Nicolas Bock wrote:

On Fri, Dec 4, 2009 at 10:10, Eugene Loh <Eugene.Loh@sun.com> wrote:

Yield helped, but not as effectively as one might have imagined.

Yes, that's the impression I get as well, the master process might be yielding, but it doesn't appear to be a lot. Maybe I should do this differently to avoid this CPU usage in master. All I really want is to execute another process somewhere on a free node in my MPI universe, wait for it to be done and go on. From my limited understanding of MPI, MPI_Comm_spawn() and MPI_Barrier() seemed just like what I needed, but as I said, maybe there are other ways to do this.

I think you might observe a world of difference if the master issued some non-blocking call and then intermixed MPI_Test calls with sleep calls.  You should see *much* more subservient behavior.  As I remember, putting such passivity into OMPI is on somebody's to-do list, but just not very high.