1) is correct. coll/sm is disqualified if the communicator is an inter
communicator or the communicator spans on several nodes.
you can have a look at the source code, and you will not that bcast does
not use send/recv. instead, it uses a shared memory, so hopefully, it is
faster than other modules
Cheers,
Gilles
On 6/30/2016 3:04 PM, Saliya Ekanayake wrote:
Hi,
Looking at the *ompi/mca/coll/sm/coll_sm_module.c* it seems this
module will be used only if the calling communicator solely groups
processes within a node. I've got two questions here.
1. So is my understanding correct that for something like
MPI_COMM_WORLD where world is multiple processes within a node across
many nodes, this module will not be used?
2. If 1, is correct then are there any shared memory optimizations
that happen when a collective like bcast or allreduce is called, so
that communicating within a node is done efficiently through memory?
Thank you,
Saliya
--
Saliya Ekanayake
Ph.D. Candidate | Research Assistant
School of Informatics and Computing | Digital Science Center
Indiana University, Bloomington
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