![©2016 CodeKaram
JOL Command Line Options
$ java -jar jol-cli.jar
Usage: jol-cli.jar <mode> [optional arguments]*
Available modes:
estimates: Simulate the class layout in different VM modes.
externals: Show the object externals: the objects reachable
from a given instance.
footprint: Estimate the footprint of all objects reachable
from a given instance
heapdump: Consume the heap dump and estimate the savings
in different layout strategies.
heapdumpstats: Consume the heap dump and print the most
frequent instances.
idealpack: Compute the object footprint under different
field layout strategies.
internals: Show the object internals: field layout and
default contents, object header
shapes: Dump the object shapes present in JAR files or
heap dumps.
string-compress: Consume the heap dumps and figures out the
savings attainable with compressed strings.
57](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-57-320.jpg)
![©2016 CodeKaram
JOL Command Line Options
$ java -jar jol-cli.jar
Usage: jol-cli.jar <mode> [optional arguments]*
Available modes:
estimates: Simulate the class layout in different VM modes.
externals: Show the object externals: the objects reachable from
a given instance.
footprint: Estimate the footprint of all objects reachable from
a given instance
heapdump: Consume the heap dump and estimate the savings in
different layout strategies.
heapdumpstats: Consume the heap dump and print the most frequent
instances.
idealpack: Compute the object footprint under different field
layout strategies.
internals: Show the object internals:
field layout and default contents, object header
shapes: Dump the object shapes present in JAR files or heap
dumps.
string-compress: Consume the heap dumps and figures out the savings
attainable with compressed strings.
58](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-58-320.jpg)
![©2016 CodeKaram
JOL: Class
java.lang.Class object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 16 (object header) N/A
16 8 Constructor Class.cachedConstructor N/A
24 8 Class Class.newInstanceCallerCache N/A
32 8 String Class.name N/A
40 8 Module Class.module N/A
48 8 (alignment/padding gap) N/A
56 8 String Class.packageName N/A
64 8 Class Class.componentType N/A
72 8 SoftReference Class.reflectionData N/A
80 8 ClassRepository Class.genericInfo N/A
88 8 Object[] Class.enumConstants N/A
96 8 Map Class.enumConstantDirectory N/A
104 8 AnnotationData Class.annotationData N/A
112 8 AnnotationType Class.annotationType N/A
120 8 ClassValueMap Class.classValueMap N/A
128 32 (alignment/padding gap) N/A
160 4 int Class.classRedefinedCount N/A
164 4 (loss due to the next object alignment)
Instance size: 168 bytes
Space losses: 40 bytes internal + 4 bytes external = 44 bytes total
86](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-86-320.jpg)
![©2016 CodeKaram
java.lang.Class object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 16 (object header)
N/A
16 8 Constructor Class.cachedConstructor N/A
24 8 Class Class.newInstanceCallerCache N/A
32 8 String Class.name N/A
40 8 Module Class.module N/A
48 8 (alignment/padding gap) N/A
56 8 String Class.packageName N/A
64 8 Class Class.componentType N/A
72 8 SoftReference Class.reflectionData N/A
80 8 ClassRepository Class.genericInfo N/A
88 8 Object[] Class.enumConstants N/A
96 8 Map Class.enumConstantDirectory N/A
104 8 AnnotationData Class.annotationData N/A
112 8 AnnotationType Class.annotationType N/A
120 8 ClassValueMap Class.classValueMap N/A
128 32 (alignment/padding gap) N/A
160 4 int Class.classRedefinedCount N/A
164 4 (loss due to the next object alignment)
Instance size: 168 bytes
Space losses: 40 bytes internal + 4 bytes external = 44 bytes total
87
JOL: Class](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-87-320.jpg)
![©2016 CodeKaram
java.lang.Class object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 16 (object header) N/A
16 8 Constructor Class.cachedConstructor N/A
24 8 Class Class.newInstanceCallerCache N/A
32 8 String Class.name N/A
40 8 Module Class.module N/A
48 8 (alignment/padding gap) N/A
56 8 String Class.packageName N/A
