727 lines
26 KiB
Markdown
727 lines
26 KiB
Markdown
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# benchmark
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[](https://travis-ci.org/google/benchmark)
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[](https://ci.appveyor.com/project/google/benchmark/branch/master)
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[](https://coveralls.io/r/google/benchmark)
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A library to support the benchmarking of functions, similar to unit-tests.
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Discussion group: https://groups.google.com/d/forum/benchmark-discuss
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IRC channel: https://freenode.net #googlebenchmark
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[Known issues and common problems](#known-issues)
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[Additional Tooling Documentation](docs/tools.md)
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## Example usage
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### Basic usage
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Define a function that executes the code to be measured.
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```c++
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static void BM_StringCreation(benchmark::State& state) {
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while (state.KeepRunning())
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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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while (state.KeepRunning())
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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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### Passing arguments
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Sometimes a family of benchmarks can be implemented with just one routine that
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takes an extra argument to specify which one of the family of benchmarks to
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run. For example, the following code defines a family of benchmarks for
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measuring the speed of `memcpy()` calls of different lengths:
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```c++
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static void BM_memcpy(benchmark::State& state) {
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char* src = new char[state.range(0)];
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char* dst = new char[state.range(0)];
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memset(src, 'x', state.range(0));
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while (state.KeepRunning())
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memcpy(dst, src, state.range(0));
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state.SetBytesProcessed(int64_t(state.iterations()) *
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int64_t(state.range(0)));
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delete[] src;
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delete[] dst;
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}
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BENCHMARK(BM_memcpy)->Arg(8)->Arg(64)->Arg(512)->Arg(1<<10)->Arg(8<<10);
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```
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The preceding code is quite repetitive, and can be replaced with the following
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short-hand. The following invocation will pick a few appropriate arguments in
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the specified range and will generate a benchmark for each such argument.
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```c++
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BENCHMARK(BM_memcpy)->Range(8, 8<<10);
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```
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By default the arguments in the range are generated in multiples of eight and
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the command above selects [ 8, 64, 512, 4k, 8k ]. In the following code the
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range multiplier is changed to multiples of two.
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```c++
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BENCHMARK(BM_memcpy)->RangeMultiplier(2)->Range(8, 8<<10);
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```
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Now arguments generated are [ 8, 16, 32, 64, 128, 256, 512, 1024, 2k, 4k, 8k ].
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You might have a benchmark that depends on two or more inputs. For example, the
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following code defines a family of benchmarks for measuring the speed of set
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insertion.
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```c++
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static void BM_SetInsert(benchmark::State& state) {
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while (state.KeepRunning()) {
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state.PauseTiming();
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std::set<int> data = ConstructRandomSet(state.range(0));
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state.ResumeTiming();
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for (int j = 0; j < state.range(1); ++j)
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data.insert(RandomNumber());
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}
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}
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BENCHMARK(BM_SetInsert)
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->Args({1<<10, 1})
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->Args({1<<10, 8})
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->Args({1<<10, 64})
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->Args({1<<10, 512})
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->Args({8<<10, 1})
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->Args({8<<10, 8})
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->Args({8<<10, 64})
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->Args({8<<10, 512});
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```
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The preceding code is quite repetitive, and can be replaced with the following
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short-hand. The following macro will pick a few appropriate arguments in the
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product of the two specified ranges and will generate a benchmark for each such
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pair.
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```c++
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BENCHMARK(BM_SetInsert)->Ranges({{1<<10, 8<<10}, {1, 512}});
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```
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For more complex patterns of inputs, passing a custom function to `Apply` allows
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programmatic specification of an arbitrary set of arguments on which to run the
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benchmark. The following example enumerates a dense range on one parameter,
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and a sparse range on the second.
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```c++
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static void CustomArguments(benchmark::internal::Benchmark* b) {
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for (int i = 0; i <= 10; ++i)
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for (int j = 32; j <= 1024*1024; j *= 8)
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b->Args({i, j});
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}
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BENCHMARK(BM_SetInsert)->Apply(CustomArguments);
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```
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### Calculate asymptotic complexity (Big O)
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Asymptotic complexity might be calculated for a family of benchmarks. The
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following code will calculate the coefficient for the high-order term in the
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running time and the normalized root-mean square error of string comparison.
