[Beowulf] multi-threading vs. MPI

Toon Knapen toon.knapen at gmail.com
Sun Dec 9 11:37:27 PST 2007

Geoff Jacobs wrote:
> If an application is going to be using only shared memory, I have no
> doubt the consensus here is to use native threads or OpenMP. If the
> application is going to be working over a network, MPI (or PVM) is the
> way to go.

If threads are better for SMP, but what about Numa like SGI Altix or HP 
Integrity ? On the latter for instance, inter-cell (cell = 1 board with 
4 cpu's) memory access suffers 200 times higher latency compared to 
intra-cell memory-access.

But also the AMD (and future Intel) processors are Numa. With threads 
you have no idea about referencing remote memory but is that a good thing?

And considering that future processors are even going more extreme in 
the Numa direction (e.g. the Intel 80-core), is'nt it more future-safe 
to go with MPI if one would start a large coding-project now?

thanks for all the reactions,


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