Thrust - Search Min

Accelerated Computing GPU-Accelerated Libraries
1

GoodMorning,
I’m going to use Thrust Library to speed my cuda code.
My cuda code evaluate an array of min value and on the host I’m going to find the min of mins.

HOST CODE:

float minSearchCudaFunction() //return min value
{
    size_t elementsPerLine = 104;

    size_t width = 5;

    size_t height = 5;
    
    int  N = 100;

    dim3 threadBlocks(tx, ty);

    dim3 blocksPerGrid((width + threadBlocks.x - 1) / threadBlocks.x, (height + threadBlocks.y - 1) / threadBlocks.y);

thrust::host_vector<float> h_vec(N);

    thrust::generate(h_vec.begin(), h_vec.end(), rand);

    thrust::device_vector<float> d_vec = h_vec; //cudaMemcpy in background

   // transfer data back to host
   thrust::copy(d_vec.begin(), d_vec.end(), h_vec.begin());

   float* d_ptr = thrust::raw_pointer_cast(&d_vec[0]);

int bxb = blocksPerGrid.x *blocksPerGrid.y;
 
   thrust::device_vector<float> d_minOut(bxb); // vector of min values
  
   float* min_ptr = thrust::raw_pointer_cast(&d_minOut[0]); 

minKernel << <blocksPerGrid, threadBlocks >> >(d_ptr, elementsPerLine, height, width, min_ptr, blocksPerGrid.x, N);
   
   thrust::host_vector<float> h_vec_put(N);

   thrust::copy(h_vec_put.begin(), h_vec_put.end(), d_minOut.begin());

// find min of mins array
   thrust::device_vector<float>::iterator iter = thrust::min(h_vec_put.begin(), h_vec_put.end());

   printf("\n\nMin Value => %3.2f \n", *iter);

system("PAUSE");
    return 0;
}

The problem of this code is that return ALWAYS 0.

Could you help me?

2

maybe you think this:

thrust::copy(h_vec_put.begin(), h_vec_put.end(), d_minOut.begin());

copies the data from d_minOut to h_vec_put

It does not.

It copies data from h_vec_put to d_minOut.