LuaJIT performance on ARM Macs

[Madrayken]

Hi folks,
As I'm getting to the end of making Moonring, and testing on a bunch of different machines, I'm noticing massive slowdows on Mac M2. Is this likely to be a LuaJIT issue, a Rosetta issue, or something else? The game is doing lots of *very* intensive processing, and using a ton of shaders etc, but so far all has worked pretty well on Intel machines 5+ years old. Any help much appreciated.

- Fluttermind

[GVovkiv]

Hi folks,
As I'm getting to the end of making Moonring, and testing on a bunch of different machines, I'm noticing massive slowdows on Mac M2. Is this likely to be a LuaJIT issue, a Rosetta issue, or something else? The game is doing lots of *very* intensive processing, and using a ton of shaders etc, but so far all has worked pretty well on Intel machines 5+ years old. Any help much appreciated.

- Fluttermind

It's LuaJIT ARM issues, in love 11.5 and love 12 will use newer version of luajit, where some issues with ARM might be fixed
Go to love 12 artefacts here: https://github.com/love2d/love/actions/runs/5513844263, (or, better, love 11.5 https://github.com/love2d/love/actions/runs/5632754795) download binaries for mac os and try run game with it and see if there any difference with performance.
You can also build manually, but download compiled binary sounds easier.

[BrotSagtMist]

I think i remember talks about jit not working on these processors.

[slime]

JIT compilation works on arm64 (the architecture used by Apple Silicon CPUs). However, right now LuaJIT can only use a really small section of memory to store JIT-compiled code on arm64 - and that small section is also shared with other parts of the app like C/C++ libraries love uses. So what ends up happening is it can run out of memory in that area really quickly, which causes it to frequently try to recompile code, which can really slow things down when it happens repeatedly like that.

There's an open bug report on the LuaJIT github page about it, but a proper fix seems like it needs quite a lot of work and Mike Pall hasn't had a lot of time to dedicate to LuaJIT in the past few years, so I don't know if or when a fix will happen.

love tries its best to maximize the amount of memory in that area that's available to LuaJIT, but there's only so much it can do. You might end up having more consistent performance by turning off JIT compilation via jit.off() at the top of main.lua. If you have any threads you'd need to do it at the top of each thread's code too, in order to turn it off there. It will be slower than the peak performance LuaJIT is able to achieve when it's working well of course, but faster than it is when it tries to recompile every block of code all the time.

[Madrayken]

Thanks so much, folks. Thought I was going nuts.