Why is the CUDA version slower than the OpenCL version?

asked 2016-12-03 07:11:36 -0500

sammoes gravatar image

updated 2016-12-04 21:24:12 -0500

Hi, I have written a CUDA (8 on my machine) version of a program and compared it to an OpenCL(1.2) / T-API version. The former clocks in quite a bit slower even when using Unified Memory (UM). Could someone advise please? The normalize() function is multi-channel in the T-API, but underneath probably isn't. I had expected Shared Virtual Memory (UM in CUDA) to be faster, which I can't do with my PC because it is limited to OpenCL1.2... I read somewhere it can depend on the size or complexity of the filters, whether pixels are reread etc. but that would be the same for the CL version, wouldn't it?

CUDA (5-6 sec.)

ma = HostMem::getAllocator(HostMem::PAGE_LOCKED);
    prev_frame = GpuMat(read_frame);

for (int i = 0; i < 100; i++) {
    d_out = ImEnhance(prev_frame);

ma = HostMem::getAllocator(HostMem::WRITE_COMBINED);
prev_frame = GpuMat(read_frame);

for (int i = 0; i < 100; i++) {
    d_out = ImEnhance(prev_frame);

ma = HostMem::getAllocator(HostMem::SHARED);
prev_frame = GpuMat(read_frame);

for (int i = 0; i < 100; i++) {
    d_out = ImEnhance(prev_frame);


GpuMat ImEnhance(GpuMat frm){
GpuMat HSV;
//    cuda::GpuMat d_hdst, d_sdst, d_vdst;
cuda::GpuMat d_matarr[3];
cv::Ptr<cv::cuda::Filter> blur = cv::cuda::createGaussianFilter(frm.type(), frm.type(),Size(3,3), 9, 9);
cv::Ptr<cv::cuda::Filter> blur2 = cv::cuda::createGaussianFilter(frm.type(), frm.type(),Size(9,9), 1, 1);
cv::cuda::cvtColor(frm, HSV, COLOR_BGR2HSV, 0);
cuda::split(HSV, d_matarr);
//cv::cuda::normalize(d_matarr[0], d_matarr[0], 0, 255, NORM_MINMAX, 0, noArray());
//cv::cuda::normalize(d_matarr[1], d_matarr[1], 0, 255, NORM_MINMAX, 0, noArray());// <- slowest call
cv::cuda::normalize(d_matarr[2], d_matarr[2], 0, 255, NORM_MINMAX, 0, noArray()); //<- my data lives in the third channel only
cv::cuda::merge(d_matarr, 3, HSV);
cv::cuda::cvtColor(HSV, frm, COLOR_HSV2BGR, 0);
blur->apply(frm, HSV);
cv::cuda::addWeighted(frm, 1.5, HSV, -1.0, 0.0, frm, -1);
frm.convertTo(frm, -1, 2, 0);
blur2->apply(frm, frm);
return frm;

OpenCL (3-4 sec)

UMat ImEnhance(UMat frm) {

UMat HSV2;
UMat HSV3;
cvtColor(frm, HSV, COLOR_BGR2HSV);
normalize(HSV, HSV2, 0, 255, NORM_MINMAX);
cvtColor(HSV2, HSV3, COLOR_HSV2BGR);
UMat img2;
GaussianBlur(HSV3, img2, Size(3, 3), 9, 9);
addWeighted(HSV3, 1.5, img2, -1.0, 0.0, frm);
UMat img3;
frm.convertTo(img3, -1, 2, 0);
GaussianBlur(img3, frm, Size(9, 9), 1, 1);
return frm;

Note. The profile image I made is no longer correct. The code here on the forum changed from my initial question. This code is the most optimized version without changing OpenCV3's source code. It must be the CPU GPU data transfers that take up nearly all the time spent. My test data were 2200x1600 images,

edit retag flag offensive close merge delete


Try calling each function you're using once before counting time. The initialization for both OpenCL and CUDA can take significant amounts of time.

For example:

d_out = ImEnhance(prev_frame);
//start time
for(int i = 0; i<100; ++i)
//end time
Tetragramm gravatar imageTetragramm ( 2016-12-03 11:09:38 -0500 )edit

Do you mean, to get to know which function call is the slowest?

cv::cuda::normalize(d_matarr[1], d_sdst, 0, 255, NORM_MINMAX, 0, noArray());// <- slowest call

this one stands out (~64ms). (I step through it repeatedly using the profiler of VS2015). It did occur to me that the CUDAFilters dll is 300MB, but the lookup time should be marginal. What else could it be? I don't think there is much reason for this normalize call to be exceptionally slow on CUDA8, I mean, it's an NVidia GPU and I try all three memory options. Same goes for the other functions compared to OpenCL1.2. I add a detailed timing image.

sammoes gravatar imagesammoes ( 2016-12-04 19:21:58 -0500 )edit

I mistakenly merged the original channels, not the output channels. By reusing the input channels for output, this saves a little bit of initialization. I also see that my data only exists in one channel, this saves a little more. The cuda version now times in at the low 4. seconds. Still slower than OpenCL unfortunately.

sammoes gravatar imagesammoes ( 2016-12-04 20:50:34 -0500 )edit