[mpich-discuss] How to specify which Ethernet / IP interface to use?

Jonathon Anderson janderson at ciq.co
Fri Jul 1 09:00:03 CDT 2022

Thanks again, Hui. It looks like I hadn't understood the structure or
delegation of responsibility between mpich and libfabric, nor the extent to
which libfabric itself comprised part of the runtime interface. I'll give
this a try, and I expect this knowledge will be useful to me for other MPI
that use libfabric as well!


On Fri, Jul 1, 2022 at 7:46 AM Zhou, Hui <zhouh at anl.gov> wrote:

> For libfabric, which used by ch4:ofi, you can these settings from
> libfabric manpages. It depends on your provider. For example,
> https://ofiwg.github.io/libfabric/v1.11.1/man/fi_tcp.7.html
> fi_tcp(7) - GitHub Pages
> <https://ofiwg.github.io/libfabric/v1.11.1/man/fi_tcp.7.html>
> NAME. fi_tcp - The msg sockets Fabric Provider. OVERVIEW. The tcp provider
> can be used on any system that supports TCP sockets. The provider is not
> intended to provide performance improvements over regular TCP sockets, but
> rather to allow developers to write, test,and debug application code even
> on platforms that do not have high-performance fabric hardware.
> ofiwg.github.io
> ------------------------------
> *From:* Jonathon Anderson <janderson at ciq.co>
> *Sent:* Friday, July 1, 2022 8:40 AM
> *To:* Zhou, Hui <zhouh at anl.gov>
> *Cc:* discuss at mpich.org <discuss at mpich.org>
> *Subject:* Re: [mpich-discuss] How to specify which Ethernet / IP
> interface to use?
> Thank you very much for this information, Hi! Can you point me to where
> these environment variables are documented for future reference? I tried to
> find something like this and was unable.
> ~jonathon
> On Fri, Jul 1, 2022, 7:35 AM Zhou, Hui <zhouh at anl.gov> wrote:
> Hi Jonathon,
> Since the binary name is "mpich-ofi-gnu9-ohpc-3.4.2-3.1.ohpc.2.4.x86_64",
> I assume it is mpich -3.4.2 configured with ch4:ofi. We no longer use
> mpich2 to refer to the project, just mpich.
> With ch4:ofi, try setting the following environment variables:
>     FI_PROVIDER=tcp
>     FI_TCP_IFACE=eth0
> That assumes you want to use the tcp provider and the private interface is
> eth0. There are other providers that you may choose and the iface selection
> variables will be different. You can set MPIR_CVAR_DEBUG_SUMMARY=1 to show
> the list of providers mpich probes during init.
> Best wishes,
> --
> Hui
> ------------------------------
> *From:* Jonathon Anderson via discuss <discuss at mpich.org>
> *Sent:* Thursday, June 30, 2022 10:49 PM
> *To:* discuss at mpich.org <discuss at mpich.org>
> *Cc:* Jonathon Anderson <janderson at ciq.co>
> *Subject:* Re: [mpich-discuss] How to specify which Ethernet / IP
> interface to use?
> I'm trying to use mpich2 [1] on a cluster of compute nodes each of
> which has two Ethernet interfaces: one, an encumbered public /
> Internet interface, and another a private / intranet interface. mpich
> is defaulting to trying to use the public interface, which then hangs
> indefinitely with both nodes in my job stuck listening via UDP.
> I experience the same behavior whether I use mpiexec or srun --mpi=pmi2.
> How do I tell mpich which interface to use?
> Thanks!
> ~jonathon
> [1]: mpich-ofi-gnu9-ohpc-3.4.2-3.1.ohpc.2.4.x86_64
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