cargo-bench(1)

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NAME

cargo-bench --- Execute benchmarks of a package

SYNOPSIS

cargo bench [options] [benchname] [-- bench-options]

DESCRIPTION

Compile and execute benchmarks.

The benchmark filtering argument benchname and all the arguments following the two dashes (--) are passed to the benchmark binaries and thus to libtest (rustc‘s built in unit-test and micro-benchmarking framework). If you are passing arguments to both Cargo and the binary, the ones after -- go to the binary, the ones before go to Cargo. For details about libtest’s arguments see the output of cargo bench -- --help and check out the rustc book's chapter on how tests work at https://doc.rust-lang.org/rustc/tests/index.html.

As an example, this will run only the benchmark named foo (and skip other similarly named benchmarks like foobar):

cargo bench -- foo --exact

Benchmarks are built with the --test option to rustc which creates a special executable by linking your code with libtest. The executable automatically runs all functions annotated with the #[bench] attribute. Cargo passes the --bench flag to the test harness to tell it to run only benchmarks, regardless of whether the harness is libtest or a custom harness.

The libtest harness may be disabled by setting harness = false in the target manifest settings, in which case your code will need to provide its own main function to handle running benchmarks.

Note: The #[bench] attribute is currently unstable and only available on the nightly channel. There are some packages available on crates.io that may help with running benchmarks on the stable channel, such as Criterion.

By default, cargo bench uses the bench profile, which enables optimizations and disables debugging information. If you need to debug a benchmark, you can use the --profile=dev command-line option to switch to the dev profile. You can then run the debug-enabled benchmark within a debugger.

Working directory of benchmarks

The working directory of every benchmark is set to the root directory of the package the benchmark belongs to. Setting the working directory of benchmarks to the package‘s root directory makes it possible for benchmarks to reliably access the package’s files using relative paths, regardless from where cargo bench was executed from.

OPTIONS

Benchmark Options

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Target Selection

When no target selection options are given, cargo bench will build the following targets of the selected packages:

  • lib --- used to link with binaries and benchmarks
  • bins (only if benchmark targets are built and required features are available)
  • lib as a benchmark
  • bins as benchmarks
  • benchmark targets

The default behavior can be changed by setting the bench flag for the target in the manifest settings. Setting examples to bench = true will build and run the example as a benchmark, replacing the example's main function with the libtest harness.

Setting targets to bench = false will stop them from being benchmarked by default. Target selection options that take a target by name (such as --example foo) ignore the bench flag and will always benchmark the given target.

See Configuring a target for more information on per-target settings.

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Compilation Options

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Output Options

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Display Options

By default the Rust test harness hides output from benchmark execution to keep results readable. Benchmark output can be recovered (e.g., for debugging) by passing --nocapture to the benchmark binaries:

cargo bench -- --nocapture

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Manifest Options

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Miscellaneous Options

The --jobs argument affects the building of the benchmark executable but does not affect how many threads are used when running the benchmarks. The Rust test harness runs benchmarks serially in a single thread.

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While cargo bench involves compilation, it does not provide a --keep-going flag. Use --no-fail-fast to run as many benchmarks as possible without stopping at the first failure. To “compile” as many benchmarks as possible, use --benches to build benchmark binaries separately. For example:

cargo build --benches --release --keep-going
cargo bench --no-fail-fast

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EXAMPLES

  1. Build and execute all the benchmarks of the current package:

    cargo bench

  2. Run only a specific benchmark within a specific benchmark target:

    cargo bench --bench bench_name -- modname::some_benchmark

SEE ALSO

{{man “cargo” 1}}, {{man “cargo-test” 1}}