1. How Fast is Your Java
Code?
Performance micro-benchmarking
Dmitry Buzdin

2. About Speaker
buzdin@gmail.com
@buzdin
Dmitry Buzdin

3. Motivation

4. Programming for
Performance

5. Situation
Some developers optimize code a lot
Good habits like:
* Putting final keyword
* Optimizing assignments
* Creating less objects
* Avoiding reflection

6. Situation
Arguing who’s code is faster

7. So how do you
measure that?

8. Macro-
benchmarking
vs
Micro-
benchmarking

9. Challenge

10. Challenge: How Fast is
That?
System.out.println("Hello, World!");

11. DEMO

12. 1 millisecond =
1 000 microseconds =
1 000 000 nanoseconds

13. Test Noise
Classloader activities
Reflection inflation
Garbage collection
JIT compilation

14. JIT Compiler
Behavior-driven
Can compile and “de-compile”
Client and Ser ver JITs are different

15. Getting JVM Stats
ManagementFactory.getXYZBean()

16. ClassLoadingMXBean
GarbageCollectorMXBean
RuntimeMXBean
MemoryMXBean
ThreadMXBean
...

17. Measurement Pitfalls
Measuring in milliseconds
Not doing warm-ups
Not doing enough warm-ups
Wrong JVM settings
Too few iterations

18. Conclusions

19. Conclusions
Do not do micro optimizations
Write first - then measure critical
places
Program readability is more important
Do perform macro optimizations
instead

20. “We should forget about small
efficiencies, say about 97% of the
time: premature optimization is the
root of all evil”
Donald Knuth

21. Some Resources
http://www.ibm.com/developer works/java/library/j-benchmark2/
index.html
http://stackoverflow.com/questions/504103/how-do-i-write-a-correct-
micro-benchmark-in-java
http://docs.oracle.com/javase/specs/
jvms/se7 /html/index.html

22. Code is on GitHub
https://github.com/buzdin/java-microbenchmarking/

23. The End