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Document bootstrap profiling

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Jakub Beránek 2025-02-12 13:48:48 +01:00
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src/building/bootstrapping/debugging-bootstrap.md
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@ -121,6 +121,14 @@ For `#[instrument]`, it's recommended to:
- Explicitly pick an instrumentation name via `name = ".."` to distinguish between e.g. `run` of different steps.
- Take care to not cause diverging behavior via tracing, e.g. building extra things only when tracing infra is enabled.
### Profiling bootstrap
You can use the `COMMAND` tracing target to trace execution of most commands spawned by bootstrap. If you also use the `BOOTSTRAP_PROFILE=1` environment variable, bootstrap will generate a Chrome JSON trace file, which can be visualized in Chrome's `chrome://tracing` page or on https://ui.perfetto.dev.
```bash
$ BOOTSTRAP_TRACING=COMMAND=trace BOOTSTRAP_PROFILE=1 ./x build library
```
### rust-analyzer integration?
Unfortunately, because bootstrap is a `rust-analyzer.linkedProjects`, you can't ask r-a to check/build bootstrap itself with `tracing` feature enabled to get relevant completions, due to lack of support as described in <https://github.com/rust-lang/rust-analyzer/issues/8521>.