[Beowulf] Shared memory
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Greg Lindahl lindahl at pathscale.comSun Jul 3 20:12:10 PDT 2005
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On Mon, Jun 27, 2005 at 12:25:13PM +0100, Kozin, I (Igor) wrote: > I think MPI/OpenMP has its niche. I think it's a tiny one. Modern interconnects like InfiniPath are getting to such low latencies that the spinlocks needed for a fully threaded MPI are very expensive. And a single thread can't necessarily max out the interconnect performance. > BTW, "taskset" worked fine with MPI but could not get a grip on OpenMP > threads on a dual core. You didn't say which compiler you were using, but in the PathScale case, our compiler default is to set process affinity for you. Our manual describes how you can turn this off, but you probably don't want to. > Unfortunately I can't recommend a simple established code or benchmark > which would allow transparent comparison of MPI versus OpenMP/MPI. MM5 runs both ways... and it's faster as pure MPI. If OpenMPI+MPI doesn't have some special benefit such as accellerating convergence, it's not going to be a win. -- greg
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