| # Performance testing |
| |
| ## rustc-perf |
| |
| A lot of work is put into improving the performance of the compiler and |
| preventing performance regressions. |
| |
| The [rustc-perf](https://github.com/rust-lang/rustc-perf) project provides |
| several services for testing and tracking performance. It provides hosted |
| infrastructure for running benchmarks as a service. At this time, only |
| `x86_64-unknown-linux-gnu` builds are tracked. |
| |
| A "perf run" is used to compare the performance of the compiler in different |
| configurations for a large collection of popular crates. Different |
| configurations include "fresh builds", builds with incremental compilation, etc. |
| |
| The result of a perf run is a comparison between two versions of the compiler |
| (by their commit hashes). |
| |
| You can also use `rustc-perf` to manually benchmark and profile the compiler |
| [locally](../profiling/with_rustc_perf.md). |
| |
| ### Automatic perf runs |
| |
| After every PR is merged, a suite of benchmarks are run against the compiler. |
| The results are tracked over time on the <https://perf.rust-lang.org/> website. |
| Any changes are noted in a comment on the PR. |
| |
| ### Manual perf runs |
| |
| Additionally, performance tests can be ran before a PR is merged on an as-needed |
| basis. You should request a perf run if your PR may affect performance, |
| especially if it can affect performance adversely. |
| |
| To evaluate the performance impact of a PR, write this comment on the PR: |
| |
| `@bors try @rust-timer queue` |
| |
| > **Note**: Only users authorized to do perf runs are allowed to post this |
| > comment. Teams that are allowed to use it are tracked in the [Teams |
| > repository](https://github.com/rust-lang/team) with the `perf = true` value in |
| > the `[permissions]` section (and bors permissions are also required). If you |
| > are not on one of those teams, feel free to ask for someone to post it for you |
| > (either on Zulip or ask the assigned reviewer). |
| |
| This will first tell bors to do a "try" build which do a full release build for |
| `x86_64-unknown-linux-gnu`. After the build finishes, it will place it in the |
| queue to run the performance suite against it. After the performance tests |
| finish, the bot will post a comment on the PR with a summary and a link to a |
| full report. |
| |
| If you want to do a perf run for an already built artifact (e.g. for a previous |
| try build that wasn't benchmarked yet), you can run this instead: |
| |
| `@rust-timer build <commit-sha>` |
| |
| You cannot benchmark the same artifact twice though. |
| |
| More information about the available perf bot commands can be found |
| [here](https://perf.rust-lang.org/help.html). |
| |
| More details about the benchmarking process itself are available in the [perf |
| collector |
| documentation](https://github.com/rust-lang/rustc-perf/blob/master/collector/README.md). |
