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Editorial Team
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Asked: 2026-05-24T17:30:48+00:00

In CUDA, there is a concept of a warp , which is defined as

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In CUDA, there is a concept of a warp, which is defined as the maximum number of threads that can execute the same instruction simultaneously within a single processing element. For NVIDIA, this warp size is 32 for all of their cards currently on the market.

In ATI cards, there is a similar concept, but the terminology in this context is wavefront. After some hunting around, I found out that the ATI card I have has a wavefront size of 64.

My question is, what can I do to query for this SIMD width at runtime for OpenCL?

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  1. Editorial Team

    I found the answer I was looking for. It turns out that you don’t query the device for this information, you query the kernel object (in OpenCL). My source is:

    http://www.hpc.lsu.edu/training/tutorials/sc10/tutorials/SC10Tutorials/docs/M13/M13.pdf

    (Page 108)

    which says:

    The most efficient work group sizes are likely to be multiples of the native hardware execution width

    • wavefront size in AMD speak/warp size in Nvidia speak
    • Query device for CL_KERNEL_PREFERRED_WORK_GROUP_SIZE_MULTIPLE

    So, in short, the answer appears to be to call the clGetKernelWorkGroupInfo() method with a param name of CL_KERNEL_PREFERRED_WORK_GROUP_SIZE_MULTIPLE. See this link for more information on this method:

    http://www.khronos.org/registry/cl/sdk/1.1/docs/man/xhtml/clGetKernelWorkGroupInfo.html

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