64 8 Class Class.componentType N/A
72 8 SoftReference Class.reflectionData N/A
80 8 ClassRepository Class.genericInfo N/A
88 8 Object[] Class.enumConstants N/A
96 8 Map Class.enumConstantDirectory N/A
104 8 AnnotationData Class.annotationData N/A
112 8 AnnotationType Class.annotationType N/A
120 8 ClassValueMap Class.classValueMap N/A
128 32 (alignment/padding gap) N/A
160 4 int Class.classRedefinedCount N/A
164 4 (loss due to the next object alignment)
Instance size: 168 bytes
Space losses: 40 bytes internal + 4 bytes external = 44 bytes total
88
JOL: Class](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-88-320.jpg)
![©2016 CodeKaram
java.lang.Class object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 12 (object header) N/A
12 4 Constructor Class.cachedConstructor N/A
16 4 Class Class.newInstanceCallerCache N/A
20 4 String Class.name N/A
24 4 Module Class.module N/A
28 4 (alignment/padding gap) N/A
32 4 String Class.packageName N/A
36 4 Class Class.componentType N/A
40 4 SoftReference Class.reflectionData N/A
44 4 ClassRepository Class.genericInfo N/A
48 4 Object[] Class.enumConstants N/A
52 4 Map Class.enumConstantDirectory N/A
56 4 AnnotationData Class.annotationData N/A
60 4 AnnotationType Class.annotationType N/A
64 4 ClassValueMap Class.classValueMap N/A
68 28 (alignment/padding gap) N/A
96 4 int Class.classRedefinedCount N/A
100 4 (loss due to the next object alignment)
90
JOL: Class](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-90-320.jpg)
![©2016 CodeKaram
java.lang.Class object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 12 (object header)
N/A
12 4 Constructor Class.cachedConstructor N/A
16 4 Class Class.newInstanceCallerCache N/A
20 4 String Class.name N/A
24 4 Module Class.module N/A
28 4 (alignment/padding gap) N/A
32 4 String Class.packageName N/A
36 4 Class Class.componentType N/A
40 4 SoftReference Class.reflectionData N/A
44 4 ClassRepository Class.genericInfo N/A
48 4 Object[] Class.enumConstants N/A
52 4 Map Class.enumConstantDirectory N/A
56 4 AnnotationData Class.annotationData N/A
60 4 AnnotationType Class.annotationType N/A
64 4 ClassValueMap Class.classValueMap N/A
68 28 (alignment/padding gap) N/A
96 4 int Class.classRedefinedCount N/A
100 4 (loss due to the next object alignment)
91
JOL: Class](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-91-320.jpg)
![©2016 CodeKaram
java.lang.Class object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 12 (object header) N/A
12 4 Constructor Class.cachedConstructor N/A
16 4 Class Class.newInstanceCallerCache N/A
20 4 String Class.name N/A
24 4 Module Class.module N/A
28 4 (alignment/padding gap) N/A
32 4 String Class.packageName N/A
36 4 Class Class.componentType N/A
40 4 SoftReference Class.reflectionData N/A
44 4 ClassRepository Class.genericInfo N/A
48 4 Object[] Class.enumConstants N/A
52 4 Map Class.enumConstantDirectory N/A
56 4 AnnotationData Class.annotationData N/A
60 4 AnnotationType Class.annotationType N/A
64 4 ClassValueMap Class.classValueMap N/A
68 28 (alignment/padding gap) N/A
96 4 int Class.classRedefinedCount N/A
100 4 (loss due to the next object alignment)
92
JOL: Class](https://image.slidesharecdn.com/hitchikersjit-161025033735/85/The-Performance-Engineer-s-Guide-To-HotSpot-Just-in-Time-Compilation-92-320.jpg)
Uploaded byMonica Beckwith
The Performance Engineer's Guide To HotSpot Just-in-Time Compilation
The document provides an extensive guide on HotSpot JIT compilation, covering key concepts such as adaptive optimization, compilation techniques (C1, C2, and tiered compilations), and various Java VM optimizations. It details the processes involved in JIT optimization, including dynamic deoptimization, inlining, and the usage of compressed oops and class pointers. Additionally, it explains advanced optimizations, profiling critical methods, and the implications of memory layout in Java objects.
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Similar to The Performance Engineer's Guide To HotSpot Just-in-Time Compilation
The Performance Engineer's Guide To HotSpot Just-in-Time Compilation
- 1.
