There is an ongoing discussion about this on issue #4067 ( Also the mailing list
contains few examples on how to tweak the collective algorithms to your


On Thu, Jun 6, 2019 at 7:42 PM hash join via users <>

> Hi all,
> I want to use the MPI_Allreduce to synchronize results from all the
> processes:
> But I want to know the background algorithm to implement Allreduce. When I
> check the coll base of MPI_Allreduce:
> There are implementations like:
> ompi_coll_base_allreduce_intra_nonoverlapping,
> ompi_coll_base_allreduce_intra_recursivedoubling,
> ompi_coll_base_allreduce_intra_ring..etc. So how can I know which exact
> implement I am using when I use MPI_Allreduce. Or can I configure these?
> For example, I only want to use ring allreduce. How should I configure it?
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