ping_pong.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <mpi.h>
 
 
#define NLOOPS          1000
#define ALIGN           4096
 
main(argc, argv)
int                     argc;
char                    *argv[];
 
{
int             i, j;
	        double          start, stop;
        int             nbytes = 0;
        int             rank, size;
        MPI_Status      status;
        char            *buf;
 
        	MPI_Init(&argc, &argv);
        MPI_Comm_rank(MPI_COMM_WORLD, &rank);
        MPI_Comm_size(MPI_COMM_WORLD, &size);
 
        if (size != 2) {
 
                   if ( ! rank) printf("ping_pong: must have two processes\n");
                   MPI_Finalize();
                   exit(0);
								        }
         
        nbytes = (argc > 1) ? atoi(argv[1]) : 0;
        if (nbytes < 0) nbytes = 0;
 
 
/*
* Page-align buffers and displace them in the cache to avoid collisions.
*/
 
        buf = (char *) malloc(nbytes + 524288 + (ALIGN - 1));
        if (buf == 0) {
                   MPI_Abort(MPI_COMM_WORLD, MPI_ERR_BUFFER);
                   exit(1);
        }
 
        buf = (char *) ((((unsigned long) buf) + (ALIGN - 1)) & ~(ALIGN - 1));
        if (rank == 1) buf += 524288;
        memset(buf, 0, nbytes);
 
/*
* Ping-pong.
*/
 
        if (rank == 0) {
                   printf("ping-pong %d bytes ...\n", nbytes);
/*
* warm-up loop
*/
 
	                   for (i = 0; i < 5; i++) {
                        MPI_Send(buf, nbytes, MPI_CHAR, 1, 1, MPI_COMM_WORLD);
                        MPI_Recv(buf, nbytes, MPI_CHAR,1, 1, 
                                               MPI_COMM_WORLD, &status);
													                   }
/*
* timing loop
*/
 
								        start = MPI_Wtime();
        for (i = 0; i < NLOOPS; i++) {
#ifdef CHECK
                   for (j = 0; j < nbytes; j++) buf[j] = (char) (j + i);
#endif
                   MPI_Send(buf, nbytes, MPI_CHAR,1, 1000 + i, MPI_COMM_WORLD);
#ifdef CHECK
                   memset(buf, 0, nbytes);
#endif
                   MPI_Recv(buf, nbytes, MPI_CHAR,1, 2000 + i, 
                                           MPI_COMM_WORLD,&status);
 
 
 
 
 
 
 
 
 
#ifdef CHECK
 
                  for (j = 0; j < nbytes; j++) {
                       if (buf[j] != (char) (j + i)) {
                              printf("error: buf[%d] = %d, not %d\n",j,
                                    buf[j], j + i);
                              break;
                       }
                   }
#endif
        }
         stop = MPI_Wtime();
 
          printf("%d bytes: %.2f usec/msg\n",
                      nbytes, (stop - start) / NLOOPS / 2 * 1000000);
 
           if (nbytes > 0) {
                   printf("%d bytes: %.2f MB/sec\n", nbytes,nbytes / 1000000./
                                       ((stop - start) / NLOOPS / 2));
           }
         }
         else {
/*
* warm-up loop
*/
         for (i = 0; i < 5; i++) {
                   MPI_Recv(buf, nbytes, MPI_CHAR,0, 1, MPI_COMM_WORLD, &status);
                   MPI_Send(buf, nbytes, MPI_CHAR, 0, 1, MPI_COMM_WORLD);
          }
 
          for (i = 0; i < NLOOPS; i++) {
                   MPI_Recv(buf, nbytes, MPI_CHAR,0, 1000 + i,
                                                  MPI_COMM_WORLD,&status);
                   MPI_Send(buf, nbytes, MPI_CHAR,0, 2000 + i, MPI_COMM_WORLD);
           }
       }
       MPI_Finalize();
       exit(0);
}