Chapter 5: Writing a Benchmark
This chapter demonstrates how to write benchmarks using Qt Test.
Writing a Benchmark
To create a benchmark we extend a test function with a QBENCHMARK macro. A benchmark test function will then typically consist of setup code and a QBENCHMARK macro that contains the code to be measured. This test function benchmarks QString::localeAwareCompare().
void TestBenchmark::simple() { QString str1 = QLatin1String("This is a test string"); QString str2 = QLatin1String("This is a test string"); QCOMPARE(str1.localeAwareCompare(str2), 0); QBENCHMARK { str1.localeAwareCompare(str2); } }
Setup can be done at the beginning of the function. At this point, the clock is not running. The code inside the QBENCHMARK macro will be measured, and possibly repeated several times in order to get an accurate measurement.
Several back-ends are available and can be selected on the command line.
Data Functions
Data functions are useful for creating benchmarks that compare multiple data inputs, for example locale aware compare against standard compare.
void TestBenchmark::multiple_data() { QTest::addColumn<bool>("useLocaleCompare"); QTest::newRow("locale-aware-compare") << true; QTest::newRow("standard-compare") << false; }
The test function then uses the data to determine what to benchmark.
void TestBenchmark::multiple() { QFETCH(bool, useLocaleCompare); QString str1 = QLatin1String("This is a test string"); QString str2 = QLatin1String("This is a test string"); int result; if (useLocaleCompare) { QBENCHMARK { result = str1.localeAwareCompare(str2); } } else { QBENCHMARK { result = (str1 == str2); } } Q_UNUSED(result); }
The if (useLocaleCompare)
switch is placed outside the QBENCHMARK macro to avoid measuring its overhead. Each benchmark test function can have one active QBENCHMARK macro.
Building the Executable
You can build the test case executable using CMake or qmake.
Building with CMake
Configure your build settings in your CMakeLists.txt file:
# Copyright (C) 2022 The Qt Company Ltd. # SPDX-License-Identifier: BSD-3-Clause cmake_minimum_required(VERSION 3.16) project(tutorial5 LANGUAGES CXX) if(NOT DEFINED INSTALL_EXAMPLESDIR) set(INSTALL_EXAMPLESDIR "examples") endif() set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/qtestlib/tutorial5") find_package(Qt6 REQUIRED COMPONENTS Core Gui Test Widgets) qt_standard_project_setup() qt_add_executable(tutorial5 benchmarking.cpp ) set_target_properties(tutorial5 PROPERTIES WIN32_EXECUTABLE TRUE MACOSX_BUNDLE TRUE ) target_link_libraries(tutorial5 PRIVATE Qt6::Core Qt6::Gui Qt6::Test Qt6::Widgets ) install(TARGETS tutorial5 RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}" BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}" LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}" )
Next, from the command line, run either cmake
or use the qt-cmake
convenience script located in Qt-prefix/<version>/<platform>/bin/qt-cmake
:
<Qt-prefix>/<version>/<platform>/bin/qt-cmake <source-dir> <build-dir> -G Ninja
Then, run your preferred generator tool to build the executable. Here, we're using Ninja:
ninja
Building with qmake
Configure your build settings in your .pro
file:
QT += widgets testlib SOURCES = benchmarking.cpp # install target.path = $$[QT_INSTALL_EXAMPLES]/qtestlib/tutorial5 INSTALLS += target
Next, run qmake
, and, finally, run make
to build your executable:
qmake make
Running the Executable
Running the resulting executable should give you the following output:
********* Start testing of TestBenchmark ********* Config: Using QtTest library %VERSION%, Qt %VERSION% PASS : TestBenchmark::initTestCase() PASS : TestBenchmark::simple() RESULT : TestBenchmark::simple(): 0.00030 msecs per iteration (total: 79, iterations: 262144) PASS : TestBenchmark::multiple(locale-aware-compare) RESULT : TestBenchmark::multiple():"locale-aware-compare": 0.00029 msecs per iteration (total: 78, iterations: 262144) ..... PASS : TestBenchmark::series(locale-aware-compare:8001) RESULT : TestBenchmark::series():"locale-aware-compare:8001": 0.039 msecs per iteration (total: 81, iterations: 2048) Totals: 15 passed, 0 failed, 0 skipped, 0 blacklisted, 3971ms ********* Finished testing of TestBenchmark *********
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