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Documentation and automation for using JITWatch to analyse JMH benchmarks
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‎build.sbt

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@@ -589,7 +589,8 @@ lazy val bench = project.in(file("test") / "benchmarks")
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else "org.scala-lang" % "scala-compiler" % benchmarkScalaVersion :: Nil
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},
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scalacOptions ++= Seq("-feature", "-opt:l:inline", "-opt-inline-from:**")
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)
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).settings(inConfig(JmhPlugin.JmhKeys.Jmh)(scalabuild.JitWatchFilePlugin.jitwatchSettings))
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lazy val junit = project.in(file("test") / "junit")
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.dependsOn(library, reflect, compiler, partest, scaladoc)

‎project/JitWatch.scala

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package scalabuild
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import java.io.FileWriter
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import java.util.Properties
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import sbt._
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import Keys._
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object JitWatchFilePlugin extends AutoPlugin {
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override def trigger = allRequirements
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override def requires = sbt.plugins.JvmPlugin
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val jitwatchConfigFileContents = taskKey[Properties]("Contents of file suitable for `jitwatch/launchUI -Djitwatch.config.file=jitwatch.properties`")
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val jitwatchConfigFile = taskKey[Unit]("file suitable for `jitwatch/launchUI.sh -Djitwatch.config.file=jitwatch.properties`")
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override lazy val projectSettings = List(Compile, Test).flatMap(c => inConfig(c)(jitwatchSettings))
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def jitwatchSettings: Seq[Setting[_]] = Seq(
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jitwatchConfigFileContents := {
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val sourcesValue = sources.value
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val depdependencyClasspathValue = dependencyClasspath.value ++ internalDependencyClasspath.value
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val props = new java.util.Properties
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val classpathString = (classDirectory.value +: depdependencyClasspathValue.map(_.data.toString)).mkString(",")
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val artifacts: Seq[Artifact] = depdependencyClasspathValue.flatMap(_.get(Keys.artifact.key))
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val dependencyModuleIds: Set[ModuleID] = depdependencyClasspathValue.flatMap(_.get(Keys.moduleID.key)).toSet
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props.put("Classes", classpathString)
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// JDK sources from $JAVA_HOME/src.zip
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val javaHomeSrc = {
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val javaDir = javaHome.value.getOrElse(new File(System.getProperty("java.home")))
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val src1 = javaDir / "src.zip"
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val src2 = javaDir.getParentFile / "src.zip"
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if (src1.exists()) src1 else src2
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}
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// Transitive sources from the projects that contribute to this classpath.
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val projects: Seq[ProjectRef] = buildDependencies.value.classpathTransitiveRefs(thisProjectRef.value) :+ thisProjectRef.value
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val projectArtifacts: Map[ProjectRef, Seq[Artifact]] = projects.map(project => (project -> (Keys.artifacts in project get settingsData.value).getOrElse(Nil))).toMap
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val artifactNameToProject: Map[String, Seq[ProjectRef]] = projects.groupBy(project => (Keys.name in project get settingsData.value).getOrElse(""))
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val transitiveSourceDirectories = projects.flatMap { project =>
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val projectArtifacts: Seq[Artifact] = (Keys.artifacts in project get settingsData.value).getOrElse(Nil)
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val matching = projectArtifacts.filter(artifacts.contains(_))
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val configs = matching.flatMap(artifact => artifact.configurations).distinct
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val sourceDirectories: Seq[File] = configs.flatMap { configRef =>
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(Keys.sourceDirectories in project in sbt.Configuration.of(configRef.name.capitalize, configRef.name)).get(settingsData.value).toList.flatten
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}
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sourceDirectories
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}.distinct
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val transitiveSourceDirectories2 = artifacts.flatMap { artifact =>
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val projects = artifactNameToProject.getOrElse(artifact.name, Nil)
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projects.flatMap { project: ProjectRef =>
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val configs = artifact.configurations
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val sourceDirectories: Seq[File] = configs.toList.flatMap { configRef =>
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(Keys.sourceDirectories in project in sbt.Configuration.of(configRef.name.capitalize, configRef.name)).get(settingsData.value).toList.flatten
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}
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sourceDirectories
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}
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}
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// Download and add transitive sources from the classpath
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val classiferArtifacts: Seq[(ModuleID, Artifact, File)] = updateClassifiers.value.configurations.flatMap(_.details.flatMap(_.modules.flatMap(report => report.artifacts.map(x => (report.module, x._1, x._2)))))
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val sourceClassiferArtifacts = classiferArtifacts.filter(tuple => tuple._2.classifier == Some("sources") && dependencyModuleIds.contains(tuple._1))
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val externalSources = sourceClassiferArtifacts.map(_._3)
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val internalAndExternalSources = (sourceDirectory.value +: javaHomeSrc +: (transitiveSourceDirectories ++ transitiveSourceDirectories2).distinct) ++ externalSources
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props.put("Sources", internalAndExternalSources.map(_.getAbsolutePath).mkString(","))
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val baseDir = baseDirectory.value
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val lastLogDir = Keys.forkOptions.value.workingDirectory match {
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case Some(dir) => dir
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case _=> baseDir
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}
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props.put("LastLogDir", lastLogDir.getAbsolutePath)
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props
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},
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jitwatchConfigFile := {
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val f = target.value / ("jitwatch-" + configuration.value.name + ".properties")
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val contents = jitwatchConfigFileContents.value
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val log = streams.value.log
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val fw = new FileWriter(f)
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try {
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jitwatchConfigFileContents.value.store(fw, null)
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log.info(s"./launchUI.sh -Djitwatch.config.file=" + f.getAbsolutePath)
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} finally {
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fw.close()
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}
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}
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)
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}