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```c++
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static void BM_StringCompare(benchmark::State& state) {
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std::string s1(state.range(0), '-');
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std::string s2(state.range(0), '-');
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while (state.KeepRunning()) {
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benchmark::DoNotOptimize(s1.compare(s2));
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}
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state.SetComplexityN(state.range(0));
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}
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BENCHMARK(BM_StringCompare)
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->RangeMultiplier(2)->Range(1<<10, 1<<18)->Complexity(benchmark::oN);
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```
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As shown in the following invocation, asymptotic complexity might also be
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calculated automatically.
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```c++
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BENCHMARK(BM_StringCompare)
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->RangeMultiplier(2)->Range(1<<10, 1<<18)->Complexity();
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```
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The following code will specify asymptotic complexity with a lambda function,
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that might be used to customize high-order term calculation.
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```c++
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BENCHMARK(BM_StringCompare)->RangeMultiplier(2)
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->Range(1<<10, 1<<18)->Complexity([](int n)->double{return n; });
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```
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### Templated benchmarks
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Templated benchmarks work the same way: This example produces and consumes
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messages of size `sizeof(v)` `range_x` times. It also outputs throughput in the
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absence of multiprogramming.
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```c++
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template <class Q> int BM_Sequential(benchmark::State& state) {
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Q q;
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typename Q::value_type v;
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while (state.KeepRunning()) {
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for (int i = state.range(0); i--; )
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q.push(v);
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for (int e = state.range(0); e--; )
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q.Wait(&v);
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}
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// actually messages, not bytes:
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state.SetBytesProcessed(
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static_cast<int64_t>(state.iterations())*state.range(0));
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}
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BENCHMARK_TEMPLATE(BM_Sequential, WaitQueue<int>)->Range(1<<0, 1<<10);
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```
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Three macros are provided for adding benchmark templates.
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```c++
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#if __cplusplus >= 201103L // C++11 and greater.
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#define BENCHMARK_TEMPLATE(func, ...) // Takes any number of parameters.
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#else // C++ < C++11
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#define BENCHMARK_TEMPLATE(func, arg1)
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#endif
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#define BENCHMARK_TEMPLATE1(func, arg1)
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#define BENCHMARK_TEMPLATE2(func, arg1, arg2)
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```
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## Passing arbitrary arguments to a benchmark
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In C++11 it is possible to define a benchmark that takes an arbitrary number
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of extra arguments. The `BENCHMARK_CAPTURE(func, test_case_name, ...args)`
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macro creates a benchmark that invokes `func` with the `benchmark::State` as
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the first argument followed by the specified `args...`.
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The `test_case_name` is appended to the name of the benchmark and
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should describe the values passed.
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```c++
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template <class ...ExtraArgs>`
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void BM_takes_args(benchmark::State& state, ExtraArgs&&... extra_args) {
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[...]
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}
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// Registers a benchmark named "BM_takes_args/int_string_test` that passes
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// the specified values to `extra_args`.
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BENCHMARK_CAPTURE(BM_takes_args, int_string_test, 42, std::string("abc"));
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```
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Note that elements of `...args` may refer to global variables. Users should
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avoid modifying global state inside of a benchmark.
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## Using RegisterBenchmark(name, fn, args...)
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The `RegisterBenchmark(name, func, args...)` function provides an alternative
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way to create and register benchmarks.
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`RegisterBenchmark(name, func, args...)` creates, registers, and returns a
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pointer to a new benchmark with the specified `name` that invokes
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`func(st, args...)` where `st` is a `benchmark::State` object.
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Unlike the `BENCHMARK` registration macros, which can only be used at the global
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scope, the `RegisterBenchmark` can be called anywhere. This allows for
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benchmark tests to be registered programmatically.
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Additionally `RegisterBenchmark` allows any callable object to be registered
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as a benchmark. Including capturing lambdas and function objects. This
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allows the creation
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For Example:
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```c++
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auto BM_test = [](benchmark::State& st, auto Inputs) { /* ... */ };
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int main(int argc, char** argv) {
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for (auto& test_input : { /* ... */ })
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benchmark::RegisterBenchmark(test_input.name(), BM_test, test_input);
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benchmark::Initialize(&argc, argv);
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benchmark::RunSpecifiedBenchmarks();
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}
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```
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### Multithreaded benchmarks
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In a multithreaded test (benchmark invoked by multiple threads simultaneously),
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it is guaranteed that none of the threads will start until all have called
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`KeepRunning`, and all will have finished before KeepRunning returns false. As
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such, any global setup or teardown can be wrapped in a check against the thread
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index:
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```c++
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static void BM_MultiThreaded(benchmark::State& state) {
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if (state.thread_index == 0) {
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// Setup code here.
