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JavaPerformanceChapter_3

Saurav Basu, profile picture
Saurav Basu

This document provides an overview of the Java Virtual Machine (JVM). It discusses the key components of the HotSpot JVM including the architecture, runtime environment, class loading process, bytecode interpretation, exception handling, synchronization, thread management, and Java Native Interface. The runtime environment is responsible for command line parsing, the JVM lifecycle such as loading, linking and initialization of classes, bytecode interpretation, and thread management. The document also describes class loading in the JVM, bytecode verification, and class data sharing. It provides details on synchronization approaches like object monitor mapping and biased locks. Finally, it discusses thread management aspects including JVM internal threads, safe points, and thread lifecycles.

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Java Performance Chapter 3 Saurav Basu 6/3/2020 1
Organization 1. Strategies, Approaches, and Methodologies 2. Operating System Performance Monitoring 3. JVM Overview 4. JVM Performance Monitoring 5. Java Application Profiling 6. Java Application Profiling - Tips & Tricks 7. Tuning the JVM - Step by Step 8. Benchmarking Java Applications 9. Benchmarking Multitiered Applications 10. Web Application Performance 11. Web Services Performance 12. Java Persistence & Enterprise Java Beans Performance 2
JVM Overview 3 ● HotSpot VM - Architecture ● VM - Runtime ● JIT Compiler ● Memory Manager JVM Components
JVM Overview 4 ● HotSpot VM - Architecture ● VM - Runtime ● JIT Compiler ● Memory Manager JVM Components
JVM Overview 5 HotSpot VM - Architecture Java Native Interface Java Method Libraries Class Loader Loading Linking Initialization Optimizer Interpreter Code Generator Target Code Generator (Metaspace) Method area Registers Heap area Stack Area Native Stack Execution Engine Run Time Data Area
JVM Overview 6 HotSpot VM Runtime - Architecture VM Runtime (Metaspace)
JVM Overview 7 HotSpot VM Architecture - Symbol Table
JVM Overview 8 HotSpot VM Architecture - Symbol Table Symbol Keys
JVM Overview 9 HotSpot VM Runtime - Symbol Table Symbol Dictionary
JVM Overview 10 HotSpot VM - Architecture Parameter 32 bit 64 bit #of JVMs More m/cs Less m/cs Administration Harder Easier DataSet Size Smaller Larger Performance High High with Compressed OOPs Memory Footprint Low High 32 bit vs 64 bit - JVM - Choose a 64 bit JVM only if latency and GC pauses induced due to higher memory footprint do not impact the application SLA
JVM Overview 11 HotSpot VM - Architecture Compressed Object Pointers 64bit JVM
JVM Overview 12 ● HotSpot VM - Architecture ● VM - Runtime ● Memory Manager ● JIT Compiler JVM Components
JVM Overview 13 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 14 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 15 VM - Runtime Command Line Parsing Sno. Category Description 1. Standard Supported on all JVM Releases 2. Non Standard (-X prefix) Subject to change without notice 3. Developer (-XX prefix) Require privileged access to system configuration parameters Subject to change without notice
JVM Overview 16 VM - Runtime Command Line Parsing Sno. Category Example 1. Boolean -XX:+AggressiveOpts -XX:-AggressiveOpts (Aggresive Optimization) 2. Non Boolean -XX:OptionName=<N>
JVM Overview 17 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 18 VM - Runtime Loading Linking Initialization Verification Preparation Resolution Load Instantiation Garbage Collection Finalization Execute Unloading Unload VM-LifeCycle
JVM Overview 19 VM - Runtime VM-LifeCycle
JVM Overview 20 VM - Life Cycle (Load) SNo. Launcher Command OS 1. java Unix/Linux 2. java / javaw Windows 3. javaws Web browser for applets
JVM Overview 21 VM - Life Cycle (Launcher) Parse command line options Establish java heap size & JIT compiler type Establish LD_LIBRARY_PATH and CLASSPATH Fetches Main-Class Name from JAR manifest Invoke Main using JNI method CallStaticVoidMethod passing marshaled arguments from the command line. Load Main class and get main method’s attributes from the Java Main-Class Create hotspot VM in a new non primordial thread using JNI_CreateJavaVM
JVM Overview 22 VM - Life Cycle (JNI_CreateJVM) - (1) Ensure no 2 threads call this method at the same time Check a) JNI version is supported b) output stream is initialized for garbage collection logging Initialize Os Modules a) Random Number Generator b) Process Id c) Hi resolutionTimer d) Memory Pages e) Guard Pages Guard pages are no access memory pages used to bound memory region access (Ex. os puts guard pages at top of each thread stack to ensure reference to end of stack are trapped Only one HotSpot VM can be created in a process space once a certain point in initialization is reached. To the engineers who develop the HotSpot VM this stage of launching a HotSpot VM is referred to as the “point of no return.” Parse Command Line Arguments
JVM Overview 23 VM - Life Cycle (JNI_CreateJVM) - (2) Libraries such as libzip, libhpi, libjava, and libthread are loaded System properties are initialized, such as java.version, java.vendor, os.name Modules for synchronization, stack, memory, & safepoint pages are initialized Signal handlers are initialized and set Thread library is initializedThe thread library is initialized
JVM Overview 24 VM - Life Cycle (JNI_CreateJVM) - (3) Thread library is initialized The output stream logger is initialized Agent libraries (hprof, jdi), if any are being used, are initialized and started The thread states and the thread local storage, which holds thread specific data required for the operation of threads, are initialized A portion of the HotSpot VM global data is initialized such as the event log, OS synchronization primitives, perfMemory (performance statistics memory), and chunkPool(memory allocator)
JVM Overview 25 VM - Life Cycle (JNI_CreateJVM) - (4) The Java version of the main thread is created and attached to the current operating system thread. Java level synchronization is initialized and enabled Bootclassloader, code cache, interpreter, JIT compiler, Java Native Interface, system dictionary, and universe are initialized Java main thread is now added to the known list of threads. The universe, a set of required global data structures, is sanity checked. The HotSpot VMThread, which performs all the HotSpot VM’s critical functions, is created. At this point the appropriate JVMTI events are posted to notify the current state of the HotSpot VM
JVM Overview 26 VM - Life Cycle (JNI_CreateJVM) - (5) The following Java classes java.lang.String, java.lang.System, java.lang.Thread, java.lang.ThreadGroup, java.lang.reflect.Method, java.lang.ref.Finalizer, java.lang.Class, and the rest of the Java System classes are loaded and initialized. At this point, the HotSpot VM is initialized and operational, but not quite fully functional The HotSpot VM’s signal handler thread is started, the JIT compiler is initialized, and the HotSpot’s compile broker thread is started. Other HotSpot VM helper threads such as watcher threads and stat sampler are started. At this time the HotSpot VM is fully functional Finally, the JNIEnv is populated and returned to the caller and the HotSpot VM is ready to service new JNI requests
JVM Overview 27 VM - Life Cycle (JNI_DestroyJVM) - (1) Wait until there is only one nondaemon thread executing noting that the HotSpot VM is still functional Call the Java method java.lang.Shutdown.shutdown(), which invokes the Java level shutdown hooks and runs Java object finalizers if finalization- on-exit is true Prepare for HotSpot VM exit by running HotSpot VM level shutdown hooks (those that were registered through JVM_OnExit()), stop the following HotSpot VM threads: profiler, stat sampler, watcher, and garbage collector threads. Post status events to JVMTI, disable JVMTI, and stop the Signal thread Call the HotSpot method JavaThread::exit() to release Java Native Interface handle blocks, remove guard pages, and remove the current thread from known threads list. From this point on the HotSpot VM cannot execute any Java code
JVM Overview 28 VM - Life Cycle (JNI_DestroyJVM) - (2) Stop the HotSpot VM thread. This causes the HotSpot VM to bring the remaining HotSpot VM threads to a safepoint and stop the JIT compiler threads Disable tracing at the Java Native Interface, HotSpot VM, and JVMTI barriers Set HotSpot “vm exited” flag for threads that may be running in native code Delete the current thread Delete or remove any input/output streams and release PerfMemory (performance statistics memory) resources. Finally return to the caller
JVM Overview 29 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 30 VM - Class Loading Definition The overall process of mapping a class or interface name to a class object.
