2013/11/14

Devoxx 2013 - Java Microbenchmark Harness: The Lesser of Two Evils

Aleksey Shipilev
micro-benchmarks:
  • depends on usage
  • aim: explore performance models
java Microbenchmark Harness
issues when running micro-benchmarks
  • warm-up all benchmarks
    • JIT
    • GC config
  • hyperthreading
  • power vs performance logic from cpu -- can change between cores (cpufreq, speedstep,...)
  • OS Scheduler logic
  • time sharing of OS
    • e.g. System.nanoTime() calcs -> de-schedule by OS influences measuring
    • do not overload system
  • avoid dead code (eliminated by the compiler)
    • JMH "BlackHoles"
  • loop unrolling
  • replay / do multiple JVM runs
  • check inlining: -XX:+PrintInlining
  • check memory footprint (SRAM cache vs slow DRAM mem)
  • cpu branch prediction (out-of-order engines) -> realistic data
conclusion: micro-benchmarks are not simple :-)
  • check everything
  • retest multiple times
  • use JMH...
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