Slow indexing of rust-analyzer on Apple Silicon

[gagbo]

Hi,

Still the same issue as pointed out on Discord:

Using:

• a M1 MBP,
• with Doom Emacs (emacs-lsp/lsp-mode@e870ce21d33ce84e1e7e29d72ed7e7451ea11dae)
• with current head here (emacs-lsp/emacs@f34bbbdc8561f5e361d7404c20280cb454051933),

when I open a rust project Rust-Analyzer starts, but it doesn't take all the resources at all, leading to a VERY (probably by a factor 10) slow initialization of the cache. See this screenshot of btop resource usage:

Opening the same project with vim spawns more threads on demand (peaks to 30 for this project) and uses all available CPU time (peaks to 100% all cores), leading to way faster indexing. I could not repro this on Linux, but I didn't try with this commit yet.

[gagbo]

(And emacs 28 upstream acts like vim, so there's a hidden regression somewhere in the fork :( )

[ericdallo]

Maybe related to https://github.com/emacs-lsp/emacs/issues/5 ?

[gagbo]

I think the issue is fixed after a rebase to emacs-29 (I'm testing https://github.com/gagbo/emacs/tree/json-rpc-29 which I'll rebase probably once a week or a fortnight). I have peak CPU usage, and the status in the modeline reported up to 8 compilation tasks in parallel when going into a Rust buffer, which is what I expected.

Therefore I'm closing the issue.

• A separate thread for lsp messaging is a "new feature".
• There's no way a  "new feature" makes it to a stable branch as emacs-28
• Therefore, having the issue only with the patch on top of emacs-28 is irrelevant.