JVM Overview 31 VM - Class Loading LOADING INITIALIZATION LINKING VERIFYING PREPARING RESOLVING Bringing Binary data from class into JVM Incorporating Binary data into JVM runtime state Class variables given proper initial values Ensure class is properly formed & fit for use by JVM Allocation of memory needed by class Transforming symbolic references into direct references
JVM Overview 32 VM - Class Loading
JVM Overview 33 VM - Class Loading Class Metadata in HotSpot
JVM Overview 34 VM - Class Loading Class Metadata in HotSpot
JVM Overview 35 VM - Class Loading Class Metadata in HotSpot
JVM Overview 36 VM - Class Loading Class Metadata in HotSpot (64 bit)
JVM Overview 37 VM - Class Loading Class Metadata in HotSpot
JVM Overview 38 VM - Class Loading Class Metadata in HotSpot SNo. Compressed Class Space Metaspace 1 Class Meta Data (C++ Klass Object) Method Code 2 Runtime Constant Pool (Symbolic Ref.) 3 Code Cache (compiled bytecodes)
JVM Overview 39 VM - Class Loading Internal Class Loading Data Sno. DictionaryName Functionality 1. SystemDictionary class name/initiating loader pairs 2. PlaceHolderDictionary contains classes that are currently being loaded. It is used for ClassCircularityError checking and for parallel class loading 3. LoaderConstraintTable tracks constraints for type safety checking.
JVM Overview 40 VM - Class Loading ByteCodeVerification Sno. Check 1. Type correctness: the arguments of an instruction are always of the types expected by the instruction. 2. No stack overflow or underflow: an instruction never pops an argument off an empty stack,nor pushes a result on a full stack. 3. Rules for accessing private data and methods are not violated 4. Local variable accesses fall within the runtime stack 5. The runtime stack does not overflow
JVM Overview 41 VM - Class Loading ByteCodeVerification
JVM Overview 42 VM - Class Loading ByteCodeVerification
JVM Overview 43 VM - Class Loading ByteCodeVerification Transfer Functions for Abstract Interpretation of Java Byte Code
JVM Overview 44 VM - Class Loading ClassData Sharing
JVM Overview 45 VM - Class Loading Class Data Sharing JVM-1 JVM-2 JVM-3 Shared Class Data (classes.jsa) -improved startup time of new jvm -reduced memory footprint
JVM Overview 46 VM - Class Loading Class Data Sharing java -Xshare:dump
JVM Overview 47 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 48 VM - Class Loading ByteCode Interpreter BCP
JVM Overview 49 VM - Class Loading ByteCode Interpreter
JVM Overview 50 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 51 VM - Exception Handling Exception Handler Search Inputs:- - current method - current bytecode - exception object
JVM Overview 52 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 53 VM - Synchronization Object Monitor Mapping Table Lookup Cost Look up Table Contention Cons Easy to implement Pros
JVM Overview 54 VM - Synchronization Direct Mapping Method Overhead of Heavy weight OS Monitors Cons Improved Scalability: No Mapping Table needed Pros
JVM Overview 55 VM - Synchronization All Java Objects Java Objects which are used for locks Java Objects whose locks are moslty used by a single thread Observation
JVM Overview 56 VM - Synchronization - Biased Locks -Kawachiya Analaysis & Acceleration
JVM Overview 57 VM - Synchronization Thin Lock (Biased Locks) Implementation Complexity Cons Optimized for Thread Locality Access Pattern Pros Biased Object
JVM Overview 58 VM - Synchronization - Biased Locks ● Optimize Clock Cycles used for Lock Operations ● Observation: Most objects held by a single JVM thread ● Strategy: Create “Fast Path” for Common Use Case
JVM Overview 59 VM - Synchronization - Biased Locks 11 Unused(25) Hashcode(31) Unused(1) Age(4) 0 01 Ptr to metadata0(62) 1 01 TId(54) Epoch(2) Unused(1) Age(4) 1 01 Ptr_to_lock_record(62) 00 Ptr_to_heavyweight_monitor(62) 10 Normal, UnlockedBiasable, Unlocked (Light weight Locked) (Heavy Weight Locked) (Marked for GC) Inital lock (CAS) Rebias (bulk) lock/unlock Revoke bias Thin Lock Inflate Lock Recursive lock unlock Allocate Object Biasing enabled Biasing disabled unlocked locked Fast Path
JVM Overview 60 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 61 VM - Runtime Thread Management - Lifecycle
JVM Overview 62 VM - Runtime Thread Management - Internal VM Thread JVM Periodic Task Garbage collection JIT compiler Signal dispatcher
JVM Overview 63 VM - Runtime Thread Management - Safe Points Mechanism to pause thread execution to perform JVM housekeeping.
