[Beowulf] Naive question: mpi-parallel program in multicore CPUs

[Tom Elken]

 > -----Original Message-----
> From: beowulf-bounces at beowulf.org 
> [mailto:beowulf-bounces at beowulf.org] On Behalf Of Geoff Jacobs
> 
> Using OpenMP per node is going to be much less portable and 
> much more complex to implement. It's better to let your MPI 
> library handle things the smart way.

At QLogic we're quite familiar with benchmarking with good OpenMP
compilers (esp. the PathScale compiler, which used to be part of QLogic)
and with various modern MPIs (InfiniPath MPI, MVAPICH, Open MPI, HP-MPI,
Scali MPI), and I totally agree with the previous two answers.  

MPI developers pay a large and increasing amount of performance-tuning
attention to the larger core counts, NUMA and SMP issues on cluster
nodes.  Even if you underwent the large effort to re-code an application
for which you had the source to an OpenMP / MPI hybrid approach, it is
as likely that you would reduce your application's performance as to
improve it.

That said, there is continuing interest in the Hybrid approach, and
large SMP nodes will keep that interest going.  A Google on "Hybrid
OpenMP MPI" will provide you with some presentations and papers on
recent work in this area.  You will find that wins with the Hybrid
approach are possible, but it is a lot of work, and by no means
required, as you move towards clusters with multi-core CPUs.

-Tom

> 
> --
> Geoffrey D. Jacobs
> 
> To have no errors
>   would be life without meaning
>   No struggle, no joy
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