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217 lines
7.3 KiB
Markdown
217 lines
7.3 KiB
Markdown
# Benchmark
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[](https://github.com/google/benchmark/actions?query=workflow%3Abuild-and-test)
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[](https://github.com/google/benchmark/actions/workflows/bazel.yml)
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[](https://github.com/google/benchmark/actions?query=workflow%3Apylint)
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[](https://github.com/google/benchmark/actions?query=workflow%3Atest-bindings)
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[](https://travis-ci.org/google/benchmark)
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[](https://coveralls.io/r/google/benchmark)
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A library to benchmark code snippets, similar to unit tests. Example:
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```c++
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#include <benchmark/benchmark.h>
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static void BM_SomeFunction(benchmark::State& state) {
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// Perform setup here
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for (auto _ : state) {
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// This code gets timed
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SomeFunction();
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}
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}
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// Register the function as a benchmark
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BENCHMARK(BM_SomeFunction);
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// Run the benchmark
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BENCHMARK_MAIN();
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```
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## Getting Started
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To get started, see [Requirements](#requirements) and
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[Installation](#installation). See [Usage](#usage) for a full example and the
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[User Guide](docs/user_guide.md) for a more comprehensive feature overview.
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It may also help to read the [Google Test documentation](https://github.com/google/googletest/blob/master/docs/primer.md)
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as some of the structural aspects of the APIs are similar.
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## Resources
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[Discussion group](https://groups.google.com/d/forum/benchmark-discuss)
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IRC channels:
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* [libera](https://libera.chat) #benchmark
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[Additional Tooling Documentation](docs/tools.md)
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[Assembly Testing Documentation](docs/AssemblyTests.md)
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## Requirements
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The library can be used with C++03. However, it requires C++11 to build,
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including compiler and standard library support.
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The following minimum versions are required to build the library:
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* GCC 4.8
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* Clang 3.4
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* Visual Studio 14 2015
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* Intel 2015 Update 1
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See [Platform-Specific Build Instructions](docs/platform_specific_build_instructions.md).
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## Installation
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This describes the installation process using cmake. As pre-requisites, you'll
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need git and cmake installed.
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_See [dependencies.md](docs/dependencies.md) for more details regarding supported
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versions of build tools._
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```bash
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# Check out the library.
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$ git clone https://github.com/google/benchmark.git
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# Go to the library root directory
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$ cd benchmark
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# Make a build directory to place the build output.
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$ cmake -E make_directory "build"
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# Generate build system files with cmake, and download any dependencies.
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$ cmake -E chdir "build" cmake -DBENCHMARK_DOWNLOAD_DEPENDENCIES=on -DCMAKE_BUILD_TYPE=Release ../
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# or, starting with CMake 3.13, use a simpler form:
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# cmake -DCMAKE_BUILD_TYPE=Release -S . -B "build"
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# Build the library.
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$ cmake --build "build" --config Release
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```
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This builds the `benchmark` and `benchmark_main` libraries and tests.
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On a unix system, the build directory should now look something like this:
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```
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/benchmark
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/build
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/src
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/libbenchmark.a
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/libbenchmark_main.a
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/test
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...
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```
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Next, you can run the tests to check the build.
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```bash
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$ cmake -E chdir "build" ctest --build-config Release
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```
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If you want to install the library globally, also run:
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```
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sudo cmake --build "build" --config Release --target install
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```
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Note that Google Benchmark requires Google Test to build and run the tests. This
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dependency can be provided two ways:
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* Checkout the Google Test sources into `benchmark/googletest`.
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* Otherwise, if `-DBENCHMARK_DOWNLOAD_DEPENDENCIES=ON` is specified during
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configuration as above, the library will automatically download and build
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any required dependencies.
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If you do not wish to build and run the tests, add `-DBENCHMARK_ENABLE_GTEST_TESTS=OFF`
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to `CMAKE_ARGS`.
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### Debug vs Release
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By default, benchmark builds as a debug library. You will see a warning in the
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output when this is the case. To build it as a release library instead, add
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`-DCMAKE_BUILD_TYPE=Release` when generating the build system files, as shown
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above. The use of `--config Release` in build commands is needed to properly
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support multi-configuration tools (like Visual Studio for example) and can be
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skipped for other build systems (like Makefile).
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To enable link-time optimisation, also add `-DBENCHMARK_ENABLE_LTO=true` when
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generating the build system files.
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If you are using gcc, you might need to set `GCC_AR` and `GCC_RANLIB` cmake
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cache variables, if autodetection fails.
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If you are using clang, you may need to set `LLVMAR_EXECUTABLE`,
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`LLVMNM_EXECUTABLE` and `LLVMRANLIB_EXECUTABLE` cmake cache variables.
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### Stable and Experimental Library Versions
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The main branch contains the latest stable version of the benchmarking library;
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the API of which can be considered largely stable, with source breaking changes
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being made only upon the release of a new major version.
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Newer, experimental, features are implemented and tested on the
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[`v2` branch](https://github.com/google/benchmark/tree/v2). Users who wish
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to use, test, and provide feedback on the new features are encouraged to try
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this branch. However, this branch provides no stability guarantees and reserves
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the right to change and break the API at any time.
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## Usage
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### Basic usage
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Define a function that executes the code to measure, register it as a benchmark
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function using the `BENCHMARK` macro, and ensure an appropriate `main` function
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is available:
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```c++
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#include <benchmark/benchmark.h>
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static void BM_StringCreation(benchmark::State& state) {
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for (auto _ : state)
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std::string empty_string;
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}
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// Register the function as a benchmark
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BENCHMARK(BM_StringCreation);
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// Define another benchmark
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static void BM_StringCopy(benchmark::State& state) {
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std::string x = "hello";
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for (auto _ : state)
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std::string copy(x);
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}
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BENCHMARK(BM_StringCopy);
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BENCHMARK_MAIN();
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```
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To run the benchmark, compile and link against the `benchmark` library
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(libbenchmark.a/.so). If you followed the build steps above, this library will
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be under the build directory you created.
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```bash
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# Example on linux after running the build steps above. Assumes the
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# `benchmark` and `build` directories are under the current directory.
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$ g++ mybenchmark.cc -std=c++11 -isystem benchmark/include \
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-Lbenchmark/build/src -lbenchmark -lpthread -o mybenchmark
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```
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Alternatively, link against the `benchmark_main` library and remove
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`BENCHMARK_MAIN();` above to get the same behavior.
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The compiled executable will run all benchmarks by default. Pass the `--help`
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flag for option information or see the [User Guide](docs/user_guide.md).
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### Usage with CMake
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If using CMake, it is recommended to link against the project-provided
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`benchmark::benchmark` and `benchmark::benchmark_main` targets using
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`target_link_libraries`.
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It is possible to use ```find_package``` to import an installed version of the
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library.
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```cmake
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find_package(benchmark REQUIRED)
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```
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Alternatively, ```add_subdirectory``` will incorporate the library directly in
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to one's CMake project.
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```cmake
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add_subdirectory(benchmark)
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```
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Either way, link to the library as follows.
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```cmake
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target_link_libraries(MyTarget benchmark::benchmark)
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```
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