JVM Overview 64 VM - Runtime Thread Management - Safe Points Why? ● Garbage collection ● Code deoptimization ● Flushing code cache ● Class redefinition (e.g. hot swap or instrumentation) ● Biased lock revocation ● Various debug operation (e.g. deadlock check or stacktrace dump)
JVM Overview 65 VM - Runtime Thread Management - Safe Points How? JIT inserts safepoint checks in code at certain points :- ● Between every 2 bytecodes (interpreter mode) ● Back edge of non counted loops ● Method Exit ● JNI call exit Safepoints are initiated using a cooperative, polling-based mechanism. In simplistic terms, every so often a thread asks “should I block for a safepoint?”
JVM Overview 66 VM - Runtime Thread Management - Safe Points
JVM Overview 67 VM - Runtime Thread Management - Safe Points
JVM Overview 68 VM - Runtime Thread Management - Safe Points
JVM Overview 69 VM - Runtime Thread Management - Safe Points
JVM Overview 70 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
JVM Overview 71 VM - Runtime JNI
JVM Overview 72 VM - Runtime JNI - Data Transfer Performance Impact
JVM Overview 73 VM - Runtime JNI - (Performance Impact) Cons ● Loss of Cross Platform Portability ● Loss of Inbuilt Type Safety Security ● Additional Security Check JVM to JNI Data Copy Impacts Application Performance
JVM Overview 74 VM - Runtime Fatal Error Investigation (hs_error_pid) Header Thread java -XX:ErrorFile=/var/log/java/java_error%p.log Process System
JVM Overview 75 VM - Runtime Fatal Error Investigation (hs_error_pid) Header
JVM Overview 76 VM - Runtime Fatal Error Investigation (hs_error_pid) Header
JVM Overview 77 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
JVM Overview 78 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
JVM Overview 79 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
JVM Overview 80 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
JVM Overview 81 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
JVM Overview 82 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread Frame Type
JVM Overview 83 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Theadlist
JVM Overview 84 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
JVM Overview 85 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Mutex(es)
JVM Overview 86 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Heap Summary
JVM Overview 87 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Memory Map
JVM Overview 88 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
JVM Overview 89 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
JVM Overview 90 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
JVM Overview 91 VM - Runtime Fatal Error Investigation (hs_error_pid) System
JVM Overview 92 ● HotSpot VM - Architecture ● VM - Runtime ● Memory Manager ● JIT Compiler JVM Components
JVM Overview 93 JVM - Memory Manager
JVM Overview 94 JVM - Memory Manager
JVM Overview 95 JVM - Memory Manager
JVM Overview 96 JVM - Memory Manager
JVM Overview 97 JVM - Memory Manager (Copying GC)
JVM Overview 98 JVM - Memory Manager (Copying GC) Cons Premature Promotions Promotion Failure
JVM Overview 99 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps
JVM Overview 100 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps Avg. ~92 MB/sec
JVM Overview 101 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps Avg. ~140 .95MB/sec
JVM Overview 102 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps Promotion Rate :(Old After - Old Before)/(timeinms) Allocation Rate :(Young Before(current GC) - Young After (prev GC))/(timeinms) Promotion Rate --> Allocation Rate = Performance Problem Ex: 92MB/s ---> 140 MB/s = Performance Issue
JVM Overview 103 JVM - Memory Manager (Fast Allocator) Eden
JVM Overview 104 JVM - Memory Manager- Types Serial GC Parallel GC Mostly Concurrent GC Garbage First GC (G1)
JVM Overview 105 JVM - Memory Manager- Types Serial GC Compacting Mark & Sweep Mark & Sweep (no compaction)
JVM Overview 106 JVM - Memory Manager- Types Serial GC
JVM Overview 107 JVM - Memory Manager- Types Serial GC ➢ Application heap size < 100 MB ➢ HIgh number of JVMS on same m/c ➢ No hard pause time requirements (ex < 2secs) java -XX:+UseSerialGC When?
JVM Overview 108 JVM - Memory Manager- Types Theads Parallel GC
JVM Overview 109 JVM - Memory Manager- Types ➢ Batch processing applications (Ex. Scientific Computing) ➢ High throughput requirement ➢ GC Latency can be met by improving GC efficiency on multi core processor java -XX:+UseParallelGC When? Parallel GC
JVM Overview 110 JVM - Memory Manager- Types Theads Mostly Concurrent GC (CMS)
JVM Overview 111 JVM - Memory Manager- Types ➢ Rapid Response Time (ex. Web Servers, Data Tracking Servers) java -XX:+UseConcMarkSweepGC When? Mostly Concurrent GC (CMS)
JVM Overview 112 JVM - Memory Manager- Types Theads Garbage First GC (G1)
JVM Overview 113 JVM - Memory Manager- Types Garbage Collector Types : Comparison
JVM Overview 114 ● HotSpot VM - Architecture ● VM - Runtime ● Memory Manager ● JIT Compiler JVM Components
JVM Overview 115 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 116 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 117 JIT Compiler Code Generation Overview Intermediate Representation Source Representation Machine Representation Front End Back End Optimizer
JVM Overview 118 JIT Compiler Code Generation Overview Intermediate Representation Structural Linear Hybrid 1. AST 2. DAG 1. 3 Address Code 2. Stack M/c Code Control Flow Graph
JVM Overview 119 JIT Compiler Code Generation Overview Structural IR: Abstract Syntax Tree
JVM Overview 120 JIT Compiler Code Generation Overview Structural IR: DAG Example
JVM Overview 121 JIT Compiler Code Generation Overview Linear IR: 3 Address Code Example
JVM Overview 122 JIT Compiler Code Generation Overview Stack Machine Code
JVM Overview 123 JIT Compiler Code Generation Overview Control Flow Graph
JVM Overview 124 JIT Compiler Code Generation Overview 1. Constant Propagation 2. Value Range Propagation 3. Sparse Conditional Constant Propagation 4. Dead Code Elimination 5. Global Value Numbering 6. Partial Redundancy Elimination 7. Strength Reduction 8. Register Allocation Compiler Optimizations
JVM Overview 125 JIT Compiler Code Generation Overview Constant Propagation
JVM Overview 126 JIT Compiler Code Generation Overview Constant Propagation
JVM Overview 127 JIT Compiler Code Generation Overview Intermediate Representation (IR) Static Single Assignment (SSA) Named Form
JVM Overview 128 JIT Compiler Code Generation Overview Static Single Assignment - Example
JVM Overview 129 JIT Compiler Code Generation Overview Static Single Assignment - Example Common SubExpression
