It might have something to do with how the load is calculated. My wild guess is that GPU does not respond when running kernels, so load is probably calculated based on how long of a unit time that the GPU was unavailable. Therefore it would probably show 100% even if all the threads were sleeping as long as the kernel appears to be running constantly.
I am guessing that, because if a task takes too long, it times out... If the driver could tell that GPU is able to progress forward or not in the task, in my opinion it wouldnt make sense to have a timeout.
Of course this is just a guess, perhaps what you can try is to run a kernel with 1 global/local size (perhaps you would need a for loop in there) then try to run with a different number, lets say 2 or 4 global/local size where the original loop is distributed based on the number of global size between threads and see how long the execution takes.
You still did not say why you need this?
