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From: Brian Barrett (bbarrett_at_[hidden])
Date: 2007-05-29 14:39:18

On May 29, 2007, at 12:25 PM, smairal_at_[hidden] wrote:

> I am doing a research on parallel computing on shared memory with
> NUMA architecture. The system is a 4 node AMD opteron with each node
> being a dual-core. I am testing an OpenMPI program with MPI-nodes <=
> MAX cores available on system (in my case 4*2=8). Can someone tell me
> whether:
> a) In such cases (where MPI-nodes<=MAX cores on shared-memory),
> OpenMPI
> implements MPI-nodes as processes or threads? If yes, then how can it
> be determined at run-time? I am wondering because processes have more
> overhead than light-weight threads.

In Open MPI, different MPI ranks are always different processes.
This is what users expect, and I'd be hesitant to change that for the
over-subscription case.