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Subject: [OMPI users] How to select specific out of multiple interfaces for communication and support for heterogeneous fabrics
From: Michael Thomadakis (drmichaelt7777_at_[hidden])
Date: 2013-07-05 17:34:47

Hello OpenMPI

We area seriously considering deploying OpenMPI 1.6.5 for production (and
1.7.2 for testing) on HPC clusters which consists of nodes with *different
types of networking interfaces*.

1) Interface selection

We are using OpenMPI 1.6.5 and was wondering how one would go about
selecting* at run time* which networking interface to use for MPI
communications in case that both IB, 10GigE and 1 GigE are present.

This issues arises in a cluster with nodes that are equipped with different
types of interfaces:

*Some *have both IB-QDR or FDR and 10- and 1-GigE. Others *only* have
10-GigE and 1-GigE and simply others only 1-GigE.

2) OpenMPI 1.6.5 level of support for Heterogeneous Fabric

Can OpenMPI support running an MPI application using a mix of nodes with
all of the above networking interface combinations ?

  2.a) Can the same MPI code (SPMD or MPMD) have a subset of its ranks run
on nodes with QDR IB and another subset on FDR IB simultaneously? These are
Mellanox QDR and FDR HCAs.

Mellanox mentioned to us that they support both QDR and FDR HCAs attached
to the same IB subnet. Do you think MVAPICH2 will have any issue with this?

2.b) Can the same MPI code (SPMD or MPMD) have a subset of its ranks run on
nodes with IB and another subset over 10GiGE simultaneously?

That is imagine nodes I1, I2, ..., IN having say QDR HCAs and nodes G1, G2,
GM having only 10GigE interfaces. Could we have the same MPI application
run across both types of nodes?

Or should there be say 2 communicators with one of them explicitly overlaid
on a IB only subnet and the other on a 10GigE only subnet?

Please let me know if the above are not very clear.

Thank you much