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## perf-event: a Rust interface to Linux performance monitoring
*This is a nascent project. Tests are lacking. The design may change.*
This uses the Linux [`perf_event_open`][man] API to access performance monitoring
hardware and software. Use `Builder` to create a perf event counter, then use
`enable` and `disable` to start and stop counting. Call `read` to get your
count.
For example, this counts the number of cycles used by the call to `println!`.
Try adjusting the length of the vector to see the cycle count change.
use perf_event::Builder;
fn main() -> std::io::Result<()> {
let mut counter = Builder::new().build()?;
let vec = (0..=51).collect::<Vec<_>>();
counter.enable()?;
println!("{:?}", vec);
counter.disable()?;
println!("{} instructions retired", counter.read()?);
Ok(())
}
Since we don't specify what sort of event we want to count, `Builder` defaults
to `PERF_COUNT_HW_INSTRUCTIONS` events, whose documentation says:
> Retired instructions. Be careful, these can be affected by various issues,
> most notably hardware interrupt counts.
The `examples` directory includes programs that count other sorts of events.
[man]: http://man7.org/linux/man-pages/man2/perf_event_open.2.html
## See also
The [`perfcnt`] crate provides more extensive coverage of the Linux
`perf_event_open` API than this crate. However, `perfcnt` does not build on
stable Rust.
[`perfcnt`]: https://crates.io/crates/perfcnt
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