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2007 JavaOneSM Conference | Session TS-2023 |

TS-2023

Whats Hot in IBMs VirtualMachine for the Java

Platform2007 Edition?Trent Gray-Donald

Java SE JVM Technical LeadIBMwww.ibm.com/java/jdk

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2007 JavaOneSM Conference | Session TS-2023 | 2 Copyright IBM Corp. 2006, 2007

Goal

Learn about IBMs Java Virtual Machine

(JVM

) offerings, see whats improvedtechnically on the way to Java platformv.6, and a dive into IBMs Real-time Java

technology offering.

Whats in It for You?

The terms Java Virtual Machine and JVM mean a Virtual Machine for the Java platform.

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Agenda

History and ArchitectureJava Platform v.6Whats New This Year?

JVM Software, GC, JIT, Shared Classes

RAS Update

WebSphere Real Time and Metronome GCReal-time Specification for Java (RTSJ):

Java Specification Request (JSR) 1

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Agenda



RAS Update

WebSphere Real Time and Metronome GCReal-time Specification for Java (RTSJ):


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Design Philosophy andArchitecture

Current offerings based on the J9 Virtual Machine

3rd generation JVM software from IBM

Designed from the ground up to be a scalable solution forembedded, desktop, and server class hardware

Common code base for all Java Platform, Micro Edition(Java ME platform) and Java Platform, Standard Edition(Java SE platform) products

Highly configurablepluggable interfaces with differentimplementations depending on the target market

Class library independence

Supports latest language features (Java SE v.6)

Scaling to available hardware

Wide rangefrom a watch to a mainframe Portable, configurable, flexible

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6/382007 JavaOneSM Conference | Session TS-2023 | 6 Copyright IBM Corp. 2006, 2007

Pluggable components

that dynamically load

into the virtual machine Calls to

C

Libraries

JavaSE 6

Operating System

Native

Applications

Java Application Code

OS-Specific Calls

Virtual Machine

Java SE 5

Garbage collector

Interpreter

Exception handler

Class loader

Thread Model

JVM Profiler

Debugger

Realtime Profiler

Port Library (file IO, sockets, memory allocation, etc.)

Uses 1 of many possible

configurations

JCL Natives

JNI

CDC

MIDP

Java calls

JNI

JIT

CLDC

Class

Library

JNI = Java Native Interface

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Agenda



RAS UpdateWebSphere Real Time and Metronome GC

Real-time Specification for Java (RTSJ):Java Specification Request (JSR) 1

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All thats new

Java Platform v.6

Standard Java SE platform v.6 classlibrary enhancements java.util.concurrent updates (and lock monitoring)

JVM technology enhancements JVM Tool Interface 1.1 (multiple agents,

better heap iterator API,)

Class loading performance boost

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Customer FeedbackResulting in Process Changes

Java platform v.5 and before => closedbeta program

Java platform v.6 => open early access program

Move to iterative development model

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Just in Time (JIT) compiler updates

Java Platform v.6

POWER 6

and Z9 exploitation Inliner and basic block layout improvements

Determine whats hot, whats not

(common path analysis) Lock reservation (IBM paper at OOPSLA 02)

Improves scaling and overall performance

Dozens of platform dependent and independentoptimizations implemented, (e.g., new registerallocators, live range reduction, idiom recognition)

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Garbage Collector (GC) updates

Java Platform v.6

Significantly faster classLoader load/unload performanceand improved footprint

Hierarchical Scanningfaster, memory hierarchy awareoptimization forXgcpolicy:gencon. Paper in ISMM 06

(Siegwart and Hirtzel) Challenge: improving locality

Commercial workloads spend 45% stalled in memory requests.

Copying GC can improve object ordering, co-locating

objects on the same page or cache line

While maintaining scalability

Parallelism and workload balancing is essential

for server workloads

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0%

5%

10%

15%

20%

25%

30%

1 2 3 4 5 6 7 8 9 1011 12 131415 16 171819 202122 23242526

Scanned Slot to Copied Object Distance

(Log2)

Propo

rtion

Breadth-FirstHierarchical

64 byte

cache line

page size (4 kB) less TLB misses, less L2 cache misses

Parent-Child Distances forHierarchical(SPECjbb2005)

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Memory Management/Garbage Collection

Minor collectiontakes place only in the young generation,normally done through direct copying => very efficient

Major collectiontakes place in the new and old generationand uses the normal mark/sweep (+compact) algorithm

How the IBM J9 generational garbage collector works

IBM J9: Xmn (-Xmns/-Xmnx)

Sun:

XX:NewSize=nn

XX:MaxNewSize=nn Xmn

Sun JVM Software Only: XX:MaxPermSize=nn

Nursery/Young Generation Old Generation Permanent Space

IBM J9: Xmo (-Xmos/-Xmox)

Sun:

XX:NewRatio=n

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Understanding Heap Sizes

occupied

free

-Xmx = max

-Xms = initial

Hint: Use -verbose:sizes to see defaults for your platform, * denotes default

GC resizes heap based on occupancy

and duration statsOccupancy Constraint:

