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Subject: Re: [OMPI devel] RFC: Add "virbr0" to [btl|oob]_tcp_if_exclude?
From: Paul H. Hargrove (PHHargrove_at_[hidden])
Date: 2012-02-10 15:32:40


On 2/10/2012 12:21 PM, Jeff Squyres wrote:
> On Feb 10, 2012, at 3:14 PM, Paul H. Hargrove wrote:
>
>> + User knows nothing about xen, and thus nothing about virbr0
>> + User has a local-only interface (eth8 in my made up example)
>> + User reads FAQ entry "220. How do I tell Open MPI which TCP networks to use?"
>> + User follows instructions given in said FAQ, yielding my example command line.
> Do you mean that eth8 is the only non-loopback interface on their laptop, and it's disconnected? (e.g., sitting on a train with no wifi and no wired ethernet)
>
> Then OMPI would have disqualified that interface, anyway (because it wasn't up).
>
> I think I'm missing the zen of your question... :-\
>

The point of the question isn't related to WHY eth8 is useless - just
assume it is.
Assume it is UP, but useless for whatever reasons motivated writing FAQ
#220.
It could be Terry's example of a port connected to the service processor.

The concern is what happens in this situation when the user, following
the advice in the FAQ, passes an explicit setting for
btl_tcp_if_exclude, which DOES NOT include virbr0?
They don't know it was there before, or that it needs to be there (the
FAQ states that lo MUST be included).
So, by following the FAQ they don't resolve their problem.
OMPI ceases any attempts use of eth8 (or whatever), but loss of the
implicit virbr0 from the exclude list results in their system attempting
to use virbr0 (and thus continue to fail). Right?

Maybe the FAQ just needs an update to address my concern.

-Paul

-- 
Paul H. Hargrove                          PHHargrove_at_[hidden]
Future Technologies Group
HPC Research Department                   Tel: +1-510-495-2352
Lawrence Berkeley National Laboratory     Fax: +1-510-486-6900