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().
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@ -5,7 +5,7 @@ pub(super) fn monotonize(raw: time::Instant) -> time::Instant {
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inner::monotonize(raw)
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}
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#[cfg(all(target_has_atomic = "64", not(target_has_atomic = "128")))]
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#[cfg(any(all(target_has_atomic = "64", not(target_has_atomic = "128")), target_arch = "aarch64"))]
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pub mod inner {
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use crate::sync::atomic::AtomicU64;
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use crate::sync::atomic::Ordering::*;
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@ -70,7 +70,7 @@ pub mod inner {
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}
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}
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#[cfg(target_has_atomic = "128")]
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#[cfg(all(target_has_atomic = "128", not(target_arch = "aarch64")))]
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pub mod inner {
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use crate::sync::atomic::AtomicU128;
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use crate::sync::atomic::Ordering::*;
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