/*                                                                      */
/* CS 4331: Parallel Programming                        Fall, 2009      */
/*                                                                      */
/* This MPI program computes does a "ping-pong" message passing     */
/* performance measurement.                     */
/*                                                                      */
#include <stdio.h>
#include "mpi.h"

#define  MAX_LEN 1 << 18    /* maximum vector length    */
#define  TRIALS  100        /* trials for each msg length   */
#define  PROC_0  0      /* processor 0          */
#define  B0_TYPE 176        /* message "types"      */
#define  B1_TYPE 177

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

{
    int numprocs, p,        /* number of processors, proc index */
    myid,           /* this processor's "rank"      */
    length,         /* vector length            */
    i, t;

    double b0[MAX_LEN], b1[MAX_LEN];    /* vectors          */

    double start_time, end_time;    /* "wallclock" times        */

    MPI_Status stat;        /* MPI structure containing return  */
                /* codes for message passing operations */

    MPI_Request send_handle, recv_handle;   /* For nonblocking msgs */

    MPI_Init(&argc,&argv);          /* initialize MPI   */

    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);   /*how many processors?  */
    MPI_Comm_rank(MPI_COMM_WORLD, &myid);   /*which one am I?   */

    if (myid == PROC_0)
    {
    srand48(0xFEEDFACE);

    /* generate processor 0's vector */

    for (i=0; i<MAX_LEN; ++i)
        b0[i] = (double) drand48();
    }

    MPI_Barrier(MPI_COMM_WORLD);

    /* warmup, if necessary */
/*
    printf("# Start warmup.\n");

    for (length=1; length<=MAX_LEN; length*=2)
    if (myid == PROC_0)
    {
        MPI_Send(b0, length, MPI_DOUBLE, 1, B1_TYPE, MPI_COMM_WORLD);
        MPI_Recv(b1, length, MPI_DOUBLE, 1, B0_TYPE, MPI_COMM_WORLD, &stat);
    }
    else
    {
        MPI_Recv(b1, length, MPI_DOUBLE, 0, B1_TYPE, MPI_COMM_WORLD, &stat);
        MPI_Send(b0, length, MPI_DOUBLE, 0, B0_TYPE, MPI_COMM_WORLD);
    }
*/
    if (myid == PROC_0)
#ifdef BLOCKING
    printf("\nPing-pong measurements for blocking send/recv pairs.\n");
#else
    printf("\nPing-pong measurements for nonblocking send/recv pairs.\n");
#endif
    /* measure message passing speed for vectors of various lengths */

    for (length=1; length<=MAX_LEN; length*=2)
    {
        MPI_Barrier(MPI_COMM_WORLD);

        if (myid == PROC_0)
            start_time = MPI_Wtime();

        for (t=0; t<TRIALS; ++t)
        {
    #ifdef BLOCKING
            if (myid == PROC_0)
            {
                MPI_Send(b0, length, MPI_DOUBLE, 1, B1_TYPE, MPI_COMM_WORLD);
                MPI_Recv(b1, length, MPI_DOUBLE, 1, B0_TYPE, MPI_COMM_WORLD, &stat);
            }
            else
            {
                MPI_Recv(b1, length, MPI_DOUBLE, 0, B1_TYPE, MPI_COMM_WORLD, &stat);
                MPI_Send(b0, length, MPI_DOUBLE, 0, B0_TYPE, MPI_COMM_WORLD);
            }
    #else
            MPI_Isend(b0, length, MPI_DOUBLE, (myid+1)%numprocs, B0_TYPE, MPI_COMM_WORLD, &send_handle);
            MPI_Irecv(b1, length, MPI_DOUBLE, (myid+1)%numprocs, B0_TYPE, MPI_COMM_WORLD, &recv_handle);

            MPI_Wait(&send_handle, &stat);
            MPI_Wait(&recv_handle, &stat);
    #endif
        }
        if (myid == PROC_0)
            {
            end_time = MPI_Wtime();

            /* gnuplot ignores output lines that begin with #. */
            printf("# Length = %d\tAverage time=%lf\n",
            length, (end_time - start_time)/(double)(2*TRIALS));
            printf(" %d\t %lf\n",
            length, (end_time - start_time)/(double)(2*TRIALS));
            }
    }

    MPI_Finalize();
}