[mpich-discuss] Restrict number of cores, not threads

Wesley Bland wbland at mcs.anl.gov
Wed Jul 10 09:46:38 CDT 2013

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.


On Jul 10, 2013, at 9:41 AM, Bob Ilgner <bobilgner at gmail.com> 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
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