CARGO-BENCH(1)

📦 version 1.81.0, in ubuntu jammy, ubuntu noble

✨ cargo-bench ✨

the manual page, but make it a group chat — this is cargo-bench from the General Commands Manual, bestie 💖

🌸 NAME 🌸

cargo-bench — Execute benchmarks of a package 💅

🎀 SYNOPSIS 🎀

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

🦋 DESCRIPTION 🦋

okay so. compile and execute benchmarks. that's the whole vibe. ✨

The benchmark-filtering argument benchname and every single argument after the two dashes (--) get passed straight to the benchmark binaries, and therefore to libtest — that's rustc's built-in unit-test-and-micro-benchmarking framework, iykyk. 🫶 If you're passing args to both Cargo and the binary: everything after -- goes to the binary, everything before it goes to Cargo. no cap. Want the full tea on libtest's arguments? peep 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 📚

Example time, bestie — this one runs only the benchmark literally named foo and skips other similarly named ones like foobar:

cargo bench -- foo --exact

Benchmarks are built with the --test option to rustc, which makes a special executable by linking your code with libtest. That executable automatically runs every function annotated with the #[bench] attribute. and Cargo? Cargo passes the --bench flag to the test harness to tell it "run benchmarks only pls" — regardless of whether the harness is libtest or a custom one. 👑

The libtest harness can be disabled by setting harness = false in the target manifest settings. in that case your code has to provide its own main function to handle running benchmarks. main character energy, honestly. 💅

Note: the #[bench] attribute (https://doc.rust-lang.org/nightly/unstable-book/library-features/test.html) is currently unstable and only available on the nightly channel (https://doc.rust-lang.org/book/appendix-07-nightly-rust.html). There are some packages on crates.io (https://crates.io/keywords/benchmark) that may help with running benchmarks on the stable channel, such as Criterion (https://crates.io/crates/criterion). 🍓

By default, cargo bench uses the bench profile (https://doc.rust-lang.org/cargo/reference/profiles.html#bench), which enables optimizations and disables debugging information. Need to debug a benchmark? use the --profile=dev command-line option to switch to the dev profile, then run the debug-enabled benchmark inside 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 it there means benchmarks can reliably grab the package's files using relative paths — no matter where you ran cargo bench from. obsessed. 🎀

✨ OPTIONS ✨

💅 Benchmark Options 💅

  • --no-run — compile, but don't run benchmarks. build only, bestie. 🛑
  • --no-fail-fast — run all benchmarks regardless of failure. Without this flag, Cargo exits after the first executable fails. The Rust test harness will run all benchmarks within the executable to completion — this flag only applies to the executable as a whole. periodt. 💀

👑 Package Selection 👑

By default, when no package selection options are given, the packages selected depend on the selected manifest file (based on the current working directory if --manifest-path isn't given). If the manifest is the root of a workspace, then the workspace's default members are selected. otherwise only the package defined by the manifest gets selected. 🌈

The default members of a workspace can be set explicitly with the workspace.default-members key in the root manifest. If that's not set: a virtual workspace includes all workspace members (equivalent to passing --workspace), and a non-virtual workspace includes only the root crate itself. iykyk. 💜

  • -p *spec*…, --package *spec*… — benchmark only the specified packages. See cargo-pkgid(1) for the SPEC format. This flag may be specified multiple times and supports common Unix glob patterns like *, ? and []. BUT — to avoid your shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each pattern. 🫶
  • --workspace — benchmark all members in the workspace. slay. 👑
  • --all — deprecated alias for --workspace. it's giving legacy, ngl.
  • --exclude *SPEC*… — exclude the specified packages. Must be used in conjunction with the --workspace flag. This flag may be specified multiple times and supports common Unix glob patterns like *, ? and []. However, to avoid your shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each pattern. 🎀

🦋 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 stops them from being benchmarked by default. Target selection options that take a target by name (like --example foo) ignore the bench flag and will always benchmark the given target.

See Configuring a target (https://doc.rust-lang.org/cargo/reference/cargo-targets.html#configuring-a-target) for more info on per-target settings. 📖

Binary targets are automatically built if there's an integration test or benchmark being selected to benchmark. This lets an integration test execute the binary to exercise and test its behavior. The CARGO_BIN_EXE_<name> environment variable (https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates) is set when the integration test is built, so it can use the env macro (https://doc.rust-lang.org/std/macro.env.html) to locate the executable. 🔥

Passing target selection flags will benchmark only the specified targets.

