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Can anybody explain why CUDA and Rocm are necessary and why OpenCL isn't the solution? (programming.dev)

submitted 3 days ago by [email protected] to c/[email protected]

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I've read multiple times that CUDA dominates, mostly because NVIDIA dominates. Rocm is the AMD equivalent, but OpenCL also exists. From my understanding, these are technologies used to program graphics cards - always thought that shaders were used for that.

There is a huge gap in my knowledge and understanding about this, so I'd appreciate somebody laying this out for me. I could ask an LLM and be misguided, but I'd rather not 🤣

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[–] [email protected] 3 points 2 days ago

Because CUDA and ROCm/HIP are far easier to program.

The Khronos competitor to CUDA/ROCm is SYCL not OpenCL.

SYCL vs these other options is a fun theoretical problem, but only Intel seems to be pushing SYCL at all. OpenCL got stuck in OCL1.2 (the 2.0 release was dead. 3.0+ OpenCL ignores OCL2.0 but it's too late, OpenCL is seen as a dead end tech these days).

The biggest issue is that OpenCL is a different language, while CUDA/HIP/SYCL are 'just' C++ extensions. This means that if you ever shared data between CPU and GPU in OpenCL (or DirectX or Vulkan for that matter), you have to carefully write and rewrite structs{} to line up between the two languages.

Meanwhile, CUDA/HIP support passing structs, classes and more between CPU and GPU (subject to conditions of course. GPUs can't do function pointers or vtables for example, but cpu-only classes can have vtables)