【发布时间】：2013-08-17 15:11:30
【问题描述】：
我试图做的是乘以矩阵 A 和矩阵 B，然后从乘积矩阵中得到每列最大值的索引。但不幸的是，只有矩阵乘法的前 128*128 个值是正确的，而其他的只是垃圾。我不太明白这是如何工作的。我请求你用这个来指导我..
#include<stdio.h>
#include "cuda.h"
#include<stdlib.h>
#define blockD 32
const int wA = 128;
const int hA = 4096;
const int wB = 4096;
const int hB = wA;
main(void){
void MatrixMultiplication(float *, float *, float *, float *);
int size_A = wA * hA * sizeof(float);
int size_B = wB * hB * sizeof(float);
int size_C = wB * hA * sizeof(float);
int size_max = 2 * wB * sizeof(float);
float *M, *N, *P, *C;
// allocate memory on the CPU
M = (float*)malloc(size_A);
N = (float*)malloc(size_B);
P = (float*)malloc(size_max);
C = (float*)malloc(size_C);
// initialize the matrices
for (int y=0; y < hA; y++) {
for (int x=0; x < wA; x++){
M[y*wA + x] = 32; //x + y*wA;
}
}
for (int y=0; y<hB; y++) {
for (int x=0; x<wB; x++){
N[y*wB + x] = 21; //x + y*wB;
}
}
MatrixMultiplication(M, N, P, C);
//Write
FILE *f1;
int i,j;
f1 = fopen("C.txt","w");
for(i = hA - 2 ; i < hA; i ++){
for(j = 0; j < wB; j++){
fprintf(f1,"%d\t",int(C[i*wB + j]));
}
fprintf(f1,"\n");
}
fclose(f1);
// free the memory allocated on the CPU
free( M );
free( N );
free( P );
free( C );
cudaDeviceReset();
return 0;
}
__device__ void MaxFunction(float* Pd, float* max)
{
int x = (threadIdx.x + blockIdx.x * blockDim.x);
int y = (threadIdx.y + blockIdx.y * blockDim.y);
int k = 0;
int temp = 0; int temp_idx = 0;
for (k = 0; k < wB; ++k) {
if(Pd[x*wB + k] > temp){
temp = Pd[x*wB + k];
temp_idx = x*wB + k;
}
}
max[y*2 + 0] = temp;
max[y*2 + 1] = temp_idx;
}
__global__ void MatrixMulKernel(float* Md, float* Nd, float* Pd, float* max)
{
// declare cache in the shared memory
__shared__ float Mds[blockD][blockD];
__shared__ float Nds[blockD][blockD];
float Pvalue = 0;
// Loop over the Md and Nd block dimension required to compute the Pd element
for (int m = (wA * blockD * blockIdx.y), n = (blockD * blockIdx.x);
m < ((wA * blockD * blockIdx.y)+wA-1);
m += blockD, n += (blockD*hB)){
// collaboratively loading of Md and Nd blocks into shared memory
Mds[threadIdx.y][threadIdx.x] = Md[m + wA * threadIdx.y + threadIdx.x];
Nds[threadIdx.y][threadIdx.x] = Nd[n + wA * threadIdx.y + threadIdx.x];
__syncthreads();
// keep track of the running sum
for (int k = 0; k < blockD; k++)
Pvalue += Mds[threadIdx.y][k] * Nds[k][threadIdx.x];
__syncthreads();
}
// write back to the global memory
int p = hB * blockD * blockIdx.y + blockD * blockIdx.x;
Pd[p + hB * threadIdx.y + threadIdx.x] = Pvalue;
__syncthreads();
MaxFunction(Pd, max);
}
void MatrixMultiplication(float *M, float *N, float *P, float *C) {
int size_A = wA * hA * sizeof(float);
int size_B = wB * hB * sizeof(float);
int size_C = wB * hA * sizeof(float);
int size_max = 2 * wB * sizeof(float);
float *Md, *Nd, *Pd, *max;
// allocate memory on the GPU
cudaMalloc((void**)&Md, size_A);
cudaMalloc((void**)&Nd, size_B);
cudaMalloc((void**)&Pd, size_C);
cudaMalloc((void**)&max, size_max);
// transfer M and N to device memory
cudaMemcpy(Md, M, size_A, cudaMemcpyHostToDevice);
cudaMemcpy(Nd, N, size_B, cudaMemcpyHostToDevice);
// kernel invocation code
dim3 dimBlock(blockD, blockD);
dim3 dimGrid(wA/blockD, hB/blockD);
//Execute Kernel
MatrixMulKernel<<<dimGrid, dimBlock>>>( Md, Nd, Pd, max);
// transfer P from device
cudaMemcpy(P, max, size_max, cudaMemcpyDeviceToHost);
cudaMemcpy(C, Pd, size_C, cudaMemcpyDeviceToHost);
// free the memory allocated on the GPU
cudaFree(Md);
cudaFree(Nd);
cudaFree(Pd);
cudaFree(max);
}
【问题讨论】：
-
这与您之前的问题中的代码和问题完全相同。请不要再次转发相同的问题。
-
我同意它的代码相同。但我找不到答案。
-
这不是发布重复问题的借口。获得帮助的关键是编辑您现有的问题，使其更容易回答。现在您的代码似乎有两个独立的问题 - 矩阵乘法和减少。选择一个问题。改进代码 - 例如，我根本看不到 CUDA API 错误检查。您甚至确定代码实际上正在运行完成吗？使用提供的工具 - 调试器、cuda-memcheck。用你发现的东西改进问题 - Stack Overflow 不是免费的调试服务，我们会为你做你的工作。帮助我们帮助您...
标签： cuda nvidia matrix-multiplication gpu