FEX-Emu on macOS arm64 | avx(2)

[Rastafabisch]

I couldn't find any information on this topic. This lead me here. Is it possible to use FEX on macOS or would that require additional developing. While Rosetta works incredible great it does not feature AVX(2) support, which is required by more and more game titles.
Especially since D3DMetal works very well (more or less a macOS DXVK & VKD3D equivalent) now and DirectX translation isn't the limiting factor anymore this now starts to be the constraint.

In my imagination there are two scenarios to mitigate this: Either FEX could be a drop-in replacement for Rosetta, or the AVX(2) translation parts could be an addition to Rosetta.

Is either of this feasible?

EDIT:
So far the only use-case, that comes to mind so far is wine. I tried some windows games like Uncharted 4 but they fail complaining about missing instructions.

[Sonicadvance1]

FEX only supports Linux. It doesn't have any plans to support MacOS.
Additionally our AVX emulation requires ARM64 hardware that supports SVE2 with 256-bit wide registers, which Apple Silicon doesn't support.

[Sonicadvance1]

Thank you for the prompt answer and technical explanation.

Just one followup: Does that mean, that while FEX works on Asahi Linux (Linux porting effort to Apple Silicon), AVX(2) emulation does not work there either?

FEX doesn't work on Asahi Linux out of the box. Asahi Linux ships a 16KB page size kernel while FEX requires a 4KB page size kernel.
Workarounds include:

• Use the MicroVM approach to run a 4KB kernel in a lightweight VM.
  • Details here: https://sinrega.org/2023-10-06-using-microvms-for-gaming-on-fedora-asahi/
• Recompile the Asahi kernel for 4KB page size, which is unsupported and only quickly put together for testing by Asahi Lina.
  • Not recommended

Apple Silicon doesn't support SVE/SVE2, so FEX's AVX/2 emulation doesn't work on that hardware.

[Spidy123222]

Thank you for the prompt answer and technical explanation.

Just one followup: Does that mean, that while FEX works on Asahi Linux (Linux porting effort to Apple Silicon), AVX(2) emulation does not work there either?

FEX doesn't work on Asahi Linux out of the box. Asahi Linux ships a 16KB page size kernel while FEX requires a 4KB page size kernel.

Workarounds include:

• Use the MicroVM approach to run a 4KB kernel in a lightweight VM.

  • Details here: https://sinrega.org/2023-10-06-using-microvms-for-gaming-on-fedora-asahi/

• Recompile the Asahi kernel for 4KB page size, which is unsupported and only quickly put together for testing by Asahi Lina.

  • Not recommended

Apple Silicon doesn't support SVE/SVE2, so FEX's AVX/2 emulation doesn't work on that hardware.

From what I saw Apple silicon chips for Mac's use armv8.5-a which has sve and sve2. Did Apple remove it some how and it's not an -a variant chip? Also couldn't NEON be used to emulate the avx instructions.

[Sonicadvance1]

No Apple Silicon device today supports SVE or SVE2. This includes Apple M1/M2/M3 and and the latest A17.
There are technical reasons why we have decided that AVX emulation requires SVE2 with 256-bit wide registers. If ARM silicon wants to play with 256-bit AVX then they need to match feature parity.

[Torinde]

Apple M4 reportedly has SVE2/SME, but I can find if it is 128-bit or 256-bit? How many execution units?

Related:

• WIP: Working PR for AVX128 #3720
• Support AVX list #581

Does that mean you plan to support AVX (and other related instructions) on 128-bit SVE2?
Would be interesting do document somewhere what requires which, e.g. F16C requires SVE2 or will run lesser ARM CPUs?

[alyssarosenzweig]

In the past few months, our technical evaluation has changed and so implementing AVX on top of 128-bit is in progress. This will work even on Apple M1 (with ASIMD).

[Rastafabisch]

Just in case someone stumbles on this in the future.
Apple now provides AVX(2) support in macOS Sequoia (beta). Remains to be seen, whether it will be back ported to older macOS releases. At the end of this reddit post you can find some preliminary benchmarks.