I’ve tested the following on a GTX 690 GPU with 4GB RAM in Windows 7 x64, Visual C++ 10:
I’ve written a function that receives 2 vectors and adds into a 3rd vector. The task is broken over 2 GPU devices. I gradually increased the vector size to benchmark GPU performance. The required time linearly increases relative to vector size up to a certain point and then it abruptly jumps up. When I disable each of the GPU cores, the required time stays linear to the end of available memory. I’ve enclosed a diagram displaying required time versus allocated memory.
Can you tell me what is wrong?
Bests,
Ramin
This is my code:
unsigned BenchMark( unsigned VectorSize )
{
unsigned * D[ 2 ][ 3 ] ;
for ( int i = 0 ; i < 2 ; i++ )
{
cudaSetDevice( i ) ;
for ( int j = 0 ; j < 3 ; j++ )
cudaMalloc( & D[ i ][ j ] , VectorSize * sizeof( unsigned ) ) ;
}
unsigned uStartTime = clock() ;
// TEST
for ( int i = 0 ; i < 2 ; i++ )
{
cudaSetDevice( i ) ;
AddKernel<<<VectorSize/256,256>>>(
D[ i ][ 0 ] ,
D[ i ][ 1 ] ,
D[ i ][ 2 ] ,
VectorSize ) ;
}
cudaDeviceSynchronize() ;
cudaSetDevice( 0 ) ;
cudaDeviceSynchronize() ;
unsigned uEndTime = clock() ;
for ( int i = 0 ; i < 2 ; i++ )
{
cudaSetDevice( i ) ;
for ( int j = 0 ; j < 3 ; j++ )
cudaFree( D[ i ][ j ] ) ;
}
return uEndTime - uStartTime ;
}
__global__ void AddKernel(
const Npp32u * __restrict__ pSource1 ,
const Npp32u * __restrict__ pSource2 ,
Npp32u * __restrict__ pDestination ,
unsigned uLength )
{
unsigned x = blockIdx.x * blockDim.x + threadIdx.x ;
if ( x < uLength )
pDestination[ x ] = pSource1[ x ] + pSource2[ x ] ;
}
This is the diagram: