Comment (by Roland Haas):

Yes, using --procs=4 --num-threads=2 will work for you. For historial reasons --procs really means "number of cores to use". Simfactory has some idea of how many threads per MPI rank one is to use by default and currently, on a laptop that numbers "as many threads as the laptop has cores". simfactory will only create more than 1 MPI rank of more cores ("procs") than threads are requested. Using --num-threads explicitly tells simfactory how many threads to use per MPI rank. The number of MPI ranks used is then procs / num-threads ie 2 in your example with both --procs and --num-threads and likely 1 without --num-threads if you workstation has more than 4 cores.

To know for sure you would have to inspect your laptop's machine.ini file in simfactory/mdb/machines/ (it will be named after the hostname of your laptop ie the name that simfactory/bin/sim whoami outputs).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2271/problem-with-mpi-process