cuda-samples/Samples/0_Introduction/simpleMPI/simpleMPI.cpp

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/* Simple example demonstrating how to use MPI with CUDA
 *
 *  Generate some random numbers on one node.
 *  Dispatch them to all nodes.
 *  Compute their square root on each node's GPU.
 *  Compute the average of the results using MPI.
 *
 *  simpleMPI.cpp: main program, compiled with mpicxx on linux/Mac platforms
 *                 on Windows, please download the Microsoft HPC Pack SDK 2008
 */

// MPI include
#include <mpi.h>

// System includes
#include <iostream>

using std::cerr;
using std::cout;
using std::endl;

// User include
#include "simpleMPI.h"

// Error handling macros
#define MPI_CHECK(call)                              \
    if ((call) != MPI_SUCCESS) {                     \
        cerr << "MPI error calling \"" #call "\"\n"; \
        my_abort(-1);                                \
    }

// Host code
// No CUDA here, only MPI
int main(int argc, char *argv[])
{
    // Dimensions of the dataset
    int blockSize       = 256;
    int gridSize        = 10000;
    int dataSizePerNode = gridSize * blockSize;

    // Initialize MPI state
    MPI_CHECK(MPI_Init(&argc, &argv));

    // Get our MPI node number and node count
    int commSize, commRank;
    MPI_CHECK(MPI_Comm_size(MPI_COMM_WORLD, &commSize));
    MPI_CHECK(MPI_Comm_rank(MPI_COMM_WORLD, &commRank));

    // Generate some random numbers on the root node (node 0)
    int    dataSizeTotal = dataSizePerNode * commSize;
    float *dataRoot      = NULL;

    // Are we the root node?
    if (commRank == 0) {
        cout << "Running on " << commSize << " nodes" << endl;
        dataRoot = new float[dataSizeTotal];
        initData(dataRoot, dataSizeTotal);
    }

    // Allocate a buffer on each node
    float *dataNode = new float[dataSizePerNode];

    // Dispatch a portion of the input data to each node
    MPI_CHECK(
        MPI_Scatter(dataRoot, dataSizePerNode, MPI_FLOAT, dataNode, dataSizePerNode, MPI_FLOAT, 0, MPI_COMM_WORLD));

    if (commRank == 0) {
        // No need for root data any more
        delete[] dataRoot;
    }

    // On each node, run computation on GPU
    computeGPU(dataNode, blockSize, gridSize);

    // Reduction to the root node, computing the sum of output elements
    float sumNode = sum(dataNode, dataSizePerNode);
    float sumRoot;

    MPI_CHECK(MPI_Reduce(&sumNode, &sumRoot, 1, MPI_FLOAT, MPI_SUM, 0, MPI_COMM_WORLD));

    if (commRank == 0) {
        float average = sumRoot / dataSizeTotal;
        cout << "Average of square roots is: " << average << endl;
    }

    // Cleanup
    delete[] dataNode;
    MPI_CHECK(MPI_Finalize());

    if (commRank == 0) {
        cout << "PASSED\n";
    }

    return 0;
}

// Shut down MPI cleanly if something goes wrong
void my_abort(int err)
{
    cout << "Test FAILED\n";
    MPI_Abort(MPI_COMM_WORLD, err);
}