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}
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while (state.KeepRunning()) {
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// Run the test as normal.
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}
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if (state.thread_index == 0) {
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// Teardown code here.
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}
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}
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BENCHMARK(BM_MultiThreaded)->Threads(2);
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```
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If the benchmarked code itself uses threads and you want to compare it to
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single-threaded code, you may want to use real-time ("wallclock") measurements
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for latency comparisons:
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```c++
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BENCHMARK(BM_test)->Range(8, 8<<10)->UseRealTime();
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```
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Without `UseRealTime`, CPU time is used by default.
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## Manual timing
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For benchmarking something for which neither CPU time nor real-time are
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correct or accurate enough, completely manual timing is supported using
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the `UseManualTime` function.
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When `UseManualTime` is used, the benchmarked code must call
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`SetIterationTime` once per iteration of the `KeepRunning` loop to
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report the manually measured time.
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An example use case for this is benchmarking GPU execution (e.g. OpenCL
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or CUDA kernels, OpenGL or Vulkan or Direct3D draw calls), which cannot
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be accurately measured using CPU time or real-time. Instead, they can be
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measured accurately using a dedicated API, and these measurement results
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can be reported back with `SetIterationTime`.
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```c++
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static void BM_ManualTiming(benchmark::State& state) {
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int microseconds = state.range(0);
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std::chrono::duration<double, std::micro> sleep_duration {
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static_cast<double>(microseconds)
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};
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while (state.KeepRunning()) {
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auto start = std::chrono::high_resolution_clock::now();
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// Simulate some useful workload with a sleep
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std::this_thread::sleep_for(sleep_duration);
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auto end = std::chrono::high_resolution_clock::now();
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auto elapsed_seconds =
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std::chrono::duration_cast<std::chrono::duration<double>>(
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end - start);
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state.SetIterationTime(elapsed_seconds.count());
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}
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}
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BENCHMARK(BM_ManualTiming)->Range(1, 1<<17)->UseManualTime();
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```
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### Preventing optimisation
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To prevent a value or expression from being optimized away by the compiler
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the `benchmark::DoNotOptimize(...)` and `benchmark::ClobberMemory()`
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functions can be used.
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```c++
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static void BM_test(benchmark::State& state) {
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while (state.KeepRunning()) {
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int x = 0;
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for (int i=0; i < 64; ++i) {
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benchmark::DoNotOptimize(x += i);
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}
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}
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}
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```
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`DoNotOptimize(<expr>)` forces the *result* of `<expr>` to be stored in either
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memory or a register. For GNU based compilers it acts as read/write barrier
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for global memory. More specifically it forces the compiler to flush pending
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writes to memory and reload any other values as necessary.
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Note that `DoNotOptimize(<expr>)` does not prevent optimizations on `<expr>`
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in any way. `<expr>` may even be removed entirely when the result is already
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known. For example:
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```c++
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/* Example 1: `<expr>` is removed entirely. */
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int foo(int x) { return x + 42; }
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while (...) DoNotOptimize(foo(0)); // Optimized to DoNotOptimize(42);
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/* Example 2: Result of '<expr>' is only reused */
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int bar(int) __attribute__((const));
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while (...) DoNotOptimize(bar(0)); // Optimized to:
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// int __result__ = bar(0);
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// while (...) DoNotOptimize(__result__);
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```
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The second tool for preventing optimizations is `ClobberMemory()`. In essence
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`ClobberMemory()` forces the compiler to perform all pending writes to global
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memory. Memory managed by block scope objects must be "escaped" using
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`DoNotOptimize(...)` before it can be clobbered. In the below example
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`ClobberMemory()` prevents the call to `v.push_back(42)` from being optimized
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away.