- 2. 2 About Me … Java/JVM/GCperformance person Current Life: Consultant who solves Managed Runtime performance issues Past Life: Worked with Oracle, Sun, AMD… - Worked with HotSpot VM: JVM heuristics, JIT compiler, GCs: Parallel(Old) GC, G1 GC, CMS GC www.codekaram.com https://www.linkedin.com/in/monicabeckwith Tweet @mon_beck
- 3. ©2016 CodeKaram Establishing theCharacters and The Plot • HotSpot Virtual Machine • Runtime Goal • Common Compilation Techniques • C1, C2 & Tiered Compilations • Adaptive Optimization - The Plot 3
- 4. ©2016 CodeKaram The Storyline •Dynamic Deoptimization • Inlining • Intrinsics 4
- 5. ©2016 CodeKaram The StoryLine •Compressed Oops + Compressed Class Pointers • Escape Analysis • Vectorization (Auto and otherwise) 5
- 6.
- 7. ©2016 CodeKaram Let’s PeekUnder The Hood 7 Java Application Java APIs Execution Engine Java VM OS + Hardware Runtime
- 8. ©2016 CodeKaram8 Java Application Java API JavaVM OS + HardwareJRE Execution Engine Runtime Java Runtime Environment
- 9. ©2016 CodeKaram The Helpers 9 JavaVM Execution Engine Runtime
- 10. ©2016 CodeKaram HotSpot VM 10 ExecutionEngine Heap Management - Garbage Collection JIT Compilation - Tiered (C1 + C2)
- 11. ©2016 CodeKaram HotSpot VM 11 Runtime VMClass loading Interpreter Bytecode Verification, Exception Handling, Synchronization , Thread Management, ….http://openjdk.java.net/groups/hotspot/ docs/RuntimeOverview.html
- 12.
- 13. ©2016 CodeKaram HotSpot VM- Template Interpreter 13 Bytecode 1 Bytecode 2 Template Native Code 1 Template Native Code 2 TemplateTable
- 14.
- 15.
- 16. ©2016 CodeKaram • CompileThreshold •Identify root of compilation • Method Compilation or On-stack replacement (Loop)? 16 Identifying Performance Critical Methods
- 17. 17 JIT Optimization -Client Compiler (C1)
- 18. ©2016 CodeKaram • Startin interpreter • CompileThreshold = 1500 • Compile with client compiler • Few optimizations 18 Client Compiler
- 19. 19 JIT Optimization -Server Compiler (C2)
- 20. ©2016 CodeKaram • Startin interpreter • CompileThreshold = 10000 • Compile with optimized server compiler • High performance optimizations 20 Server Compiler
- 21. 21 JIT Optimization -Tiered Compilation
- 22.
- 23. ©2016 CodeKaram • Startin interpreter • Tiered optimization with client compiler • Code profiled information • Enable server compiler 23 Tiered Compilation
- 24. ©2016 CodeKaram24 Tiered Compilation- Effect on Code Cache Tiered Compilation Code Cache Compiled Native Code
- 25. ©2016 CodeKaram • C1compilation threshold for tiered is about a 100 invocations • Tiered Compilation has a lot more profiled information for C1 compiled methods • CodeCache needs to be 5x larger than non-tiered • Default on JDK8 when tiered is enabled (240MB vs 48MB) • Need more? Use -XX:ReservedCodeCacheSize 25 Tiered Compilation - Effect on Code Cache
- 26. 26 Advanced Optimizations - AdaptiveOptimization
- 27. ©2016 CodeKaram27 The Plot Startup (Adaptive)JIT Optimizations Profiling of critical hot- spots Interpreter
- 28. ©2016 CodeKaram28 The Plot Startup (Adaptive)JIT Optimizations Profiling of critical hot- spots Interpreter
- 29.
- 30.
- 31. ©2016 CodeKaram • Oopsie! •dependencies invalidation • classes unloading and redefinition • uncommon path in compiled code • misguided profiled information 31 Dynamic Deoptimization
- 32.
