Why Opencv GPU code is slower than CPU?

Question

I\'m using opencv242 + VS2010 by a notebook.
I tried to do some simple test of the GPU block in OpenCV, but it showed the GPU is 100 times slower than CPU codes. In this

Answer 1

Most answers above are actually wrong. The reason why it is slow by a factor 20.000 is of course not because of 'CPU clockspeed is faster' and 'it has to copy it to the GPU' (accepted answers). These are factors, but by saying that you omit the fact that you have vastly more computing power for a problem that is disgustingly parallel. Saying 20.000x performance difference is because of the latter is just so plain ridiculous. The author here knew something was wrong that's not straight forward. Solution:

Your problem is that CUDA needs to initialize! It will always initialize for the first image and generally takes between 1-10 seconds, depending on the alignment of Jupiter and Mars. Now try this. Do the computation twice and then time them both. You will probably see in this case that the speeds are within the same order of magnutide, not 20.000x, that's ridiculous. Can you do something about this initialization? Nope, not that I know of. It's a snag.

edit: I just re-read the post. You say you're running on a notebook. Those often have shabby GPU's, and CPU's with a fair turbo.