Cabana_Migrate_Mpi.hpp

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/****************************************************************************
 * Copyright (c) 2018-2023 by the Cabana authors                            *
 * All rights reserved.                                                     *
 *                                                                          *
 * This file is part of the Cabana library. Cabana is distributed under a   *
 * BSD 3-clause license. For the licensing terms see the LICENSE file in    *
 * the top-level directory.                                                 *
 *                                                                          *
 * SPDX-License-Identifier: BSD-3-Clause                                    *
 ****************************************************************************/

#ifndef CABANA_MIGRATE_MPI_HPP
#define CABANA_MIGRATE_MPI_HPP
 
#include <Cabana_AoSoA.hpp>
#include <Cabana_Slice.hpp>
 
#include <Kokkos_Core.hpp>
#include <Kokkos_Profiling_ScopedRegion.hpp>
 
#include <mpi.h>
 
#include <exception>
#include <vector>
 
//---------------------------------------------------------------------------//
namespace Cabana
{
 
namespace Impl
{
//---------------------------------------------------------------------------//
// Synchronously move data between a source and destination AoSoA by executing
// the forward communication plan.
template <class ExecutionSpace, class Distributor_t, class AoSoA_t>
void migrateData(
    Mpi, ExecutionSpace, const Distributor_t& distributor, const AoSoA_t& src,
    AoSoA_t& dst,
    typename std::enable_if<( ( is_distributor<Distributor_t>::value ) &&
                              is_aosoa<AoSoA_t>::value ),
                            int>::type* = 0 )
{
    Kokkos::Profiling::ScopedRegion region( "Cabana::migrate" );
 
    static_assert( is_accessible_from<typename Distributor_t::memory_space,
                                      ExecutionSpace>{},
                   "" );
 
    // Get the MPI rank we are currently on.
    int my_rank = -1;
    MPI_Comm_rank( distributor.comm(), &my_rank );
 
    // Get the number of neighbors.
    int num_n = distributor.numNeighbor();
 
    // Calculate the number of elements that are staying on this rank and
    // therefore can be directly copied. If any of the neighbor ranks are this
    // rank it will be stored in first position (i.e. the first neighbor in
    // the local list is always yourself if you are sending to yourself).
    std::size_t num_stay =
        ( num_n > 0 && distributor.neighborRank( 0 ) == my_rank )
            ? distributor.numExport( 0 )
            : 0;
 
    // Allocate a send buffer.
    std::size_t num_send = distributor.totalNumExport() - num_stay;
    Kokkos::View<typename AoSoA_t::tuple_type*,
                 typename Distributor_t::memory_space>
        send_buffer( Kokkos::ViewAllocateWithoutInitializing(
                         "distributor_send_buffer" ),
                     num_send );
 
    // Allocate a receive buffer.
    Kokkos::View<typename AoSoA_t::tuple_type*,
                 typename Distributor_t::memory_space>
        recv_buffer( Kokkos::ViewAllocateWithoutInitializing(
                         "distributor_recv_buffer" ),
                     distributor.totalNumImport() );
 
    // Get the steering vector for the sends.
    auto steering = distributor.getExportSteering();
 
    // Gather the exports from the source AoSoA into the tuple-contiguous send
    // buffer or the receive buffer if the data is staying. We know that the
    // steering vector is ordered such that the data staying on this rank
    // comes first.
    auto build_send_buffer_func = KOKKOS_LAMBDA( const std::size_t i )
    {
        auto tpl = src.getTuple( steering( i ) );
        if ( i < num_stay )
            recv_buffer( i ) = tpl;
        else
            send_buffer( i - num_stay ) = tpl;
    };
    Kokkos::RangePolicy<ExecutionSpace> build_send_buffer_policy(
        0, distributor.totalNumExport() );
    Kokkos::parallel_for( "Cabana::Impl::distributeData::build_send_buffer",
                          build_send_buffer_policy, build_send_buffer_func );
    Kokkos::fence();
 
    // The distributor has its own communication space so choose any tag.
    const int mpi_tag = 1234;
 
    // Post non-blocking receives.
    std::vector<MPI_Request> requests;
    requests.reserve( num_n );
    std::pair<std::size_t, std::size_t> recv_range = { 0, 0 };
    for ( int n = 0; n < num_n; ++n )
    {
        recv_range.second = recv_range.first + distributor.numImport( n );
 
        if ( ( distributor.numImport( n ) > 0 ) &&
             ( distributor.neighborRank( n ) != my_rank ) )
        {
            auto recv_subview = Kokkos::subview( recv_buffer, recv_range );
 
            requests.push_back( MPI_Request() );
 
