Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

recently I wrote several versions of the same program (generating Julia Sets - fractals pictures at size 17200x17200 pixels) to check the performance of a few different solutions.

I wrote versions:

  • CPU (pthreads) - 252s/1 thread, 131s/2 threads, 114s/3 threads, 95s/4 threads
  • CUDA - 2.51s ;)
  • OpenCL - 3.39s on GPU Nvidia implementation, 16.51s on CPU Intel implementation

Testing platform: Intel Core i5 520M, GeForce 330M

My question is: How to explain OpenCL CPU score? I expected the result near 4 threads on standard implementation - about 95s, but it took much less time. While program was working CPU was busy in 390%. How could it be?

Is OpenCL using both my Core i5 and integrated Intel HD Graphics?

share|improve this question

Intel also provides a OpenCL driver for the Intel HD graphic. So it looks like your tools used the Intel HD graphic.

It is also discussed here:

OpenCL support in graphics cards & on the Intel HD3000

share|improve this answer
That was my first thought, but why my CPU was completely busy? – Marcin Włodarczyk Apr 21 '13 at 19:05

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.