[Mpi-forum] Per communicator parameterisation

Torsten Hoefler htor at illinois.edu
Wed Dec 21 12:14:21 CST 2011

Dear Martyn,

Thanks for bringing this up, the Forum appreciates any user input and
comments. See my answers below.

> Firstly, apologies if this is the wrong place to post - I couldn't see
> a particularly relevant subgroup or forum for discussion, so if this
> is the wrong place, redirection is more than welcome....
The right place would probably be the collectives and topology working
group, but I think the general forum list is ok as long as the thread
does not grow too much.

> [snip]
> As it stands there is no practical way of setting this up - even with
> the generous support of my vendor. This is in stark contrast to MPI-IO
> where I have data structures available to pass either vendor specific
> or generic hints allowing me to modify behaviour on a per-file basis,
> in application, at runtime. I really want to be able to perform a
> similar thing when I create communicators, such that when I perform,
> say, a comm_split, I can create unique characteristics for each of the
> new communicators.
You are correct and this is indeed a missing functionality in MPI-2.2.
There is a proposal that allows to attach info objects during
communicator duplication (see item #2 "MPI_COMM_DUP_INFO" in
https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/271). This has been
discussed in the Forum but I don't know the status of this ticket. Adam,
can you comment?

> So I guess the first question is has any work been taking place in
> this area, and if not, how do I go about spurring the discussion?
Yes, Adam and I worked on this issue a while ago and Adam created the
referenced ticket. Would this functionality suffice for your use-case?

All the Best,

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Torsten Hoefler         | Performance Modeling and Simulation Lead
Blue Waters Directorate | University of Illinois (UIUC)
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