Java performance jit
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We’ll dive into the mystic arts used by Java to gain significant performance improvements. Particularly into how Java's dynamic compilers (C1 and C2) work, optimizing our code and transitioning into different stages based on its profile. We'll also look at some of the primitive, complex and aggressive optimization techniques used by Java. Travel to a different realm of Java performance, Dr Strange style, to defeat the monster that is poor Java performance.
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Java performance jit
- 1. JAVA PERFORMANCE IMPROVEMENTS MYSTIC ARTSUKEN SHAH SHINE EA
- 2. JAVA PERFORMANCE IMPROVEMENTS - DIMENSIONS ▸Fix Memory leaks ▸Fine tune Garbage collection ▸Improve ORM performance ▸ Fix Inefficient code ▸JIT and code cache
- 3. JIT OPTIMISATIONS - WTF? DEMO
- 4. JIT - WHAT IS IT???? ▸Dynamic compiler - Hotspot ▸Profile Guided Optimisation (PGO) ▸Aggressive optimisations ▸Tiered compilation mode
- 5. JIT - UNIT OF COMPILATION ▸Method ▸Loop ▸Hot methods ▸Hot loops ▸Warm methods and warm loops
- 6. JIT - HOT STUFF -XX:+PRINTFLAGSFINAL
- 7. JIT - LIFE CYCLE Interpreting Profiling Optimisation De-optimisation
- 8. JIT - COMPILERS C1 - CLIENT COMPILER ▸ Fast acting compiler ▸ Invocation count > 2000 ▸ 10x faster than interpreter ▸ Backendge count > 65000 C2 - SERVER COMPILER ▸ Smart slow compiler ▸ Invocation count > 15000 ▸ 2x faster than C1 ▸ Backendge count > 40000
- 9. JIT - TIERED COMPILATION 0 3 4 0 0 2 3 4 3 Interpreter C1 C2 none counters details 1 preferred C2 busy Trivial
- 10. JIT OPTIMISATIONS - DEAD CODE, COMMON EXPRESSIONS ELIMINATION Dead code elimination Common expression elimination
- 11. JIT OPTIMISATIONS - OSR (ON STACK REPLACEMENT) For loop will be optimised by C1 compiler to level 3
- 12. JIT OPTIMISATIONS - LOOP PEELING
- 13. JIT OPTIMISATIONS - LOOP INVERSION
- 14. JIT OPTIMISATIONS - CODE MOTION, CONSTANT FOLDING
- 15. JIT OPTIMISATIONS - INTRINSICS ▸ Use hardware optimised compiled code ▸ System.arraycopy(), Math.sin() / cos() / tan(), System.currentMillis(), Unsafe.compareAndSwapInt(), String.indexOf() /compareTo()/equals()
- 16. JIT OPTIMISATIONS - INLINING
- 17. JIT OPTIMISATIONS - CLASS HIERARCHY ANALYSIS & INLINING Call site A PROCES S() A1 PROCES S() A2 PROCES S() SERVI CE
- 18. JIT OPTIMISATIONS - CLASS HIERARCHY ANALYSIS & INLINING FUNC PLUS MINUS DIVIDE Megamorphic Inline till bimorphic scenario Discovering new type leads to stop the world deoptimisation FUNC PLUS Monomorphic Inline the method when possible after CHA Always has uncommon trap for type.
- 19. JIT OPTIMISATIONS - CLASS HIERARCHY ANALYSIS & INLINING DEMO
- 20. JIT OPTIMISATIONS - SPECULATIVE OPTIMISATIONS ▸Implicite null assertions ▸Type assertions ▸Untaken branch pruning ▸Optimistic megamorphic inline
- 22. JIT COMPILER LOGGING ▸Light logging ▸Full logging ▸Tools -> {JITWatch, jitwatch-intellij} ▸JMH Benchmark
- 23. JIT COMPILER LOGGING - LIGHT -XX:+PRINTCOMPILATION Time ID Flags Lvl Method Size Flags -> b (blocking), s (static), n (native), % (OnStackReplacement), * (Generating native wrapper), ! (found exception handler)
- 24. JIT COMPILER LOGGING - FULL -XX:+UNLOCKDIAGNOSTICVMOPTIONS -XX:+LOGCOMPILATION - XX:LOGFILE=<PATH_TO_LOG_FILE>
- 25. JIT COMPILER - MY OWN EFFORT
- 26. JIT OPTIMISATIONS - WHAT TO DO NEXT? ▸ Exhaust other options. ▸ Find out critical or most used code paths ▸ Capture and analyse compilation logs ▸ Fix, test and measure performance ▸ Write good code (smaller methods, unnecessary inheritance, make static utilities)
- 27. JIT OPTIMISATIONS - WHAT IS JAVA DOING? VS
- 28. JIT OPTIMISATIONS - WHAT IS JAVA DOING? ▸ JVMCI (JVM Compiler Interface) http://openjdk.java.net/jeps/243 ▸ Set of interfaces used by JVM to perform compilation. ▸ Use Java to write C1/C2 compilers. ▸ Project Graal http://openjdk.java.net/projects/graal/ #ThorRagnarok
- 29. JIT OPTIMISATIONS - WHAT IS JAVA DOING? ▸ AOT Compilation http://openjdk.java.net/jeps/295 #ThorRagnarok ▸ Java 9 is packed with jaotc tool. ▸ Restricted to Linux x64
- 30. JIT COMPILER - MORE INFO Slides —> https://www.slideshare.net/SukenShah2/java-jit-compilers- and-optimisations Github —> https://github.com/suken/jit-reporter LinkedIn —> https://www.linkedin.com/in/suken-shah-b805b937/ Email —> suken.3@gmail.com
- 31. THANK YOU
Editor's Notes
- Dynamic compilation means that the compilation happens at runtime along side program execution Captures data about code
- invocation counters and backendge counters
- Max Inline size for not hot methods = 35 bytes (250 invocations) Max Inline size for hot hot methods is 325 bytes, max inline level = 9, recursion = 1. Inline small methods. (max size = 325 bytes, max inline level = 9, recursion = 1) static, private and constructor calls.
- Explain call sites. Monomorphic, biomorphic and metamorphic. Sets uncommon trap. Abstract class - deoptimsation if new type is discovered Interfaces - no deoptimization is performed
- Explain call sites. Monomorphic, biomorphic and metamorphic. Sets uncommon trap. Abstract class - deoptimsation if new type is discovered Interfaces - no deoptimization is performed
- Adds implicit null checks when required (only after observing > 3 NPE) Adds implicit type assertions (monomorphic inline) Set uncommon traps for untaken branches of code. As explained earlier slide.
- JMH benchmarks are like junit tests but has its own annotations to force compilers to do inlining, measuring benchmark.
- Write dynamic compilers faster with Java. Better code quality, extensible and quick to develop.
- Ahead Of Time compilation can be used to compile some modules of java and/or your code as part of your builds avoiding runtime compilation. Its an experimental feature. It cannot replace c2 compile code as it doesn’t have any profile data. So no speculative optimisations.