are two ways you can call MPI_collectives.
Automatic decision by OpenMPI which in turn call tuned collectives
Forced decision, where you can override OpenMPI to call certain algorithms
available for collective say MPI_Bcast.
logic for 1. can be found in function ompi_coll_tuned_bcast_intra_dec_fixed
at (file :ompi/mca/coll/tuned/coll_tuned_decision_fixed.c , line 221, version
default, openmpi switches algo based on message size, communicator size
which they have put based on some heuristics which may differ from one
network topology to another.
that case, i would suggest you to run benchmark programs with 2. option
and fine tune the MPI Collectives suited for your cluster architecture.
Member of Technical Staff
Computational Research Laboratories Limited
(A wholly Owned Subsidiary of TATA SONS Ltd)
|shan axida <email@example.com>
Sent by: firstname.lastname@example.org
04/28/2009 03:25 PM
Please respond to
Open MPI Users <email@example.com>
|[OMPI users] OpenMPI MPI_Bcast Algorithms|
I think there are several algorithms
used in MPI_Bcast.
I am wondering how are they decided
to be excuted ?
I mean, How to decide which algorithm
will be used?
Is it depending on the message
size or something ?
Would some people help me?
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