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Subject: Re: [OMPI docs] Behavior of --host and --hostfile flags on mpirun
From: Shao-Ching Huang (huangsc_at_[hidden])
Date: 2013-10-11 16:46:08


Kel,

This is the case when the hosts are connected by both ethernet and
infiniband. The hosts are identified by the ethernet setup (e.g.
/etc/hosts) but the MPI communication could go through infiniband.

Maybe this is a good topic to include in user docs. I will try a first cut
and send pull request.

Shao-Ching

On Fri, Oct 11, 2013 at 1:31 PM, Kelly Black <kjblack_at_[hidden]> wrote:

> Dear Jeff,
>
> Yeah, it never occurred to me to use both, but when I was double checking
> things on the Open MPI website I came across a blurb that said that when
> used together the behavior is different. The documentation said that if the
> names in the --host command are not contained in the host file then the
> mpirun command fails. It was not clear if you do not use a fully qualified
> name in one but not the other how it would be handled.
>
> Thanks for the info on the network interface. I did not realize that.
>
> Sincerely,
> Kel
>
> _______________________________________________________
> Kelly Black Phone: (315) 600-8334
> Clarkson University Fax: (315) 268-2371
> Department of Math. & C.S.
> PO Box 5815
> Potsdam, NY 13699-5815
> USA
>
>
> On Fri, Oct 11, 2013 at 4:10 PM, Jeff Squyres (jsquyres) <
> jsquyres_at_[hidden]> wrote:
>
>> Also, it's more common to use a hostfile *or* the --host option. It's
>> fairly uncommon to use both.
>>
>> As to whether one should use FQDN or a basename, it doesn't matter to
>> MPI. If the system resolves the name, OMPI can use it.
>>
>> Finally, a point that is worth noting (because so many people make the
>> wrong assumption): the hostnames that are listed in the hostfile or --host
>> option have nothing to do with what network interfaces are used for MPI
>> traffic. The hosts specified by the hostfile (or --hosts) are *only* used
>> to determine on which nodes MPI processes are launched. The determination
>> of which network interfaces are used are controlled by other MCA parameters
>> (e.g., the "btl" MCA parameter, and various mca_btl_*_if_include /
>> mca_btl_*_if_exclude MCA parameters).
>>
>>
>> On Oct 11, 2013, at 1:57 PM, Kelly Black <kjblack_at_[hidden]> wrote:
>>
>> > Dear Shao-Ching,
>> >
>> > oops, I see what you mean. Sorry, I got sloppy and in a hurry. I should
>> have the slots= flag in that file.
>> >
>> > Sincerely,
>> > Kel
>> >
>> > _______________________________________________________
>> > Kelly Black Phone: (315) 600-8334
>> > Clarkson University Fax: (315) 268-2371
>> > Department of Math. & C.S.
>> > PO Box 5815
>> > Potsdam, NY 13699-5815
>> > USA
>> >
>> >
>> > On Fri, Oct 11, 2013 at 1:54 PM, Kelly Black <kjblack_at_[hidden]> wrote:
>> > Hello,
>> >
>> > I thought that the "slots" flag was optional in the host file format
>> where the slots option gives the max no. of slots?
>> >
>> > -Kel
>> >
>> > _______________________________________________________
>> > Kelly Black Phone: (315) 600-8334
>> > Clarkson University Fax: (315) 268-2371
>> > Department of Math. & C.S.
>> > PO Box 5815
>> > Potsdam, NY 13699-5815
>> > USA
>> >
>> >
>> > On Fri, Oct 11, 2013 at 1:24 PM, Shao-Ching Huang <huangsc_at_[hidden]>
>> wrote:
>> > Kel:
>> >
>> > I believe the ompi hostfile format is:
>> >
>> > # myhosts.txt
>> > thingOne.clarkson.edu slots=4
>> > thingTwo.clarkson.edu slots=4
>> >
>> > Shao-Ching
>> >
>> >
>> > On Fri, Oct 11, 2013 at 10:21 AM, Ralph Castain <rhc_at_[hidden]>
>> wrote:
>> > I *think* that should work, but I haven't personally tested it.
>> >
>> > On Oct 11, 2013, at 9:27 AM, Kelly Black <kjblack_at_[hidden]> wrote:
>> >
>> >> Hello,
>> >>
>> >> I have a question about the --host and --hostfile flags used by
>> mpirun. Do you have to use fully qualified host names in the arguments to
>> the --host option if the fully qualified domain name is given in the host
>> file?
>> >>
>> >> For example, if I have a host file like this:
>> >>
>> >> # myhosts.txt
>> >> thingOne.clarkson.edu=4
>> >> thingTwo.clarkson.edu=4
>> >>
>> >> Can I then use the following command?
>> >>
>> >> mpirun --hostfile myhosts.txt --host thingOne -np 3 bubba
>> >>
>> >> Sincerely,
>> >> kel
>> >> _______________________________________________________
>> >> Kelly Black Phone: (315) 600-8334
>> >> Clarkson University Fax: (315) 268-2371
>> >> Department of Math. & C.S.
>> >> PO Box 5815
>> >> Potsdam, NY 13699-5815
>> >> USA
>> >> _______________________________________________
>> >> docs mailing list
>> >> docs_at_[hidden]
>> >> http://www.open-mpi.org/mailman/listinfo.cgi/docs
>> >
>> >
>> > _______________________________________________
>> > docs mailing list
>> > docs_at_[hidden]
>> > http://www.open-mpi.org/mailman/listinfo.cgi/docs
>> >
>> >
>> >
>> > _______________________________________________
>> > docs mailing list
>> > docs_at_[hidden]
>> > http://www.open-mpi.org/mailman/listinfo.cgi/docs
>>
>>
>> --
>> Jeff Squyres
>> jsquyres_at_[hidden]
>> For corporate legal information go to:
>> http://www.cisco.com/web/about/doing_business/legal/cri/
>>
>>
>
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