‎test/benchmarks/README.md

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you may also need to copy or link the disassembler library
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to the `jre/lib/`_`architecture`_ directory inside your JVM installation directory.
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The JITWatch project has [hsdis build instructions](https://github.com/AdoptOpenJDK/jitwatch/wiki/Building-hsdis).
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One way to obtain HSDIS is to use [the binaries](https://lafo.ssw.uni-linz.ac.at/pub/graal-external-deps/hsdis/intel/) which are used in the [Graal build](https://github.com/oracle/graal/blob/master/compiler/mx.compiler/mx_graal_tools.py#L94-L119).
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To show the assembly code corresponding to the code generated by the JIT compiler for specific methods,
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add `-XX:CompileCommand=print,scala.collection.mutable.OpenHashMap::*`,
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for example, to show all of the methods in the `scala.collection.mutable.OpenHashMap` class.
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To show it for _all_ methods, add `-XX:+PrintAssembly`.
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(This is usually excessive.)
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### Using JITWatch
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[JITWatch](https://github.com/AdoptOpenJDK/jitwatch) is useful to understand how the JVM has JIT compiled
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code.
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If you install `hsdis`, as described above, machine code disassembly is also created.
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You can generate the `hotspot.log` file for a benchmark run by adding the [required JVM options](https://github.com/AdoptOpenJDK/jitwatch/wiki/Building-hsdis)
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to JMH benchmark execution:
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```
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sbt:root> bench/jmh:run scala.collection.mutable.ArrayOpsBenchmark.insertInteger -psize=1000 -f1 -jvmArgs -XX:+UnlockDiagnosticVMOptions -jvmArgs -XX:+TraceClassLoading -jvmArgs -XX:+LogCompilation -jvmArgs -XX:LogFile=hotspot.log -jvmArgs -XX:+PrintAssembly
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...
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[info] Loaded disassembler from /Users/jz/.jabba/jdk/1.8.172/Contents/Home/jre/lib/hsdis-amd64.dylib
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[info] Decoding compiled method 0x0000000113f60bd0:
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[info] Code:
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[info] [Disassembling for mach='i386:x86-64']
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[info] [Entry Point]
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[info] [Constants]
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[info] # {method} {0x000000010ffa0000} 'hashCode' '()I' in 'java/lang/String'
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[info] # [sp+0x40] (sp of caller)
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[info] 0x0000000113f60d40: mov r10d,DWORD PTR [rsi+0x8]
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[info] 0x0000000113f60d44: shl r10,0x3
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...
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[info] # Run complete. Total time: 00:00:30
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[info] Benchmark (size) Mode Cnt Score Error Units
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[info] ArrayOpsBenchmark.insertInteger 1000 avgt 10 188199.582 ± 5930.520 ns/op
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```
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JITWatch requires configuration of the class and source path. We can generate that with a custom
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task in our build:
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```
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sbt> bench/jmh:jitwatchConfigFile
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[info] Resolving jline#jline;2.14.6 ...
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jmh
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[info] ./launchUI.sh -Djitwatch.config.file=/Users/jz/code/scala/test/benchmarks/target/jitwatch-jmh.properties
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sbt> ^C
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```
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Build jitwatch.
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```
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$ git clone https://github.com/AdoptOpenJDK/jitwatch
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$ cd jitwatch
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$ mvn install
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```
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Launch with the generated config file.
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```
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$ ./launchUI.sh -Djitwatch.config.file=/Users/jz/code/scala/test/benchmarks/target/jitwatch-jmh.properties
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```
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Select the generated `hotspot.log`, `start`, and then browse the the benchmark to start gleaning insights!
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## Useful reading
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* [OpenJDK advice on microbenchmarks](https://wiki.openjdk.java.net/display/HotSpot/MicroBenchmarks)
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* Brian Goetz's "Java theory and practice" articles:

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