Fix #1692: Add example for profiling diff locally #2696

Mattias-Petersson · 2025-12-14T16:30:50Z

Added an example for profiling an external crate diff locally. #1692 also mentions that the debuginfo-level = 1 should be mentioned, but that has been solved by a different commit and as such was not included here.

rustbot · 2025-12-14T16:30:53Z

Thanks for the PR. If you have write access, feel free to merge this PR if it does not need reviews. You can request a review using r? rustc-dev-guide or r? <username>.

Mattias-Petersson · 2025-12-14T16:34:13Z

r? rustc-dev-guide

tshepang · 2025-12-17T12:01:19Z

src/profiling/with_rustc_perf.md

could you show this command instead

cargo run --release --bin collector

this would remove the need to indicate where the exe is located

Done now, apologize for taking so long. I have also updated the branch to be on the latest main. (Took a few commits to get right but now it should be proper :)) Does it look okay now? :)

I would not have bothered with updating the branch, unless there was a conflict with main. I have submitted #2712 to remove the bot messages.

Perfect, thank you for the update :) There was no conflict with main, just how I am used to working to rebase onto the latest main branch. Good to know that it is not necessary!

Added an example for profiling an external crate diff locally. The original issue also mentions that the debuginfo-level = 1 should be highlighted, but that has been solved by a different commit and as such was not included here.

Changed so cargo specifies the binary collector, removing the need to link to its local binary. Clarified that the SHAs should be from the rustc-repo, but the command should be ran in the rustc-perf repo.

tshepang · 2026-01-01T12:13:10Z

src/profiling/with_rustc_perf.md

+The collector can then be run using cargo, specifying the collector binary. It expects the following arguments:
+- `<PROFILE>`: Profiler selection for how performance should be measured. For this example we will use Cachegrind.
+- `<RUSTC>`: The Rust compiler revision to benchmark, specified as a commit SHA from `rust-lang/rust`.
+Optional arguments allow running profiles and scenarios as described above. `--include` in `x perf` is instead `--exact-match`. More information regarding the mandatory and


what does this mean

--include in x perf is instead --exact-match

tshepang · 2026-01-01T12:14:43Z

src/profiling/with_rustc_perf.md

+Optional arguments allow running profiles and scenarios as described above. `--include` in `x perf` is instead `--exact-match`. More information regarding the mandatory and
+optional arguments can be found in the [rustc-perf-readme-profilers].
+
+Then, for the case of generating a profile diff for the crate `serve_derive-1.0.136`, for two commits `<SHA1>` and `<SHA2>` from the `rust-lang/rust` repository, run the following in the `rustc-perf` repo (where the collector was built in the previous step):


regarding

where the collector was built in the previous step

I would not show the command to build it, since the command to run it also builds it

tshepang · 2026-01-01T12:18:43Z

sorry this is taking so long, but had to learn how this works so I can confidently approve... just really one more thing before I can do so

rustbot added the S-waiting-on-review Status: this PR is waiting for a reviewer to verify its content label Dec 14, 2025