valdar/java-puzzles

JBoss Engineers Meeting

Java Benchmark puzzles

SimpleInliningTest

This test shows the performance impact of 2 different (logging) code patterns.

SimpleInliningTest::wrongLong is supposed to be too big (bytecode wise) to be inlined; it can be verified using:

• the compilation log by running the application with -XX:+PrintCompilation -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlining
• JITWatch by copying the source as it is into the SandBox and playing with it

notes: it uses an ancient and unsafe technique to avoid dead code removal, JMH would be better, but JitWatch's Sandbox is the main consumer of this.

ProfilerFallacyExample

The profilers that worths to be tried are:

1. JVisualVM CPU Sample Profiler: JvmtiEnv::GetAllStackTraces based
2. perf-map-agent: "mostly" perf based
3. async-profiler: AsyncGetCallTrace + perf hybrid

The instruction for the perf-map-agent case are packed directly in the javadoc of the test.

In summary:

1. JVisualVM could just samples Java stack while on safepoint
2. perf-map-agent uses perf, can profile any stack (native + Java), but need to force the JVM to preserve the frame pointer and could read broken frames
3. async-profiler uses perf for native (JVM/Kernel) calls while AsyncGetCallTrace for Java ones (JFR, Solaris Studio do the same) trying to match between the two worlds (could read broken frames on both sides)

notes: Please remember to kill it or it will kill your CPU!!!!Hot stuff

ArrayfillBenchmark

It is mostly based on the awesome Nitsan Wakart article and it helps to understand how most legends around byte[] common operations are false and need proper (and correct) measurements.