"parallel-rustc" isn't working (on my PC at least)

[frederikhors]

I tried the instructions using:

• Windows 10 x64
• i7-4790 CPU @ 3.60GHz, Cores: 4, Logical processors: 8
• nightly-x86_64-pc-windows-msvc - rustc 1.75.0-nightly (0f44eb3 2023-11-09)
• stable-x86_64-pc-windows-msvc - rustc 1.73.0 (cc66ad4 2023-10-03)

I'm using config.toml in .cargo dir in the project root:

[build]
rustflags = ["-Z", "threads=8"]

Results

Dev build

• Without, 2m 45s
• With, 2m 47s

Release build

• Without, 11m 37s
• With, 11m 37s (exactly 37s !)

What am I doing wrong?

[bjorn3]

(I've moved this issue to the rust repo as the compiler-team repo is meant for organizational purposes and MCP's (major change proposals).)

[bjorn3]

Are you using the same nightly both when using -Zthreads=8 and without -Zthreads=8.

[frederikhors]

Are you using the same nightly both when using -Zthreads=8 and without -Zthreads=8.

Yep. With nightly build I'm using -Zthreads=8. With stable I'm not using it.

[bjorn3]

I mean are you comparing nightly with -Zthreads=8 against nightly without or nightly with -Zthreads=8 against stable without?

[frederikhors]

Nope. I'm comparing nightly with -Zthreads=8 against stable without -Zthreads=8.

[bjorn3]

Could you try comparing against nightly without -Zthreads=8 just to check that it works at all?

[frederikhors]

Yes I can try right now (I'm also doing a cargo clean every time, the target directory is recreated from scratch every time) but I think this is pretty obvious that the new parallel frontend isn't working, right?

[bjorn3]

Quite some people have reported wins already, so I'm trying to figure out if it is an issue with your local setup somehow ignoring the flag, it not working for your specific project, something windows specific or something else.

[frederikhors]

• Nightly, dev, without -Zthreads=8: dev [unoptimized + debuginfo] target(s) in 2m 54s
• Nightly, dev, with -Zthreads=8: dev [unoptimized + debuginfo] target(s) in 2m 58s

[SparrowLii]

Have you tried using env variable to set RUSTFLAGS? And maybe try other threads like 4 or 16 too