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Rollup merge of #88651 - AGSaidi:monotonize-inner-64b-aarch64, r=dtolnay

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Use the 64b inner:monotonize() implementation not the 128b one for aarch64

aarch64 prior to v8.4 (FEAT_LSE2) doesn't have an instruction that guarantees
untorn 128b reads except for completing a 128b load/store exclusive pair
(ldxp/stxp) or compare-and-swap (casp) successfully. The requirement to
complete a 128b read+write atomic is actually more expensive and more unfair
than the previous implementation of monotonize() which used a Mutex on aarch64,
especially at large core counts.  For aarch64 switch to the 64b atomic
implementation which is about 13x faster for a benchmark that involves many
calls to Instant::now().
This commit is contained in:
Manish Goregaokar 2021-10-04 23:56:17 -07:00 committed by GitHub
commit dd223d5c6d
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1 changed files with 2 additions and 2 deletions
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4
library/std/src/time/monotonic.rs
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@ -5,7 +5,7 @@ pub(super) fn monotonize(raw: time::Instant) -> time::Instant {
inner::monotonize(raw)
}
#[cfg(all(target_has_atomic = "64", not(target_has_atomic = "128")))]
#[cfg(any(all(target_has_atomic = "64", not(target_has_atomic = "128")), target_arch = "aarch64"))]
pub mod inner {
use crate::sync::atomic::AtomicU64;
use crate::sync::atomic::Ordering::*;
@ -71,7 +71,7 @@ pub mod inner {
}
}
#[cfg(target_has_atomic = "128")]
#[cfg(all(target_has_atomic = "128", not(target_arch = "aarch64")))]
pub mod inner {
use crate::sync::atomic::AtomicU128;
use crate::sync::atomic::Ordering::*;