- 33. ©2016 CodeKaram PrintCompilation 33 timestamp compilation-idflags tiered- compilation-level Method <@ osr_bci> code- size <deoptimization>
- 34. ©2016 CodeKaram PrintCompilation 34 Flags: %: is_osr_method s:is_synchronized !: has_exception_handler b: is_blocking n: is_native
- 35. ©2016 CodeKaram PrintCompilation 35 567 693% ! 3 org.h2.command.dml.Insert::insertRows @ 76 (513 bytes) 656 797 n 0 java.lang.Object::clone (native) 779 835 s 4 java.lang.StringBuffer::append (13 bytes)
- 36. ©2016 CodeKaram36 573 7042 org.h2.table.Table::fireAfterRow (17 bytes) 7963 2223 4 org.h2.table.Table::fireAfterRow (17 bytes) 7964 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made not entrant 33547 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made zombie Dynamic Deoptimization
- 37. ©2016 CodeKaram37 573 7042 org.h2.table.Table::fireAfterRow (17 bytes) 7963 2223 4 org.h2.table.Table::fireAfterRow (17 bytes) 7964 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made not entrant 33547 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made zombie Dynamic Deoptimization
- 38. ©2016 CodeKaram38 573 7042 org.h2.table.Table::fireAfterRow (17 bytes) 7963 2223 4 org.h2.table.Table::fireAfterRow (17 bytes) 7964 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made not entrant 33547 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made zombie Dynamic Deoptimization
- 39. ©2016 CodeKaram39 573 7042 org.h2.table.Table::fireAfterRow (17 bytes) 7963 2223 4 org.h2.table.Table::fireAfterRow (17 bytes) 7964 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made not entrant 33547 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made zombie Dynamic Deoptimization
- 40. ©2016 CodeKaram40 573 7042 org.h2.table.Table::fireAfterRow (17 bytes) 7963 2223 4 org.h2.table.Table::fireAfterRow (17 bytes) 7964 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made not entrant 33547 704 2 org.h2.table.Table::fireAfterRow (17 bytes) made zombie Dynamic Deoptimization
- 41. 41 JIT Optimization -Inlining
- 42. ©2016 CodeKaram HotSpot hasstudied Inlining to it’s max potential! 42 Inlining
- 43. ©2016 CodeKaram MinInliningThreshold, MaxFreqInlineSize, InlineSmallCode,MaxInlineSize, MaxInlineLevel, DesiredMethodLimit … 43 Inlining
- 44.
- 45. ©2016 CodeKaram PrintInling* 45 @ 76java.util.zip.Inflater::setInput (74 bytes) too big @ 80 java.io.BufferedInputStream::getBufIfOpen (21 bytes) inline (hot) @ 91 java.lang.System::arraycopy (0 bytes) (intrinsic) @ 2 java.lang.ClassLoader::checkName (43 bytes) callee is too large * needs -XX:+UnlockDiagnosticVMOptions
- 46. ©2016 CodeKaram PrintInling* 46 @ 76java.util.zip.Inflater::setInput (74 bytes) too big @ 80 java.io.BufferedInputStream::getBufIfOpen (21 bytes) inline (hot) @ 91 java.lang.System::arraycopy (0 bytes) (intrinsic) @ 2 java.lang.ClassLoader::checkName (43 bytes) callee is too large * needs -XX:+UnlockDiagnosticVMOptions
- 47. 47 JIT Optimization -Intrinsics
- 48. ©2016 CodeKaram48 Without Intrinsics JavaMethod JIT Compilation Execute Generated Code
- 49. ©2016 CodeKaram49 Intrinsics Java Method JITCompilation Execute Optimized Code Call Hand- Optimized Assembly Code
- 50. ©2016 CodeKaram PrintInling* 50 @ 76java.util.zip.Inflater::setInput (74 bytes) too big @ 80 java.io.BufferedInputStream::getBufIfOpen (21 bytes) inline (hot) @ 91 java.lang.System::arraycopy (0 bytes) (intrinsic) @ 2 java.lang.ClassLoader::checkName (43 bytes) callee is too large * needs -XX:+UnlockDiagnosticVMOptions
- 51. 51 Advanced Optimizations - CompressedOops + Compressed Class Pointers
- 52.
- 53.
