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/******************************************************************************
* FILE: mpi_latency.c
* DESCRIPTION:
* MPI Latency Timing Program - C Version
* In this example code, a MPI communication timing test is performed.
* MPI task 0 will send "reps" number of 1 byte messages to MPI task 1,
* waiting for a reply between each rep. Before and after timings are made
* for each rep and an average calculated when completed.
* AUTHOR: Blaise Barney
* LAST REVISED: 04/13/05
******************************************************************************/
#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <time.h>
#define NUMBER_REPS 1000
int main (int argc, char *argv[])
{
int reps, /* number of samples per test */
tag, /* MPI message tag parameter */
numtasks, /* number of MPI tasks */
rank, /* my MPI task number */
dest, source, /* send/receive task designators */
avgT, /* average time per rep in microseconds */
rc, /* return code */
n;
double T1, T2, /* start/end times per rep */
sumT, /* sum of all reps times */
deltaT; /* time for one rep */
char msg; /* buffer containing 1 byte message */
MPI_Status status; /* MPI receive routine parameter */
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&numtasks);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
if (rank == 0 && numtasks != 2) {
printf("Number of tasks = %d\n",numtasks);
printf("Only need 2 tasks - extra will be ignored...\n");
}
MPI_Barrier(MPI_COMM_WORLD);
sumT = 0;
msg = 'x';
tag = 1;
reps = NUMBER_REPS;
if (rank == 0) {
/* round-trip latency timing test */
printf("task %d has started...\n", rank);
printf("Beginning latency timing test. Number of reps = %d.\n", reps);
printf("***************************************************\n");
printf("Rep# T1 T2 deltaT\n");
dest = 1;
source = 1;
for (n = 1; n <= reps; n++) {
T1 = MPI_Wtime(); /* start time */
/* send message to worker - message tag set to 1. */
/* If return code indicates error quit */
rc = MPI_Send(&msg, 1, MPI_BYTE, dest, tag, MPI_COMM_WORLD);
if (rc != MPI_SUCCESS) {
printf("Send error in task 0!\n");
MPI_Abort(MPI_COMM_WORLD, rc);
exit(1);
}
/* Now wait to receive the echo reply from the worker */
/* If return code indicates error quit */
rc = MPI_Recv(&msg, 1, MPI_BYTE, source, tag, MPI_COMM_WORLD,
&status);
if (rc != MPI_SUCCESS) {
printf("Receive error in task 0!\n");
MPI_Abort(MPI_COMM_WORLD, rc);
exit(1);
}
T2 = MPI_Wtime(); /* end time */
/* calculate round trip time and print */
deltaT = T2 - T1;
printf("%4d %8.8f %8.8f %2.8f\n", n, T1, T2, deltaT);
sumT += deltaT;
}
avgT = (sumT*1000000)/reps;
printf("***************************************************\n");
printf("\n*** Avg round trip time = %d microseconds\n", avgT);
printf("*** Avg one way latency = %d microseconds\n", avgT/2);
}
else if (rank == 1) {
printf("task %d has started...\n", rank);
dest = 0;
source = 0;
for (n = 1; n <= reps; n++) {
rc = MPI_Recv(&msg, 1, MPI_BYTE, source, tag, MPI_COMM_WORLD,
&status);
if (rc != MPI_SUCCESS) {
printf("Receive error in task 1!\n");
MPI_Abort(MPI_COMM_WORLD, rc);
exit(1);
}
rc = MPI_Send(&msg, 1, MPI_BYTE, dest, tag, MPI_COMM_WORLD);
if (rc != MPI_SUCCESS) {
printf("Send error in task 1!\n");
MPI_Abort(MPI_COMM_WORLD, rc);
exit(1);
}
}
}
MPI_Finalize();
exit(0);
}
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