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Subject: [OMPI users] Mixed Threaded MPI code, how to launch?
From: Brock Palen (brockp_at_[hidden])
Date: 2008-10-25 17:36:51

We have a user with a code that uses threaded solvers inside each MPI
rank. They would like to run two threads per process.

The question is how to launch this? The default -byslot puts all the
processes on the first sets of cpus not leaving any cpus for the
second thread for each process. And half the cpus are wasted.

The -bynode option works in theory, if all our nodes had the same
number of core (they do not).

So right now the user did:

#PBS -l nodes=22:ppn=2
mpirun -np 22 app

Which made me aware of the problem.

How can I basically tell OMPI that a 'slot' is two cores on the same
machine? This needs to work inside out torque based queueing system.

Sorry If I was not clear about my goal.

Brock Palen
Center for Advanced Computing