- 54. ©2016 CodeKaram Objects, Fields& Alignment • Objects are 8 byte aligned (default). • Fields: • are aligned by their type. • can fill a gap that maybe required for alignment. • are accessed using offset from the start of the object 54
- 55. 55 Java Object Layoutin Memory
- 56. ©2016 CodeKaram56 -Tool toanalyze Java object layout :) Java Object Layout (JOL)
- 57. ©2016 CodeKaram JOL CommandLine Options $ java -jar jol-cli.jar Usage: jol-cli.jar <mode> [optional arguments]* Available modes: estimates: Simulate the class layout in different VM modes. externals: Show the object externals: the objects reachable from a given instance. footprint: Estimate the footprint of all objects reachable from a given instance heapdump: Consume the heap dump and estimate the savings in different layout strategies. heapdumpstats: Consume the heap dump and print the most frequent instances. idealpack: Compute the object footprint under different field layout strategies. internals: Show the object internals: field layout and default contents, object header shapes: Dump the object shapes present in JAR files or heap dumps. string-compress: Consume the heap dumps and figures out the savings attainable with compressed strings. 57
- 58. ©2016 CodeKaram JOL CommandLine Options $ java -jar jol-cli.jar Usage: jol-cli.jar <mode> [optional arguments]* Available modes: estimates: Simulate the class layout in different VM modes. externals: Show the object externals: the objects reachable from a given instance. footprint: Estimate the footprint of all objects reachable from a given instance heapdump: Consume the heap dump and estimate the savings in different layout strategies. heapdumpstats: Consume the heap dump and print the most frequent instances. idealpack: Compute the object footprint under different field layout strategies. internals: Show the object internals: field layout and default contents, object header shapes: Dump the object shapes present in JAR files or heap dumps. string-compress: Consume the heap dumps and figures out the savings attainable with compressed strings. 58
- 59. ©2016 CodeKaram Compressed OOPsand Compressed Class Pointers 59 # Running 64-bit HotSpot VM. # Using compressed oop with 3-bit shift. # Using compressed klass with 3-bit shift.
- 60. ©2016 CodeKaram Compressed OOPsand Compressed Class Pointers 60 # Running 64-bit HotSpot VM. # Using compressed oop with 3-bit shift. # Using compressed klass with 3-bit shift.
- 61. 61 A Java ObjectHeader
- 62. ©2016 CodeKaram A JavaObject Header 62 Header Klass Mark Word Array Length
- 63. 63 Java Object LayoutSamples - Uncompressed
- 64. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) a8 07 c0 34 (10101000 00000111 11000000 00110100) (885000104) 12 4 (object header) 02 00 00 00 (00000010 00000000 00000000 00000000) (2) 16 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 20 4 (alignment/padding gap) N/A 24 8 byte [B.<elements> N/A Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 64
- 65. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) a8 07 c0 34 (10101000 00000111 11000000 00110100) (885000104) 12 4 (object header) 02 00 00 00 (00000010 00000000 00000000 00000000) (2) 16 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 20 4 (alignment/padding gap) N/A 24 8 byte [B.<elements> N/A Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 65 Mark Word
- 66. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) a8 07 c0 34 (10101000 00000111 11000000 00110100) (885000104) 12 4 (object header) 02 00 00 00 (00000010 00000000 00000000 00000000) (2) 16 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 20 4 (alignment/padding gap) N/A 24 8 byte [B.<elements> N/A Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 66 Klass
- 67. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) a8 07 c0 34 (10101000 00000111 11000000 00110100) (885000104) 12 4 (object header) 02 00 00 00 (00000010 00000000 00000000 00000000) (2) 16 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 20 4 (alignment/padding gap) N/A 24 8 byte [B.<elements> N/A Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 67
- 68. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) a8 07 c0 34 (10101000 00000111 11000000 00110100) (885000104) 12 4 (object header) 02 00 00 00 (00000010 00000000 00000000 00000000) (2) 16 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 20 4 (alignment/padding gap) N/A 24 8 byte [B.<elements> N/A Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 68 Array Length