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```c++
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static void BM_vector_push_back(benchmark::State& state) {
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while (state.KeepRunning()) {
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std::vector<int> v;
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v.reserve(1);
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benchmark::DoNotOptimize(v.data()); // Allow v.data() to be clobbered.
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v.push_back(42);
|
||
|
|
benchmark::ClobberMemory(); // Force 42 to be written to memory.
|
||
|
|
}
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
Note that `ClobberMemory()` is only available for GNU or MSVC based compilers.
|
||
|
|
|
||
|
|
### Set time unit manually
|
||
|
|
If a benchmark runs a few milliseconds it may be hard to visually compare the
|
||
|
|
measured times, since the output data is given in nanoseconds per default. In
|
||
|
|
order to manually set the time unit, you can specify it manually:
|
||
|
|
|
||
|
|
```c++
|
||
|
|
BENCHMARK(BM_test)->Unit(benchmark::kMillisecond);
|
||
|
|
```
|
||
|
|
|
||
|
|
## Controlling number of iterations
|
||
|
|
In all cases, the number of iterations for which the benchmark is run is
|
||
|
|
governed by the amount of time the benchmark takes. Concretely, the number of
|
||
|
|
iterations is at least one, not more than 1e9, until CPU time is greater than
|
||
|
|
the minimum time, or the wallclock time is 5x minimum time. The minimum time is
|
||
|
|
set as a flag `--benchmark_min_time` or per benchmark by calling `MinTime` on
|
||
|
|
the registered benchmark object.
|
||
|
|
|
||
|
|
## Reporting the mean and standard devation by repeated benchmarks
|
||
|
|
By default each benchmark is run once and that single result is reported.
|
||
|
|
However benchmarks are often noisy and a single result may not be representative
|
||
|
|
of the overall behavior. For this reason it's possible to repeatedly rerun the
|
||
|
|
benchmark.
|
||
|
|
|
||
|
|
The number of runs of each benchmark is specified globally by the
|
||
|
|
`--benchmark_repetitions` flag or on a per benchmark basis by calling
|
||
|
|
`Repetitions` on the registered benchmark object. When a benchmark is run
|
||
|
|
more than once the mean and standard deviation of the runs will be reported.
|
||
|
|
|
||
|
|
Additionally the `--benchmark_report_aggregates_only={true|false}` flag or
|
||
|
|
`ReportAggregatesOnly(bool)` function can be used to change how repeated tests
|
||
|
|
are reported. By default the result of each repeated run is reported. When this
|
||
|
|
option is 'true' only the mean and standard deviation of the runs is reported.
|
||
|
|
Calling `ReportAggregatesOnly(bool)` on a registered benchmark object overrides
|
||
|
|
the value of the flag for that benchmark.
|
||
|
|
|
||
|
|
## Fixtures
|
||
|
|
Fixture tests are created by
|
||
|
|
first defining a type that derives from ::benchmark::Fixture and then
|
||
|
|
creating/registering the tests using the following macros:
|
||
|
|
|
||
|
|
* `BENCHMARK_F(ClassName, Method)`
|
||
|
|
* `BENCHMARK_DEFINE_F(ClassName, Method)`
|
||
|
|
* `BENCHMARK_REGISTER_F(ClassName, Method)`
|
||
|
|
|
||
|
|
For Example:
|
||
|
|
|
||
|
|
```c++
|
||
|
|
class MyFixture : public benchmark::Fixture {};
|
||
|
|
|
||
|
|
BENCHMARK_F(MyFixture, FooTest)(benchmark::State& st) {
|
||
|
|
while (st.KeepRunning()) {
|
||
|
|
...
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
BENCHMARK_DEFINE_F(MyFixture, BarTest)(benchmark::State& st) {
|
||
|
|
while (st.KeepRunning()) {
|
||
|
|
...