JVM Overview 130 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 131 JIT Compiler Class Hierarchy Analysis Inlining critical to Performance! Java Compiler constructs the Call graph using Class Hierarchy Analysis (CHA) to enable method Inlining
JVM Overview 132 JIT Compiler Class Hierarchy Analysis
JVM Overview 133 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms (Further Reading) Reachability Analysis (RA) Class Hierarchy Analysis (CHA) Rapid Type Analysis (RTA) Class Type Analysis (CTA) Accuracy, Cost
JVM Overview 134 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Reachability Analysis (RA)
JVM Overview 135 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Class Hierarchy Analysis (CHA)
JVM Overview 136 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Rapid Type Analysis (RTA)
JVM Overview 137 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Class Type Analysis (CTA)
JVM Overview 138 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 139 JIT Compiler Compilation Policy
JVM Overview 140 JIT Compiler Compilation Policy Backedge CounterInvocation Counter Compilation Tier
JVM Overview 141 JIT Compiler Compilation Policy
JVM Overview 142 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 143 JIT Compiler ●Changing an optimized stack frame to an unoptimized one. ●Throwing away code with invalid optimistic optimizations, and replacing it by less-optimized, more robust code. Deoptimization
JVM Overview 144 JIT Compiler Deoptimization
JVM Overview 145 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 146 JIT Compiler Client JIT Compiler Does not need a profiler Fast code generation of acceptable quality Rock solid and proved optimization Compilation threshold 1.5k invocation
JVM Overview 147 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 148 JIT Compiler Server JIT Compiler Does need a profiler Highly optimized code Many aggressive and speculative optimizations Compilation threshold 10k invocations
JVM Overview 149 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
JVM Overview 150 JIT Compiler SSA Program Dependence Graph 1. SSA Graph ➢ Global Value Numbering ➢ Constant Propogation ➢ Register Optimization 1. Uncommon Traps 2. Iteration Splitting 3. Machine Code Generation
JVM Overview 151 JIT Compiler SSA Program Dependence Graph SSA Graph
JVM Overview 152 JIT Compiler SSA Program Dependence Graph Global Value Numbering Constant Propagation Register Optimization SSA Graph
JVM Overview 153 JIT Compiler SSA Program Dependence Graph Global Value Numbering Categorize expression in program that compute same value Eliminate redundant computation SSA Graph
JVM Overview 154 JIT Compiler SSA Program Dependence Graph Global Value Numbering FInput Pool Output Pool Optimizing function SSA Graph
JVM Overview 155 JIT Compiler SSA Program Dependence Graph Global Value Numbering Pool A partition of a set of expressions SSA Graph
JVM Overview 156 JIT Compiler SSA Program Dependence Graph Global Value Numbering PT : {∅} PU : {a,b,a+b,r} PU : {a,b | a+b,r} PT : {∅} PV : {a,b |a+b,r | x | r+x} PV : {a,b |a+b,r | x | r+x} PW : {a,b | a+b, r | x | r+x | (a+b)+x} PW : {a,b | a+b, r | x | r+x, (a+b)+x} Partition Restructure SSA Graph
JVM Overview 157 JIT Compiler SSA Program Dependence Graph Discover values that are constant in all possible executions of a program and to propagate these constant values as far forward through the program as possible SSA Graph Constant Propagation
JVM Overview 158 JIT Compiler SSA Program Dependence Graph Constant Propagation SSA Graph
JVM Overview 159 JIT Compiler SSA Program Dependence Graph Constant Propagation SSA Graph
JVM Overview 160 JIT Compiler SSA Program Dependence Graph Constant Propogation Pₙⁱ : Propogated Constant Pool at Entry Point to Node n at ith iteration SSA Graph
JVM Overview 161 JIT Compiler SSA Program Dependence Graph Constant Propogation Pₙⁱ : Propagated Constant Pool at Entry Point to Node n at ith iteration SSA Graph
JVM Overview 162 JIT Compiler SSA Program Dependence Graph Constant Propogation Pₙ : Propagated Constant Pool at Entry Point to Node N SSA Graph
JVM Overview 163 JIT Compiler SSA Program Dependence Graph Constant Propagation Pₙⁱ : Propagated Constant Pool at Entry Point to Node n at ith iteration SSA Graph
JVM Overview 164 JIT Compiler SSA Program Dependence Graph Register Optimization SSA Graph
JVM Overview 165 JIT Compiler SSA Program Dependence Graph Register Optimization SSA Graph
JVM Overview 166 JIT Compiler SSA Program Dependence Graph Register Optimization redundant No change in Pool
JVM Overview 167 JIT Compiler SSA Program Dependence Graph Uncommon Traps Uncommon trap is a situation when a speculative precondition in the compiled code fails. It usually results in deoptimization - switching from compiled code back to interpreter
JVM Overview 168 JIT Compiler SSA Program Dependence Graph Uncommon Traps - Why? 1. Unloaded or Uninitialized Class 1. Unreached Path
JVM Overview 169 JIT Compiler SSA Program Dependence Graph Uncommon Traps - Why? TraceDeoptimization
JVM Overview 170 JIT Compiler SSA Program Dependence Graph Iteration Splitting

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JavaPerformanceChapter_3

  • 2. Organization 1. Strategies, Approaches, and Methodologies 2. Operating System Performance Monitoring 3. JVM Overview 4. JVM Performance Monitoring 5. Java Application Profiling 6. Java Application Profiling - Tips & Tricks 7. Tuning the JVM - Step by Step 8. Benchmarking Java Applications 9. Benchmarking Multitiered Applications 10. Web Application Performance 11. Web Services Performance 12. Java Persistence & Enterprise Java Beans Performance 2
  • 3. JVM Overview 3 ● HotSpot VM - Architecture ● VM - Runtime ● JIT Compiler ● Memory Manager JVM Components
  • 4. JVM Overview 4 ● HotSpot VM - Architecture ● VM - Runtime ● JIT Compiler ● Memory Manager JVM Components
  • 5. JVM Overview 5 HotSpot VM - Architecture Java Native Interface Java Method Libraries Class Loader Loading Linking Initialization Optimizer Interpreter Code Generator Target Code Generator (Metaspace) Method area Registers Heap area Stack Area Native Stack Execution Engine Run Time Data Area
  • 6. JVM Overview 6 HotSpot VM Runtime - Architecture VM Runtime (Metaspace)
  • 7. JVM Overview 7 HotSpot VM Architecture - Symbol Table
  • 8. JVM Overview 8 HotSpot VM Architecture - Symbol Table Symbol Keys
  • 9. JVM Overview 9 HotSpot VM Runtime - Symbol Table Symbol Dictionary
