Conversation
`RUSTFLAGS=-Ctarget-cpu=native cargo bench` on x86_64 AMD Ryzen Threadripper 2990WX.
dtolnay
commented
Sep 1, 2025
| (1, 22) | ||
| (2, 29) | ||
| (3, 27) | ||
| (4, 34) |
Owner
Author
There was a problem hiding this comment.
Looking more into this significant regression in libstd times, it seems to be relatively recent but spread over multiple Rust releases. Here are the recent u64::MAX timings (the others follow a similar ratio):
- Rust 1.50–1.82: 23ns
- Rust 1.83–1.86: 26ns
- Rust 1.87–1.90-beta: 28ns
- Rust 1.91-nightly: 34ns
The regression in 1.91 bisects to nightly-2025-08-29.
Owner
Author
There was a problem hiding this comment.
Based on RUSTFLAGS=-Ctarget-cpu=native cargo bisect-rustc --start 2025-08-28 --end 2025-08-29 --prompt -- bench bench_std_fmt::bench_u64_max it's rust-lang/rust#145877.
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
1 participant
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
Closes #59.
Measured using
RUSTFLAGS=-Ctarget-cpu=native cargo benchon x86_64 AMD Ryzen Threadripper 2990WX.