thomas, today you should start thinking about other possibilities to solve your problem. this mpi rma stuff is crappy. 2014/1/21 Thomas Jahns <[email protected]>

Hello,

should this be the wrong mailing list[1], I apologize in advance and hope for directions to the correct place to pose my question.

From the wording of the MPI 2.2 and 3.0 standards I can see (first paragraph of 11.2.1 in MPI 2.2, procedurce specification of MPI_WIN_CREATE in MPI 3.0) that MPI_WIN_CREATE is only allowed for intracommunicators.

I was wondering why this restriction is there, when

1. cases where an intercommunicator is more clear for point-to-point communications, communications using rma would equally gain in clarity with an intercommunicator (from my POV at least),

2. the required resources (because the number of potential communication paths would be much lower) could be reduced because the intercommunicator not only specifies two groups communicating with each other but also not communicating (at least via the intercommunicator) within each group. I.e. when it is already known that the any two processes within one of the two groups of an intercommunicator would not issue RMA calls for the other, corresponding resources need not be reserved. Intra-communicator RMA on the other hand leaves the possibility of any communication pair open.

Clearly with two groups of processes of sizes N and M the number of potential pairs is N * M where a corresponding intercommunicator is concerned but (N * M)**2 for an intracommunicator and

3. the semantics appropriate for an intercommunicator should be easy to emulate with MPI_INTERCOMM_MERGE and MPI_GROUP_TRANSLATE_RANKS.

Since allowing intercommunicators in MPI_WIN_CREATE would consequently

1. be aesthetically pleasing, 2. offer increased potential for efficient execution, 3. seem to have an easy proof-of-concept implementation strategy and 4. forms a pattern arising naturally from the rest of the standard in my eyes,

I'm clearly missing some ambiguity or technical/definition difficulty here, but can't figure out which, why else would the standard explicitly restrict MPI_WIN_CREATE to intracommunicators if the above were the whole story?

Kind regards, Thomas Jahns

[1] I've done some searching and came up with either <[email protected]> or <[email protected]> -- Thomas Jahns DKRZ GmbH, Department: Application software

Deutsches Klimarechenzentrum Bundesstraße 45a D-20146 Hamburg

Phone: +49-40-460094-151 Fax: +49-40-460094-270 Email: Thomas Jahns <[email protected]>

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