学步园

MPI通信，的确存在通信的启动时间。

#include "mpi.h"<br /> #include <stdio.h><br /> #include <stdlib.h><br /> #include <time.h><br /> #include <string.h><br /> int main(int argc, char **argv)<br /> {<br /> int i, myid, other, numprocs;<br /> double start, end;<br /> MPI_Status status;</p> <p> MPI_Init(&argc, &argv);<br /> MPI_Comm_rank(MPI_COMM_WORLD, &myid);<br /> MPI_Comm_size(MPI_COMM_WORLD, &numprocs);<br /> int N = 1024;<br /> int *buf = (int *)malloc(sizeof(int) * (N + 1));<br /> if (buf == NULL) printf("Not enouth memory!/n");<br /> for (i = 0; i < N; i++){<br /> buf[i] = myid + i;<br /> }<br /> if(myid == 0) other = 1;<br /> if(myid == 1) other = 0;</p> <p> start = MPI_Wtime();<br /> if(myid == 0)<br /> MPI_Send(buf, N, MPI_INT, other, 99, MPI_COMM_WORLD);<br /> else<br /> MPI_Recv(buf, N, MPI_INT, other, 99, MPI_COMM_WORLD, &status);<br /> end = MPI_Wtime();<br /> if(myid == 1) printf("case 1: %f/n", end - start);</p> <p> start = MPI_Wtime();<br /> i = N;<br /> while (i--) {<br /> if(myid == 0)<br /> MPI_Send(&buf[i], 1, MPI_INT, other, 99, MPI_COMM_WORLD);<br /> else<br /> MPI_Recv(&buf[i], 1, MPI_INT, other, 99, MPI_COMM_WORLD, &status);<br /> }<br /> end = MPI_Wtime();<br /> if(myid == 1) printf("case 2: %f/n", end - start);<br /> free(buf);<br /> buf = NULL;<br /> //printf("process %d freeing memory.../n",myid);</p> <p> MPI_Finalize();<br /> }<br />  

result:

[root@c0108 zlt]# mpicc comm.c -o comm<br /> [root@c0108 zlt]# mpiexec -n 2 ./comm<br /> case 1: 0.002562<br /> case 2: 0.004875