Improve inlining of scope latch counters #1057
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The `increment` and `set` methods now have `#[inline]` hints, and the `counter` fields in `CountLatch` and `CountLockLatch` are now listed first to increase the chance that layout puts them at the same offset. (That layout is not critical to ensure, but works out nicely.)
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This was referenced Jun 20, 2023
cuviper
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The former `enum ScopeLatch` forced a `match` during both `increment` and `set` (decrement), even though both variants only need to update an `AtomicUsize` most of the time. rayon-rs#1057 helped hide that for `increment`, but `set` branching still showed up in perf profiles. Now this is refactored to a unified `CountLatch` that has a direct field for its `counter` used in the frequent case, and then an internal enum for the one-time notification variants. Therefore, most of its updates will have no `match` reached at all. The only other use of the former `CountLatch` was the one-shot termination latch in `WorkerThread`, so that's now renamed to `OnceLatch`.
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1059: Refactor scope latches to reduce matching r=cuviper a=cuviper The former `enum ScopeLatch` forced a `match` during both `increment` and `set` (decrement), even though both variants only need to update an `AtomicUsize` most of the time. #1057 helped hide that for `increment`, but `set` branching still showed up in perf profiles. Now this is refactored to a unified `CountLatch` that has a direct field for its `counter` used in the frequent case, and then an internal enum for the one-time notification variants. Therefore, most of its updates will have no `match` reached at all. The only other use of the former `CountLatch` was the one-shot termination latch in `WorkerThread`, so that's now renamed to `OnceLatch`. Co-authored-by: Josh Stone <cuviper@gmail.com>
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The
incrementandsetmethods now have#[inline]hints, and thecounterfields inCountLatchandCountLockLatchare now listedfirst to increase the chance that layout puts them at the same offset.
(That layout is not critical to ensure, but works out nicely.)