System get stuck on running matrix multiplication using CUDA

Question

When i'm running this code on my system, after some seconds my system get stuck and i have to restart system again. So my question is what's i'm doing wrong here? Any suggestion will appreciated.

__global__ void matMul(float* d_M, float* d_N, float* d_P, int width) {
int row = blockIdx.y*width + threadIdx.y;
int col = blockIdx.x*width + threadIdx.x;

if (row < width && col < width) {
    float product_val = 0;
        for (int k = 0; k < width; k++) {
            product_val += d_M[row*width + k] * d_N[k*width + col];
        }
    d_P[row*width + col] = product_val;
 }
}


int main() {
const int n = 9;
float* d_M;
float* d_N;
float* d_P;

cudaMallocManaged(&d_M, SIZE * sizeof(float));
cudaMallocManaged(&d_N, SIZE * sizeof(float));
cudaMallocManaged(&d_P, SIZE * sizeof(float));

for (int i = 0; i < n; ++i) {
    d_P[i] = 0;
}

int count = 0;
for (int i = 0; i < n; ++i) {
    d_N[i] = ++count;
}

count = 0;
for (int i = 0; i < n; ++i) {
    d_M[i] = ++count;
}

matMul <<<1, n>>> (d_M, d_N, d_P, 3);
cudaDeviceSynchronize();

for (int i = 0; i < n; ++i) {
    printf("%f\n", d_P[i]);
}
cudaFree(d_N);
cudaFree(d_M);
cudaFree(d_P);
return 0;

}

Answer 1

Assuming that when you mean your system gets stuck, you get some kind of error in your program, it's likely that you're accessing memory that is invalid.

This could be in the higher indexes of your d_M and d_N iterations when k + row*width is indexing beyond the size of memory that you've allocated in cudaMallocManaged.

It's always good practice in situations like these to add some error handling using commands such as cudaPeekatLastError().

This link might be helpful for implementing some debugging.