OpenCV/OpenCL - a) performance

Hi - Fired up the OpenCV/OpenCL docker environment. Great, btw!

First, I noticed on your fast_corners demo that the GPU was much slower than the CPU. CPU=0.475 and GPU=3.77. This seems like there has to be a bug, either that or the GPU is totally unsuited here for OpenCV tasks.

I repeated this on my own and had similar results - CPU=1.3, GPU=3.9. A different ratio I might add - though I used a larger image - 480x640.

Question - why is GPU performance so bad on OpenCV - in this case cv::FAST ?