錯誤值與MPI IO讀取時文件

Question

下面是一個簡單的C程序並行讀取一個文件MPI IO：與一個突未

#include <stdio.h> 
#include <stdlib.h> 

#include "mpi.h" 

#define N 10 

main(int argc, char **argv) 
{ 
    int rank, size; 
    MPI_Init(&argc, &argv); 
    MPI_Comm_rank(MPI_COMM_WORLD, &rank); 
    MPI_Comm_size(MPI_COMM_WORLD, &size); 

    int i0 = N * rank/size; 
    int i1 = N * (rank+1)/size; 
    printf("rank: %d, i0: %d, i1: %d\n", rank, i0, i1); 

    int i; 
    double* data = malloc((i1-i0)*sizeof(double)); 
    for (i = 0 ; i < i1-i0 ; i++) 
     data[i] = 123.; 

    MPI_File f; 
    MPI_File_open(MPI_COMM_WORLD, "data.bin", MPI_MODE_RDONLY, 
        MPI_INFO_NULL, &f); 

    MPI_File_set_view(f, i0, MPI_DOUBLE, MPI_DOUBLE, "native", 
         MPI_INFO_NULL); 

    MPI_Status status; 
    MPI_File_read(f, data, i1-i0, MPI_DOUBLE, &status); 

    int count; 
    MPI_Get_count(&status, MPI_DOUBLE, &count); 
    printf("rank %d, %d value read\n", rank, count); 

    for (i = 0 ; i < i1-i0 ; i++) { 
     printf("rank: %d index: %d value: %.2f\n", rank, i, data[i]); 
    } 

    MPI_File_close(&f); 

    MPI_Finalize(); 

    free(data); 

    return 0; 
} 

：

./read_mpi_io 

值讀是正確的：

rank: 0, i0: 0, i1: 10 
rank 0, 10 value read 
rank: 0 index: 0 value: 0.00 
rank: 0 index: 1 value: 1.00 
rank: 0 index: 2 value: 2.00 
rank: 0 index: 3 value: 3.00 
rank: 0 index: 4 value: 4.00 
rank: 0 index: 5 value: 5.00 
rank: 0 index: 6 value: 6.00 
rank: 0 index: 7 value: 7.00 
rank: 0 index: 8 value: 8.00 
rank: 0 index: 9 value: 9.00 

但是有兩個處理：

mpirun -n 2 ./read_mpi_io 

我得到錯誤的值（零）：

rank: 0, i0: 0, i1: 5 
rank: 1, i0: 5, i1: 10 
rank 0, 5 value read 
rank: 0 index: 0 value: 0.00 
rank 1, 5 value read 
rank: 1 index: 0 value: 0.00 
rank: 0 index: 1 value: 1.00 
rank: 0 index: 2 value: 2.00 
rank: 1 index: 1 value: 0.00 
rank: 1 index: 2 value: 0.00 
rank: 1 index: 3 value: 0.00 
rank: 1 index: 4 value: 0.00 
rank: 0 index: 3 value: 3.00 
rank: 0 index: 4 value: 4.00 

什麼是錯誤的，我的C代碼？

Answer 1

您在致電MPI_File_set_view()時遇到的問題：它是第二個參數，起始視圖的偏移量預計爲字節數，而不是元素數。因此，在這裏，您需要將您的i0參數乘以您想要讀取的元素的大小，即sizeof(double)。

通過更換相應的線路：

MPI_File_set_view(f, i0 * sizeof(double), MPI_DOUBLE, MPI_DOUBLE, 
        "native", MPI_INFO_NULL); 

就解決了這個問題，並使得預期的代碼工作。