- 69. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) a8 07 c0 34 (10101000 00000111 11000000 00110100) (885000104) 12 4 (object header) 02 00 00 00 (00000010 00000000 00000000 00000000) (2) 16 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 20 4 (alignment/padding gap) N/A 24 8 byte [B.<elements> N/A Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 69
- 70. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) a8 07 c0 34 (10101000 00000111 11000000 00110100) (885000104) 12 4 (object header) 02 00 00 00 (00000010 00000000 00000000 00000000) (2) 16 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 20 4 (alignment/padding gap) N/A 24 8 byte [B.<elements> N/A Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 70
- 71. 71 Java Object LayoutSamples - Compressed
- 72. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) f5 00 00 f8 (11110101 00000000 00000000 11111000) (-134217483) 12 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 16 8 byte [B.<elements> N/A Instance size: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total 72
- 73. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) f5 00 00 f8 (11110101 00000000 00000000 11111000) (-134217483) 12 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 16 8 byte [B.<elements> N/A Instance size: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total 73 Mark Word
- 74. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) f5 00 00 f8 (11110101 00000000 00000000 11111000) (-134217483) 12 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 16 8 byte [B.<elements> N/A Instance size: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total 74
- 75. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) f5 00 00 f8 (11110101 00000000 00000000 11111000) (-134217483) 12 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 16 8 byte [B.<elements> N/A Instance size: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total 75 Klass
- 76. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) f5 00 00 f8 (11110101 00000000 00000000 11111000) (-134217483) 12 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 16 8 byte [B.<elements> N/A Instance size: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total 76
- 77. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) f5 00 00 f8 (11110101 00000000 00000000 11111000) (-134217483) 12 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 16 8 byte [B.<elements> N/A Instance size: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total 77 Array Length
- 78. ©2016 CodeKaram JOL: 8Byte Array [B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4 (object header) 01 00 00 00 (00000001 00000000 00000000 00000000) (1) 4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0) 8 4 (object header) f5 00 00 f8 (11110101 00000000 00000000 11111000) (-134217483) 12 4 (object header) 08 00 00 00 (00001000 00000000 00000000 00000000) (8) 16 8 byte [B.<elements> N/A Instance size: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total 78
- 79. 79 Java Object LayoutHeader Comparison
- 80. ©2016 CodeKaram Compressed vs Uncompressed Compressed: Instancesize: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total vs Uncompressed: Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 80
- 81. ©2016 CodeKaram Compressed vs Uncompressed Compressed: Instancesize: 24 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total vs Uncompressed: Instance size: 32 bytes Space losses: 4 bytes internal + 0 bytes external = 4 bytes total 81
- 82.
- 83.
- 84. ©2016 CodeKaram Compressed OOPsand Compressed Class Pointers 84 # Running 64-bit HotSpot VM. # Using compressed oop with 3-bit shift. # Using compressed klass with 3-bit shift.
- 85. 85 Java Object LayoutSamples - UnCompressed
- 86. ©2016 CodeKaram JOL: Class java.lang.Classobject internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 16 (object header) N/A 16 8 Constructor Class.cachedConstructor N/A 24 8 Class Class.newInstanceCallerCache N/A 32 8 String Class.name N/A 40 8 Module Class.module N/A 48 8 (alignment/padding gap) N/A 56 8 String Class.packageName N/A 64 8 Class Class.componentType N/A 72 8 SoftReference Class.reflectionData N/A 80 8 ClassRepository Class.genericInfo N/A 88 8 Object[] Class.enumConstants N/A 96 8 Map Class.enumConstantDirectory N/A 104 8 AnnotationData Class.annotationData N/A 112 8 AnnotationType Class.annotationType N/A 120 8 ClassValueMap Class.classValueMap N/A 128 32 (alignment/padding gap) N/A 160 4 int Class.classRedefinedCount N/A 164 4 (loss due to the next object alignment) Instance size: 168 bytes Space losses: 40 bytes internal + 4 bytes external = 44 bytes total 86
