MPI: mpiexec third parameter not clear

Question

What exactly is the third parameter in the following MPI command

mpiexec -n 2 cpi

Is it no. of cores? So if I am running on Pentium 4 , shall I make it 1?

Answer 1

• -n 2: spawn two processes.
• cpi: the executable.

Experiment with what is faster, one or two or more processes. Some codes run best with one process per core, some codes benefit from oversubscription.