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From: Brian Barrett (brbarret_at_[hidden])
Date: 2006-03-13 08:42:59

On Mar 11, 2006, at 1:00 PM, Jayabrata Chakrabarty wrote:

> Hi I have been looking for information on how to use multiple
> Gigabit Ethernet Interface for MPI communication.
> So far what i have found out is i have to use mca_btl_tcp.
> But what i wish to know, is what IP Address to assign to each
> Network Interface. I also wish to know if there will be any change
> in the format of "hostfile"
> I have two Gigabit Ethernet Interface on a cluster of 5 nodes at
> present.

Open MPI will use all available (and active) ethernet devices for MPI
communication by default. It does a relatively simplistic netmask
comparison to prefer connections in the same subnet (so if host A has
addresses and and host B has addresses and, OMPI will make a connection
between the two 192.168.1 addresses and another between the two
192.168.2 addresses). If you have two separate switches for your two
networks (which I would think would give best performance), make sure
that the two have IP address ranges that are in different subnet mask
ranges. Other than that, Open MPI will do the rest.

In Open MPI, the hostfile is completely independent of the MPI
communication network names, so no change is needed there.

I believe (but I could be wrong) that there was an issue with
multiple TCP networks in 1.0.1. I believe this might have been
resolved in our upcoming 1.0.2 release. You may want to try one of
the 1.0.2 pre-releases if you run into trouble with the 1.0.1 release.

Hope this helps,


   Brian Barrett
   Open MPI developer