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Open MPI has a very fancy collective implementation. While we don't
use multicast, we dynamically change the algorithm used for the
collective based on the number of nodes, the size and type of the
message, and eventually the operation involved if any. Moreover, we
detect hierarchies, and we can potentially change the algorithms to
take advantage of this knowledge.
If you want more information, please refer to this paper (Flexible
collective communication tuning architecture applied to Open MPI) for
more information, http://www.netlib.org/netlib/utk/people/JackDongarra/PAPERS/Flex-collective-euro-pvmmpi-2006.pdf
On Dec 9, 2008, at 21:49 , Brock Palen wrote:
> Is OpenMPI using Multicast for things like MPI_Bcast() ?
> Some simple tests of really old versions (1.0.2) showed binary tree
> type performance, while latter versions gave me the same run time no
> matter how many CPU's I used.
> Thus this lead me to believe that something like multicast is in
> use. Is it?
> Brock Palen
> Center for Advanced Computing
> users mailing list