This document discusses the performance improvements to the Java Virtual Machine (JVM) over time. It notes that early versions of Java from 1995-1998 had performance issues compared to modern versions and other languages due to the immaturity of JIT compilation and garbage collection techniques. The document outlines many specific performance optimizations added to the JVM over subsequent releases, such as just-in-time compilation, generational garbage collection, escape analysis, speculative optimizations, and multithreading improvements. It concludes that with these ongoing enhancements, Java now has performance on par with C/C++ in many cases and continues to improve for multicore processors.

1. Ask not what you can do for
your JVM, ask what your JVM
can do for you
Ett långsamt mellanlager eller har vi
någon nytta av den sett till
prestanda?
Mattias Isegran Bergander

2. Hur kom denna hit nu då...

3. Och den här?!

4. Det u ppenbara svaret...
Kommer ni ihåg Java 1.0/1.1?
Jämför med nu...
(förutom att datorerna är snabbare)

5. Historik
1995: Java 1.0
1996: Java 1.1
1998: Java 1.2
2000: Java 1.3
2002: Java 1.4
2004: Java 1.5
2006: Java 1.6
...
...
...
2011: Java 1.7

6. Historik: Prestanda
1995: Java 1.0
1996: Java 1.1 Symantec JIT
1998: Java 1.2 Generational GC
1999: Hotspot
2000: Java 1.3 Hotspot default, Math, BigInteger
2002: Java 1.4
2003: Java 1.4.2 Prestanda, ännu fler GC, SSE, SSE2, ...
2004: Java 1.5 Class data sharing, GC ergonomics
2006: Java 1.6 Biased locking, lock coarsening, adaptive
spinning, arraycopy, SSE4.2, large page heap

7. Historik: Prestanda
2006: Java 1.6
2007: u4: Hotspot får separat version, 10.0
2008: u10: Plugin2, GUI prestanda, kernel installer
2009: u14: Hotspot 14, 1:a escape analysis,
compressed object pointers, experimental G1
2009: u1x: Hotspot 15, SSE 4.2 string intrinsics
2010 : u18: Hotspot 16,
2010: u21: Hotspot 17,
2011: u23: Hotspot 19, Escape analysis default enabled
2011: u25: Hotspot 20
2011: u30:
2011: Java 1.7 Hotspot 21
2011: u2: Hotspot 22

8. Förbättringar genom åren 1.2 1.3 1.4

9. Förbättringar genom åren 1.2 1.3 1.4

10. Förbättringar genom åren 1.4.2

11. Förbättringar genom åren 1.5

12. Förbättringar genom åren 1.5

13. Förbättringar genom åren 1.6

14. Förbättringar genom åren 1.5 1.6 1.7
http://geeknizer.com/java-7-whats-new-performance-benchmark-1-5-1-6-1-7/

15. Det längre svaret...
Några uppenbara:
● GC i separat(a) tråd(ar)
● JIT kompilering i bakgrunden
● Bättre utnyttjande av CPU, i386, i586,
Core2, ..., 32/64bit, SSE/1/2/4.2
○ Ny JVM => bättre prestanda gratis
utan omkompilering
● Fler intrinsics

16. Det längre svaret...
Bättre analys ger tex:
● Null check elimination, VM behöver göra:
if (object == null) throw
new NullPointerException()
● Array bounds check elimination
0>=i && i < array.length
● Hoist duplicates & repeated use
int length = array.length;
for (int i=0;i<array.length;i++) {
if (array.length ...) {

17. Det längre svaret...
VM-lager inte bara nackdelar i prestanda:
● Pointers make optimizations hard
x = y + 2 * (...)
*p = ...
arr[j] = ...
z = x + ...
● Garbage Collection -> memory locality
● Runtime optimeringar
○ CPU, P4, Sandy Bridge, SSE, cache sizes, cores, ...
○ Current class hierarchy and inlining
○ Branch predications

18. Det längre svaret...
Fler:
● Generational Garbage Collector
● Inlining
● Spekulativa optimeringar
● Förbättrade Garbage Collectors
○ Senaste: G1, "Garbage First"
● Tiered compilation (vs client/server)
● Locks:
○ Lock elision
○ Lock coarsining
○ Adaptive locking
○ Biased locks
● NUMA aware
● Large pages (Solaris, Linux)
● ...

19. Det längre svaret...
Några intressanta
● Virtual method inlining
● Escape Analysis (java 6u14, default enabled java7)

20. Så vad har vi nu då?
Programspråket Java hör till kategorin "de
snabba språken", tillsammans med Fortran
och C/C++
~50-100% av C/C++ prestanda
Ibland snabbare!
Quake2 vs Jake2 (Java5)
Men går utan problem att hitta fall
där C++ är snabbare...

21. Escape Analysis
Tex Dimension, Point, get/set, men inte begränsat till det...
http://weblogs.java.net/blog/forax/archive/2009/10/06/jdk7-do-escape-analysis-default

22. Escape Analysis

23. Escape Analysis
Off: ~430ms
On: ~110ms

24. Generational and Copying GC
Allokera en större bit Heap i förväg
Effektivisera per tråd med trådlokalt
minne så ingen contention...

25. Generational and Copying GC
Generational:
● Young, Old (and Perm)
Young
● De flesta objekt är kortlivade, 92-98%
● Bevara (kopiera) bara de levande!
Minne:

26. Generational and Copying GC
Young

27. Generational and Copying GC
Young

28. Speculative virtual method inlining

29. Speculative virtual method inlining

30. Speculative virtual method inlining

31. February 2, 2004
Bill Venners: When I asked you earlier (In Part IV) about why non-virtual methods are the
default in C#, one of your reasons was performance. You said:
We can observe that as people write code in Java, they forget to mark their methods final.
Therefore, those methods are virtual. Because they're virtual, they don't perform as well.
There's just performance overhead associated with being a virtual method.
Another thing that happens in the adaptive optimizing JVMs is they'll inline virtual method
invocations, because a lot of times only one or two implementations are actually being used.
Anders Hejlsberg:
They can never inline a virtual method invocation.
http://www.artima.com/intv/choices.html

32. Framtiden
● Tiered compilation default?
● Disruptor pattern
● Azul ZingVM -Cliff Click
○ Scalability
○ 512GB heap
○ Pauseless Garbage Collection
● Java 8
○ Hotspot <-> JRockit
○ Mer multicore i VM och API (ForkJoin med lambda tex)
● Java 9
○ Self-tuning JVM
○ Hypervisor integration
○ Tail calls, continuations
○ "Massive multicore scalability"

33. References & Further reading
http://java.sun.com/j2se/1.4.2/performance.guide.html
http://java.sun.com/j2se/1.4.2/1.4.2_whitepaper.html
http://java.sun.com/performance/reference/whitepapers/5.0_performance.html
http://java.sun.com/performance/reference/whitepapers/6_performance.html
http://docs.oracle.com/javase/7/docs/technotes/guides/vm/performance-
enhancements-7.html
http://www.ibm.com/developerworks/java/library/j-jtp09275/index.html
http://www.ibm.com/developerworks/java/library/j-jtp10185/
http://www.ibm.com/developerworks/java/library/j-jtp12214/index.html
http://scribblethink.org/Computer/javaCbenchmark.html

34. Tack
Mattias Isegran Bergander
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