计算C中耗时

Question

我是 C 新手，我正在使用 Linux。我被这个大学任务困住了。我需要评估程序，并且需要制作一个程序来显示执行所用的时间。这是原始程序。

/*
 * Simple MPI program to sum the numbers from 1 to 1000
 *
 * The output of this program should look like this:
 *
 * $ mpirun -n 4 ./su
 * node 1 of 4 starting at 251 and ending at 500
 * node 2 of 4 starting at 501 and ending at 750
 * node 3 of 4 starting at 751 and ending at 1000
 * node 0 of 4 starting at 1 and ending at 250
 * The sum from 1 to 1000 is: 500500
 *
 * Author: Kevan Buckley
 */

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

int main(int argc, char **argv) {
    // Rank is which process this code is executing in.
    // Rank 0 is the initial process.
    int rank;
    int size;
    int sum = 0;
    int start, end, accum, i;

    // These lines must appear at the start of any
    // MPI program.
    MPI_Status status;
    MPI_Init(&argc, &argv);

    // These lines tell MPI that rank and size are values
    // that we want to communicate between processes.
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    // Only compute part of the sum.
    // This splits the work over the different processes.
    start = (1000*rank/size)+1;
    end = 1000*(rank+1)/size;

    printf("node %d of %d start: %d end: at %d\n",\
           rank, size, start, end);

    for(i=start; i<=end; i++){
        sum = sum + i;
    }

    if(rank == 0) {
        for(i=1; i<size; i++){
            // Receive a message from another process.
            MPI_Recv(&accum, 1, MPI_INT, i, 1, \
                     MPI_COMM_WORLD,  &status);
            sum = sum + accum;
        }
        printf("The sum from 1 to 1000 is: %d\n", sum );
    }
    else {
       // Send data to the process at rank 0.
       MPI_Send(&sum, 1, MPI_INT, 0, 1, MPI_COMM_WORLD);
    }

    // This code must end any MPI program.
    MPI_Finalize();

    return 0;
}

这是我的更新版本 - Gist 。我从我正在处理的其他代码中获取了所有时间计算。我尝试了很多东西，但仍然无法让它发挥作用。

任何帮助都会有帮助，谢谢!

Answer 1

如果我理解正确的话，你想为你的程序的一部分计时。下面是使用 MPI_Wtime 进行并行编程的示例代码。

#include <mpi.h>

double start, finish;

MPI_Init (&argc, &argv);
start=MPI_Wtime(); /*start timer*/

/*put the code you want to time here*/

finish=MPI_Wtime(); /*stop timer*/
MPI_Finalize();

printf("Parallel Elapsed time: %f seconds\n", finish-start);