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From: Michael Kluskens (mklus_at_[hidden])
Date: 2006-07-26 17:55:06

On Jul 26, 2006, at 5:07 PM, Mauricio Felga Gobbi wrote:

> Newbie question:
> How is the message passing of Open-MPI implemented when I have
> say 4 nodes with 4 processors (SMP) each, nodes connected by a gigabit
> ethernet ?... in other words, how does it manage SMP nodes when I
> want to use all CPUs, but each with its own process. Does it take
> any advantage of the SMP at each node?

Someone can give you a more complete/correct answer but I'll give you
my understanding.

All communication in OpenMPI is handled via the MCA module (term?)

self - process communicating with itself
sm - ... via shared memory to other processes
tcp - ... via tcp
openib - ... via Infiniband OpenIB stack
gm & mx - ... via Myrinet GM/MX
mvapi - ... via Infiniband Mellanox Verbs

If you launch your process so that four processes are on a node then
those would use shared memory to communicate.