- 87. ©2016 CodeKaram java.lang.Class objectinternals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 16 (object header) N/A 16 8 Constructor Class.cachedConstructor N/A 24 8 Class Class.newInstanceCallerCache N/A 32 8 String Class.name N/A 40 8 Module Class.module N/A 48 8 (alignment/padding gap) N/A 56 8 String Class.packageName N/A 64 8 Class Class.componentType N/A 72 8 SoftReference Class.reflectionData N/A 80 8 ClassRepository Class.genericInfo N/A 88 8 Object[] Class.enumConstants N/A 96 8 Map Class.enumConstantDirectory N/A 104 8 AnnotationData Class.annotationData N/A 112 8 AnnotationType Class.annotationType N/A 120 8 ClassValueMap Class.classValueMap N/A 128 32 (alignment/padding gap) N/A 160 4 int Class.classRedefinedCount N/A 164 4 (loss due to the next object alignment) Instance size: 168 bytes Space losses: 40 bytes internal + 4 bytes external = 44 bytes total 87 JOL: Class
- 88. ©2016 CodeKaram java.lang.Class objectinternals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 16 (object header) N/A 16 8 Constructor Class.cachedConstructor N/A 24 8 Class Class.newInstanceCallerCache N/A 32 8 String Class.name N/A 40 8 Module Class.module N/A 48 8 (alignment/padding gap) N/A 56 8 String Class.packageName N/A 64 8 Class Class.componentType N/A 72 8 SoftReference Class.reflectionData N/A 80 8 ClassRepository Class.genericInfo N/A 88 8 Object[] Class.enumConstants N/A 96 8 Map Class.enumConstantDirectory N/A 104 8 AnnotationData Class.annotationData N/A 112 8 AnnotationType Class.annotationType N/A 120 8 ClassValueMap Class.classValueMap N/A 128 32 (alignment/padding gap) N/A 160 4 int Class.classRedefinedCount N/A 164 4 (loss due to the next object alignment) Instance size: 168 bytes Space losses: 40 bytes internal + 4 bytes external = 44 bytes total 88 JOL: Class
- 89. 89 Java Object LayoutSamples - Compressed
- 90. ©2016 CodeKaram java.lang.Class objectinternals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 12 (object header) N/A 12 4 Constructor Class.cachedConstructor N/A 16 4 Class Class.newInstanceCallerCache N/A 20 4 String Class.name N/A 24 4 Module Class.module N/A 28 4 (alignment/padding gap) N/A 32 4 String Class.packageName N/A 36 4 Class Class.componentType N/A 40 4 SoftReference Class.reflectionData N/A 44 4 ClassRepository Class.genericInfo N/A 48 4 Object[] Class.enumConstants N/A 52 4 Map Class.enumConstantDirectory N/A 56 4 AnnotationData Class.annotationData N/A 60 4 AnnotationType Class.annotationType N/A 64 4 ClassValueMap Class.classValueMap N/A 68 28 (alignment/padding gap) N/A 96 4 int Class.classRedefinedCount N/A 100 4 (loss due to the next object alignment) 90 JOL: Class
- 91. ©2016 CodeKaram java.lang.Class objectinternals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 12 (object header) N/A 12 4 Constructor Class.cachedConstructor N/A 16 4 Class Class.newInstanceCallerCache N/A 20 4 String Class.name N/A 24 4 Module Class.module N/A 28 4 (alignment/padding gap) N/A 32 4 String Class.packageName N/A 36 4 Class Class.componentType N/A 40 4 SoftReference Class.reflectionData N/A 44 4 ClassRepository Class.genericInfo N/A 48 4 Object[] Class.enumConstants N/A 52 4 Map Class.enumConstantDirectory N/A 56 4 AnnotationData Class.annotationData N/A 60 4 AnnotationType Class.annotationType N/A 64 4 ClassValueMap Class.classValueMap N/A 68 28 (alignment/padding gap) N/A 96 4 int Class.classRedefinedCount N/A 100 4 (loss due to the next object alignment) 91 JOL: Class
- 92. ©2016 CodeKaram java.lang.Class objectinternals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 12 (object header) N/A 12 4 Constructor Class.cachedConstructor N/A 16 4 Class Class.newInstanceCallerCache N/A 20 4 String Class.name N/A 24 4 Module Class.module N/A 28 4 (alignment/padding gap) N/A 32 4 String Class.packageName N/A 36 4 Class Class.componentType N/A 40 4 SoftReference Class.reflectionData N/A 44 4 ClassRepository Class.genericInfo N/A 48 4 Object[] Class.enumConstants N/A 52 4 Map Class.enumConstantDirectory N/A 56 4 AnnotationData Class.annotationData N/A 60 4 AnnotationType Class.annotationType N/A 64 4 ClassValueMap Class.classValueMap N/A 68 28 (alignment/padding gap) N/A 96 4 int Class.classRedefinedCount N/A 100 4 (loss due to the next object alignment) 92 JOL: Class
- 93. ©2016 CodeKaram Compressed OOPsand Compressed Class Pointers 93 # Running 64-bit HotSpot VM. # Using compressed oop with 3-bit shift. # Using compressed klass with 3-bit shift. P P
- 94. 94 … but whatis the 3-bit shift?
