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::cout;
using std::cerr;
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);
}