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

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

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18 changes: 18 additions & 0 deletions src/profiling/with_rustc_perf.md
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@tshepang tshepang Dec 17, 2025

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could you show this command instead

cargo run --release --bin collector

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

Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,24 @@ You can use the following options for the `x perf` command, which mirror the cor
- `--profiles`: Select profiles (`Check`, `Debug`, `Opt`, `Doc`) which should be profiled/benchmarked.
- `--scenarios`: Select scenarios (`Full`, `IncrFull`, `IncrPatched`, `IncrUnchanged`) which should be profiled/benchmarked.

## Example profiling diff for external crates
It can be of interest to generate a local diff for two commits of the compiler for external crates.
To start, in the `rustc-perf` repo, build the collector, which runs the Rust compiler benchmarks as follows.
```
cargo build --release -p collector
```
After this the collector can be located in `.\target\release\collector`, can be run locally with `bench_local` and 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
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>` in the `rust-lang/rust` repository, run the following
```
./target/release/collector profile_local cachegrind +<SHA1> --rustc2 +<SHA2> --exact-match serde_derive-1.0.136 --profiles Check --scenarios IncrUnchanged
```


[samply]: https://github.com/mstange/samply
[cachegrind]: https://www.cs.cmu.edu/afs/cs.cmu.edu/project/cmt-40/Nice/RuleRefinement/bin/valgrind-3.2.0/docs/html/cg-manual.html
[rustc-perf]: https://github.com/rust-lang/rustc-perf
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