# Objective
Improve compile times.
## Solution
The `-Z threads=0` option has been introduced into nightly rust somewhat
recently, and was showcased in this [rust-lang
article](https://blog.rust-lang.org/2023/11/09/parallel-rustc.html).
This option improves multithreading in rust and speeds up compilation. I
added this option to `config_fast_builds.toml` so others can also use
this option to improve compile times.
`-Z threads=0` automatically uses the same amount of threads as the
amount of threads in your system (See [rustc source
code](6b4f1c5e78/compiler/rustc_session/src/options.rs (L617))).
### Benchmarks
> **Disclaimer:** This section was written before I knew of `-Z
threads=0`, so it uses `-Z threads=8` instead.
I compiled bevy with/without the `-Z threads=8` and saw about a 7%
improvement in compliation times on my Kubuntu system with a 13th Gen
Intel® Core™ i5-13400.
Also the compile times go down over time, probably because I had other
things running in the background.
#### Without `-Z threads=8`
- 42.33s
- 40.90s
- 38.27s
- 38.07s
- 37.17s
- 37.67s
- 36.63s
- 37.24s
**Average**: 38.535
#### With `-Z threads=8`
- 36.77s
- 39.50s
- 38.86s
- 35.61s
- 34.37s
- 34.32s
- 34.44s
- 33.74s
**Average**: 35.95125
# Objective
Theres no explaination for what the compiler flags
`config_fast_builds.toml` do
## Solution
Explain what the flags in `config_fast_builds.toml` do.