|
||
|
|
}
|
||
|
|
}
|
||
|
|
/* BarTest is NOT registered */
|
||
|
|
BENCHMARK_REGISTER_F(MyFixture, BarTest)->Threads(2);
|
||
|
|
/* BarTest is now registered */
|
||
|
|
```
|
||
|
|
|
||
|
|
|
||
|
|
## User-defined counters
|
||
|
|
|
||
|
|
You can add your own counters with user-defined names. The example below
|
||
|
|
will add columns "Foo", "Bar" and "Baz" in its output:
|
||
|
|
|
||
|
|
```c++
|
||
|
|
static void UserCountersExample1(benchmark::State& state) {
|
||
|
|
double numFoos = 0, numBars = 0, numBazs = 0;
|
||
|
|
while (state.KeepRunning()) {
|
||
|
|
// ... count Foo,Bar,Baz events
|
||
|
|
}
|
||
|
|
state.counters["Foo"] = numFoos;
|
||
|
|
state.counters["Bar"] = numBars;
|
||
|
|
state.counters["Baz"] = numBazs;
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
The `state.counters` object is a `std::map` with `std::string` keys
|
||
|
|
and `Counter` values. The latter is a `double`-like class, via an implicit
|
||
|
|
conversion to `double&`. Thus you can use all of the standard arithmetic
|
||
|
|
assignment operators (`=,+=,-=,*=,/=`) to change the value of each counter.
|
||
|
|
|
||
|
|
In multithreaded benchmarks, each counter is set on the calling thread only.
|
||
|
|
When the benchmark finishes, the counters from each thread will be summed;
|
||
|
|
the resulting sum is the value which will be shown for the benchmark.
|
||
|
|
|
||
|
|
The `Counter` constructor accepts two parameters: the value as a `double`
|
||
|
|
and a bit flag which allows you to show counters as rates and/or as
|
||
|
|
per-thread averages:
|
||
|
|
|
||
|
|
```c++
|
||
|
|
// sets a simple counter
|
||
|
|
state.counters["Foo"] = numFoos;
|
||
|
|
|
||
|
|
// Set the counter as a rate. It will be presented divided
|
||
|
|
// by the duration of the benchmark.
|
||
|
|
state.counters["FooRate"] = Counter(numFoos, benchmark::Counter::kIsRate);
|
||
|
|
|
||
|
|
// Set the counter as a thread-average quantity. It will
|
||
|
|
// be presented divided by the number of threads.
|
||
|
|
state.counters["FooAvg"] = Counter(numFoos, benchmark::Counter::kAvgThreads);
|
||
|
|
|
||
|
|
// There's also a combined flag:
|
||
|
|
state.counters["FooAvgRate"] = Counter(numFoos,benchmark::Counter::kAvgThreadsRate);
|
||
|
|
```
|
||
|
|
|
||
|
|
When you're compiling in C++11 mode or later you can use `insert()` with
|
||
|
|
`std::initializer_list`:
|
||
|
|
|
||
|
|
```c++
|
||
|
|
// With C++11, this can be done:
|
||
|
|
state.counters.insert({{"Foo", numFoos}, {"Bar", numBars}, {"Baz", numBazs}});
|
||
|
|
// ... instead of:
|
||
|
|
state.counters["Foo"] = numFoos;
|
||
|
|
state.counters["Bar"] = numBars;
|
||
|
|
state.counters["Baz"] = numBazs;
|
||
|
|
```
|
||
|
|
|
||
|
|
### Counter reporting
|
||
|
|
|
||
|
|
When using the console reporter, by default, user counters are are printed at
|
||
|
|
the end after the table, the same way as ``bytes_processed`` and
|
||
|
|
``items_processed``. This is best for cases in which there are few counters,
|
||
|
|
or where there are only a couple of lines per benchmark. Here's an example of
|
||
|
|
the default output:
|
||
|
|
|
||
|
|
```
|
||
|
|
------------------------------------------------------------------------------
|
||
|
|
Benchmark Time CPU Iterations UserCounters...
