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I am currently doing some Java optimization. It seems the best approach to assess my progress is to do repeated runs and collect run time statistics using System.nanoTime.

Most of my background has been with embedded DSP applications. In my embedded developments, I would have access to CPU cycle counters (which are a great measure for optimization). The JRE acts like a synthetic CPU, is there a way to get information of the number of instructions or JRE clock equivalents that were executed?

Thanks in advance for any hints. J.R.

J. R. Schweitzer
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The byte code count is almost certainly useless for what you want. They are entirely virtual/notional in terms of performance at run time. The only thing which matters is elapse time for code which has been warmed up.

I suggest you have a look at JMH for micro-benchmarking your code. http://openjdk.java.net/projects/code-tools/jmh/

If you come from the DSP/realtime background I suggest looking at the latency distribution and minimising your allocation rate.

NOTE: The JVM injects "safe points" between instructions to check if the thread needs to stop e.g. to perform garbage collection. A garbage collection can take seconds. However safepoints are often optimised away to avoid slowing down your program.

In short this means the time between instructions might be nothing, it might be something, it might be seconds or even minutes so I wouldn't bother counting them.

Peter Lawrey
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