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Installation

For all Rust integrations, you will need the cargo-codspeed command to build and run your CodSpeed benchmarks
Install the bencher compatibility layer: 
cargo add --dev codspeed-bencher-compat --rename bencher
Or directly change your Cargo.toml if you already have bencher installed: 
[dev-dependencies]
bencher = { package = "codspeed-bencher-compat", version = "*" }
If you prefer, you can also install codspeed-bencher-compat as is and change your imports to use this new crate name.
This will install the codspeed-bencher-compat crate and rename it to bencher in your Cargo.toml. This way, you can keep your existing imports and the compatibility layer will take care of the rest.
The compatibility layer is a passthrough when not using cargo codspeed, running cargo bench will behave exactly as with the default bencher crate.

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Usage

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Creating benchmarks

Let’s start with the example from the bencher documentation, creating a benchmark suite for 2 simple functions:
benches/example.rs
use bencher::{benchmark_group, benchmark_main, Bencher};

fn a(bench: &mut Bencher) {
    bench.iter(|| {
        (0..1000).fold(0, |x, y| x + y)
    })
}

fn b(bench: &mut Bencher) {
    const N: usize = 1024;
    bench.iter(|| {
        vec![0u8; N]
    });

    bench.bytes = N as u64;
}

benchmark_group!(benches, a, b);
benchmark_main!(benches);
The last step in creating the Bencher benchmark is to add the new benchmark target in your Cargo.toml:
Cargo.toml
[[bench]]
name = "example"
harness = false
And that’s it! You can now run your benchmark suite with CodSpeed

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Testing the benchmarks locally

terminal
$ cargo codspeed build
    Finished release [optimized] target(s) in 0.12s
    Finished built 1 benchmark suite(s)

$ cargo codspeed run
   Collected 1 benchmark suite(s) to run
     Running example
Using codspeed-bencher-compat v1.0.0 compatibility layer
NOTICE: codspeed is enabled, but no performance measurement will be made since it's running in an unknown environment.
Checked: benches/example.rs::a (group: benches)
Checked: benches/example.rs::b (group: benches)
        Done running bencher_example
    Finished running 1 benchmark suite(s)
Congrats! 🎉 You can now run those benchmark in your CI to get the actual performance measurements 👇.
Use --measurement-mode / -m to select the CodSpeed instrument:
  • simulation (default): Runs benchmarks once on a simulated CPU for consistent measurements.
  • walltime: Measures wall-clock time for real-world scenarios.
  • memory: Benchmarks are run once using memory profiling to track heap allocations and memory usage.
See the cargo-codspeed reference for more information.

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Running the benchmarks in your CI

To generate performance reports, you need to run the benchmarks in your CI. This allows CodSpeed to automatically run benchmarks and warn you about regressions during development.
If you want more details on how to configure the CodSpeed action, you can check out the Continuous Reporting section.
Here is an example of a GitHub Actions workflow that runs the benchmarks and reports the results to CodSpeed on every push to the main branch and every pull request:

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Recipes

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Running benchmarks in parallel CI jobs

With Rust, if you use multiple packages, a first sharding optimization is to split your benchmarks across these packages. For example, using Github Actions:
It is not required to pass a -p flag as only the benchmarks built by cargo codspeed build will be run.
For more information about multiple packages, check the cargo-codspeed docs.
Same benchmark with different variationsFor now, you cannot run the same benchmarks several times within the same run. If the same benchmark is run multiple times, you will receive the following comment on your pull request:Multiple Benchmark Variations Error Message
Learn more about benchmark sharding and how to integrate with your CI provider.
To combine measurement modes like simulation and memory, check out the documentation on running multiple instruments serially.