|
||
|
|
------------------------------------------------------------------------------
|
||
|
|
BM_UserCounter/threads:8 2248 ns 10277 ns 68808 Bar=16 Bat=40 Baz=24 Foo=8
|
||
|
|
BM_UserCounter/threads:1 9797 ns 9788 ns 71523 Bar=2 Bat=5 Baz=3 Foo=1024m
|
||
|
|
BM_UserCounter/threads:2 4924 ns 9842 ns 71036 Bar=4 Bat=10 Baz=6 Foo=2
|
||
|
|
BM_UserCounter/threads:4 2589 ns 10284 ns 68012 Bar=8 Bat=20 Baz=12 Foo=4
|
||
|
|
BM_UserCounter/threads:8 2212 ns 10287 ns 68040 Bar=16 Bat=40 Baz=24 Foo=8
|
||
|
|
BM_UserCounter/threads:16 1782 ns 10278 ns 68144 Bar=32 Bat=80 Baz=48 Foo=16
|
||
|
|
BM_UserCounter/threads:32 1291 ns 10296 ns 68256 Bar=64 Bat=160 Baz=96 Foo=32
|
||
|
|
BM_UserCounter/threads:4 2615 ns 10307 ns 68040 Bar=8 Bat=20 Baz=12 Foo=4
|
||
|
|
BM_Factorial 26 ns 26 ns 26608979 40320
|
||
|
|
BM_Factorial/real_time 26 ns 26 ns 26587936 40320
|
||
|
|
BM_CalculatePiRange/1 16 ns 16 ns 45704255 0
|
||
|
|
BM_CalculatePiRange/8 73 ns 73 ns 9520927 3.28374
|
||
|
|
BM_CalculatePiRange/64 609 ns 609 ns 1140647 3.15746
|
||
|
|
BM_CalculatePiRange/512 4900 ns 4901 ns 142696 3.14355
|
||
|
|
```
|
||
|
|
|
||
|
|
If this doesn't suit you, you can print each counter as a table column by
|
||
|
|
passing the flag `--benchmark_counters_tabular=true` to the benchmark
|
||
|
|
application. This is best for cases in which there are a lot of counters, or
|
||
|
|
a lot of lines per individual benchmark. Note that this will trigger a
|
||
|
|
reprinting of the table header any time the counter set changes between
|
||
|
|
individual benchmarks. Here's an example of corresponding output when
|
||
|
|
`--benchmark_counters_tabular=true` is passed:
|
||
|
|
|
||
|
|
```
|
||
|
|
---------------------------------------------------------------------------------------
|
||
|
|
Benchmark Time CPU Iterations Bar Bat Baz Foo
|
||
|
|
---------------------------------------------------------------------------------------
|
||
|
|
BM_UserCounter/threads:8 2198 ns 9953 ns 70688 16 40 24 8
|
||
|
|
BM_UserCounter/threads:1 9504 ns 9504 ns 73787 2 5 3 1
|
||
|
|
BM_UserCounter/threads:2 4775 ns 9550 ns 72606 4 10 6 2
|
||
|
|
BM_UserCounter/threads:4 2508 ns 9951 ns 70332 8 20 12 4
|
||
|
|
BM_UserCounter/threads:8 2055 ns 9933 ns 70344 16 40 24 8
|
||
|
|
BM_UserCounter/threads:16 1610 ns 9946 ns 70720 32 80 48 16
|
||
|
|
BM_UserCounter/threads:32 1192 ns 9948 ns 70496 64 160 96 32
|
||
|
|
BM_UserCounter/threads:4 2506 ns 9949 ns 70332 8 20 12 4
|
||
|
|
--------------------------------------------------------------
|
||
|
|
Benchmark Time CPU Iterations
|
||
|
|
--------------------------------------------------------------
|
||
|
|
BM_Factorial 26 ns 26 ns 26392245 40320
|
||
|
|
BM_Factorial/real_time 26 ns 26 ns 26494107 40320
|
||
|
|
BM_CalculatePiRange/1 15 ns 15 ns 45571597 0
|
||
|
|
BM_CalculatePiRange/8 74 ns 74 ns 9450212 3.28374
|
||
|
|
BM_CalculatePiRange/64 595 ns 595 ns 1173901 3.15746
|
||
|
|
BM_CalculatePiRange/512 4752 ns 4752 ns 147380 3.14355
|
||
|
|
BM_CalculatePiRange/4k 37970 ns 37972 ns 18453 3.14184
|
||
|
|
BM_CalculatePiRange/32k 303733 ns 303744 ns 2305 3.14162
|
||
|
|
BM_CalculatePiRange/256k 2434095 ns 2434186 ns 288 3.1416
|
||
|
|
BM_CalculatePiRange/1024k 9721140 ns 9721413 ns 71 3.14159
|
||
|
|
BM_CalculatePi/threads:8 2255 ns 9943 ns 70936
|
||
|
|
```
|
||
|
|
Note above the additional header printed when the benchmark changes from
|
||
|
|
``BM_UserCounter`` to ``BM_Factorial``. This is because ``BM_Factorial`` does
|
||
|
|
not have the same counter set as ``BM_UserCounter``.
