/* * Copyright (c) 2014, Oracle America, Inc. * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * * Redistributions of source code must retain the above copyright notice, * this list of conditions and the following disclaimer. * * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * * Neither the name of Oracle nor the names of its contributors may be used * to endorse or promote products derived from this software without * specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF * THE POSSIBILITY OF SUCH DAMAGE. */ package org.openjdk.jmh.samples; import org.openjdk.jmh.annotations.Benchmark; import org.openjdk.jmh.annotations.OutputTimeUnit; import org.openjdk.jmh.annotations.Scope; import org.openjdk.jmh.annotations.State; import org.openjdk.jmh.runner.Runner; import org.openjdk.jmh.runner.RunnerException; import org.openjdk.jmh.runner.options.Options; import org.openjdk.jmh.runner.options.OptionsBuilder; import java.util.concurrent.TimeUnit; @State(Scope.Thread) @OutputTimeUnit(TimeUnit.MILLISECONDS) public class JMHSample_17_SyncIterations { /* * This is the another thing that is enabled in JMH by default. * * Suppose we have this simple benchmark. */ private double src; @Benchmark public double test() { double s = src; for (int i = 0; i < 1000; i++) { s = Math.sin(s); } return s; } /* * It turns out if you run the benchmark with multiple threads, * the way you start and stop the worker threads seriously affects * performance. * * The natural way would be to park all the threads on some sort * of barrier, and the let them go "at once". However, that does * not work: there are no guarantees the worker threads will start * at the same time, meaning other worker threads are working * in better conditions, skewing the result. * * The better solution would be to introduce bogus iterations, * ramp up the threads executing the iterations, and then atomically * shift the system to measuring stuff. The same thing can be done * during the rampdown. This sounds complicated, but JMH already * handles that for you. * */ /* * ============================== HOW TO RUN THIS TEST: ==================================== * * You will need to oversubscribe the system to make this effect * clearly visible; however, this effect can also be shown on the * unsaturated systems.* * * Note the performance of -si false version is more flaky, even * though it is "better". This is the false improvement, granted by * some of the threads executing in solo. The -si true version more stable * and coherent. * * -si true is enabled by default. * * Say, $CPU is the number of CPUs on your machine. * * You can run this test with: * * a) Via the command line: * $ mvn clean install * $ java -jar target/benchmarks.jar JMHSample_17 \ * -i 20 -wi 1 -f 1 -t ${CPU*16} -si {true|false} * (we requested 1 warmup iterations, 20 iterations, single fork, * lots of threads, and changeable "synchronize iterations" option) * * b) Via the Java API: * (see the JMH homepage for possible caveats when running from IDE: * http://openjdk.java.net/projects/code-tools/jmh/) */ public static void main(String[] args) throws RunnerException { Options opt = new OptionsBuilder() .include(JMHSample_17_SyncIterations.class.getSimpleName()) .warmupIterations(1) .measurementIterations(20) .threads(Runtime.getRuntime().availableProcessors()*16) .forks(1) .syncIterations(true) // try to switch to "false" .build(); new Runner(opt).run(); } }