Gilles, Thanx for the valuable information. So this solves part of the puzzle. The next thing is know the cost of these algorithms. Some of them seem to be standard, however, I am afraid there could be some modifications that will ultimately alter the cost. Hence I asked for a paper. I will look around..again Thanx
--------------- Daniel Faraj From: users [mailto:users-boun...@open-mpi.org] On Behalf Of Gilles Gouaillardet Sent: Monday, November 17, 2014 10:07 PM To: Open MPI Users Subject: Re: [OMPI users] collective algorithms Daniel, you can run $ ompi_info --parseable --all | grep _algorithm: | grep enumerator that will give you the list of supported algo for the collectives, here is a sample output : mca:coll:tuned:param:coll_tuned_allreduce_algorithm:enumerator:value:0:ignore mca:coll:tuned:param:coll_tuned_allreduce_algorithm:enumerator:value:1:basic_linear mca:coll:tuned:param:coll_tuned_allreduce_algorithm:enumerator:value:2:nonoverlapping mca:coll:tuned:param:coll_tuned_allreduce_algorithm:enumerator:value:3:recursive_doubling mca:coll:tuned:param:coll_tuned_allreduce_algorithm:enumerator:value:4:ring mca:coll:tuned:param:coll_tuned_allreduce_algorithm:enumerator:value:5:segmented_ring the decision (which algo is used based on communicator size/message size/...) is made in ompi/mca/coll/tuned/coll_tuned_decision_fixed.c and can be overriden via config file or environment variable i cannot point you to a paper, and hopefully someone else will Cheers, Gilles On 2014/11/18 12:53, Faraj, Daniel A wrote: I am trying to survey the collective algorithms in Open MPI. I looked at the src code but could not make out the guts of the communication algorithms. There are some open mpi papers but not detailed, where they talk about what algorithms are using in certain collectives. Has anybody done this sort of work, or point me to a paper? Basically, for a given collective operation, what are: a) Communication algorithm being used for a given criteria (i.e. message size or np) b) What is theoretical algorithm cost Thanx --------------- Daniel Faraj _______________________________________________ users mailing list us...@open-mpi.org<mailto:us...@open-mpi.org> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users Link to this post: http://www.open-mpi.org/community/lists/users/2014/11/25831.php