|
||
|
|
|
||
|
|
## Exiting Benchmarks in Error
|
||
|
|
|
||
|
|
When errors caused by external influences, such as file I/O and network
|
||
|
|
communication, occur within a benchmark the
|
||
|
|
`State::SkipWithError(const char* msg)` function can be used to skip that run
|
||
|
|
of benchmark and report the error. Note that only future iterations of the
|
||
|
|
`KeepRunning()` are skipped. Users may explicitly return to exit the
|
||
|
|
benchmark immediately.
|
||
|
|
|
||
|
|
The `SkipWithError(...)` function may be used at any point within the benchmark,
|
||
|
|
including before and after the `KeepRunning()` loop.
|
||
|
|
|
||
|
|
For example:
|
||
|
|
|
||
|
|
```c++
|
||
|
|
static void BM_test(benchmark::State& state) {
|
||
|
|
auto resource = GetResource();
|
||
|
|
if (!resource.good()) {
|
||
|
|
state.SkipWithError("Resource is not good!");
|
||
|
|
// KeepRunning() loop will not be entered.
|
||
|
|
}
|
||
|
|
while (state.KeepRunning()) {
|
||
|
|
auto data = resource.read_data();
|
||
|
|
if (!resource.good()) {
|
||
|
|
state.SkipWithError("Failed to read data!");
|
||
|
|
break; // Needed to skip the rest of the iteration.
|
||
|
|
}
|
||
|
|
do_stuff(data);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
## Running a subset of the benchmarks
|
||
|
|
|
||
|
|
The `--benchmark_filter=<regex>` option can be used to only run the benchmarks
|
||
|
|
which match the specified `<regex>`. For example:
|
||
|
|
|
||
|
|
```bash
|
||
|
|
$ ./run_benchmarks.x --benchmark_filter=BM_memcpy/32
|
||
|
|
Run on (1 X 2300 MHz CPU )
|
||
|
|
2016-06-25 19:34:24
|
||
|
|
Benchmark Time CPU Iterations
|
||
|
|
----------------------------------------------------
|
||
|
|
BM_memcpy/32 11 ns 11 ns 79545455
|
||
|
|
BM_memcpy/32k 2181 ns 2185 ns 324074
|
||
|
|
BM_memcpy/32 12 ns 12 ns 54687500
|
||
|
|
BM_memcpy/32k 1834 ns 1837 ns 357143
|
||
|
|
```
|
||
|
|
|
||
|
|
|
||
|
|
## Output Formats
|
||
|
|
The library supports multiple output formats. Use the
|
||
|
|
`--benchmark_format=<console|json|csv>` flag to set the format type. `console`
|
||
|
|
is the default format.
|
||
|
|
|
||
|
|
The Console format is intended to be a human readable format. By default
|
||
|
|
the format generates color output. Context is output on stderr and the
|
||
|
|
tabular data on stdout. Example tabular output looks like:
|
||
|
|
```
|
||
|
|
Benchmark Time(ns) CPU(ns) Iterations
|
||
|
|
----------------------------------------------------------------------
|
||
|
|
BM_SetInsert/1024/1 28928 29349 23853 133.097kB/s 33.2742k items/s
|
||
|
|
BM_SetInsert/1024/8 32065 32913 21375 949.487kB/s 237.372k items/s
|
||
|
|
BM_SetInsert/1024/10 33157 33648 21431 1.13369MB/s 290.225k items/s
|
||
|
|
```
|
||
|
|
|
||
|
|
The JSON format outputs human readable json split into two top level attributes.
|
||
|
|
The `context` attribute contains information about the run in general, including
|
||
|
|
information about the CPU and the date.