  • 10. JVM Overview 10 HotSpot VM - Architecture Parameter 32 bit 64 bit #of JVMs More m/cs Less m/cs Administration Harder Easier DataSet Size Smaller Larger Performance High High with Compressed OOPs Memory Footprint Low High 32 bit vs 64 bit - JVM - Choose a 64 bit JVM only if latency and GC pauses induced due to higher memory footprint do not impact the application SLA
  • 11. JVM Overview 11 HotSpot VM - Architecture Compressed Object Pointers 64bit JVM
  • 12. JVM Overview 12 ● HotSpot VM - Architecture ● VM - Runtime ● Memory Manager ● JIT Compiler JVM Components
  • 13. JVM Overview 13 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 14. JVM Overview 14 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 15. JVM Overview 15 VM - Runtime Command Line Parsing Sno. Category Description 1. Standard Supported on all JVM Releases 2. Non Standard (-X prefix) Subject to change without notice 3. Developer (-XX prefix) Require privileged access to system configuration parameters Subject to change without notice
  • 16. JVM Overview 16 VM - Runtime Command Line Parsing Sno. Category Example 1. Boolean -XX:+AggressiveOpts -XX:-AggressiveOpts (Aggresive Optimization) 2. Non Boolean -XX:OptionName=<N>
  • 17. JVM Overview 17 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 18. JVM Overview 18 VM - Runtime Loading Linking Initialization Verification Preparation Resolution Load Instantiation Garbage Collection Finalization Execute Unloading Unload VM-LifeCycle
  • 19. JVM Overview 19 VM - Runtime VM-LifeCycle
  • 20. JVM Overview 20 VM - Life Cycle (Load) SNo. Launcher Command OS 1. java Unix/Linux 2. java / javaw Windows 3. javaws Web browser for applets
  • 21. JVM Overview 21 VM - Life Cycle (Launcher) Parse command line options Establish java heap size & JIT compiler type Establish LD_LIBRARY_PATH and CLASSPATH Fetches Main-Class Name from JAR manifest Invoke Main using JNI method CallStaticVoidMethod passing marshaled arguments from the command line. Load Main class and get main method’s attributes from the Java Main-Class Create hotspot VM in a new non primordial thread using JNI_CreateJavaVM
  • 22. JVM Overview 22 VM - Life Cycle (JNI_CreateJVM) - (1) Ensure no 2 threads call this method at the same time Check a) JNI version is supported b) output stream is initialized for garbage collection logging Initialize Os Modules a) Random Number Generator b) Process Id c) Hi resolutionTimer d) Memory Pages e) Guard Pages Guard pages are no access memory pages used to bound memory region access (Ex. os puts guard pages at top of each thread stack to ensure reference to end of stack are trapped Only one HotSpot VM can be created in a process space once a certain point in initialization is reached. To the engineers who develop the HotSpot VM this stage of launching a HotSpot VM is referred to as the “point of no return.” Parse Command Line Arguments
  • 23. JVM Overview 23 VM - Life Cycle (JNI_CreateJVM) - (2) Libraries such as libzip, libhpi, libjava, and libthread are loaded System properties are initialized, such as java.version, java.vendor, os.name Modules for synchronization, stack, memory, & safepoint pages are initialized Signal handlers are initialized and set Thread library is initializedThe thread library is initialized
  • 24. JVM Overview 24 VM - Life Cycle (JNI_CreateJVM) - (3) Thread library is initialized The output stream logger is initialized Agent libraries (hprof, jdi), if any are being used, are initialized and started The thread states and the thread local storage, which holds thread specific data required for the operation of threads, are initialized A portion of the HotSpot VM global data is initialized such as the event log, OS synchronization primitives, perfMemory (performance statistics memory), and chunkPool(memory allocator)
  • 25. JVM Overview 25 VM - Life Cycle (JNI_CreateJVM) - (4) The Java version of the main thread is created and attached to the current operating system thread. Java level synchronization is initialized and enabled Bootclassloader, code cache, interpreter, JIT compiler, Java Native Interface, system dictionary, and universe are initialized Java main thread is now added to the known list of threads. The universe, a set of required global data structures, is sanity checked. The HotSpot VMThread, which performs all the HotSpot VM’s critical functions, is created. At this point the appropriate JVMTI events are posted to notify the current state of the HotSpot VM
  • 26. JVM Overview 26 VM - Life Cycle (JNI_CreateJVM) - (5) The following Java classes java.lang.String, java.lang.System, java.lang.Thread, java.lang.ThreadGroup, java.lang.reflect.Method, java.lang.ref.Finalizer, java.lang.Class, and the rest of the Java System classes are loaded and initialized. At this point, the HotSpot VM is initialized and operational, but not quite fully functional The HotSpot VM’s signal handler thread is started, the JIT compiler is initialized, and the HotSpot’s compile broker thread is started. Other HotSpot VM helper threads such as watcher threads and stat sampler are started. At this time the HotSpot VM is fully functional Finally, the JNIEnv is populated and returned to the caller and the HotSpot VM is ready to service new JNI requests
  • 27. JVM Overview 27 VM - Life Cycle (JNI_DestroyJVM) - (1) Wait until there is only one nondaemon thread executing noting that the HotSpot VM is still functional Call the Java method java.lang.Shutdown.shutdown(), which invokes the Java level shutdown hooks and runs Java object finalizers if finalization- on-exit is true Prepare for HotSpot VM exit by running HotSpot VM level shutdown hooks (those that were registered through JVM_OnExit()), stop the following HotSpot VM threads: profiler, stat sampler, watcher, and garbage collector threads. Post status events to JVMTI, disable JVMTI, and stop the Signal thread Call the HotSpot method JavaThread::exit() to release Java Native Interface handle blocks, remove guard pages, and remove the current thread from known threads list. From this point on the HotSpot VM cannot execute any Java code
  • 28. JVM Overview 28 VM - Life Cycle (JNI_DestroyJVM) - (2) Stop the HotSpot VM thread. This causes the HotSpot VM to bring the remaining HotSpot VM threads to a safepoint and stop the JIT compiler threads Disable tracing at the Java Native Interface, HotSpot VM, and JVMTI barriers Set HotSpot “vm exited” flag for threads that may be running in native code Delete the current thread Delete or remove any input/output streams and release PerfMemory (performance statistics memory) resources. Finally return to the caller
  • 29. JVM Overview 29 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 30. JVM Overview 30 VM - Class Loading Definition The overall process of mapping a class or interface name to a class object.
