Running multiple processes on the same host

[Pete Wyckoff]

kwb1 at cec.wustl.edu wrote on Tue, 28 Feb 2006 14:33 -0600:
> I am trying to use mpiexec to start an mpi job with two processes running on
> some of the physical processors.  If I was using mpirun, I would just repeat
> some of the processors on the hostlist or just allow it to wrap around, but
> I'm having some issues doing this with mpiexec.  I took a look at hacking
> into the code, but I wanted to see if anyone has a less drastic solution.

Mpiexec actually goes out of its way to make sure you can't do this.
You could certainly hack the code to allow oversubscription of
processor resources, and I've toyed with adding an option to let
people like you say "I know what I'm doing".  The problem is, some
sites use multi-CPU nodes and will schedule individual processors
from those nodes.  They don't want a user running more than one
thread on his assigned processor as that would interfere with other
jobs on the same node.  Yes, there are many other ways jobs fight
each other in such an allocation scheme, so this is far from
foolproof.

I'm curious what your code does that it makes sense to overallocate
procesosrs.  If you do hack the code, a ./configure time option to
enable this would let admins somewhat set policy.  I'd want to force
users to give another flag (beyond "-numproc 27") to indicate they
know what they're doing too.

		-- Pete