            MPI_Irecv( recv_subview.data(),
                       recv_subview.size() *
                           sizeof( typename AoSoA_t::tuple_type ),
                       MPI_BYTE, distributor.neighborRank( n ), mpi_tag,
                       distributor.comm(), &( requests.back() ) );
        }
 
        recv_range.first = recv_range.second;
    }
 
    // Do blocking sends.
    std::pair<std::size_t, std::size_t> send_range = { 0, 0 };
    for ( int n = 0; n < num_n; ++n )
    {
        if ( ( distributor.numExport( n ) > 0 ) &&
             ( distributor.neighborRank( n ) != my_rank ) )
        {
            send_range.second = send_range.first + distributor.numExport( n );
 
            auto send_subview = Kokkos::subview( send_buffer, send_range );
 
            MPI_Send( send_subview.data(),
                      send_subview.size() *
                          sizeof( typename AoSoA_t::tuple_type ),
                      MPI_BYTE, distributor.neighborRank( n ), mpi_tag,
                      distributor.comm() );
 
            send_range.first = send_range.second;
        }
    }
 
    // Wait on non-blocking receives.
    std::vector<MPI_Status> status( requests.size() );
    const int ec =
        MPI_Waitall( requests.size(), requests.data(), status.data() );
    if ( MPI_SUCCESS != ec )
        throw std::logic_error(
            "Cabana::Distributor: Failed MPI Communication" );
 
    // Extract the receive buffer into the destination AoSoA.
    auto extract_recv_buffer_func = KOKKOS_LAMBDA( const std::size_t i )
    {
        dst.setTuple( i, recv_buffer( i ) );
    };
    Kokkos::RangePolicy<ExecutionSpace> extract_recv_buffer_policy(
        0, distributor.totalNumImport() );
    Kokkos::parallel_for( "Cabana::Impl::distributeData::extract_recv_buffer",
                          extract_recv_buffer_policy,
                          extract_recv_buffer_func );
    Kokkos::fence();
 
    // Barrier before completing to ensure synchronization.
    MPI_Barrier( distributor.comm() );
}
 
//---------------------------------------------------------------------------//
template <class ExecutionSpace, class Distributor_t, class Slice_t>
void migrateSlice(
    Mpi, ExecutionSpace, const Distributor_t& distributor, const Slice_t& src,
    Slice_t& dst,
    typename std::enable_if<( ( is_distributor<Distributor_t>::value ) &&
                              is_slice<Slice_t>::value ),
                            int>::type* = 0 )
{
    // Get the number of components in the slices.
    size_t num_comp = 1;
    for ( size_t d = 2; d < src.viewRank(); ++d )
        num_comp *= src.extent( d );
 
    // Get the raw slice data.
    auto src_data = src.data();
    auto dst_data = dst.data();
 
    // Get the MPI rank we are currently on.
    int my_rank = -1;
    MPI_Comm_rank( distributor.comm(), &my_rank );
 
    // Get the number of neighbors.
    int num_n = distributor.numNeighbor();
 
    // Calculate the number of elements that are staying on this rank and
    // therefore can be directly copied. If any of the neighbor ranks are this
    // rank it will be stored in first position (i.e. the first neighbor in
    // the local list is always yourself if you are sending to yourself).
    std::size_t num_stay =
        ( num_n > 0 && distributor.neighborRank( 0 ) == my_rank )
            ? distributor.numExport( 0 )
            : 0;
 
    // Allocate a send buffer. Note this one is layout right so the components
    // of each element are consecutive in memory.
    std::size_t num_send = distributor.totalNumExport() - num_stay;
    Kokkos::View<typename Slice_t::value_type**, Kokkos::LayoutRight,
                 typename Distributor_t::memory_space>
        send_buffer( Kokkos::ViewAllocateWithoutInitializing(
                         "distributor_send_buffer" ),
                     num_send, num_comp );
 
    // Allocate a receive buffer. Note this one is layout right so the
    // components of each element are consecutive in memory.
    Kokkos::View<typename Slice_t::value_type**, Kokkos::LayoutRight,
                 typename Distributor_t::memory_space>
        recv_buffer( Kokkos::ViewAllocateWithoutInitializing(
                         "distributor_recv_buffer" ),
                     distributor.totalNumImport(), num_comp );
 
