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Subject: Re: [OMPI users] Processor/core selection/affinity for large shared memory systems
From: Ralph Castain (rhc_at_[hidden])
Date: 2008-12-04 15:20:44

I confess to confusion. OpenMPI will by default map your processes in
a round-robin fashion based on process slot. If you are in a resource
managed environment (e.g., TM or SLURM), then the slots correspond to
cores. If you are in an unmanaged environment, then your hostfile
needs to specify a single hostname, and the slots=x number should
reflect the total number of cores on your machine.

If you then set mpi_paffinity_alone=1, OMPI will bind each rank to its
associated core.

Is that not what you are trying to do?

On Dec 4, 2008, at 12:50 PM, V. Ram wrote:

> We have an 8-way, 32-core AMD processor machine (single system image)
> and are at present running OpenMPI 1.2.8 . Jobs are launched
> locally on
> the machine itself. As far as I can see, there doesn't seem to be any
> way to tell OpenMPI to launch the MPI processes on adjacent cores.
> Presumably such functionality is technically possible via PLPA. Is
> there in fact a way to specify such a thing with 1.2.8, and if not,
> will
> 1.3 support these kinds arguments?
> Thank you.
> --
> V. Ram
> v_r_959_at_[hidden]
> --
> - Or how I learned to stop worrying and
> love email again
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