Right, I tried using a hostfile, and it made no difference. This is running OpenMPI 1.4.4 on CentOS 5.x machines. The original issue was an error trap built into my code, where it said one of the cores was asking for information it already owned. I'm sorry to be vague, but I can't share anything from the code in this forum. Basically, it is a CFD code, parallelized by splitting the grid points in the simulation up amongst the processors assigned to the job. As a pre-processing step, each processor must figure out which other processors it must communicate with by virtue of sharing neighboring gridpoints. The error I received told me that the grid points were not being split amongst different processors. I have used this exact same code using OpenMPI on other (larger) architectures, which, combined with the MPI error I shared before, leads me to believe I must have something not configured correctly, or there is some run time option I'm not setting properly, etc.
From: Ralph Castain <email@example.com>
Subject: Re: [OMPI users] MPI doesn't recognize multiple cores
available on multicore machines
To: Open MPI Users <firstname.lastname@example.org>
Content-Type: text/plain; charset=us-ascii
You don't need a hostfile to run multiple procs on the localhost.
What version of OMPI are you using? What was the original issue?