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cli: Tweak default thread count logic

This commit is contained in:
Tavian Barnes 2023-11-29 16:53:24 -05:00 committed by David Peter
parent 00b64f3ccb
commit fea1622724
2 changed files with 12 additions and 20 deletions
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8
CHANGELOG.md
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@ -5,15 +5,17 @@
- Breaking: `.git/` is now ignored by default when using `--hidden` / `-H`, use `--no-ignore` / `-I` or - Breaking: `.git/` is now ignored by default when using `--hidden` / `-H`, use `--no-ignore` / `-I` or
`--no-ignore-vcs` to override, see #1387 and #1396 (@skoriop) `--no-ignore-vcs` to override, see #1387 and #1396 (@skoriop)
## Bugfixes ## Bugfixes
- Fix `NO_COLOR` support, see #1421 (@acuteenvy) - Fix `NO_COLOR` support, see #1421 (@acuteenvy)
## Changes ## Changes
- The default number of threads is now constrained to be at most 16. This should improve startup time on - Performance has been significantly improved, both due to optimizations in the underlying `ignore`
systems with many CPU cores. (#1203) crate (#1429), and in `fd` itself (#1422).
- The default number of threads is now constrained to be at most 64. This should improve startup time on
systems with many CPU cores. (#1203, #1412, #1431)
## Other ## Other

24
src/cli.rs
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@ -715,24 +715,14 @@ impl Opts {
fn default_num_threads() -> NonZeroUsize { fn default_num_threads() -> NonZeroUsize {
// If we can't get the amount of parallelism for some reason, then // If we can't get the amount of parallelism for some reason, then
// default to a single thread, because that is safe. // default to a single thread, because that is safe.
// Note that the minimum value for a NonZeroUsize is 1. let fallback = NonZeroUsize::MIN;
// Unfortunately, we can't do `NonZeroUsize::new(1).unwrap()` // To limit startup overhead on massively parallel machines, don't use more
// in a const context. // than 64 threads.
const FALLBACK_PARALLELISM: NonZeroUsize = NonZeroUsize::MIN; let limit = NonZeroUsize::new(64).unwrap();
// As the number of threads increases, the startup time suffers from
// initializing the threads, and we get diminishing returns from additional
// parallelism. So set a maximum number of threads to use by default.
//
// This value is based on some empirical observations, but the ideal value
// probably depends on the exact hardware in use.
//
// Safety: The literal "20" is known not to be zero.
const MAX_DEFAULT_THREADS: NonZeroUsize = unsafe { NonZeroUsize::new_unchecked(20) };
std::cmp::min( std::thread::available_parallelism()
std::thread::available_parallelism().unwrap_or(FALLBACK_PARALLELISM), .unwrap_or(fallback)
MAX_DEFAULT_THREADS, .min(limit)
)
} }
#[derive(Copy, Clone, PartialEq, Eq, ValueEnum)] #[derive(Copy, Clone, PartialEq, Eq, ValueEnum)]