Introduction to JVM JIT Optimizations
- 1. Introduction to JVMIntroduction to JVM JIT OptimizationsJIT Optimizations Diego Parra | @dpsoft | Core Team @ Kamon
- 2. AgendaAgenda What is JIT? Tiered Compilation Optimizations Conclusion
- 3. JITJIT Just-In-Time compilation Compilation work happens during application execution JIT'ing requires Pro鍖ling for more e鍖cient optimization Because you don't want JIT everything Aggressively optimize based on pro鍖le information Tiered compilation Runtime Overhead?
- 4. JITJIT Just-In-Time compilation Compilation work happens during application execution JIT'ing requires Pro鍖ling for more e鍖cient optimization Because you don't want JIT everything Aggressively optimize based on pro鍖le information Tiered compilation Runtime Overhead?
- 6. JIT CompilersJIT Compilers C1 Client C2 ServerVS Fast compiler Invocation count > 1500 Produces Compilations quickly Generated code runs Slow Pro鍖le is about counters: https://github.com/dmlloyd/openjdk/blob/jdk8u/jdk8u/hotspot/src/share/vm/oops/methodCounters.hpp Smart compiler Invocation count > 10000 Produces Compilations slowly Generated code runs Fast 10x faster than Interpreter 2x faster than C1
- 7. JIT CompilersJIT Compilers C1 Client C2 ServerVS Fast compiler Invocation count > 1500 Produces Compilations quickly Generated code runs Slow Pro鍖le is about counters: https://github.com/dmlloyd/openjdk/blob/jdk8u/jdk8u/hotspot/src/share/vm/oops/methodCounters.hpp Smart compiler Invocation count > 10000 Produces Compilations slowly Generated code runs Fast Pro鍖led Guided Speculative 10x faster than Interpreter 2x faster than C1
- 8. Tiered CompilationTiered Compilation Available in Java 7 Default in Java 8 Client Startup Server Performance Tiered : https://github.com/dmlloyd/openjdk/blob/jdk8u/jdk8u/hotspot/src/share/vm/runtime/advancedThresholdPolicy.hpp#L35-L158
- 9. Tiered CompilationTiered Compilation Available in Java 7 Default in Java 8 Client Startup Server Performance Best of Both Worlds - C1 + C2 Tiered : https://github.com/dmlloyd/openjdk/blob/jdk8u/jdk8u/hotspot/src/share/vm/runtime/advancedThresholdPolicy.hpp#L35-L158
- 11. Common TransitionsCommon Transitions Common Transitions Patterns : /maddocig/tiered Notes: https://github.com/dmlloyd/openjdk/blob/jdk8u/jdk8u/hotspot/src/share/vm/runtime/advancedThresholdPolicy.cpp
- 12. JIT OptimizationsJIT Optimizations Compiler tacticsCompiler tactics delayed compilation tiered compilation on-stack replacement delayed reoptimization program dependence graph representation static single assignment representation Speculative (profile-based)Speculative (profile-based) optimistic nullness assertions optimistic type assertions optimistic type strengthening optimistic array length strengthening untaken branch pruning optimistic N-morphic inlining branch frequency prediction call frequency prediction Proof-based techniquesProof-based techniques exact type inference memory value inference memory value tracking constant folding reassociation operator strength reduction null check elimination type test strength reduction type test elimination algebraic simpli鍖cation common subexpression elimination integer range typing Flow-sensitive rewritesFlow-sensitive rewrites conditional constant propagation dominating test detection 鍖ow-carried type narrowing dead code elimination Text and much more..
- 13. Null check EliminationNull check Elimination
- 14. Null check EliminationNull check Elimination In equivalent machine code
- 15. Null check EliminationNull check Elimination In equivalent machine code
- 16. Null check EliminationNull check Elimination In equivalent machine code
- 17. Null check EliminationNull check EliminationInto the rabbit hole -XX:+PrintCompilation
- 18. Null check EliminationNull check EliminationInto the rabbit hole -XX:+PrintCompilation Compilation Level
- 19. Null check EliminationNull check EliminationInto the rabbit hole -XX:+PrintCompilation Compilation Level
- 20. Null check EliminationNull check EliminationInto the rabbit hole -XX:+PrintCompilation Compilation Level
- 21. Null check EliminationNull check EliminationInto the rabbit hole -XX:+PrintCompilation Compilation Level
- 22. Null check EliminationNull check EliminationInto the rabbit hole -XX:+PrintCompilation Compilation Level Deoptimizations
- 23. Null check EliminationNull check EliminationInto the rabbit hole -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:CompileCommand=print,NullCheck::isPowerOfTwo
- 24. Null check EliminationNull check EliminationInto the rabbit hole -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:CompileCommand=print,NullCheck::isPowerOfTwo Someone said Assembly?
- 25. Null check EliminationNull check EliminationInto the rabbit hole -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:CompileCommand=print,NullCheck::isPowerOfTwo Someone said Assembly?
