[Beowulf] Naive question: mpi-parallel program in multicore CPUs

Greg Lindahl lindahl at pbm.com
Tue Oct 2 17:16:00 EDT 2007


On Tue, Oct 02, 2007 at 02:52:21PM -0400, Larry Stewart wrote:

> On the other hand, here's a fellow who got a 4X speedup by going to hybrid:
> 
> www.nersc.gov/nusers/services/training/classes/NUG/Jun04/NUG2004_yhe_hybrid.ppt

It's always hard to evaluate how real such claims are. But I will note
that this guy is on an IBM SP, which for a while (dunno if it's fixed
now) had some really horribly slow MPI library code for in-box
communications. Code so bad that it made OpenMP and hybrid programming
look good.

He also claims MM5 gets a win with hybrid programming, but the numbers
I've seen say that pure MPI is best on that code.

-- greg


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