[Mpi-forum] Question about MPI_Info set on communicators
skjellum at auburn.edu
Mon Feb 15 16:51:50 CST 2016
Jeff, if the value can change over time, is it thread safe?
Anthony Skjellum, PhD
Professor of Computer Science and Software Engineering
COLSA Professor of Cybersecurity and Information Assurance
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Samuel Ginn College of Engineering
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From: mpi-forum <mpi-forum-bounces at lists.mpi-forum.org> on behalf of Jeff Squyres (jsquyres) <jsquyres at cisco.com>
Sent: Monday, February 15, 2016 4:34 PM
To: MPI list
Subject: [Mpi-forum] Question about MPI_Info set on communicators
This question has come up in the Open MPI community:
MPI_Info_set(myinfo, "use_shared_memory", "yes");
// Assume here that there was not enough shared memory available to use shared-memory for
// communication on this comm, so MPI_Info_get() tells us that use_shared_memory is "no".
// ...time passes, and now assume there is more shared-memory available
Should newcom have "use_shared_memory" set to "yes" or "no"?
Arguments for "yes":
- the user originally asked for "yes"
- now there is shared memory available
Arguments for "no":
- the current value for "used_shared_memory" on the parent communicator is "no"
Which should it be?
MPI-3.1 6.4.2 p238 says:
"...Returns in newcomer a new communicator with the same group or groups, same topology, same info hints, any copied cached information, but a new context (see Section 6.7.1)."
So the specific question here is: what exactly does "Same info hints" mean? The user-specific hint, or the current value of the hint?
jsquyres at cisco.com
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