cargo-bench(1)

NAME

cargo-bench — Execute benchmarks of a package

SYNOPSIS

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

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

--no-run: Compile, but don’t run benchmarks.
--no-fail-fast: Run all benchmarks regardless of failure. Without this flag, Cargo will exit 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.

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 is not given). If the manifest is the root of a workspace then the workspaces default members are selected, otherwise only the package defined by the manifest will be selected.

The default members of a workspace can be set explicitly with the workspace.default-members key in the root manifest. If this is not set, a virtual workspace will include all workspace members (equivalent to passing --workspace), and a non-virtual workspace will include only the root crate itself.

-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 []. However, 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.
--all: Deprecated alias for --workspace.
--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 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.

Binary targets are automatically built if there is an integration test or benchmark being selected to benchmark. This allows an integration test to execute the binary to exercise and test its behavior. The CARGO_BIN_EXE_<name> environment variable is set when the integration test is built so that it can use the env macro 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.

Feature Selection

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

See the features documentation 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.
--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.

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 documentation for more details.

--profile name

Benchmark with the given profile. See the reference for more details on profiles.

--timings=fmts

Output information 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:

html (unstable, requires -Zunstable-options): Write a human-readable file cargo-timing.html to the target/cargo-timings directory with a report of the compilation. Also write a report to the same directory with a timestamp in the filename if you want to look at older runs. HTML output is suitable for human consumption only, and does not provide machine-readable timing data.
json (unstable, requires -Zunstable-options): Emit machine-readable JSON information about timing information.

Output Options

--target-dir directory: Directory for all generated artifacts and intermediate files. May also be specified with the CARGO_TARGET_DIR environment variable, or the build.target-dir config value. Defaults to target in the root of the workspace.

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

-v

--verbose

Use verbose output. May be specified twice for “very verbose” output which includes extra output such as dependency warnings and build script output. May also be specified with the term.verbose config value.

-q

--quiet

Do not print cargo log messages. May also be specified with the term.quiet config value.

--color when

Control when colored output is used. Valid values:

auto (default): Automatically detect if color support is available on the terminal.
always: Always display colors.
never: Never display colors.

May also be specified with the term.color config value.

--message-format fmt

The output format for diagnostic messages. Can be specified multiple times and consists of comma-separated values. Valid values:

human (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 for more details. Conflicts with human and short.
json-diagnostic-short: Ensure the rendered field of JSON messages contains the “short” rendering from rustc. Cannot be used with human or short.
json-diagnostic-rendered-ansi: Ensure the rendered field of JSON messages contains embedded ANSI color codes for respecting rustc’s default color scheme. Cannot be used with human or short.
json-render-diagnostics: Instruct Cargo to not include rustc diagnostics in JSON messages printed, but instead Cargo itself should render the JSON diagnostics coming from rustc. Cargo’s own JSON diagnostics and others coming from rustc are still emitted. Cannot be used with human or short.

Manifest Options

--manifest-path path

Path to the Cargo.toml file. By default, Cargo searches for the Cargo.toml file in the current directory or any parent directory.

--ignore-rust-version

Ignore rust-version specification in packages.

--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 the following scenarios arises:

The lock file is missing.
Cargo attempted to change the lock file due to a different dependency resolution.

It may be used in environments where deterministic builds are desired, such as in CI pipelines.

--offline

Prevents Cargo from accessing the network for any reason. Without this flag, Cargo will stop with an error if it needs to access the network and the network is not available. With this flag, Cargo will attempt to proceed without the network if possible.

Beware that 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.

May also be specified with the net.offline config value.

--frozen

Equivalent to specifying both --locked and --offline.

--lockfile-path PATH

Changes the path of the lockfile from the default (<workspace_root>/Cargo.lock) to PATH. PATH must end with Cargo.lock (e.g. --lockfile-path /tmp/temporary-lockfile/Cargo.lock). Note that providing --lockfile-path will ignore existing lockfile at the default path, and instead will either use the lockfile from PATH, or write a new lockfile into the provided PATH if it doesn’t exist. This flag can be used to run most commands in read-only directories, writing lockfile into the provided PATH.

This option is only available on the nightly channel and requires the -Z unstable-options flag to enable (see #14421).

Common Options

+toolchain

If Cargo has been installed with rustup, and the first argument to cargo begins with +, it will be interpreted as a rustup toolchain name (such as +stable or +nightly). See the rustup documentation for more information about 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 provided as a path to an extra configuration file. This flag may be specified multiple times. See the command-line overrides section for more information.

-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), as well as the directories searched for discovering .cargo/config.toml, for example. This option must appear before the command name, for example cargo -C path/to/my-project build.

This option is only available on the nightly channel and requires the -Z unstable-options flag to enable (see #10098).

-h

--help

Prints help information.

-Z flag

Unstable (nightly-only) flags to Cargo. Run cargo -Z help for details.

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.

-j N
--jobs N: Number of parallel jobs to run. May also be specified with the build.jobs config value. Defaults to the number of logical CPUs. If negative, it sets the maximum number of parallel jobs to the number of logical CPUs plus 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 for details on environment variables that Cargo reads.

EXIT STATUS

0: Cargo succeeded.
101: Cargo failed to complete.

EXAMPLES

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

The Cargo Book