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Subject: Re: [OMPI users] (no subject)
From: Gus Correa (gus_at_[hidden])
Date: 2009-10-30 12:35:23

Hi Konstantinos, list

If you want "qsub" you need to install the resource manager /
queue system in your PC.
Assuming your PC is a Linux box, if your resource manager
is Torque/PBS on some Linux distributions it can be installed
from an rpm through yum (or equivalent mechanism), for instance.
I am not sure, but I would guess SGE and SLURM may also be available
through rmps also.
Or you can install the resource manager from source.
We have workstations/PCs here running Torque (installed through yum and
rpm), for the convenience of submitting jobs as in a cluster,
and letting the queue control them.

You could also use just "mpiexec" directly.
This doesn't require a resource manager, but you have to be
the resource manager yourself, baby-sitting the jobs,
submitting one at a time, waiting for completion, etc.

On another related issue,
let's say your 2 processors are dual core,
for a total of 4 cores.
Then you can count on submitting "mpiexec" with a number of processes
up to 4 ( "-n 4" or "-np 4").

If you use more than that 4, say "-np 6",
you are oversubscribing the physical cores.
Linux will have to make the 6 processes take turns in using the
4 cores.
(Some resource managers won't let you do this.)
Oversubscription can work for lightweight MPI jobs, but in my
experience it eventually hangs for heavier computation/communication

Also, note that any interactive work that you may be doing on your PC,
concurrently with the MPI jobs, will have an impact on performance,
and may even take the MPI jobs to a halt.
We had this experience here, when the user of the aforementioned
workstation insisted in running Matlab, browsing the web,
watching streaming video, listening to music, while the MPI jobs
were running. :)

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

Konstantinos Angelopoulos wrote:
> good part of the day,
> I am trying to run a parallel program (that used to run in a cluster) in my double core pc. Could openmpi simulate the distribution of the parallel jobs to my 2 processors meaning will qsub work even if it is not a real cluster?
> thank you for reading my message and for any answer.
> Konstantinos Angelopoulos
> Post-Graduate Student
> Brunel University
> School of Engineering and Design
> Uxbridge, Middlesex
> UB8 3PH
> UK
> Contact emails: mepgkka1_at_[hidden]
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