2

I'm new to cuda and C++ and just can't seem to figure this out.

What I want to do is copy a 2d array A to the device then copy it back to an identical array B.

I would expect that the B array would have the same values as A, but there is something that I'm doing wrong.

CUDA - 4.2, compiling for win32, 64 bit machine, NVIDIA Quadro K5000

Here is the code.

void main(){

cout<<"Host main" << endl;

// Host code
const int width = 3;
const int height = 3;
float* devPtr;
float a[width][height]; 

//load and display input array
cout << "a array: "<< endl;
for (int i = 0 ; i < width; i ++)
{
    for (int j = 0 ; j < height; j ++)
    {
        a[i][j] = i + j;
        cout << a[i][j] << " ";

    }
    cout << endl;
}
cout<< endl;


//Allocating Device memory for 2D array using pitch
size_t host_orig_pitch = width * sizeof(float); //host original array pitch in bytes
size_t pitch;// pitch for the device array 

cudaMallocPitch(&devPtr, &pitch, width * sizeof(float), height);

cout << "host_orig_pitch: " << host_orig_pitch << endl;
cout << "sizeof(float): " << sizeof(float)<< endl;
cout << "width: " << width << endl;
cout << "height: " << height << endl;
cout << "pitch:  " << pitch << endl;
cout << endl;

cudaMemcpy2D(devPtr, pitch, a, host_orig_pitch, width, height, cudaMemcpyHostToDevice);

float b[width][height];
//load b and display array
cout << "b array: "<< endl;
for (int i = 0 ; i < width; i ++)
{
    for (int j = 0 ; j < height; j ++)
    {
        b[i][j] = 0;
        cout << b[i][j] << " ";
    }
    cout << endl;
}
cout<< endl;


//MyKernel<<<100, 512>>>(devPtr, pitch, width, height);
//cudaThreadSynchronize();


//cudaMemcpy2d(dst, dPitch,src ,sPitch, width, height, typeOfCopy )
cudaMemcpy2D(b, host_orig_pitch, devPtr, pitch, width, height, cudaMemcpyDeviceToHost);


// should be filled in with the values of array a.
cout << "returned array" << endl;
for(int i = 0 ; i < width ; i++){
    for (int j = 0 ; j < height ; j++){
        cout<< b[i][j] << " " ;
    }
    cout<<endl;
}

cout<<endl;
system("pause");

}

Here is the output.

Host main A Array 0 1 2 1 2 3 2 3 4

host_orig_pitch: 12 sizeof(float): 4 width: 3 height: 3 pitch: 512

b array: 0 0 0 0 0 0 0 0 0

returned array 0 0 0 1.17549e-038 0 0 0 0 0

Press any key to continue . . .

If more information is need let me know and I'll post it.

Any help would be greatly appreciated.

4

1 回答 1

5

正如评论中所指出的，最初的发帖人在cudaMemcpy2D电话中提供了不正确的论据。传输的宽度参数始终以字节为单位，因此在上面的代码中：

cudaMemcpy2D(b, host_orig_pitch, devPtr, pitch, width, height, cudaMemcpyDeviceToHost);

应该

cudaMemcpy2D(b, host_orig_pitch, devPtr, pitch, width * sizeof(float), height, cudaMemcpyDeviceToHost);

请注意，此答案已作为社区 wiki 添加，以将此问题从未回答列表中删除

于 2014-05-03T09:11:16.610 回答