    // Get the steering vector for the sends.
    auto steering = distributor.getExportSteering();
 
    // Gather from the source Slice into the contiguous send buffer or,
    // if it is part of the local copy, put it directly in the destination
    // Slice.
    auto build_send_buffer_func = KOKKOS_LAMBDA( const std::size_t i )
    {
        auto s_src = Slice_t::index_type::s( steering( i ) );
        auto a_src = Slice_t::index_type::a( steering( i ) );
        std::size_t src_offset = s_src * src.stride( 0 ) + a_src;
        if ( i < num_stay )
            for ( std::size_t n = 0; n < num_comp; ++n )
                recv_buffer( i, n ) =
                    src_data[src_offset + n * Slice_t::vector_length];
        else
            for ( std::size_t n = 0; n < num_comp; ++n )
                send_buffer( i - num_stay, n ) =
                    src_data[src_offset + n * Slice_t::vector_length];
    };
    Kokkos::RangePolicy<ExecutionSpace> build_send_buffer_policy(
        0, distributor.totalNumExport() );
    Kokkos::parallel_for( "Cabana::migrate::build_send_buffer",
                          build_send_buffer_policy, build_send_buffer_func );
    Kokkos::fence();
 
    // The distributor has its own communication space so choose any tag.
    const int mpi_tag = 1234;
 
    // Post non-blocking receives.
    std::vector<MPI_Request> requests;
    requests.reserve( num_n );
    std::pair<std::size_t, std::size_t> recv_range = { 0, 0 };
    for ( int n = 0; n < num_n; ++n )
    {
        recv_range.second = recv_range.first + distributor.numImport( n );
 
        if ( ( distributor.numImport( n ) > 0 ) &&
             ( distributor.neighborRank( n ) != my_rank ) )
        {
            auto recv_subview =
                Kokkos::subview( recv_buffer, recv_range, Kokkos::ALL );
 
            requests.push_back( MPI_Request() );
 
            MPI_Irecv( recv_subview.data(),
                       recv_subview.size() *
                           sizeof( typename Slice_t::value_type ),
                       MPI_BYTE, distributor.neighborRank( n ), mpi_tag,
                       distributor.comm(), &( requests.back() ) );
        }
 
        recv_range.first = recv_range.second;
    }
 
    // Do blocking sends.
    std::pair<std::size_t, std::size_t> send_range = { 0, 0 };
    for ( int n = 0; n < num_n; ++n )
    {
        if ( ( distributor.numExport( n ) > 0 ) &&
             ( distributor.neighborRank( n ) != my_rank ) )
        {
            send_range.second = send_range.first + distributor.numExport( n );
 
            auto send_subview =
                Kokkos::subview( send_buffer, send_range, Kokkos::ALL );
 
            MPI_Send( send_subview.data(),
                      send_subview.size() *
                          sizeof( typename Slice_t::value_type ),
                      MPI_BYTE, distributor.neighborRank( n ), mpi_tag,
                      distributor.comm() );
 
            send_range.first = send_range.second;
        }
    }
 
    // Wait on non-blocking receives.
    std::vector<MPI_Status> status( requests.size() );
    const int ec =
        MPI_Waitall( requests.size(), requests.data(), status.data() );
    if ( MPI_SUCCESS != ec )
        throw std::logic_error( "Cabana::migrate: Failed MPI Communication" );
 
    // Extract the data from the receive buffer into the destination Slice.
    auto extract_recv_buffer_func = KOKKOS_LAMBDA( const std::size_t i )
    {
        auto s = Slice_t::index_type::s( i );
        auto a = Slice_t::index_type::a( i );
        std::size_t dst_offset = s * dst.stride( 0 ) + a;
        for ( std::size_t n = 0; n < num_comp; ++n )
            dst_data[dst_offset + n * Slice_t::vector_length] =
                recv_buffer( i, n );
    };
    Kokkos::RangePolicy<ExecutionSpace> extract_recv_buffer_policy(
        0, distributor.totalNumImport() );
    Kokkos::parallel_for( "Cabana::migrate::extract_recv_buffer",
                          extract_recv_buffer_policy,
                          extract_recv_buffer_func );
    Kokkos::fence();
 
    // Barrier before completing to ensure synchronization.
    MPI_Barrier( distributor.comm() );
}
 
//---------------------------------------------------------------------------//
} // end namespace Impl
 
} // end namespace Cabana
 
#endif // CABANA_MIGRATE_MPI_HPP