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Use -Z threads=0 option in config_fast_builds.toml #11541

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Jan 29, 2024
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Use -Z threads=0 option in config_fast_builds.toml #11541

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835ebd1
Use `-Z threads=8` option in `config_fast_builds.toml`
doonv Jan 26, 2024
a977c7e
Use `-Z threads=0` instead of `8`
doonv Jan 27, 2024
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9 changes: 7 additions & 2 deletions .cargo/config_fast_builds.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ linker = "clang"
rustflags = [
"-Clink-arg=-fuse-ld=lld", # Use LLD Linker
"-Zshare-generics=y", # (Nightly) Make the current crate share its generic instantiations
"-Zthreads=8", # (Nightly) Use improved multithreading with 8 threads.
]

# NOTE: you must install [Mach-O LLD Port](https://lld.llvm.org/MachO/index.html) on mac. you can easily do this by installing llvm which includes lld with the "brew" package manager:
Expand All @@ -16,6 +17,7 @@ rustflags = [
rustflags = [
"-Clink-arg=-fuse-ld=/usr/local/opt/llvm/bin/ld64.lld", # Use LLD Linker
"-Zshare-generics=y", # (Nightly) Make the current crate share its generic instantiations
"-Zthreads=8", # (Nightly) Use improved multithreading with 8 threads.
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Can any MacOS users test if this works well? It might reduce performance on MacOS or even not work at all.

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@BD103 BD103 Jan 29, 2024 •
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After testing it on my M1 Mac, this option actually seems to slow down the compilation process. I built with the --timings option to generate the following charts. The time increases from 58.4 seconds to 63.6 seconds.

Before:

image image

After:

image image

Edit: Redid timings so the only difference between "Before" and "After" was commenting out -Zthreads=0.

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Is this an average or just one test?

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That was just one test. Here's my results running cargo clean && cargo +nightly build with and without -Zthreads=0 commented out.

Before

  • 1:03s
  • 1:06s
  • 1:11s
  • 1:12s
  • 1:08s
  • 0:59.4s
  • 1:03s

Average: 1:06.05s

After

  • 1:05s
  • 1:11s
  • 1:13s
  • 1:20s
  • 1:07s
  • 1:11s
  • 1:12s

Average: 1:11.29s

]

[target.aarch64-apple-darwin]
Expand All @@ -25,8 +27,11 @@ rustflags = [
]

[target.x86_64-pc-windows-msvc]
linker = "rust-lld.exe" # Use LLD Linker
rustflags = ["-Zshare-generics=n"]
linker = "rust-lld.exe" # Use LLD Linker
rustflags = [
"-Zshare-generics=n",
"-Zthreads=8", # (Nightly) Use improved multithreading with 8 threads.
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Windows users should also test this out

]

# Optional: Uncommenting the following improves compile times, but reduces the amount of debug info to 'line number tables only'
# In most cases the gains are negligible, but if you are on macos and have slow compile times you should see significant gains.
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