[keldaris]

How are you writing compute shaders that work on all platforms, including Mac? Are you just writing Vulkan and relying on MoltenVK?

AFAIK, the only solution that actually works on all major platforms without additional compatibility layers today is OpenCL 1.2 - which also happens to be officially deprecated on MacOS, but still works for now.

[coffeeaddict1]

Yes, MoltenVK works fine. Alternatively, you can also use WebGPU (there are C++ and Rust native libs) which is a simpler but more limiting API.

[keldaris]

WebGPU has no support for tensor cores (or their Apple Silicon equivalents). Vulkan has an Nvidia extension for it, is there any way to make MoltenVK use simdgroup_matrix instructions in compute shaders?

[coffeeaddict1]

AFAIK, MoltenVK doesn't. Dawn (Google's C++ WebGPU implementation) does have some experimental support for it [0][1].

[0] https://issues.chromium.org/issues/348702031

[1] https://github.com/gpuweb/gpuweb/issues/4195

[pjmlp]

And is stuck with C99, versus C++20, Fortran, Julia, Haskell, C#, anything else someone feels like targeting PTX with.

[keldaris]

Technically, OpenCL can also include inline PTX assembly in kernels (unlike any compute shader API I've ever seen), which is relevant for targeting things like tensor cores. You're absolutely right about the language limitation, though.

[pjmlp]

At which point why bother, PTX is CUDA.

[keldaris]

Generally, the reason to bother with this approach is if you have a project that only needs tensor cores in a tiny part of the code and otherwise benefits from the cross platform nature of OpenCL, so you have a mostly shared codebase with a small vendor-specific optimization in a kernel or two. I've been in that situation and do find that approach valuable, but I'll be the first to admit the modern GPGPU landscape is full of unpleasant compromises whichever way you look.