A tool to turn the output of -XX:+TraceBytecodes (a JDK debug-only feature to print every bytecode executed by the interpreter) into a simple stack format, and a script to turn that into flame graphs showing what happened during program execution, bytecode-by-bytecode: 
This is a diagnostic tool I've developed and used to visualize what is going on at startup at a high granularity. Since it relies on a very verbose and slow debug option it's not by any means a good estimator of how long time things actually take.
As such, this is more a diagnostic tool than a profiler, but a tool that has served us well to disentangle various startup dependencies and inefficiencies in the JDK itself - and been a valuable aid in diagnosing a number of startup regressions.
Most profiling tools either have a blind spot when it comes to capturing what happens during the very early initialization of a JVM, e.g., agent based instrumentation, JFR etc, or they are native profiling tools that would attribute everything to "something in the interpreter".
- Perl is required to run FlameGraph.
- Git and access to GitHub are required on the first run unless FlameGraph is
already present in the
FlameGraphdirectory next to thebytestackslauncher. - a fastdebug (recommended) or slowdebug build of OpenJDK
- Build:
./gradlew build - With a fastdebug build of java, run any (small) program with
-XX:+TraceBytecodes -XX:+IgnoreUnrecognizedVMOptions -XX:+TraceBytecodesTruncated, e.g.:java -XX:+TraceBytecodes -XX:+IgnoreUnrecognizedVMOptions -XX:+TraceBytecodesTruncated HelloWorld | ./bytestacks helloworld- On first use the launcher clones
FlameGraph into
./FlameGraphif not already present. - This generates
helloworld.stacksandhelloworld.svgonly.
- On first use the launcher clones
FlameGraph into
- Open
helloworld.svgin your favorite SVG viewer. A modern web browser should suffice.
To build a distributable intended to run without GitHub access you must include the FlameGraph checkout alongside the launcher:
git clone --depth 1 https://github.com/brendangregg/FlameGraph.git FlameGraphThe resulting layout must contain both ./bytestacks and
./FlameGraph/flamegraph.pl.
- To get the full picture of what's going on, especially on a longer running program, it can be enlightening to run your program with
-Xint, since as things start to get compiled they will disappear from view. - For performance reasons there is a granularity option which allows setting a threshold for how small methods are output in the stack output, defaulting to 25. By setting this to a lower value, the generated flame graph will become more detailed, but may also become very heavy to render.