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With Intel-MPI I can pin the MPI processes started by mpirun to a certain cores on a node. For example with 24 cores and Intel-MPI:

mpirun -np 12 -genv I_MPI_PIN_PROCESSOR_LIST=0-11 ./some.exe &
mpirun -np 12 -genv I_MPI_PIN_PROCESSOR_LIST=12-23 ./other.exe &

With OpenMPI there is the option --bind-to with one these arguments: none, hwthread, core, l1cache, l2cache, l3cache, socket, numa, board.

I noticed that --bind-to socket binds process 0 to socket 0 and process 1 to socket 1, and so on. This is bad, since for best communication between some.exe processes, all of them should be on one socket and other.exe processes should be on the other socket.

Is there no equivalent pin option in OpenMPI?

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    try mpirun --cpu-set 0,1,2,3,4,5,6,7,8,9,10,11 ./some.exe Commented May 14, 2020 at 8:35
  • does not work as ``` --report-bindings ``` tells me then MCW rank 0 is not bound (or bound to all available processors) MCW rank 1 is not bound (or bound to all available processors) and so on Commented Oct 20, 2022 at 17:03
  • the binding report could be wrong here ... try mpirun --tag-output ... grep Cpus_allowed_list /proc/self/status to confirm how tasks are pinned. Commented Oct 20, 2022 at 23:54
  • you can also give a try to the --map-by core option. Use --map-by core --bind-to socket instead if you only want to pin on sockets instead of cores. Commented Oct 20, 2022 at 23:56
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    Two mpirun "instances" are independent and have no knowledge of each other, so yes, both jobs will end up time sharing. Consider using a resource manager such as Slurm in order to prevent this. Commented Oct 22, 2022 at 1:47
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