| # Benchmarking and Profiling |
| |
| ## Internal profiler |
| |
| Cargo leverages [tracing](https://crates.io/crates/tracing) |
| as a basic, hierarchical built-in profiler. |
| |
| Environment variables: |
| - `CARGO_LOG_PROFILE=<true|1>`: log tracing events to a file in the current working directory |
| - `CARGO_LOG_PROFILE_CAPTURE_ARGS=<true|1>`: include arguments in the events |
| |
| At process exit, your trace will be in a file like `trace-1668480819035032.json`. |
| Open that file with [ui.perfetto.dev](https://ui.perfetto.dev) (or chrome://tracing) to browse your trace. |
| |
| Example: |
| ```console |
| $ # Output first three levels of profiling info |
| $ CARGO_LOG_PROFILE=true cargo generate-lockfile |
| ``` |
| |
| **Note:** This is intended for the development of cargo and there are no compatibility guarantees on this functionality. |
| |
| ## Benchmarking |
| |
| ### Benchsuite |
| |
| Head over to the [`benches` |
| directory](https://github.com/rust-lang/cargo/tree/master/benches) for more |
| information about the benchmarking suite. |
| |
| ### Informal benchmarking |
| |
| The overhead for starting a build should be kept as low as possible |
| (preferably, well under 0.5 seconds on most projects and systems). Currently, |
| the primary parts that affect this are: |
| |
| * Running the resolver. |
| * Querying the index. |
| * Checking git dependencies. |
| * Scanning the local project. |
| * Building the unit dependency graph. |
| |
| One way to test this is to use [hyperfine]. This is a tool that can be used to |
| measure the difference between different commands and settings. Usually this |
| is done by measuring the time it takes for `cargo build` to finish in a large |
| project where the build is fresh (no actual compilation is performed). Just |
| run `cargo build` once before using hyperfine. |
| |
| [hyperfine]: https://github.com/sharkdp/hyperfine |
