latbw.c

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


#define ONE_MIL      (1000000)
#define MAX_SIZE_LOG (22)
#define MAX_SIZE     (1<<MAX_SIZE_LOG)

char sdata[MAX_SIZE];
char rdata[MAX_SIZE];

main( int argc, char **argv )
{
  int              size,rank, i, j, rounds, next, prev;
  long msglen;
  MPI_Status       status;
  double           startt,endt;
  char             buf[128];
  int  namelen;
  char processor_name[MPI_MAX_PROCESSOR_NAME];


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

  MPI_Get_processor_name(processor_name,&namelen);

  printf("Process %d on %s\n", rank, processor_name);

  if (rank == 0) {
    printf("STARTING LATENCY AND BANDWIDTH BENCHMARK\n");
    fflush(stdout);
  }

  next = (rank + 1 ) % size;
  prev = (rank + size - 1 ) % size;
  msglen = 0;

  while (msglen <= MAX_SIZE) {

    if (msglen <= (1<<9))       rounds = 1 << 15;
    else if (msglen <= (1<<12)) rounds = 1 << 12;
    else if (msglen <= (1<<18)) rounds = 1 << 10;
    else                        rounds = 1 << 8;                 
  
    MPI_Barrier ( MPI_COMM_WORLD );

    startt = MPI_Wtime();

    for (j=rounds; j--; ) {
      if (rank == 0) {
        MPI_Send(sdata,msglen,MPI_BYTE,next,0,MPI_COMM_WORLD);
        MPI_Recv(rdata,msglen,MPI_BYTE,prev,0,MPI_COMM_WORLD,&status);
      } else {
        MPI_Recv(rdata,msglen,MPI_BYTE,prev,0,MPI_COMM_WORLD,&status);
        MPI_Send(sdata,msglen,MPI_BYTE,next,0,MPI_COMM_WORLD);
      }
    }

    if (rank == 0) {
      double latency,bandwidth, elapse;

      endt = MPI_Wtime();
      elapse = endt - startt;

      latency   = elapse / (double)(size*rounds) * (double)ONE_MIL;
      bandwidth = ((double)(size*rounds*msglen))/elapse/(double)ONE_MIL;
      printf("%3d %8.3f %8.3f\n",msglen,latency,bandwidth);
      fflush(stdout);
    }
    if (msglen == 0) msglen = 1;
    else msglen = 2 * msglen;
  }
  MPI_Finalize();
}