@nightseas,
This is a good news about OpenCL and RK3399. It's interesting to see your results about OpenCV + OpenCL on RK3399.
I have found that ARM released their own Compute library . It supports both NEON and OpenCL and they claim that it has better performance than OpenCV.
I am also playing with RK3399 (Yundoo Y8) and was able to compile ARM compute library and I'm planning to do some perf tests.