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scalajvmmeasurement

Measuring the number of JVM instructions in a class

I need to count the number of JVM instructions for executing a method with multiple parameters. I give various arguments to the method to measure the number of JVM instructions executed for each case.

What tools can I use? The source is written in Scala, but it will produce class file anyway, so any JVM aware tool will work fine. I was thinking about profiler, but I think profiler may be used for different purposes.

Solution

  • There is an excellent tool for understanding the behavior of the Java HotSpot Just-In-Time (JIT) compiler during the execution of your program - JITWatch.

    Warning: Modern JVMs are too complex, and do all kinds of optimization so the number of JVM's instructions means nothing from performance point of view. If you try to measure some small piece of code, it is really complicated to do it correctly without very, very detailed knowledge of what the JVM is doing. Please be aware(http://shipilev.net/blog/2014/java-scala-divided-we-fail/) and use it on your own risk:

    • Always include a warmup phase which runs your method all the way through, enough to trigger all initializations and compilations before timing phase(s).
    • Be aware of the difference between -client and -server, and OSR and regular compilations.