time: Improve Instant::now() perf with test-util#5513
Merged
carllerche merged 4 commits intomasterfrom Feb 27, 2023
Merged
Conversation
The test-util feature flag is only intended to be use with tests. However, it is possible to accidentally enable it in release mode. This patch reduces the overhead of `Instant::now()` when the `test-util` feature flag is enabled but `time::pause()` is not called. The optimization is implemented by adding a static atomic flag that tracks if `time::pause()` has ever been called. In `Instant::now()`, the atomic flag is first checked before the thread-local and mutex are accessed.
carllerche
added
C-enhancement
Darksonn
reviewed
Feb 27, 2023
tokio/src/time/clock.rs
Outdated
Comment on lines
+69
to
+74
| // Used to track if the clock was ever paused. This is an optimization to | ||
| // avoid touching the mutex if `test-util` was accidentally enabled in | ||
| // release mode. | ||
| // | ||
| // A static is used so we can avoid accessing the thread-local as well. | ||
| static DID_PAUSE_CLOCK: AtomicBool = AtomicBool::new(false); |
Member
There was a problem hiding this comment.
This fails with loom. How about using the std atomic here and initializing it to true when #[cfg(loom)]?
Member
Author
There was a problem hiding this comment.
I just switched it to a std bool. Loom tests don't make sense with time right now anyway, so it shouldn't be hit.
Member
|
You should double-check that this still works when using |
Member
Author
Good point. I will have to think about how to test this... |
Member
Author
|
@Darksonn I added a test. It looks like it was already handled. |
Noah-Kennedy
added a commit
that referenced
this pull request
Mar 1, 2023
# 1.26.0 (March 1st, 2023) ### Fixed - sync: don't leak tracing spans in mutex guards ([#5469]) - sync: drop wakers after unlocking the mutex in Notify ([#5471]) - sync: drop wakers outside lock in semaphore ([#5475]) - macros: fix empty `join!` and `try_join!` ([#5504]) ### Added - fs: add `fs::try_exists` ([#4299]) - net: add types for named unix pipes ([#5351]) - sync: add `MappedOwnedMutexGuard` ([#5474]) ### Documented - task: clarify what happens to spawned work during runtime shutdown ([#5394]) - task: clarify `process::Command` docs (#5406) ([#5413]) - sync: add doc aliases for `blocking_*` methods ([#5448]) - task: fix wording with 'unsend' ([#5452]) - signal: updated Documentation for Signals ([#5459]) - sync: fix docs for Send/Sync bounds in broadcast ([#5480]) - io: improve AsyncFd example ([#5481]) - tokio: document supported platforms ([#5483]) - runtime: document the nature of the main future ([#5494]) - sync: document drop behavior for channels ([#5497]) - time: document immediate completion guarantee for timeouts ([#5509]) - runtime: remove extra period in docs ([#5511]) ### Changed - net: use Message Read Mode for named pipes ([#5350]) - chore: update windows-sys to 0.45 ([#5386]) - sync: mark lock guards with `#[clippy::has_significant_drop]` ([#5422]) - sync: reduce contention in watch channel ([#5464]) - time: remove cache padding in timer entries ([#5468]) - time: Improve `Instant::now()` perf with test-util ([#5513]) ### Internal Changes - tests: port proptest fuzz harnesses to use cargo-fuzz ([#5392]) - time: don't store deadline twice in sleep entries ([#5410]) - rt: remove Arc from Clock ([#5434]) - sync: make `notify_waiters` calls atomic ([#5458]) - net: refactor named pipe builders to not use bitfields ([#5477]) - io: use `poll_fn` in `copy_bidirectional` ([#5486]) - fs: add more tests for filesystem functionality ([#5493]) - net: fix test compilation failure ([#5506]) - io: ignore SplitByUtf8BoundaryIfWindows test on miri ([#5507]) ### Unstable - metrics: add a new metric for budget exhaustion yields ([#5517]) [#4299]: #4299 [#5350]: #5350 [#5351]: #5351 [#5386]: #5386 [#5392]: #5392 [#5394]: #5394 [#5410]: #5410 [#5413]: #5413 [#5422]: #5422 [#5434]: #5434 [#5448]: #5448 [#5452]: #5452 [#5458]: #5458 [#5459]: #5459 [#5464]: #5464 [#5468]: #5468 [#5469]: #5469 [#5471]: #5471 [#5474]: #5474 [#5475]: #5475 [#5477]: #5477 [#5480]: #5480 [#5481]: #5481 [#5483]: #5483 [#5486]: #5486 [#5493]: #5493 [#5494]: #5494 [#5497]: #5497 [#5504]: #5504 [#5506]: #5506 [#5507]: #5507 [#5509]: #5509 [#5511]: #5511 [#5513]: #5513 [#5517]: #5517
Noah-Kennedy
added a commit
that referenced
this pull request
Mar 1, 2023
