我正在研究一些cudatutorial将 RGBA 图片转换为灰度图。
但我不明白为什么要改变blockSize
and gridSize
改进了 X33 时间。
__global__
void rgba_to_greyscale(const uchar4* const rgbaImage,
unsigned char* const greyImage,
int numRows, int numCols)
{
int i = blockIdx.x*numCols + threadIdx.x;
float channelSum = .299f * rgbaImage[i].x + .587f * rgbaImage[i].y + .114f * rgbaImage[i].z;
greyImage[i]= channelSum;
}
void your_rgba_to_greyscale(const uchar4 * const h_rgbaImage, uchar4 * const d_rgbaImage,
unsigned char* const d_greyImage, size_t numRows, size_t numCols)
{
const dim3 blockSize(numCols, 1, 1);
const dim3 gridSize(numRows, 1 , 1);
rgba_to_greyscale<<<gridSize, blockSize>>>(d_rgbaImage, d_greyImage, numRows, numCols);
cudaDeviceSynchronize(); checkCudaErrors(cudaGetLastError());
}
当我按上面设置时:
const dim3 blockSize(numCols, 1, 1);
const dim3 gridSize(numRows, 1 , 1);
I get Your code executed in 0.030304 ms
当我设置时:
const dim3 blockSize(1, 1, 1);
const dim3 gridSize(numRows, numCols , 1);
并更新线程函数以使用新索引:
int i = blockIdx.x*numCols + blockIdx.y;
I get Your code executed in 0.995456 ms
.
- 我希望它是相反的,因为 GPU 可以计算所有
第二次网格分割时单独的像素是否与
缓存一致性问题?为什么我会得到这些结果?
- 从理论上来说,这个问题的最佳网格和块大小是多少?是否可以在运行时计算它?
FYI:
numRows = 313 numCols =557
技术性能:
#uname -a && /usr/bin/nvidia-settings -v
Linux ip-10-16-23-92 3.2.0-39-virtual #62-Ubuntu SMP Thu Feb 28 00:48:27 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
nvidia-settings: version 304.54 (buildmeister@swio-display-x86-rhel47-11)