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Thread: OpenMP / OpenCL CPU

  1. #1
    Senior Member
    Join Date
    Nov 2009
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    118

    OpenMP / OpenCL CPU

    How OpenCL could be faster than OpenMP on the same device?

    I use a very simple perlin algorithm on my core i7, and I have these results :
    33554432 elements, 8 work groups

    simple CPU : 1.33 sec
    OpenMP CPU : 0.27 sec (4.9 time faster than simple CPU)
    OpenCL CPU : 0.15 sec (8.7 time faster than simple CPU)

    Is it normal or even possible, or just a bug in my opencl code?

    configuration:
    Vista 64
    nVidia gtx 275, 195.62
    intel core i7
    amd ati stream sdk 2 beta 4
    visual studio 2008

  2. #2
    Senior Member
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    Sep 2002
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    Santa Clara
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    Re: OpenMP / OpenCL CPU

    It is certainly possible that OpenCL can be faster than OpenMP. Are you using OpenCL vector types in your kernel? If so, these should get mapped to the appropriate SSE instructions on your CPU which should give you an additional speedup in CL. I do not believe OpenMP compilers generate SSE so there is a 2 - 2.5x delta in performance that can be achieved using CL vector types.

  3. #3
    Senior Member
    Join Date
    Nov 2009
    Posts
    118

    Re: OpenMP / OpenCL CPU

    I just use float type : float buffer and float operations.
    Perhaps AMD OpenCL compiler is very smart (even on an intel processor :P ).

    It's great that it can be even more powerfull that openMP on CPU.

    thanks for your lighting.

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