# 1.26.0 (March 1st, 2023) ### Fixed - macros: fix empty `join!` and `try_join!` ([#5504]) - sync: don't leak tracing spans in mutex guards ([#5469]) - sync: drop wakers after unlocking the mutex in Notify ([#5471]) - sync: drop wakers outside lock in semaphore ([#5475]) ### Added - fs: add `fs::try_exists` ([#4299]) - net: add types for named unix pipes ([#5351]) - sync: add `MappedOwnedMutexGuard` ([#5474]) ### Changed - chore: update windows-sys to 0.45 ([#5386]) - net: use Message Read Mode for named pipes ([#5350]) - sync: mark lock guards with `#[clippy::has_significant_drop]` ([#5422]) - sync: reduce contention in watch channel ([#5464]) - time: remove cache padding in timer entries ([#5468]) - time: Improve `Instant::now()` perf with test-util ([#5513]) ### Internal Changes - io: use `poll_fn` in `copy_bidirectional` ([#5486]) - net: refactor named pipe builders to not use bitfields ([#5477]) - rt: remove Arc from Clock ([#5434]) - sync: make `notify_waiters` calls atomic ([#5458]) - time: don't store deadline twice in sleep entries ([#5410]) ### Unstable - metrics: add a new metric for budget exhaustion yields ([#5517]) ### Documented - io: improve AsyncFd example ([#5481]) - runtime: document the nature of the main future ([#5494]) - runtime: remove extra period in docs ([#5511]) - signal: updated Documentation for Signals ([#5459]) - sync: add doc aliases for `blocking_*` methods ([#5448]) - sync: fix docs for Send/Sync bounds in broadcast ([#5480]) - sync: document drop behavior for channels ([#5497]) - task: clarify what happens to spawned work during runtime shutdown ([#5394]) - task: clarify `process::Command` docs ([#5413]) - task: fix wording with 'unsend' ([#5452]) - time: document immediate completion guarantee for timeouts ([#5509]) - tokio: document supported platforms ([#5483]) [#4299]: #4299 [#5350]: #5350 [#5351]: #5351 [#5386]: #5386 [#5394]: #5394 [#5410]: #5410 [#5413]: #5413 [#5422]: #5422 [#5434]: #5434 [#5448]: #5448 [#5452]: #5452 [#5458]: #5458 [#5459]: #5459 [#5464]: #5464 [#5468]: #5468 [#5469]: #5469 [#5471]: #5471 [#5474]: #5474 [#5475]: #5475 [#5477]: #5477 [#5480]: #5480 [#5481]: #5481 [#5483]: #5483 [#5486]: #5486 [#5494]: #5494 [#5497]: #5497 [#5504]: #5504 [#5509]: #5509 [#5511]: #5511 [#5513]: #5513 [#5517]: #5517
Noah-Kennedy
added a commit
that referenced
this pull request
Mar 1, 2023
# 1.26.0 (March 1st, 2023) ### Fixed - macros: fix empty `join!` and `try_join!` ([#5504]) - sync: don't leak tracing spans in mutex guards ([#5469]) - sync: drop wakers after unlocking the mutex in Notify ([#5471]) - sync: drop wakers outside lock in semaphore ([#5475]) ### Added - fs: add `fs::try_exists` ([#4299]) - net: add types for named unix pipes ([#5351]) - sync: add `MappedOwnedMutexGuard` ([#5474]) ### Changed - chore: update windows-sys to 0.45 ([#5386]) - net: use Message Read Mode for named pipes ([#5350]) - sync: mark lock guards with `#[clippy::has_significant_drop]` ([#5422]) - sync: reduce contention in watch channel ([#5464]) - time: remove cache padding in timer entries ([#5468]) - time: Improve `Instant::now()` perf with test-util ([#5513]) ### Internal Changes - io: use `poll_fn` in `copy_bidirectional` ([#5486]) - net: refactor named pipe builders to not use bitfields ([#5477]) - rt: remove Arc from Clock ([#5434]) - sync: make `notify_waiters` calls atomic ([#5458]) - time: don't store deadline twice in sleep entries ([#5410]) ### Unstable - metrics: add a new metric for budget exhaustion yields ([#5517]) ### Documented - io: improve AsyncFd example ([#5481]) - runtime: document the nature of the main future ([#5494]) - runtime: remove extra period in docs ([#5511]) - signal: updated Documentation for Signals ([#5459]) - sync: add doc aliases for `blocking_*` methods ([#5448]) - sync: fix docs for Send/Sync bounds in broadcast ([#5480]) - sync: document drop behavior for channels ([#5497]) - task: clarify what happens to spawned work during runtime shutdown ([#5394]) - task: clarify `process::Command` docs ([#5413]) - task: fix wording with 'unsend' ([#5452]) - time: document immediate completion guarantee for timeouts ([#5509]) - tokio: document supported platforms ([#5483]) [#4299]: #4299 [#5350]: #5350 [#5351]: #5351 [#5386]: #5386 [#5394]: #5394 [#5410]: #5410 [#5413]: #5413 [#5422]: #5422 [#5434]: #5434 [#5448]: #5448 [#5452]: #5452 [#5458]: #5458 [#5459]: #5459 [#5464]: #5464 [#5468]: #5468 [#5469]: #5469 [#5471]: #5471 [#5474]: #5474 [#5475]: #5475 [#5477]: #5477 [#5480]: #5480 [#5481]: #5481 [#5483]: #5483 [#5486]: #5486 [#5494]: #5494 [#5497]: #5497 [#5504]: #5504 [#5509]: #5509 [#5511]: #5511 [#5513]: #5513 [#5517]: #5517
This was referenced Mar 1, 2023
This was referenced Feb 20, 2026
This was referenced Feb 28, 2026
This was referenced Mar 11, 2026
Open
This was referenced Mar 19, 2026
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
2 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.
The test-util feature flag is only intended to be used with tests. However, it is possible to enable it in release mode accidentally. This patch reduces the overhead of
Instant::now()when thetest-utilfeature flag is enabled buttime::pause()is not called.The optimization is implemented by adding a static atomic flag that tracks if
time::pause()has ever been called. InInstant::now(), the atomic flag is first checked before the thread-local and mutex are accessed.On my dev box, the patch reduces the benchmark from ~175ns/iteration to ~145ns/iteration, which is in line with running the benchmark without
test-util.