Newsgroups: comp.parallel.mpi
From: Erik Brakkee <erik.brakkee@gmd.de>
Subject: Efficiency of communication using inter-communicators.
Organization: GMD/SCAI
Date: Tue, 19 Nov 1996 16:21:28 +0100
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Message-ID: <3291D078.687C@gmd.de>

Hello MPI'ers,


We have a question which concerns the efficiency of communication 
operations on inter-communicators. 

The book 'MPI: the complete reference' mentions that for
the construction of MPI inter-communicators, so-called 
bridges have to be formed between the group leaders of different
groups. Of course, these bridges can be used to reduce communication
overhead in the construction of inter-communicators. 

Our question is now: are these group leaders also used by an MPI
implementation later in other MPI subroutines? In particular, 
is communication between processes of the local and remote
groups always direct, or does some communication always go 
through the group leader. Do we get a large load imbalance when
we take very large local and remote groups? Does the MPI standard
say anything useful about this?


Sincerely,
  Erik Brakkee, Dac Phuoc Ho, Klaus Wolf
  erik.brakkee@gmd.de,  dac.phuoc.ho@gmd.de, klaus.wolf@gmd.de

