/******************************************************************************
* FILE: eager_vs_rend.c
* DESCRIPTION:
*   Demonstrates use of eager vs rendevous protocols for IBM's MPI.   
*   To time messages sent with eager protocol:
*     setenv MP_EAGER_LIMIT 64000
*   To time messages sent with rendezvous protocol:
*     setenv MP_EAGER_LIMIT 1
* LAST REVISED: 2/15/99 Blaise Barney
******************************************************************************/

#include "mpi.h"
#include <stdio.h>


#define EAGERLIMIT 64000        /* Max eager limit under POE */
/* #define NLOOPS 100000  */
#define NLOOPS 100

#define STEP 1000

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

int        numtasks, rank, dest=1, i, tag=111, source=0, size;
double     start, end;
char       data[EAGERLIMIT];
MPI_Status status;

MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);

if (numtasks != 2) {
  printf("Please run this test with 2 tasks. Terminating\n");
  MPI_Finalize();
  }
printf ("MPI task %d started...\n", rank);


/* Send task */
if (rank == 0) {

  /* Initialize */
  for(i=0; i<EAGERLIMIT; i++)
     data[i] =  'x';
  size = 0;

  while (size <= EAGERLIMIT) {
    start = MPI_Wtime();
    for (i=0; i<NLOOPS; i++) {
      MPI_Send(data, size, MPI_BYTE, dest, tag, MPI_COMM_WORLD);
      }
    end = MPI_Wtime();
    printf("message size= %d  avg. time= %f\n", size, (end-start)/NLOOPS);
    size = size + STEP;
    }
  }


/* Receive task */
if (rank == 1) {
  size = 0;
  while (size <= EAGERLIMIT) {
    for (i=0; i<NLOOPS; i++) {
      MPI_Recv(data, size, MPI_BYTE, source, tag, MPI_COMM_WORLD, &status);
      }
    size = size + STEP;
    }
  }

MPI_Finalize();
}