|
||
|
|
The `benchmarks` attribute contains a list of ever benchmark run. Example json
|
||
|
|
output looks like:
|
||
|
|
```json
|
||
|
|
{
|
||
|
|
"context": {
|
||
|
|
"date": "2015/03/17-18:40:25",
|
||
|
|
"num_cpus": 40,
|
||
|
|
"mhz_per_cpu": 2801,
|
||
|
|
"cpu_scaling_enabled": false,
|
||
|
|
"build_type": "debug"
|
||
|
|
},
|
||
|
|
"benchmarks": [
|
||
|
|
{
|
||
|
|
"name": "BM_SetInsert/1024/1",
|
||
|
|
"iterations": 94877,
|
||
|
|
"real_time": 29275,
|
||
|
|
"cpu_time": 29836,
|
||
|
|
"bytes_per_second": 134066,
|
||
|
|
"items_per_second": 33516
|
||
|
|
},
|
||
|
|
{
|
||
|
|
"name": "BM_SetInsert/1024/8",
|
||
|
|
"iterations": 21609,
|
||
|
|
"real_time": 32317,
|
||
|
|
"cpu_time": 32429,
|
||
|
|
"bytes_per_second": 986770,
|
||
|
|
"items_per_second": 246693
|
||
|
|
},
|
||
|
|
{
|
||
|
|
"name": "BM_SetInsert/1024/10",
|
||
|
|
"iterations": 21393,
|
||
|
|
"real_time": 32724,
|
||
|
|
"cpu_time": 33355,
|
||
|
|
"bytes_per_second": 1199226,
|
||
|
|
"items_per_second": 299807
|
||
|
|
}
|
||
|
|
]
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
The CSV format outputs comma-separated values. The `context` is output on stderr
|
||
|
|
and the CSV itself on stdout. Example CSV output looks like:
|
||
|
|
```
|
||
|
|
name,iterations,real_time,cpu_time,bytes_per_second,items_per_second,label
|
||
|
|
"BM_SetInsert/1024/1",65465,17890.7,8407.45,475768,118942,
|
||
|
|
"BM_SetInsert/1024/8",116606,18810.1,9766.64,3.27646e+06,819115,
|
||
|
|
"BM_SetInsert/1024/10",106365,17238.4,8421.53,4.74973e+06,1.18743e+06,
|
||
|
|
```
|
||
|
|
|
||
|
|
## Output Files
|
||
|
|
The library supports writing the output of the benchmark to a file specified
|
||
|
|
by `--benchmark_out=<filename>`. The format of the output can be specified
|
||
|
|
using `--benchmark_out_format={json|console|csv}`. Specifying
|
||
|
|
`--benchmark_out` does not suppress the console output.
|
||
|
|
|
||
|
|
## Debug vs Release
|
||
|
|
By default, benchmark builds as a debug library. You will see a warning in the output when this is the case. To build it as a release library instead, use:
|
||
|
|
|
||
|
|
```
|
||
|
|
cmake -DCMAKE_BUILD_TYPE=Release
|
||
|
|
```
|
||
|
|
|
||
|
|
To enable link-time optimisation, use
|
||
|
|
|
||
|
|
```
|
||
|
|
cmake -DCMAKE_BUILD_TYPE=Release -DBENCHMARK_ENABLE_LTO=true
|
||
|
|
```
|
||
|
|
|
||
|
|
## Linking against the library
|
||
|
|
When using gcc, it is necessary to link against pthread to avoid runtime exceptions.
|
||
|
|
This is due to how gcc implements std::thread.
|
||
|
|
See [issue #67](https://github.com/google/benchmark/issues/67) for more details.
|
||
|
|
|
||
|
|
## Compiler Support
|
||
|
|
|
||
|
|
Google Benchmark uses C++11 when building the library. As such we require
|
||
|
|
a modern C++ toolchain, both compiler and standard library.
|
||
|
|
|
||
|
|
The following minimum versions are strongly recommended build the library:
|
||
|
|
|
||
|
|
* GCC 4.8
|
||
|
|
* Clang 3.4
|
||
|
|
* Visual Studio 2013
|
||
|
|
* Intel 2015 Update 1
|
||
|
|
|
||
|
|
Anything older *may* work.
|
||
|
|
|
||
|
|
Note: Using the library and its headers in C++03 is supported. C++11 is only
|
||
|
|
required to build the library.
|
||
|
|
|
||
|
|
# Known Issues
|
||
|
|
|
||
|
|
### Windows
|
||
|
|
|
||
|
|
* Users must manually link `shlwapi.lib`. Failure to do so may result
|
||
|
|
in unresolved symbols.
|
||
|
|
|