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cudaopencl

What is the relation between compute units, SMXs, CUDA cores, etc.?

I'm quite confused with these terminologies... I understand that an nVidia GPU has some streaming multiprocessors (SMX), each consisting of a number of CUDA cores (streaming processor, SP). However I can't seem to figure out how this applies to OpenCL compute units.

For example, my GeForce GTS 250 says it has 16 compute units. The official nVidia site says it has 128 CUDA cores. However, some papers say the compute unit itself is a core.

So which one is which? Also, which one of these executes an OpenCL workgroup? So far I thought a work group gets executed on a CUDA core. But the OpenCL spec says it gets executed on a compute unit (which should be an SMX then).

Honestly, WTF???

Solution

  • I would completely ignore the term 'core' when thinking about OpenCL, because different hardware vendors have different opinions about what it actually means (as you have already found out). Neither an SM nor a 'CUDA core' is directly comparable to a traditional CPU core.

    For NVIDIA hardware, an SM is an OpenCL compute unit. Each work-group will therefore be assigned to an SM, although each SM is capable of running multiple work-groups concurrently.