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268 ensemble multi rank mpi tasks launch multiple processes but each reports a singleton mpi world - #269
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markcoletti wants to merge 3 commits into
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…ing bound to Mpich and not Openmpi
Lance-Drane
reviewed
Nov 6, 2026
| raise Exception('Missing %s command in $PATH' % (mpi_binary)) | ||
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| nproc_flag = '-np' | ||
| nproc_flag = '-n' |
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What does this actually do? I checked the output of prun --help using version 3.0.8 and I noted that these flags are referenced differently, but have the same description:
+----------------------+-----------------------------------------------+
| | Launch Options |
+----------------------+-----------------------------------------------+
| Option | Description |
|======================|===============================================|
| "--runtime-options | Comma-delimited list of runtime directives |
| <arg0>" | for the job (e.g., do not abort if a process |
| | exits on non-zero status) |
+----------------------+-----------------------------------------------+
| "-c" | "--np | Number of processes to run |
| <num_procs>" | |
+----------------------+-----------------------------------------------+
| "-n" | "--n | Number of processes to run |
| <num_procs>" | |
+----------------------+-----------------------------------------------+
I couldn't find any documentation for mpirun 5.0.7 (perlmutter), but for version 4.1.6 I did find this, where the options are also listed separately but have the same description:
mpirun (Open MPI) 4.1.6
Usage: mpirun [OPTION]... [PROGRAM]...
Start the given program using Open RTE
-c|-np|--np <arg0> Number of processes to run
-h|--help <arg0> This help message
-n|--n <arg0> Number of processes to run
In any case this seems to work fine on my end
Lance-Drane
approved these changes
Nov 6, 2026
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This makes some changes to the
pruncommand line to ensure that we get the desired behavior for specifying multiple ranks and cores-per-rank for launched tasks. A note warning of Mich MPI vs. OpenMPI compatibility has been added to the ensemble readthedocs page.