

I'm asking all this because I think it is a bit strange to see the processing time increasing each time I put one more process to run, once in my mind it should be the contrary. I'll give some examples:

mpiexec -n 1 ./cpi
wall clock time = 0.000579

mpiexec -n 2 ./cpi
wall clock time = 0.002442

mpiexec -n 3 ./cpi
wall clock time = 0.004568

mpiexec -n 4 ./cpi
wall clock time = 0.005150

mpiexec -n 5 ./cpi
wall clock time = 0.008923

mpiexec -n 6 ./cpi
wall clock time = 0.009309

mpiexec -n 12 ./cpi
wall clock time = 0.019445

mpiexec -n 18 ./cpi
wall clock time = 0.032204

mpiexec -n 24 ./cpi
wall clock time = 0.045413

mpiexec -n 48 ./cpi
wall clock time = 0.089815

mpiexec -n 96 ./cpi
wall clock time = 0.218894

mpiexec -n 192 ./cpi
wall clock time = 0.492870

So, as you all can see is that as more processes I add, more time it takes, what makes me think that mpi is performing this test 192 times in the end and due to this the time increased. Is that correct that mpi performed the same test 192? Or did it divide the process into 192 pieces, calculated and then gathered the results and mounted the output again? I really would like to understand this relationship processor # x process # x .

I have the feeling that my questions are a bit "poor" and really from a newbie, but the answer will help me on utilizing other programs that will need mpi to run.

Thanks to all!

Ari - UFAM - Brazil




      
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