"Balaji, Pavan" <[email protected]> writes:

If you want to try the approach with oversubscription, I’d recommend configuring mpich using --with-device=ch3:sock. That build will not be as optimized for the common case of dedicated cores for each MPI process, but also won't hurt the oversubscription case as much. I already warned you that this is a bad idea, so use at your own risk. :-)

It's a bad idea for performance, but great for testing and debugging. It's crazy to not be able to run a 9-process correctness test on a laptop. For this reason, PETSc's --download-mpich feature (used by people that don't have MPI installed, or whose OS provides a broken MPI) still uses ch3:sock by default.