  • 31. JVM Overview 31 VM - Class Loading LOADING INITIALIZATION LINKING VERIFYING PREPARING RESOLVING Bringing Binary data from class into JVM Incorporating Binary data into JVM runtime state Class variables given proper initial values Ensure class is properly formed & fit for use by JVM Allocation of memory needed by class Transforming symbolic references into direct references
  • 32. JVM Overview 32 VM - Class Loading
  • 33. JVM Overview 33 VM - Class Loading Class Metadata in HotSpot
  • 34. JVM Overview 34 VM - Class Loading Class Metadata in HotSpot
  • 35. JVM Overview 35 VM - Class Loading Class Metadata in HotSpot
  • 36. JVM Overview 36 VM - Class Loading Class Metadata in HotSpot (64 bit)
  • 37. JVM Overview 37 VM - Class Loading Class Metadata in HotSpot
  • 38. JVM Overview 38 VM - Class Loading Class Metadata in HotSpot SNo. Compressed Class Space Metaspace 1 Class Meta Data (C++ Klass Object) Method Code 2 Runtime Constant Pool (Symbolic Ref.) 3 Code Cache (compiled bytecodes)
  • 39. JVM Overview 39 VM - Class Loading Internal Class Loading Data Sno. DictionaryName Functionality 1. SystemDictionary class name/initiating loader pairs 2. PlaceHolderDictionary contains classes that are currently being loaded. It is used for ClassCircularityError checking and for parallel class loading 3. LoaderConstraintTable tracks constraints for type safety checking.
  • 40. JVM Overview 40 VM - Class Loading ByteCodeVerification Sno. Check 1. Type correctness: the arguments of an instruction are always of the types expected by the instruction. 2. No stack overflow or underflow: an instruction never pops an argument off an empty stack,nor pushes a result on a full stack. 3. Rules for accessing private data and methods are not violated 4. Local variable accesses fall within the runtime stack 5. The runtime stack does not overflow
  • 41. JVM Overview 41 VM - Class Loading ByteCodeVerification
  • 42. JVM Overview 42 VM - Class Loading ByteCodeVerification
  • 43. JVM Overview 43 VM - Class Loading ByteCodeVerification Transfer Functions for Abstract Interpretation of Java Byte Code
  • 44. JVM Overview 44 VM - Class Loading ClassData Sharing
  • 45. JVM Overview 45 VM - Class Loading Class Data Sharing JVM-1 JVM-2 JVM-3 Shared Class Data (classes.jsa) -improved startup time of new jvm -reduced memory footprint
  • 46. JVM Overview 46 VM - Class Loading Class Data Sharing java -Xshare:dump
  • 47. JVM Overview 47 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 48. JVM Overview 48 VM - Class Loading ByteCode Interpreter BCP
  • 49. JVM Overview 49 VM - Class Loading ByteCode Interpreter
  • 50. JVM Overview 50 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 51. JVM Overview 51 VM - Exception Handling Exception Handler Search Inputs:- - current method - current bytecode - exception object
  • 52. JVM Overview 52 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 53. JVM Overview 53 VM - Synchronization Object Monitor Mapping Table Lookup Cost Look up Table Contention Cons Easy to implement Pros
  • 54. JVM Overview 54 VM - Synchronization Direct Mapping Method Overhead of Heavy weight OS Monitors Cons Improved Scalability: No Mapping Table needed Pros
  • 55. JVM Overview 55 VM - Synchronization All Java Objects Java Objects which are used for locks Java Objects whose locks are moslty used by a single thread Observation
  • 56. JVM Overview 56 VM - Synchronization - Biased Locks -Kawachiya Analaysis & Acceleration
  • 57. JVM Overview 57 VM - Synchronization Thin Lock (Biased Locks) Implementation Complexity Cons Optimized for Thread Locality Access Pattern Pros Biased Object
  • 58. JVM Overview 58 VM - Synchronization - Biased Locks ● Optimize Clock Cycles used for Lock Operations ● Observation: Most objects held by a single JVM thread ● Strategy: Create “Fast Path” for Common Use Case
  • 59. JVM Overview 59 VM - Synchronization - Biased Locks 11 Unused(25) Hashcode(31) Unused(1) Age(4) 0 01 Ptr to metadata0(62) 1 01 TId(54) Epoch(2) Unused(1) Age(4) 1 01 Ptr_to_lock_record(62) 00 Ptr_to_heavyweight_monitor(62) 10 Normal, UnlockedBiasable, Unlocked (Light weight Locked) (Heavy Weight Locked) (Marked for GC) Inital lock (CAS) Rebias (bulk) lock/unlock Revoke bias Thin Lock Inflate Lock Recursive lock unlock Allocate Object Biasing enabled Biasing disabled unlocked locked Fast Path
  • 60. JVM Overview 60 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 61. JVM Overview 61 VM - Runtime Thread Management - Lifecycle
  • 62. JVM Overview 62 VM - Runtime Thread Management - Internal VM Thread JVM Periodic Task Garbage collection JIT compiler Signal dispatcher
  • 63. JVM Overview 63 VM - Runtime Thread Management - Safe Points Mechanism to pause thread execution to perform JVM housekeeping.
  • 64. JVM Overview 64 VM - Runtime Thread Management - Safe Points Why? ● Garbage collection ● Code deoptimization ● Flushing code cache ● Class redefinition (e.g. hot swap or instrumentation) ● Biased lock revocation ● Various debug operation (e.g. deadlock check or stacktrace dump)
  • 65. JVM Overview 65 VM - Runtime Thread Management - Safe Points How? JIT inserts safepoint checks in code at certain points :- ● Between every 2 bytecodes (interpreter mode) ● Back edge of non counted loops ● Method Exit ● JNI call exit Safepoints are initiated using a cooperative, polling-based mechanism. In simplistic terms, every so often a thread asks “should I block for a safepoint?”
