You can do: mpirun -n 10 myprog This will launch 10 MPI processes. Each process can create any number of threads. You might also need specific core binding for each process, so processes don't migrate all over the place. Look into mpiexec -bind-to -help for this. -- Pavan On 07/10/2013 12:27 PM, Bob Ilgner wrote:

Let me phrase this question differently. I want my mpi executable to only use 10 out of the 256 cores on this smp machine. Is it possible to configure mpi to do this? If so, what would one do this with mpi. bob

On Wed, Jul 10, 2013 at 4:46 PM, Wesley Bland <[email protected] <mailto:[email protected]>> wrote:

Threads in MPI are not ranks. When you say you want to launch with -n 100, you will always get 100 processes, not threads. If you want 10 threads on 10 cores, you will need to launch with -n 10, then add your threads according to your threading library.

Note that threads in MPI do not get their own rank currently. They all share the same rank as the process in which they reside, so if you need to be able to handle things with different ranks, you'll need to use actual processes.

Wesley

On Jul 10, 2013, at 9:41 AM, Bob Ilgner <[email protected] <mailto:[email protected]>> wrote:

> Dear all, > > I am working on a shared memory processor with 256 cores. I am working from the command line directly. > > Can I restict the number of cores that I deploy.The command > > mpirun -n 100 myprog > > > will automatically start on 100 cores. I wish to use only 10 cores and have 10 threads on each core. Can I do this with mpich ? Rememebre that this an smp abd I can not identify each core individually(as in a cluster) > > Regards, bob > _______________________________________________ > discuss mailing list [email protected] <mailto:[email protected]> > To manage subscription options or unsubscribe: > https://lists.mpich.org/mailman/listinfo/discuss

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-- Pavan Balaji http://www.mcs.anl.gov/~balaji