In short I copied a program written by someone else (from here: http://llpanorama.wordpress.com/2008/05/21…-cuda-program/) and added in a bit where the cpu carries out the same operation. The CPU runs much faster, and I’m not sure why? here is the code:
[codebox] // Kernel that executes on the CUDA device
global void square_array(float *a, int N)
{
int idx = blockIdx.x * blockDim.x + threadIdx.x;
if (idx<N) a[idx] = a[idx] * a[idx] ;
__syncthreads();
}
// main routine that executes on the host
int main(void)
{
float *a_h, *a_d; // Pointer to host & device arrays
float *a,*b;
unsigned int timer = 0;
cutCreateTimer( &timer );
unsigned int timercpu = 0;
cutCreateTimer( &timercpu );
const int N = 400; // Number of elements in arrays
size_t size = N * sizeof(float);
a_h = (float *)malloc(size); // Allocate array on host
a = (float *)malloc(size);
b = (float *)malloc(size);
cudaMalloc((void **) &a_d, size); // Allocate array on device
// Initialize host array and copy it to CUDA device
for (int i=0; i<N; i++)
a_h[i] = (float)i;
cudaMemcpy(a_d, a_h, size, cudaMemcpyHostToDevice);
// Do calculation on device:
int block_size = 1;
int n_blocks = N/block_size + (N%block_size == 0 ? 0:1);
cutStartTimer( timer ); // Start timer
square_array <<< n_blocks, block_size >>> (a_d, N);
cutStopTimer( timer ); // Stop timer
// Retrieve result from device and store it in host array
cudaMemcpy(a_h, a_d, sizeof(float)*N, cudaMemcpyDeviceToHost);
// Print results
printf(“CUDA execution time = %f ms\n”,cutGetTimerValue( timer ));
// Cleanup
free(a_h); cudaFree(a_d);
system(“pause”);
cutStartTimer( timercpu ); // Start timer
for (int i=0; i<N; i++) { a[i] = (float)i;
b[i]= a[i] * a[i] ;
}
cutStopTimer( timercpu ); // Stop timer
printf("CPU execution time = %f ms\n",cutGetTimerValue( timercpu ));
system(“pause”);
return 0;
} [/codebox]
