@mtlprintf

[tgymnich]

Implement @mtlprintf and friends using os_log

TODO:

• Printing of floats does not work since they will be converted to doubles due to the vararg calling convention which will be caught by our IR checker
• Version check the @mtlprintf macro
• Add tests
• Capturing and logging are mutually exclusive

depends on: JuliaGPU/GPUCompiler.jl#630

[tgymnich]

@maleadt Any idea how we can implement the version check for the @mtlprintf macro? I know we could check the air version inside the kernel but I'd like to avoid that.

Also can we get rid of the double check in check_ir?

[christiangnrd]

Would it be worth benchmarking the performance difference between having logging active vs not?

[tgymnich]

Would it be worth benchmarking the performance difference between having logging active vs not?

@christiangnrd Sure. I don't expect there to be much overhead besides allocation of the log buffer and checking it for logs after running a kernel. But we might want to look into only conditionally adding MTLLogState since logging also prevents GPU frame capture.

[maleadt]

@maleadt Any idea how we can implement the version check for the @mtlprintf macro? I know we could check the air version inside the kernel but I'd like to avoid that.

Given that the macro expands way to early, I don't think there's anything we can do but checking in the kernel. Why are you opposed to that? GPUCompiler.jl has infrastructure to optimize those checks away, see e.g. how CUDA.jl exposes the device capability and PTX ISA version to the kernel.

[tgymnich]

We could also wrap the macro and accompanying functions in if Metal.macos_version() >= v"15".

[christiangnrd]

I we do that we should have definitions in both cases and give an informative error if Metal.macos_version() < v"15".

[maleadt]

Actually, looks like I provided the run-time queries already:

Metal.jl/src/device/intrinsics/version.jl

Lines 64 to 65 in 6c82916

	@device_function @inline metal_version() = SimpleVersion(metal_major(), metal_minor())
	@device_function @inline air_version() = SimpleVersion(air_major(), air_minor())

So we can just use that in the generated code, generating an error when emitting code for an older platform. That of course depends on #416 for meaningful reporting, but we'll get there.

I'd rather not simply check based on the macOS version during macro expansion, since we might want to target older Metal versions than the system supports.

[christiangnrd]

Looks good! However do you know what's causing the tests to hang?

[christiangnrd]

Can you also add the printing docstrings in the API section of the Docs?

[tgymnich]

Looks good! However do you know what's causing the tests to hang?

@christiangnrd The hangs are caused by this one line:

@print_and_throw "@mtlprintf requires Metal 3.2 (macOS 15) or higher"