Note that --bin, --example, --test and --bench flags also support common Unix glob patterns like *, ? and []. However, to avoid your shell accidentally expanding glob patterns before Cargo handles them, you must use single quotes or double quotes around each glob pattern. 💅

  • --lib — benchmark the package's library. 📚
  • --bin *name*… — benchmark the specified binary. This flag may be specified multiple times and supports common Unix glob patterns.
  • --bins — benchmark all binary targets.
  • --example *name*… — benchmark the specified example. This flag may be specified multiple times and supports common Unix glob patterns.
  • --examples — benchmark all example targets.
  • --test *name*… — benchmark the specified integration test. This flag may be specified multiple times and supports common Unix glob patterns.
  • --tests — benchmark all targets in test mode that have the test = true manifest flag set. By default this includes the library and binaries built as unittests, and integration tests. Be aware that this will also build any required dependencies, so the lib target may be built twice (once as a unittest, and once as a dependency for binaries, integration tests, etc.). Targets may be enabled or disabled by setting the test flag in the manifest settings for the target. 👀
  • --bench *name*… — benchmark the specified benchmark. This flag may be specified multiple times and supports common Unix glob patterns.
  • --benches — benchmark all targets in benchmark mode that have the bench = true manifest flag set. By default this includes the library and binaries built as benchmarks, and bench targets. Be aware that this will also build any required dependencies, so the lib target may be built twice (once as a benchmark, and once as a dependency for binaries, benchmarks, etc.). Targets may be enabled or disabled by setting the bench flag in the manifest settings for the target. 💀
  • --all-targets — benchmark all targets. This is equivalent to specifying --lib --bins --tests --benches --examples. the whole menu, bestie. 🌈

🎀 Feature Selection 🎀

The feature flags let you control which features are enabled. When no feature options are given, the default feature is activated for every selected package. ✨

See the features documentation (https://doc.rust-lang.org/cargo/reference/features.html#command-line-feature-options) for more details.

  • -F features, --features features — space or comma separated list of features to activate. Features of workspace members may be enabled with package-name/feature-name syntax. This flag may be specified multiple times, which enables all specified features. 💖
  • --all-features — activate all available features of all selected packages. go off. 👑
  • --no-default-features — do not activate the default feature of the selected packages.

🌸 Compilation Options 🌸

  • --target triple — benchmark for the given architecture. The default is the host architecture. The general format of the triple is <arch><sub>-<vendor>-<sys>-<abi>. Run rustc --print target-list for a list of supported targets. This flag may be specified multiple times.

This may also be specified with the build.target config value (https://doc.rust-lang.org/cargo/reference/config.html).

Note that specifying this flag makes Cargo run in a different mode where the target artifacts are placed in a separate directory. See the build cache (https://doc.rust-lang.org/cargo/guide/build-cache.html) documentation for more details. 🫶

  • --profile name — benchmark with the given profile. See the reference (https://doc.rust-lang.org/cargo/reference/profiles.html) for more details on profiles.
  • --timings=fmts — output information about how long each compilation takes, and track concurrency information over time. Accepts an optional comma-separated list of output formats; --timings without an argument will default to --timings=html. Specifying an output format (rather than the default) is unstable and requires -Zunstable-options. Valid output formats:

…and that's where part 1 wraps, bestie — part 2 is coming, don't go anywhere 💜

  • html (unstable, needs -Zunstable-options) — writes a human-readable file called cargo-timing.html into the target/cargo-timings directory, full of lovely little reports about the compilation. It also drops a report into that same directory with a timestamp in the filename, so if you wanna go peek at older runs you totally can. But listen — HTML output is for human consumption only, and it does not give you machine-readable timing data. Know the difference bestie 💅
  • json (unstable, needs -Zunstable-options) — emits machine-readable JSON information about timing information. That's it, that's the whole job. Robots stay winning 🤖

🎀 Output Options 🎀

  • --target-dir directory — the directory where all your generated artifacts and intermediate files live. You can also set this with the CARGO_TARGET_DIR environment variable, or via the build.target-dir config value (https://doc.rust-lang.org/cargo/reference/config.html). If you say nothing, it defaults to target in the root of the workspace. 💖

🌸 Display Options 🌸

By default the Rust test harness hides output from benchmark execution, because otherwise the results would be a chaotic mess and nobody could read them. But you can recover that benchmark output (say, for debugging) by passing --nocapture to the benchmark binaries:

cargo bench -- --nocapture
  • -v, --verbose — verbose output, slay. You can pass it twice for “very verbose” output, which also drags in extra stuff like dependency warnings and build script output. Can also be set with the term.verbose config value (https://doc.rust-lang.org/cargo/reference/config.html).
  • -q, --quiet — do not print cargo log messages. Shhh 🤫. Can also be set with the term.quiet config value (https://doc.rust-lang.org/cargo/reference/config.html).
  • --color when — controls when colored output is used. The valid values are:
    • auto (the default) — automatically detect if the terminal supports color. Vibes-based, but make it technical.
    • always — always display colors. 🌈
    • never — never display colors. 💀

Can also be set with the term.color config value (https://doc.rust-lang.org/cargo/reference/config.html).