- 26. Null check EliminationNull check EliminationInto the rabbit hole
- 27. Null check EliminationNull check EliminationInto the rabbit hole
- 28. Null check EliminationNull check EliminationInto the rabbit hole implicit exception: dispatches to 0x00007fd鍖5318274
- 29. Null check EliminationNull check Elimination JVM usesJVM uses SIGSEGVSIGSEGV as control flowas control flow Into the rabbit hole Handle Signals: https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/signals001.html#CIHBBDED Speculative OptimizationSpeculative Optimization FasterFaster IFIF not null are encountered (Uncommon Trap)not null are encountered (Uncommon Trap)
- 30. Null check EliminationNull check Elimination JVM usesJVM uses SIGSEGVSIGSEGV as control flowas control flow Into the rabbit hole Handle Signals: https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/signals001.html#CIHBBDED Speculative OptimizationSpeculative Optimization FasterFaster IFIF not null are encountered (Uncommon Trap)not null are encountered (Uncommon Trap) Implicit Null Check? Field and Array access is null checked
- 36. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods
- 37. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining?
- 38. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining?
- 39. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining? Monomorphic
- 40. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining? Monomorphic Bimorphic
- 41. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining? Monomorphic Bimorphic Megamorphic
- 42. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining? Black Magic: https://shipilev.net/blog/2015/black-magic-method-dispatch/ Monomorphic Bimorphic Megamorphic
- 43. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining? Black Magic: https://shipilev.net/blog/2015/black-magic-method-dispatch/ Monomorphic Bimorphic Megamorphic Class Hierarchy Analysis
- 44. Method InliningMethod Inlining Inlining is the most important optimization Combine caller and callee into one unit Expands the scope for other optimizations Bytecode size < 35 bytes Bytecode size < 325 bytes for inlining hot methods What about virtual call inlining? Black Magic: https://shipilev.net/blog/2015/black-magic-method-dispatch/ Monomorphic Bimorphic Megamorphic Class Hierarchy Analysis Devirtualization
- 48. On-Stack ReplacementOn-Stack Replacement -XX:+PrintCompilation -XX:+PrintInlining
- 49. On-Stack ReplacementOn-Stack Replacement -XX:+PrintCompilation -XX:+PrintInlining
- 50. On-Stack ReplacementOn-Stack Replacement -XX:+PrintCompilation -XX:+PrintInlining Compilation is OSR
- 51. Dead Code EliminationDead Code Elimination
- 52. Dead Code EliminationDead Code Elimination Dead-Code: http://hg.openjdk.java.net/code-tools/jmh/鍖le/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_08_DeadCode.java
- 53. Dead Code EliminationDead Code Elimination Dead-Code: http://hg.openjdk.java.net/code-tools/jmh/鍖le/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_08_DeadCode.java
- 54. Dead Code EliminationDead Code Elimination Dead-Code: http://hg.openjdk.java.net/code-tools/jmh/鍖le/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_08_DeadCode.java
- 55. Dead Code EliminationDead Code Elimination Dead-Code: http://hg.openjdk.java.net/code-tools/jmh/鍖le/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_08_DeadCode.java
- 56. Dead Code EliminationDead Code Elimination Dead-Code: http://hg.openjdk.java.net/code-tools/jmh/鍖le/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_08_DeadCode.java
- 57. Dead Code EliminationDead Code Elimination Dead-Code: http://hg.openjdk.java.net/code-tools/jmh/鍖le/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_08_DeadCode.java Result is not used and the entire method is optimized away!
- 59. Escape AnalysisEscape Analysis No synchronization lock when calling getNoEscapeSum method Escape Analysis for Java: http://www.research.ibm.com/people/j/jdchoi/escape.ps
- 60. Escape AnalysisEscape Analysis No synchronization lock when calling getNoEscapeSum method No allocate a Sum object at all, just keep track of the individual 鍖elds of the object Escape Analysis for Java: http://www.research.ibm.com/people/j/jdchoi/escape.ps
- 61. DeoptimizationDeoptimization The compiler can back to previous versions of compiled code E鍖ect in performance when code is deoptimized Deoptimize when previous optimizations are no longer valid There are two cases of deoptimization not entrant -> don't let new calls enter zombi -> on this way to deadness
- 65. IntrinsicsIntrinsics Intrinsics: https://github.com/dmlloyd/openjdk/blob/jdk8u/jdk8u/hotspot/src/share/vm/class鍖le/vmSymbols.hpp#L603 Special code build-into the VM for a particular method Often use special hardware capabilities Not writen in Java
- 67. ConclusionConclusion Please use JMH, Don't lie to yourself Code will be Optimized and De-optimized JVM require Warmup JVM is Smart Keep It Simple, Stupid!, is perfect for JIT to make his job
- 68. ConclusionConclusion Please use JMH, Don't lie to yourself Code will be Optimized and De-optimized JVM require Warmup JVM is Smart Keep It Simple, Stupid!, is perfect for JIT to make his job Learn Assembly
- 69. ResourcesResources Java Performance: http://shop.oreilly.com/product/0636920028499.do Optimizing Java: http://shop.oreilly.com/product/0636920042983.do Aleksey Shipil谷v (blog): https://shipilev.net/ Nitsan Wakart (blog): http://psy-lob-saw.blogspot.com.ar/ JVM Source Code: https://github.com/dmlloyd/openjdk Open JDK Wiki: https://wiki.openjdk.java.net/dashboard.action