Hi Axida, There are two ways you can call MPI_collectives. 1) Automatic decision by OpenMPI which in turn call tuned collectives 2) Forced decision, where you can override OpenMPI to call certain algorithms available for collective say MPI_Bcast.
The 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 openmpi-1.3.2). By 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. In that case, i would suggest you to run benchmark programs with 2. option and fine tune the MPI Collectives suited for your cluster architecture. Regards Neeraj Chourasia Member of Technical Staff Computational Research Laboratories Limited (A wholly Owned Subsidiary of TATA SONS Ltd) P: +91.9225520634 shan axida <axida2...@yahoo.com> Sent by: users-boun...@open-mpi.org 04/28/2009 03:25 PM Please respond to Open MPI Users <us...@open-mpi.org> To us...@open-mpi.org cc Subject [OMPI users] OpenMPI MPI_Bcast Algorithms Hi all, 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? Thank you! _______________________________________________ users mailing list us...@open-mpi.org http://www.open-mpi.org/mailman/listinfo.cgi/users =====-----=====-----===== Notice: The information contained in this e-mail message and/or attachments to it may contain confidential or privileged information. If you are not the intended recipient, any dissemination, use, review, distribution, printing or copying of the information contained in this e-mail message and/or attachments to it are strictly prohibited. If you have received this communication in error, please notify us by reply e-mail or telephone and immediately and permanently delete the message and any attachments. Internet communications cannot be guaranteed to be timely, secure, error or virus-free. The sender does not accept liability for any errors or omissions.Thank you =====-----=====-----=====