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Video introduction to JITWatch

https://skillsmatter.com/skillscasts/5243-chris-newland-hotspot-profiling-with-jit-watch

Slides from my LJC lightning talk on JITWatch:

http://www.chrisnewland.com/images/jitwatch/HotSpot_Profiling_Using_JITWatch.pdf

Description

A tool for understanding the behaviour of the Java HotSpot Just-In-Time (JIT) compiler during the execution of your program.

Works by processing the hotspot.log file output by the JVM.

I built this tool as a learning vehicle to gain a better understanding of HotSpot and JavaFX.

Mailing list

For usage questions, bug reports, feature requests, and general chat about JIT, HotSpot, JVM, bytecode and performance tuning please join the list at https://groups.google.com/forum/#!forum/jitwatch

Why would I use this tool?

To verify whether methods you believe to be performance-critical were JIT-compiled during the program's execution.
To learn when your performance-critical methods were compiled.
For visualising the effects of tuning JVM compilation thresholds.
To gain a better understanding of the HotSpot JIT compiler.
To have a nice interface for inspecting method bytecode and assembly?

Features

Browse class trees and view which methods were JIT-compiled, when JIT-compilation occurred, and information about the compilation.
Mount your source, jars, and class trees to jump to the source, bytecode, and assembly for a method.
Plot JIT compilations over time and visualise when a method was JIT-compiled.
View toplists of the largest native methods, methods with most bytecodes, longest compilation times, etc.
Open sourced under the Simplified BSD licence.

Download a pre-built jar

Pre-built jars are now produced by Jenkins CI. See the README for details

Instructions

To generate the hotspot.log file used by JITWatch run your program with the following JVM switches.

-XX:+UnlockDiagnosticVMOptions -XX:+TraceClassLoading -XX:+LogCompilation -XX:+PrintAssembly

The hotspot.log file is generated in the program execution directory.

If you want to use the -XX:+PrintAssembly switch to view the assembly language (disassembled JIT-compiled native code) then you need to use a debug JVM build or have built the hsdis (HotSpot disassembler) binary. The source for hsdis is part of OpenJDK.

Instructions for building hsdis (for Windows) are here: Building hsdis on Windows

Instructions for building hsdis (for Linux) are here: [Building hsdis on Linux] (http://www.chrisnewland.com/building-hsdis-on-linux-amd64-on-debian-369)

-XX:+TraceClassLoading is required. This is how JITWatch builds the class model.

JavaFX (JAVA_HOME/jre/lib/jfxrt.jar for jdk1.7 or JAVA_HOME/jre/lib/ext/jfxrt.jar for jdk8) and tools.jar (JDK_HOME/lib/tools.jar) are required to run JITWatch.

Example launch script (Linux):

#!/bin/sh

export CP=$JDK_HOME/lib/tools.jar:$JDK_HOME/jre/lib/jfxrt.jar:jitwatch.jar

$JDK_HOME/bin/java -cp $CP com.chrisnewland.jitwatch.launch.LaunchUI