  • 66. JVM Overview 66 VM - Runtime Thread Management - Safe Points
  • 67. JVM Overview 67 VM - Runtime Thread Management - Safe Points
  • 68. JVM Overview 68 VM - Runtime Thread Management - Safe Points
  • 69. JVM Overview 69 VM - Runtime Thread Management - Safe Points
  • 70. JVM Overview 70 VM - Runtime Responsibilities 1. Command Line Parsing 2. VM - LifeCycle 3. Class Loading 4. ByteCode Interpreter 5. Exception Handling 6. Synchronization 7. Thread Management 8. Java Native Interface
  • 71. JVM Overview 71 VM - Runtime JNI
  • 72. JVM Overview 72 VM - Runtime JNI - Data Transfer Performance Impact
  • 73. JVM Overview 73 VM - Runtime JNI - (Performance Impact) Cons ● Loss of Cross Platform Portability ● Loss of Inbuilt Type Safety Security ● Additional Security Check JVM to JNI Data Copy Impacts Application Performance
  • 74. JVM Overview 74 VM - Runtime Fatal Error Investigation (hs_error_pid) Header Thread java -XX:ErrorFile=/var/log/java/java_error%p.log Process System
  • 75. JVM Overview 75 VM - Runtime Fatal Error Investigation (hs_error_pid) Header
  • 76. JVM Overview 76 VM - Runtime Fatal Error Investigation (hs_error_pid) Header
  • 77. JVM Overview 77 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
  • 78. JVM Overview 78 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
  • 79. JVM Overview 79 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
  • 80. JVM Overview 80 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
  • 81. JVM Overview 81 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread
  • 82. JVM Overview 82 VM - Runtime Fatal Error Investigation (hs_error_pid) Thread Frame Type
  • 83. JVM Overview 83 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Theadlist
  • 84. JVM Overview 84 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
  • 85. JVM Overview 85 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Mutex(es)
  • 86. JVM Overview 86 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Heap Summary
  • 87. JVM Overview 87 VM - Runtime Fatal Error Investigation (hs_error_pid) Process Memory Map
  • 88. JVM Overview 88 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
  • 89. JVM Overview 89 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
  • 90. JVM Overview 90 VM - Runtime Fatal Error Investigation (hs_error_pid) Process
  • 91. JVM Overview 91 VM - Runtime Fatal Error Investigation (hs_error_pid) System
  • 92. JVM Overview 92 ● HotSpot VM - Architecture ● VM - Runtime ● Memory Manager ● JIT Compiler JVM Components
  • 93. JVM Overview 93 JVM - Memory Manager
  • 94. JVM Overview 94 JVM - Memory Manager
  • 95. JVM Overview 95 JVM - Memory Manager
  • 96. JVM Overview 96 JVM - Memory Manager
  • 97. JVM Overview 97 JVM - Memory Manager (Copying GC)
  • 98. JVM Overview 98 JVM - Memory Manager (Copying GC) Cons Premature Promotions Promotion Failure
  • 99. JVM Overview 99 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps
  • 100. JVM Overview 100 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps Avg. ~92 MB/sec
  • 101. JVM Overview 101 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps Avg. ~140 .95MB/sec
  • 102. JVM Overview 102 JVM - Memory Manager (Copying GC) XX:+PrintGCDetails -XX:+PrintGCTimeStamps Promotion Rate :(Old After - Old Before)/(timeinms) Allocation Rate :(Young Before(current GC) - Young After (prev GC))/(timeinms) Promotion Rate --> Allocation Rate = Performance Problem Ex: 92MB/s ---> 140 MB/s = Performance Issue
  • 103. JVM Overview 103 JVM - Memory Manager (Fast Allocator) Eden
  • 104. JVM Overview 104 JVM - Memory Manager- Types Serial GC Parallel GC Mostly Concurrent GC Garbage First GC (G1)
  • 105. JVM Overview 105 JVM - Memory Manager- Types Serial GC Compacting Mark & Sweep Mark & Sweep (no compaction)
  • 106. JVM Overview 106 JVM - Memory Manager- Types Serial GC
  • 107. JVM Overview 107 JVM - Memory Manager- Types Serial GC ➢ Application heap size < 100 MB ➢ HIgh number of JVMS on same m/c ➢ No hard pause time requirements (ex < 2secs) java -XX:+UseSerialGC When?
  • 108. JVM Overview 108 JVM - Memory Manager- Types Theads Parallel GC
  • 109. JVM Overview 109 JVM - Memory Manager- Types ➢ Batch processing applications (Ex. Scientific Computing) ➢ High throughput requirement ➢ GC Latency can be met by improving GC efficiency on multi core processor java -XX:+UseParallelGC When? Parallel GC
  • 110. JVM Overview 110 JVM - Memory Manager- Types Theads Mostly Concurrent GC (CMS)
  • 111. JVM Overview 111 JVM - Memory Manager- Types ➢ Rapid Response Time (ex. Web Servers, Data Tracking Servers) java -XX:+UseConcMarkSweepGC When? Mostly Concurrent GC (CMS)
  • 112. JVM Overview 112 JVM - Memory Manager- Types Theads Garbage First GC (G1)
  • 113. JVM Overview 113 JVM - Memory Manager- Types Garbage Collector Types : Comparison
  • 114. JVM Overview 114 ● HotSpot VM - Architecture ● VM - Runtime ● Memory Manager ● JIT Compiler JVM Components
  • 115. JVM Overview 115 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 116. JVM Overview 116 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 117. JVM Overview 117 JIT Compiler Code Generation Overview Intermediate Representation Source Representation Machine Representation Front End Back End Optimizer
  • 118. JVM Overview 118 JIT Compiler Code Generation Overview Intermediate Representation Structural Linear Hybrid 1. AST 2. DAG 1. 3 Address Code 2. Stack M/c Code Control Flow Graph
  • 119. JVM Overview 119 JIT Compiler Code Generation Overview Structural IR: Abstract Syntax Tree
  • 120. JVM Overview 120 JIT Compiler Code Generation Overview Structural IR: DAG Example
  • 121. JVM Overview 121 JIT Compiler Code Generation Overview Linear IR: 3 Address Code Example
  • 122. JVM Overview 122 JIT Compiler Code Generation Overview Stack Machine Code
  • 123. JVM Overview 123 JIT Compiler Code Generation Overview Control Flow Graph
  • 124. JVM Overview 124 JIT Compiler Code Generation Overview 1. Constant Propagation 2. Value Range Propagation 3. Sparse Conditional Constant Propagation 4. Dead Code Elimination 5. Global Value Numbering 6. Partial Redundancy Elimination 7. Strength Reduction 8. Register Allocation Compiler Optimizations
