From: Wolfgang Bangerth Date: Wed, 29 Dec 2021 02:06:18 +0000 (-0700) Subject: Treat compute_n_point_to_point_communications() the same way. X-Git-Tag: v9.4.0-rc1~660^2 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F13147%2Fhead;p=dealii.git Treat compute_n_point_to_point_communications() the same way. --- diff --git a/source/base/mpi.cc b/source/base/mpi.cc index 63355aa8f5..697fc29b28 100644 --- a/source/base/mpi.cc +++ b/source/base/mpi.cc @@ -544,22 +544,34 @@ namespace Utilities const MPI_Comm & mpi_comm, const std::vector &destinations) { - // check if destinations contain duplicates - auto destinations_unique = destinations; - std::sort(destinations_unique.begin(), destinations_unique.end()); - destinations_unique.erase(std::unique(destinations_unique.begin(), - destinations_unique.end()), - destinations_unique.end()); - - if (Utilities::MPI::min(destinations.size() == - destinations_unique.size(), - mpi_comm)) + // Have a little function that checks if destinations provided + // to the current process are unique: + const bool my_destinations_are_unique = [destinations]() { + std::vector my_destinations = destinations; + const unsigned int n_destinations = my_destinations.size(); + std::sort(my_destinations.begin(), my_destinations.end()); + my_destinations.erase(std::unique(my_destinations.begin(), + my_destinations.end()), + my_destinations.end()); + return (my_destinations.size() == n_destinations); + }(); + + // If all processes report that they have unique destinations, + // then we can short-cut the process using a consensus algorithm (which + // is implemented only for the case of unique destinations, and also only + // for MPI 3 and later): +# if DEAL_II_MPI_VERSION_GTE(3, 0) + if (Utilities::MPI::min((my_destinations_are_unique ? 1 : 0), mpi_comm) == + 1) { - return compute_point_to_point_communication_pattern(mpi_comm, - destinations) - .size(); + ConsensusAlgorithms::AnonymousProcess process( + [&]() { return destinations; }); + ConsensusAlgorithms::NBX consensus_algorithm(process, + mpi_comm); + return consensus_algorithm.run().size(); } else +# endif { const unsigned int n_procs = Utilities::MPI::n_mpi_processes(mpi_comm); @@ -594,31 +606,31 @@ namespace Utilities return n_recv_from; # else - // Find out how many processes will send to this one - // by reducing with sum and then scattering the - // results over all processes - std::vector buffer(dest_vector.size()); - unsigned int n_recv_from = 0; - - int ierr = MPI_Reduce(dest_vector.data(), - buffer.data(), - dest_vector.size(), - MPI_UNSIGNED, - MPI_SUM, - 0, - mpi_comm); - AssertThrowMPI(ierr); - ierr = MPI_Scatter(buffer.data(), - 1, - MPI_UNSIGNED, - &n_recv_from, - 1, - MPI_UNSIGNED, - 0, - mpi_comm); - AssertThrowMPI(ierr); + // Find out how many processes will send to this one + // by reducing with sum and then scattering the + // results over all processes + std::vector buffer(dest_vector.size()); + unsigned int n_recv_from = 0; + + int ierr = MPI_Reduce(dest_vector.data(), + buffer.data(), + dest_vector.size(), + MPI_UNSIGNED, + MPI_SUM, + 0, + mpi_comm); + AssertThrowMPI(ierr); + ierr = MPI_Scatter(buffer.data(), + 1, + MPI_UNSIGNED, + &n_recv_from, + 1, + MPI_UNSIGNED, + 0, + mpi_comm); + AssertThrowMPI(ierr); - return n_recv_from; + return n_recv_from; # endif } }