How to measure the total execut?on t?me most efficiently

Hi everyone
I am experimenting with opencl via c language on a GPU of NVIDIA . And I wonder ?f there is a way to measure the total execution time of opencl part of the code. When I use timer class of c, the time is given in unit of seconds. If I use GPU timer I need to calculate all actions(at least I know that much). If you show me a better way, I believe I can improve myself easily. Thanks for your help

If you are using OSX, call gettimeofday() and you can get microseconds.