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Hi Junchao Zhang,
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<div class="">My understanding of the current API for MPI-3.1 is that:</div>
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<div class="">1) the virtual topology does not actually restrict communication via the communicator to the edges specified in the topology - messages can be sent along any edge in either direction, and even between pairs of processes for which no edge was specified.</div>
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<div class="">2) the virtual topology can be specified as a symmetric graph - for every ‘forward’ edge (e.g. from A to B), the ‘backward’ edge (i.e. from B to A) can be included as well.</div>
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<div class="">3) there is already language in the MPI Standard regarding how MPI handles symmetric and non-symmetric graph topologies for neighbourhood collective operations.</div>
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<div class="">Thus, there is no need to create two distributed graph topology communicators to achieve ‘forward and backward communication along the edges’.<br class="">
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Cheers,</div>
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Dan.</div>
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—<br class="">
Dr Daniel Holmes PhD<br class="">
Applications Consultant in HPC Research<br class="">
<a href="mailto:d.holmes@epcc.ed.ac.uk" class="">d.holmes@epcc.ed.ac.uk</a><br class="">
Phone: +44 (0) 131 651 3465<br class="">
Mobile: +44 (0) 7940 524 088<br class="">
Address: Room 3415, JCMB, The King’s Buildings, Edinburgh, EH9 3FD</div>
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—</div>
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The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.</div>
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—</div>
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<div class="">On 15 Jul 2018, at 10:42, Anthony Skjellum <<a href="mailto:tony@runtimecomputing.com" class="">tony@runtimecomputing.com</a>> wrote:</div>
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<div dir="ltr" class="">Hi, I just saw this.
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<div class="">We definitely need to consider this concern. </div>
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<div class="">I also need to go review the APIs.</div>
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<div class="">Thanks,</div>
<div class="">Tony</div>
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<div class="gmail_quote">On Sat, Jul 14, 2018 at 12:27 AM, Junchao Zhang <span dir="ltr" class="">
<<a href="mailto:jczhang@mcs.anl.gov" target="_blank" class="">jczhang@mcs.anl.gov</a>></span> wrote:<br class="">
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<div class=""> I want to try MPI neighborhood collectives. I have a communication graph and want to do both forward and backward communication along the edges. With current APIs, it looks I need to create two comm_dist_graphs. It is a waste since MPI implementations
can do similar optimizations for the two.</div>
<div class=""> Should MPI support this scenario? Thanks.</div>
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<div dir="ltr" class="">--Junchao Zhang</div>
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-- <br class="">
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<div class="">Tony Skjellum, PhD<br class="">
RunTime Computing Solutions, LLC<br class="">
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direct: +1-205-918-7514<br class="">
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