/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */

/*

 *  (C) 2008 by Argonne National Laboratory.

 *      See COPYRIGHT in top-level directory.

 */

#include "mpi.h"

#include <stdio.h>

#include <stdlib.h>

#include <sys/time.h>

#define SIZE 100000

#define ITER 1000

#define ERROR_MARGIN 0.5

static int verbose = 0;

int main(int argc, char *argv[])

{

    char *sbuf, *rbuf;

    int i, j;

    double t1, t2, t, ts;

    int rank, size;

    MPI_Status status;

    MPI_Init(&argc, &argv);

    MPI_Comm_rank(MPI_COMM_WORLD, &rank;;

    MPI_Comm_size(MPI_COMM_WORLD, &size);

    if (getenv("MPITEST_VERBOSE"))

        verbose = 1;

    /* Allocate memory regions to communicate */

    sbuf = (char *) malloc(SIZE);

    rbuf = (char *) malloc(size * SIZE);

    /* Touch the buffers to make sure they are allocated */

    for (i = 0; i < SIZE; i++)

        sbuf[i] = '0';

    for (i = 0; i < SIZE * size; i++)

        rbuf[i] = '0';

    /* Time when rank 0 gathers the data */

    MPI_Barrier(MPI_COMM_WORLD);

    t1 = MPI_Wtime();

    for (i = 0; i < ITER; i++) {

        MPI_Gather(sbuf, SIZE, MPI_BYTE, rbuf, SIZE, MPI_BYTE, 0, MPI_COMM_WORLD);

        MPI_Barrier(MPI_COMM_WORLD);

    }

    t2 = MPI_Wtime();

    t = (t2 - t1) / ITER;

    /* Time when rank 1 gathers the data */

    MPI_Barrier(MPI_COMM_WORLD);

    t1 = MPI_Wtime();

    for (j = 0; j < ITER; j++) {

        MPI_Gather(sbuf, SIZE, MPI_BYTE, rbuf, SIZE, MPI_BYTE, 1, MPI_COMM_WORLD);

        MPI_Barrier(MPI_COMM_WORLD);

    }

    t2 = MPI_Wtime();

    ts = (t2 - t1) / ITER;

    if (rank == 1)

        MPI_Send(&ts, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);

    if (rank == 0)

        MPI_Recv(&ts, 1, MPI_DOUBLE, 1, 0, MPI_COMM_WORLD, &status);

    /* Print out the results */

    if (!rank) {

        if ((ts / t) > (1 + ERROR_MARGIN)) {    /* If the difference is more than 10%, it's an error */

            printf("%.3f\t%.3f\n", 1000000.0 * ts, 1000000.0 * t);

            printf("Too much difference in performance\n");

        }

        else

            printf(" No Errors\n");

    }

    MPI_Finalize();

    return 0;

}