具有散点图收集的MPI矩阵乘法 [英] MPI Matrix Multiplication with scatter gather
问题描述
我正在尝试使用C中的MPI进行矩阵乘法，并且我们必须执行一个顺序版本和一个并行版本.我的并行版本没有给出正确的答案，我不确定为什么.我认为我没有向流程发送正确的通信，但是我不确定.教授只是浏览了不同的发送/接收/收集等消息，但并没有真正涉及太多细节...我已经看到了很多不同的示例，但是都没有完成，也没有使用分散/收集.如果有人可以看一下我的代码，并告诉我是否有任何弹出的代码，我将不胜感激.我很确定我的问题出在散布/聚集消息或c矩阵的实际计算中.
I'm trying to do matrix multiplication using MPI in C and we have to do a version that sequential and one parallel version. My parallel version is not giving the correct answers and I'm not sure why. I think I'm not sending the right communications to the processes but I can't be sure. The professor just went over the different send/receive/gather etc messages, but didn't really get into much detail... I've seen a lot of different examples but none complete and none using scatter/gather. If anyone can take a look at my code and tell me if anything pops out at them I'd appreciate it. I'm pretty sure my problem is in the scatter/gather messages or the actual calculation of the c matrix.
#define N 512
#include <stdio.h>
#include <math.h>
#include <sys/time.h>
#include <stdlib.h>
#include <stddef.h>
#include "mpi.h"
print_results(char *prompt, float a[N][N]);
int main(int argc, char *argv[])
{
int i, j, k, rank, size, tag = 99, blksz, sum = 0;
float a[N][N], b[N][N], c[N][N];
char *usage = "Usage: %s file\n";
FILE *fd;
double elapsed_time, start_time, end_time;
struct timeval tv1, tv2;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
if (argc < 2) {
fprintf (stderr, usage, argv[0]);
return -1;
}
if ((fd = fopen (argv[1], "r")) == NULL) {
fprintf (stderr, "%s: Cannot open file %s for reading.\n",
argv[0], argv[1]);
fprintf (stderr, usage, argv[0]);
return -1;
}
for (i = 0; i < N; i++)
for (j = 0; j < N; j++)
fscanf (fd, "%f", &a[i][j]);
for (i = 0; i < N; i++)
for (j = 0; j < N; j++)
fscanf (fd, "%f", &b[i][j]);
MPI_Barrier(MPI_COMM_WORLD);
gettimeofday(&tv1, NULL);
MPI_Scatter(a, N*N/size, MPI_INT, a, N*N/size, MPI_INT, 0,
MPI_COMM_WORLD);
MPI_Bcast(b, N*N, MPI_INT, 0, MPI_COMM_WORLD);
if (rank != 0) {
for (i = 0; i < N; i++)
{
for (j = 0; j < N; j++)
{
for (k = 0; k < N; k++)
{
sum = sum + a[i][k] * b[k][j];
}
c[i][j] = sum;
sum = 0;
}
}
}
MPI_Gather(c, N*N/size, MPI_INT, c, N*N/size, MPI_INT, 0,
MPI_COMM_WORLD);
MPI_Finalize();
gettimeofday(&tv2, NULL);
elapsed_time = (tv2.tv_sec - tv1.tv_sec) + ((tv2.tv_usec - tv1.tv_usec)/1000000.0);
printf ("elapsed_time=\t%lf (seconds)\n", elapsed_time);
print_results("C = ", c);
}
print_results(char *prompt, float a[N][N])
{
int i, j;
printf ("\n\n%s\n", prompt);
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++) {
printf(" %.2f", a[i][j]);
}
printf ("\n");
}
printf ("\n\n");
}
代码的更新部分:
for (i=0;i<size; i++)
{
if (rank == i)
{
for (i = rank*(N/size); i < (rank*(N/size)+(N/size)); i++)
{
for (j = rank*(N/size); j < (rank*(N/size)+(N/size)); j++)
{
for (k = rank*N; k < rank*N+N; k++)
{
sum = sum + a[i][k] * b[k][j];
}
c[i][j] = sum;
sum = 0;
}
}
}
}
推荐答案
代码中的第一个问题是size可能不会划分N.这意味着长度为N*N/size的散射size数据包不一定发送整个矩阵.这可能是最难解决的问题.
A first problem in your code is that size might not divide N. Which means that scattering size packets of length N*N/size does not necessarily send the whole matrix. This is probably the hardest point to get right.
正如Greg Inozemtsev指出的那样，第二个问题是您将进程0排除在计算之外，尽管它负责矩阵的一部分.
As Greg Inozemtsev points out, a second problem is that you exclude process 0 from the computation, although it is responsible for a part of the matrix.
还有一个问题是，所有I/O操作(从开头读取系数并在结尾输出结果)只能由进程0完成.
And yet another problem is that all I/O operations (reading the coefficients at the beginning and outputting the results at the end) should be done only by process 0.
另一方面，您应该在前向声明和定义中指定print_result函数的返回类型(在这种情况下为void).
On another note, you should specify the return type (void in this case) of your print_result function, both in the forward declaration and in the definition.
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