config to switch linker to mold for linux target #51
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PROBLEM: dev hot-rebuilds currently take ~10s on a 4c8t intel laptop from circa 2017. (rustc 1.61.0) SOLUTION: After switching to mold, this time drops to ~3.5s. FURTHER INFORMATION: Profiling via rustc --self-profile reveals that most of the time for a hot reload comes from linking. mold is a faster linker than lld or ld. POSSIBLE IMPROVEMENTS: Switching to rust nightly (currently 1.63.0) yield further 20-30% improvements.
PROBLEM: unit tests and integration tests error out because mold not installed on gh actions machines SOLUTION: Use Rui Ueyama's first party github action https://github.com/rui314/setup-mold
PROBLEM: Ueyama's gh action installs mold to /usr/local/bin/mold whereas cargo configured to look for it at /usr/bin/mold SOLUTION: change cargo path to /usr/local/bin/mold POSSIBLE IMPROVEMENTS: I really wish it was possible to have the config file include macros somehow. (so something like /usr/bin/env mold, or which mold), but that doesn't seem feasible without having a config generator which seems excessive for just this, but might be good if there's more dynamic configuration in the future.
paulgb
reviewed
Jun 14, 2022
.cargo/config.toml
Outdated
| @@ -0,0 +1,3 @@ | |||
| [target.x86_64-unknown-linux-gnu] | |||
| linker = "/usr/bin/clang" | |||
| rustflags = ["-C", "link-arg=--ld-path=/usr/local/bin/mold"] | |||
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Should this be:
rustflags = ["-C", "link-arg=-fuse-ld=/usr/local/bin/mold"]
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yea, it's deprecated, but is fine for now. esp considering stuff like this
rust-lang/rust#94347
PROBLEM: gh-actions clang is old and does not support --ld-path SOLUTION: switch to deprecated -fuse-ld NOTES: I suspect that the rust project will switch to mold as default linker for linux before we have to worry about changing this path anyhow.
|
OK that should be good. In the future, or if we decide to switch to nightly, something like this might be worthwhile: https://github.com/dimensionhq/fleet |
pretentious7
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Jun 15, 2022
This reverts commit 860547f. PROBLEM: messes up docker push SOLUTION: remove linker switch NOTE: issues mentioned in 86054 still apply, and will be addressed in this PR.
pretentious7
added a commit
that referenced
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Jun 15, 2022
* Revert "config to switch linker to mold for linux target (#51)" This reverts commit 860547f. PROBLEM: messes up docker push SOLUTION: remove linker switch NOTE: issues mentioned in 86054 still apply, and will be addressed in this PR. * add fast_build script that runs cargo build with the mold linker PROBLEM: as mentioned in 86054, hot-reloads take around 10s, mostly due to linker. SOLUTION: use mold, this time via a fast_build script that sets the necessary cargo env vars, ensures that mold and clang are installed, and runs cargo build with the correct path for the mold linker. POSSIBLE IMPROVEMENTS: may be a good idea to switch the shell script for a zx script. Also would be nice if `cargo build` automatically ran fast_build.sh as a wrapper if the host and profile are correct (ie. linux host, with dev profile) * CLEANUP: remove .cargo from dockerignore Co-authored-by: Abhishek Cherath <[email protected]>
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PROBLEM:
dev hot-rebuilds currently take ~10s on a 4c8t intel laptop
from circa 2017. (rustc 1.61.0)
SOLUTION:
After switching to mold, this time drops to ~3.5s.
FURTHER INFORMATION:
Profiling via rustc --self-profile reveals that most of the time
for a hot reload comes from linking. mold is a faster linker than
lld or ld.
POSSIBLE IMPROVEMENTS:
Switching to rust nightly (currently 1.63.0) yield further 20-30%
improvements.