计算CUDA内核中的循环数

Question

How can I count the number of cycles performed by a function like the following. Should I count straight forward the number of sums and muls and divs? Where can I check how many cycles an addition takes in CUDA?

__global__
void mandelbrotSet_per_element(Grayscale *image){
    float minR = -2.0f, maxR = 1.0f;
    float minI = -1.2f, maxI = minI + (maxR-minR) * c_rows / c_cols;
    float realFactor = (maxR - minR) / (c_cols-1);
    float imagFactor = (maxI - minI) / (c_rows-1);

    bool isInSet;
    float c_real, c_imag, z_real, z_imag;

    int y = blockDim.y * blockIdx.y + threadIdx.y;
    int x = blockDim.x * blockIdx.x + threadIdx.x;

    while (y < c_rows){
        while (x < c_cols) {
            c_real = minR + x * realFactor;
            c_imag = maxI - y * imagFactor;
            z_real = c_real;    z_imag = c_imag;
            isInSet = true;

            for (int k = 0; k < c_iterations; k++){
                float z_real2 = z_real * z_real;
                float z_imag2 = z_imag * z_imag;
                if (z_real2 + z_imag2 > 4){
                    isInSet = false;
                    break;
                }
                z_imag = 2 * z_real * z_imag + c_imag;
                z_real = z_real2 - z_imag2 + c_real;
            }
            if (isInSet)    image[y*c_cols+x] = 255;
            else            image[y*c_cols+x] = 0;

            x += blockDim.x * gridDim.x;
        }
        x = blockDim.x * blockIdx.x + threadIdx.x;
        y += blockDim.y * gridDim.y;
    }
}

Answer 1

Instruction throughput is described in the programming guide here

You can also try measuring a sequence of instructions using the native clock() function described here

The compiler tends to obscure actual counts of operations at the source code level (increasing or possibly decreasing apparent arithmetic intensity) so if you want to indentify exactly what the machine is doing you may want to inspect the ptx (nvcc -ptx ...) or possibly the machine assembly level code, called SASS, which you can extract from an executable using the cuobjdump utility.