This are the slides from presentation I gave on JMH during the first edition of jProfessional conference.

1. BENCHMARKING ON
JVM
Introduction to JMH
Vladimir Tsanev

2. ABOUT ME
Developer

3. WHAT IS JMH
Java Microbenchmark Harness
Building, running and analysing benchmarks written in
Java
Licensed under and
BSD for samples
Developed @
GPL 2, with the Classpath Exception
OpenJDK

4. WHY
Warm up
Dead code elimination
Loop unrolling
Branch prediction
False sharing
etc…​

5. GET STARTED
It is as simple as generating project with maven archetype
mvn archetype:generate
­DinteractiveMode=false
­DarchetypeGroupId=org.openjdk.jmh
­DarchetypeArtifactId=jmh­java­benchmark­archetype
­DgroupId=jpro.introjmh
­DartifactId=get­started
­Dversion=1.0­SNAPSHOT
Archetypes for kotlin, groovy, scala and java are
provided.

6. @BENCHMARK
JMH benchmarks code is placed in methods annotated with
@Benchmark
package jpro.introjmh;
import org.openjdk.jmh.annotations.Benchmark;
public class MyBenchmark {
@Benchmark
public void testMethod() {
// This is a demo/sample template for building your JMH benchmarks.
// Put your benchmark code here.
}
}

7. POM.XML
<!­­
This is the demo/sample template build script for building Java bench
Edit as needed.
­­>
<prerequisites>
<maven>3.0</maven>
</prerequisites>
<dependencies>
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh­core</artifactId>
<version>${jmh.version}</version>
</dependency>
<dependency>
<groupId>org.openjdk.jmh</groupId>

8. DEMO - FIRST BENCHMARK
java ­jar benchmarks.jar ­help

9. RTFM
(annotations are good place to get started)
Look around in the
This presentation :-)
JavaDoc
Samples
Mailing List

10. ANNOTATIONS
@AuxCounters @Benchmark @BenchmarkMode
@CompilerControl @Fork @Group
@GroupThreads @Measurement @OperationsPerInvoca
@OutputTimeUnit @Param @Setup
@State @TearDown @Threads
@Timeout @Warmup

11. @BENCHMARK
@Benchmark
Annotates the benchmark method

12. @BENCHMARKMODE
@BenchmarkMode(Mode.Throughput)
May be put at @Benchmarkmethod or at enclosing class
Available modes
Throughput- operations per time unit
AverageTime- average time per operation
SampleTime- sample time per operation
SingleShotTime- for single operation
any combination of the above

13. @STATE
@State(Scope.Benchmark)
public static class BenchmarkState {
volatile double x = Math.PI;
}
Encapsulate benchmark state
May be injected in @Benchmarkmethods and fixtures
May be used on the benchmark instance - default state.
Available scopes
Benchmark
Group
Thread

14. @SETUP AND @TEARDOWN
@State(Scope.Thread)
public static class BenchmarkState {
@Setup(Level.Trial)
public void up() {
}
@TearDown(Level.Trial)
public void down() {
}
}
State fixtures
Available levels
Trial- executed before/after each run
Iteration- executed before/after each iteration
Invocation- HERE BE DRAGONS!

15. @PARAM
@Param({"1", "1", "2", "3", "5", "7"})
public int arg;
Mark benchmark parameter
Supports primitive/wrapper, strings and enums
Should be non-final fields
Value is given as string and coerced if needed
When multiple @ParamJMH will compute the outer
product

16. @GROUP AND @GROUPTHREADS
@Benchmark
@Group("g")
@GroupThreads(3)
public int produce(){
}
@Benchmark
@Group("g")
@GroupThreads(1)
public int consume(){
}
Very useful for concurrent (producer/consumer)
benchmarks

17. DEFAULTS
@Warmup
@Measurement
@OutputTimeUnit
@Fork
@Threads
@Timeout

18. MISC
@OperationsPerInvocation - number of operations per
invocation
@CompilerControl - affect JIT compilation
@AuxCounters - state object int/long fields and methods

19. INFRASTRUCTURE
BenchmarkParams Blackhole Control
IterationParams ThreadParams

20. DCE
Dead-Code Elimination
return
Blackhole

21. WAITING VS CPU
Blackholes can consume not only the values, but also the
time
Blackhole.consumeCPU(1000);

22. INFRASTRUCTURE PARAMETERS
BenchmarkParams- benchmark configuration
IterationParams- type (warmup/measurement),
count, time, batch size
ThreadParams- group configuration

23. DEMO - DEAD CODE & FALSE
SHARING

24. PROFILERS
java ­jar benchmarks.jar ­lprof
Internal profiler - run in the benchmark JVM, and may
query the internal facilities
External profiler - run outside of JVM

25. STANDARD MBEANS
Profiling via standard MBeans
cl - Classloader profiling
comp - JIT compiler profiling
gc - GC profiling

26. HOTSPOT (TM)
Profiling via implementation-specific MBeans
hs_cl - HotSpot (tm) classloader profiling
hs_comp - HotSpot (tm) JIT compiler profiling
hs_gc - HotSpot (tm) memory manager (GC) profiling
hs_rt - HotSpot (tm) runtime profiling
hs_thr - HotSpot (tm) threading subsystem

27. SAMPLING
stack - Simple and naive Java stack profiler

28. PERF/XPERF
perf - Linux perf Statistics
perfnorm - Linux perf statistics, normalized by operation
count
perfasm - Linux perf + PrintAssembly Profiler
xperf - Windows xperf + PrintAssembly Profiler
For PrintAssemby profiler you will need hsdis plugin
https://wiki.openjdk.java.net/display/HotSpot/PrintAssembly

29. DEMO - BRANCH PREDICTOR

30. GENERATORS
Annotation processor
JMH Bytecode Generator
Reflection
ASM

31. RESULTS FORMAT
java ­jar benchmarks.jar ­lrf
Text
CSV - (but also SCSV)
JSON
LaTeX
rfc4180

32. DEMO - URL VALIDATOR
java ­jar benchmarks.jar ­rf csv ­rff url.csv

33. RESOURCES
http://shipilev.net/talks/jvmls-July2014-
benchmarking.pdf
http://shipilev.net/blog/2014/nanotrusting-nanotime
http://shipilev.net/talks/devoxx-Nov2013-
benchmarking.pdf
http://psy-lob-saw.blogspot.bg/p/jmh-related-posts.html

34. Q & A