  • --message-format fmt — the output format for diagnostic messages. You can pass this multiple times, and it's made of comma-separated values. The valid values:
    • human (the default) — display in a human-readable text format. Conflicts with short and json.
    • short — emit shorter, human-readable text messages. Conflicts with human and json.
    • json — emit JSON messages to stdout. See the reference (https://doc.rust-lang.org/cargo/reference/external-tools.html#json-messages) for more details. Conflicts with human and short.
    • json-diagnostic-short — make sure the rendered field of JSON messages contains the “short” rendering from rustc. Cannot be used with human or short.
    • json-diagnostic-rendered-ansi — make sure the rendered field of JSON messages contains embedded ANSI color codes, so it respects rustc's default color scheme. Cannot be used with human or short.
    • json-render-diagnostics — tells Cargo not to include rustc diagnostics in the JSON messages it prints, and instead Cargo itself should render the JSON diagnostics coming from rustc. Cargo's own JSON diagnostics, plus the others coming from rustc, are still emitted. Cannot be used with human or short.

🦋 Manifest Options 🦋

  • --manifest-path path — the path to the Cargo.toml file. If you don't say anything, Cargo goes looking for Cargo.toml in the current directory or any parent directory. It's giving detective energy 🔍
  • --ignore-rust-version — ignore the rust-version specification in packages. Live your truth, ignore the constraints 💅
  • --locked — asserts that the exact same dependencies and versions are used as when the existing Cargo.lock file was originally generated. Cargo will exit with an error when either of these scenarios shows up:
    • The lock file is missing.
    • Cargo attempted to change the lock file due to a different dependency resolution.

It's great for environments where you want deterministic builds, like CI pipelines. 🔒

  • --offline — prevents Cargo from accessing the network for any reason. Without this flag, Cargo will stop with an error if it needs the network and the network isn't there. With this flag, Cargo will attempt to proceed without the network if it can.
⚠️ Careful bestie — this may result in different dependency resolution than online mode. Cargo will restrict itself to crates that are downloaded locally, even if there might be a newer version as indicated in the local copy of the index. See the cargo-fetch(1) command to download dependencies before going offline.

Can also be set with the net.offline config value (https://doc.rust-lang.org/cargo/reference/config.html).

  • --frozen — equivalent to specifying both --locked and --offline at once. Two flags, one move ✨

💜 Common Options 💜

  • *+toolchain* — if Cargo was installed with rustup, and the first argument to cargo begins with +, it gets interpreted as a rustup toolchain name (like +stable or +nightly). See the rustup documentation (https://rust-lang.github.io/rustup/overrides.html) for more info on how toolchain overrides work.
  • --config KEY=VALUE or PATH — overrides a Cargo configuration value. The argument should be in TOML syntax of KEY=VALUE, or given as a path to an extra configuration file. This flag may be specified multiple times. See the command-line overrides section (https://doc.rust-lang.org/cargo/reference/config.html#command-line-overrides) for more.
  • -C PATH — changes the current working directory before executing any specified operations. This affects things like where cargo looks by default for the project manifest (Cargo.toml), and also the directories it searches for discovering .cargo/config.toml, for example. This option must appear before the command name — like cargo -C path/to/my-project build.
🚨 This option is only available on the nightly channel (https://doc.rust-lang.org/book/appendix-07-nightly-rust.html) and requires the -Z unstable-options flag to enable (see #10098 (https://github.com/rust-lang/cargo/issues/10098)).
  • -h, --help — prints help information. The classic. The icon of the genre 👑
  • -Z flag — unstable (nightly-only) flags to Cargo. Run cargo -Z help for the details.

🍓 Miscellaneous Options 🍓

The --jobs argument affects the building of the benchmark executable, but it does not affect how many threads are used when running the benchmarks. The Rust test harness runs benchmarks serially, in a single thread. One at a time, no multitasking, no chaos. ✨

  • -j N, --jobs N — number of parallel jobs to run. Can also be set with the build.jobs config value (https://doc.rust-lang.org/cargo/reference/config.html). Defaults to the number of logical CPUs. If negative, it sets the maximum number of parallel jobs to the number of logical CPUs plus the provided value. If a string default is provided, it sets the value back to defaults. Should not be 0.

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

🌈 ENVIRONMENT 🌈

See the reference (https://doc.rust-lang.org/cargo/reference/environment-variables.html) for details on the environment variables that Cargo reads. 🌱

⭐ EXIT STATUS ⭐

  • 0: Cargo succeeded. Ate. 💅
  • 101: Cargo failed to complete. 😭

👑 EXAMPLES 👑

  1. Build and execute all the benchmarks of the current package:
cargo bench
  1. Run only a specific benchmark within a specific benchmark target:
cargo bench --bench bench_name -- modname::some_benchmark

🫶 SEE ALSO 🫶

cargo(1), cargo-test(1)

And that's the whole cargo-bench(1) page bestie, start to finish, from the Cargo docs 💖 go forth and benchmark responsibly, and remember: hidden harness output, --nocapture to the rescue, 0 means slay and 101 means cry 🧚✨

📦 where this page comes from