- 95. ©2016 CodeKaram Compressed OOPs 95 <wide-oop>= <narrow-oop-base> + (<narrow-oop> << 3) + <field-offset>
- 96. ©2016 CodeKaram Compressed OOPs 96 HeapSize? <4 GB (no encoding/ decoding needed) >4GB; <28GB (zero-based) <wide-oop> = <narrow-oop> <narrow-oop> << 3
- 97. ©2016 CodeKaram Compressed OOPs 97 HeapSize? >28 GB; <32 GB (regular) >32 GB; <64 GB * (change alignment) <wide-oop> = <narrow-oop-base> + (<narrow-oop> << 3) + <field- offset> <narrow-oop-base> + (<narrow-oop> << 4) + <field- offset>
- 98. ©2016 CodeKaram Compressed OOPs 98 HeapSize? <4 GB >4GB; <28GB <32GB <64GB Object Alignment? 8 bytes 8 bytes 8 bytes 16 bytes Offset Required? No No Yes Yes Shift by? No shift 3 3 4
- 99.
- 100. ©2016 CodeKaram • Fastdynamic type tests for type safety • Range check elimination • Loop unrolling • Escape Analysis • Vectorization! 100 Other Optimizations
- 101. ©2016 CodeKaram • Fastdynamic type tests for type safety • Range check elimination • Loop unrolling • Escape Analysis • Vectorization! 101 Other Optimizations
- 102.
- 103. ©2016 CodeKaram • EntireIR graph • escaping allocations? • not stored to a static field or non-static field of an external object, • not returned from method, • not passed as parameter to another method where it escapes. 103 Escape Analysis
- 104. ©2016 CodeKaram104 Escape Analysis allocatedobject doesn’t escape the compiled method allocated object not passed as a parameter + remove allocation and keep field values in registers =
- 105. ©2016 CodeKaram105 Escape Analysis allocatedobject is passed as a parameter + remove locks associated with object and use optimized compare instructions = allocated object doesn’t escape the compiled method
- 106. ©2016 CodeKaram • Fastdynamic type tests for type safety • Range check elimination • Loop unrolling • Escape Analysis • Vectorization! 106 Other JIT Compiler Optimizations
- 107.
- 108.
- 109. ©2016 CodeKaram Vectorization 109 • UtilizeSIMD (Single Instruction Multiple Data) instructions offered by the processor. • Generate assembly stubs • Get benefits of operating on cache line size data chunks
- 110.
- 111.
- 112. 112 Look Ma, nostubs!!
- 113.
- 114. ©2016 CodeKaram SuperWord LevelParallelism 114 http://groups.csail.mit.edu/cag/slp/SLP-PLDI-2000.pdf
- 115. ©2016 CodeKaram SuperWord LevelParallelism 115 • Loop Unrolling • Alignment Analysis • Pre-Optimization • Identifying Adjacent Memory References • Extending the “PackSet” • Combination and SIMD operation http://groups.csail.mit.edu/cag/slp/SLP-PLDI-2000.pdf
- 116. ©2016 CodeKaram Q &A 116
- 117.
- 118. ©2016 CodeKaram Compressed ClassPointers 118 • JDK 8 —> Perm Gen Removal —> Class Data outside of heap • Compressed class pointer space • contains class metadata • is a part of Metaspace
- 119. ©2016 CodeKaram Compressed ClassPointers 119 PermGen Removal Overview by Coleen Phillimore + Jon Masamitsu @JavaOne 2013
- 120. ©2016 CodeKaram120 Mark Word- 32 bit vs 64 bit Klass - 32 bit vs 64 bit Array Length - 32 bit on both boolean, byte, char, float, int, short - 32 bit on both double, long - 64 bit on both ILP32 vs. LP64 Field Sizes