  • 125. JVM Overview 125 JIT Compiler Code Generation Overview Constant Propagation
  • 126. JVM Overview 126 JIT Compiler Code Generation Overview Constant Propagation
  • 127. JVM Overview 127 JIT Compiler Code Generation Overview Intermediate Representation (IR) Static Single Assignment (SSA) Named Form
  • 128. JVM Overview 128 JIT Compiler Code Generation Overview Static Single Assignment - Example
  • 129. JVM Overview 129 JIT Compiler Code Generation Overview Static Single Assignment - Example Common SubExpression
  • 130. JVM Overview 130 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 131. JVM Overview 131 JIT Compiler Class Hierarchy Analysis Inlining critical to Performance! Java Compiler constructs the Call graph using Class Hierarchy Analysis (CHA) to enable method Inlining
  • 132. JVM Overview 132 JIT Compiler Class Hierarchy Analysis
  • 133. JVM Overview 133 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms (Further Reading) Reachability Analysis (RA) Class Hierarchy Analysis (CHA) Rapid Type Analysis (RTA) Class Type Analysis (CTA) Accuracy, Cost
  • 134. JVM Overview 134 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Reachability Analysis (RA)
  • 135. JVM Overview 135 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Class Hierarchy Analysis (CHA)
  • 136. JVM Overview 136 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Rapid Type Analysis (RTA)
  • 137. JVM Overview 137 JIT Compiler Class Hierarchy Analysis Call Graph Algorithms Class Type Analysis (CTA)
  • 138. JVM Overview 138 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 140. JVM Overview 140 JIT Compiler Compilation Policy Backedge CounterInvocation Counter Compilation Tier
  • 142. JVM Overview 142 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 143. JVM Overview 143 JIT Compiler ●Changing an optimized stack frame to an unoptimized one. ●Throwing away code with invalid optimistic optimizations, and replacing it by less-optimized, more robust code. Deoptimization
  • 145. JVM Overview 145 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 146. JVM Overview 146 JIT Compiler Client JIT Compiler Does not need a profiler Fast code generation of acceptable quality Rock solid and proved optimization Compilation threshold 1.5k invocation
  • 147. JVM Overview 147 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 148. JVM Overview 148 JIT Compiler Server JIT Compiler Does need a profiler Highly optimized code Many aggressive and speculative optimizations Compilation threshold 10k invocations
  • 149. JVM Overview 149 ● Code Generation Overview ● Class Hierarchy Analysis ● Compilation Policy ● Deoptimization ● Client JIT Compiler ● Server JIT Compiler ● SSA - Program Dependence Graph ● Future Enhancements JIT Compiler
  • 150. JVM Overview 150 JIT Compiler SSA Program Dependence Graph 1. SSA Graph ➢ Global Value Numbering ➢ Constant Propogation ➢ Register Optimization 1. Uncommon Traps 2. Iteration Splitting 3. Machine Code Generation
  • 151. JVM Overview 151 JIT Compiler SSA Program Dependence Graph SSA Graph
  • 152. JVM Overview 152 JIT Compiler SSA Program Dependence Graph Global Value Numbering Constant Propagation Register Optimization SSA Graph
  • 153. JVM Overview 153 JIT Compiler SSA Program Dependence Graph Global Value Numbering Categorize expression in program that compute same value Eliminate redundant computation SSA Graph
  • 154. JVM Overview 154 JIT Compiler SSA Program Dependence Graph Global Value Numbering FInput Pool Output Pool Optimizing function SSA Graph
  • 155. JVM Overview 155 JIT Compiler SSA Program Dependence Graph Global Value Numbering Pool A partition of a set of expressions SSA Graph
  • 156. JVM Overview 156 JIT Compiler SSA Program Dependence Graph Global Value Numbering PT : {∅} PU : {a,b,a+b,r} PU : {a,b | a+b,r} PT : {∅} PV : {a,b |a+b,r | x | r+x} PV : {a,b |a+b,r | x | r+x} PW : {a,b | a+b, r | x | r+x | (a+b)+x} PW : {a,b | a+b, r | x | r+x, (a+b)+x} Partition Restructure SSA Graph
  • 157. JVM Overview 157 JIT Compiler SSA Program Dependence Graph Discover values that are constant in all possible executions of a program and to propagate these constant values as far forward through the program as possible SSA Graph Constant Propagation
  • 158. JVM Overview 158 JIT Compiler SSA Program Dependence Graph Constant Propagation SSA Graph
  • 159. JVM Overview 159 JIT Compiler SSA Program Dependence Graph Constant Propagation SSA Graph
  • 160. JVM Overview 160 JIT Compiler SSA Program Dependence Graph Constant Propogation Pₙⁱ : Propogated Constant Pool at Entry Point to Node n at ith iteration SSA Graph
  • 161. JVM Overview 161 JIT Compiler SSA Program Dependence Graph Constant Propogation Pₙⁱ : Propagated Constant Pool at Entry Point to Node n at ith iteration SSA Graph
  • 162. JVM Overview 162 JIT Compiler SSA Program Dependence Graph Constant Propogation Pₙ : Propagated Constant Pool at Entry Point to Node N SSA Graph
  • 163. JVM Overview 163 JIT Compiler SSA Program Dependence Graph Constant Propagation Pₙⁱ : Propagated Constant Pool at Entry Point to Node n at ith iteration SSA Graph
  • 164. JVM Overview 164 JIT Compiler SSA Program Dependence Graph Register Optimization SSA Graph
  • 165. JVM Overview 165 JIT Compiler SSA Program Dependence Graph Register Optimization SSA Graph
  • 166. JVM Overview 166 JIT Compiler SSA Program Dependence Graph Register Optimization redundant No change in Pool
  • 167. JVM Overview 167 JIT Compiler SSA Program Dependence Graph Uncommon Traps Uncommon trap is a situation when a speculative precondition in the compiled code fails. It usually results in deoptimization - switching from compiled code back to interpreter
  • 168. JVM Overview 168 JIT Compiler SSA Program Dependence Graph Uncommon Traps - Why? 1. Unloaded or Uninitialized Class 1. Unreached Path
  • 169. JVM Overview 169 JIT Compiler SSA Program Dependence Graph Uncommon Traps - Why? TraceDeoptimization
  • 170. JVM Overview 170 JIT Compiler SSA Program Dependence Graph Iteration Splitting