Some opencv cudafilter functions is slower than CPU code on Jetson Xavier NX

C++
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1

I have tested some cudafilter functions but found it slower than CPU code on Jetson Xavier NX. The opencv version is 4.5.0. CUDA version is 10.2. The code as follows:

const int iternum = 100;

Mat img = imread("../../LenaGRAY.bmp", 0);
resize(img, img, Size(8000, 4000));
Mat element = getStructuringElement(MORPH_RECT, Size(15, 15));

Mat dst0 = Mat::zeros(img.size(), CV_8UC1);
Mat img0 = img.clone();
double t0_start = getTickCount();
for(int i = 0; i < iternum; i++)
{
    boxFilter(img0, dst0, CV_8UC1, Size(10, 10));
    //GaussianBlur(img0, dst0, CV_8UC1, Size(5, 5), 0);
    //morphologyEx(img0, dst0, MORPH_DILATE, element);
}
double t0_end = getTickCount();
cout<<"time:"<<(t0_end - t0_start) / getTickFrequency() * 1000 / iternum << "ms"<<endl;

cuda::GpuMat imgGpu;
imgGpu.upload(img);
cuda::GpuMat dstGpu;
dstGpu.create(img.size(), CV_8UC1);
Mat dst1;
double t1_start = getTickCount();
for(int i = 0; i < iternum; i++)
{
    cv::Ptr<cv::cuda::Filter>f1 = cv::cuda::createBoxFilter(CV_8UC1, CV_8UC1, Size(10, 10));
    f1->apply(imgGpu, dstGpu);
    //cv::Ptr<cv::cuda::Filter>f2 = cv::cuda::createGaussianFilter(CV_8UC1, CV_8UC1, Size(5, 5), 0);
    //f2->apply(imgGpu, dstGpu);
    //cv::Ptr<cv::cuda::Filter>f3 = cv::cuda::createMorphologyFilter(MORPH_DILATE,  CV_8UC1, element);
    //f3->apply(imgGpu, dstGpu);
}
double t1_end = getTickCount();
cout<<"time:"<<(t1_end - t1_start) / getTickFrequency() * 1000 / iternum << "ms"<<endl;
dstGpu.download(dst1);

I have tested boxFilter GaussianBlur and morpholoyEx, cuda functions is slower than on CPU.
I have also tested on Windows 10 PC. The GPU is NVIDIA GeForce RTX 3060, and CUDA version is 11.1. CUDA filter functions are still slower than CPU.

2

There’s a number of possible reasons:

  1. You are including the timing of the filter creation - remove this and time again.
  2. You may be timing the initialization overhead of loading cudafilters or opencv world libs - check the effect of calling your CUDA functions once outside of the timing loop first.
  3. You are using a filter size which cannot be processed in shared memory - check the effect of reducing it to 5.
  4. Your using CPU timers and the default stream so the resulting times will include the launch latency and some overhead for the stall resulting from the internal calls to cudaDeviceSynchronize - time with CUDA events to get the kernel execution time.
  5. Its slower on your hardware.