Migrate to core::hint::black_box()#16980
Merged
alice-i-cecile merged 3 commits intobevyengine:mainfrom Dec 29, 2024
Merged
Conversation
…tead `core::hint::black_box()` has no performance overhead, and is the preferred method of blocking optimizations in benchmarks. It was likely introduced after our benchmarks were created, which is why we didn't use it before.
BD103
added
D-Trivial
hymm
approved these changes
Dec 26, 2024
BD103
added
S-Ready-For-Final-Review
mnmaita
approved these changes
Dec 26, 2024
BenjaminBrienen
approved these changes
Dec 27, 2024
This was referenced Dec 27, 2024
ecoskey
pushed a commit
to ecoskey/bevy
that referenced
this pull request
Jan 6, 2025
# Objective Many of our benchmarks use [`criterion::black_box()`](https://docs.rs/criterion/latest/criterion/fn.black_box.html), which is used to prevent the compiler from optimizing away computation that we're trying to time. This can be slow, though, because `criterion::black_box()` forces a point read each time it is called through [`ptr::road_volatile()`](https://doc.rust-lang.org/stable/std/ptr/fn.read_volatile.html). In Rust 1.66, the standard library introduced [`core::hint::black_box()`](https://doc.rust-lang.org/nightly/std/hint/fn.black_box.html) (and `std::hint::black_box()`). This is an intended replacement for `criterion`'s version that uses compiler intrinsics instead of volatile pointer reads, and thus has no runtime overhead. This increases benchmark accuracy, which is always nice 👍 Note that benchmarks may _appear_ to improve in performance after this change, but that's just because we are eliminating the pointer read overhead. ## Solution - Deny `criterion::black_box` in `clippy.toml`. - Fix all imports. ## Testing - `cargo clippy -p benches --benches`
mrchantey
pushed a commit
to mrchantey/bevy
that referenced
this pull request
Feb 4, 2025
# Objective Many of our benchmarks use [`criterion::black_box()`](https://docs.rs/criterion/latest/criterion/fn.black_box.html), which is used to prevent the compiler from optimizing away computation that we're trying to time. This can be slow, though, because `criterion::black_box()` forces a point read each time it is called through [`ptr::road_volatile()`](https://doc.rust-lang.org/stable/std/ptr/fn.read_volatile.html). In Rust 1.66, the standard library introduced [`core::hint::black_box()`](https://doc.rust-lang.org/nightly/std/hint/fn.black_box.html) (and `std::hint::black_box()`). This is an intended replacement for `criterion`'s version that uses compiler intrinsics instead of volatile pointer reads, and thus has no runtime overhead. This increases benchmark accuracy, which is always nice 👍 Note that benchmarks may _appear_ to improve in performance after this change, but that's just because we are eliminating the pointer read overhead. ## Solution - Deny `criterion::black_box` in `clippy.toml`. - Fix all imports. ## Testing - `cargo clippy -p benches --benches`
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
5 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Objective
Many of our benchmarks use
criterion::black_box(), which is used to prevent the compiler from optimizing away computation that we're trying to time. This can be slow, though, becausecriterion::black_box()forces a point read each time it is called throughptr::road_volatile().In Rust 1.66, the standard library introduced
core::hint::black_box()(andstd::hint::black_box()). This is an intended replacement forcriterion's version that uses compiler intrinsics instead of volatile pointer reads, and thus has no runtime overhead. This increases benchmark accuracy, which is always nice 👍Note that benchmarks may appear to improve in performance after this change, but that's just because we are eliminating the pointer read overhead.
Solution
criterion::black_boxinclippy.toml.Testing
cargo clippy -p benches --benches