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Subject: Re: [OMPI users] mpirun is using one PBS node only
From: Gus Correa (gus_at_[hidden])
Date: 2009-12-01 15:42:30

Hi Belaid Moa

Belaid MOA wrote:
> Hi everyone,
> Here is another elementary question. I tried the following steps found
> in the FAQ section of with a simple hello world example
> (with PBS/torque):
> $ qsub -l nodes=2
> is pasted below:
> ========================
> #!/bin/sh -l
> #PBS -N helloTest
> #PBS -j eo
> echo `cat $PBS_NODEFILE` # shows two nodes: WN1 WN2
> /usr/local/bin/mpirun hello
> ========================
> When the job is submitted, only one process is ran. When I add the -n 2
> option to the mpirun command,
> two processes are ran but on one node only.

Do you have a single CPU/core per node?
Or are they multi-socket/multi-core?

Check "man mpiexec" for the options that control on which nodes and
slots, etc your program will run.
("Man mpiexec" will tell you more than I possibly can.)

The default option is "-byslot",
which will use all "slots" (actually cores
or CPUs) available on a node before it moves to the next node.
Reading your question and your surprise with the result,
I would guess what you want is "-bynode" (not the default).

Also, if you have more than one CPU/core per node,
you need to put this information in your Torque/PBS "nodes" file
(and restart your pbs_server daemon).
Something like this (for 2 CPUs/cores per node):

WN1 np=2
WN2 np=2

I hope this helps,
Gus Correa
Gustavo Correa
Lamont-Doherty Earth Observatory - Columbia University
Palisades, NY, 10964-8000 - USA

> Note that echo `cat
> $PBS_NODEFILE` outputs
> the two nodes I am using: WN1 and WN2.
> The output from ompi_info is shown below:
> $ ompi_info | grep tm
> MCA memory: ptmalloc2 (MCA v2.0, API v2.0, Component v1.3.3)
> MCA ras: tm (MCA v2.0, API v2.0, Component v1.3.3)
> MCA plm: tm (MCA v2.0, API v2.0, Component v1.3.3)
> Any help on why openMPI/mpirun is using only one PBS node is very
> appreciated.
> Thanks a lot in advance and sorry for bothering you guys with my
> elementary questions!
> ~Belaid.
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