30%* < free < 60%*

-Xminf< free < -Xmaxf

Duration Constraint:

5%* < duration < 13%*

-Xmint < duration < -Xmaxt

Adjustment Size:

1Mb* < adjustment < *

-Xmine < adjustment < -Xmaxe

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Overview

Java Platform v.6SharedClasses

Target: server environments where multipleJVM implementations exist on the same box

Goal: improve startup time and memory footprint

Sharing of common data For classes, granularity is .class file

Multiple sharing strategies Standard classloaders (including application

Classloader) exploit the feature when enabled

API to extend custom ClassLoaders available

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Improvements

Java Platform v.6Shared Classes

Pre-compilation of Java code Idea: JIT the code ahead of time (during first run)

and share it from then on

Result: improved startup time Shared classes is becoming

Shared JVM software data

Other JVM software data will be stored in future

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Sharing helps speed up JVM software start-up

Java Platform v.6Shared Classes

Startup Improvements with Shared Classes and AOT

0

5

10

15

20

25

30

eclipse 3.2.2 tomcat 5.5 WAS 6.1

Seconds

default

-Xshareclasses

(Java 5.0)"

-Xshareclasses

(Java 6.0)

Lower is better

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Cluster Server Memory Savings forv6.1

With the addition of the Shared Classes feature to the IBM Java Development Kit (JDK)WebSphere instances are able to share non-changing class files amongst each other limiting thememory overhead of each JVM machine

Typically for a base WebSphere install each JVM machine uses about 30MB less memory withShared Classes on its process size

-9

27

62

79

102

0

100

200

300

400

500

600

700

One Two Three Four Five

ProcessSize(MB)

-20

0

20

40

60

80

100

120

MemorySav

ed(MB)

Shared Classes Enabled Clustered Server Memory Footprint (bytes)Regular Clustered Server Memory Footprint (bytes)Memory Saved with class sharing

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Agenda

History and Architecture

Java Platform v.6Whats New This Year?JVM Software, GC, JIT, Shared Classes

RAS UpdateWebSphere Real Time and Metronome GC

Real-time Specification for Java (RTSJ):Java Specification Request (JSR) 1

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Reliability,Availability, andServiceability

Centralization of tools Central customer visible repository of supported, maintained tools

Extensible, open tools, with programmable extension interfaces

Tools must be usable everywhere

GUI mode for interactive use

Report generation for headless environments

Documentation

Improvements to problem determination doc

Aggregated search in IBM support assistant

Iterate!

Tools being deployed very regularlylooking forcustomer feedback

RAS strategy

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Improvements across releases

Reliability,Availability, andServiceability

IBM Support Assistant

Java platform 1.4.2, Java platform v.5, and (soon)Java platform v.6 plug-ins

Diagnostics Tooling Framework For Java (DTFJ) Presented at the 2006 JavaOneSM conference

DumpAnalyzer (using DTFJ)

First stop analysis engine for common Java problems(OutOfMemoryError and crashes)

Extensible Verbose ToolKit (EVTK)

Verbose GC visualization and analysis

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EVTKHeap Visualization

Heap occupancy

Pause times

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EVTKComparison and Advice

Compare runs

Performance advisor

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IBM SDK for Java Platform v6Early Release Program

Download early release software packagesand documentation from the program website https://www14.software.ibm.com/iwm/web/cc/

earlyprograms/ibm/java6/

Participate in technical discussion on anIBM-moderated forum

The early release version of the IBM SDKis available on Linux, IBM AIX, Linux onSystem z, and IBM z/OS

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Agenda

History and Architecture

Java Platform v.6Whats New This Year?JVM Software, GC, JIT, Shared Classes

RAS UpdateWebSphereReal Time and Metronome GC

Real-time Specification for Java (RTSJ):


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What Does Real-Time Mean?

Real-time = Predictability of performance

HardViolation of timing constraints are hard failures

SoftTiming constraints are simply performance goals

Constraints vary in magnitude (microseconds to seconds)

Consequences of missing a timing constraint:

From service level agreement miss (stock trading)

To life in jeopardy (airplanes)

Real-fast is not real-time, but real-slow is not real-good

Need a balance between predictability and throughput

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WebSphereReal Time (WRT)

1.0 generally available in August 2006

WRT is a Java technology runtime providinghighly predictable operation

Real-time garbage collection Static and dynamic compilation

Full support for RTSJ (JSR 1)

Java SE platform 5.0 compliant Built and rigorously tested on a RT Linux OS

with IBM System x blades

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Linux Support for Real-Time

WebSphere Real Time runs on a variant of RHEL 4.2 Updated Linux kernel (2.6.16+)

Pre-emptive Kernel (priority inheritance in kernel locks)

High precision timing (precise microsecond sleep)

Extended POSIX APIs (priority-based pthreads)

Supported on key System x platforms by the IBM LTC

Primary target is the System x blades

Goal is to have changes adopted into the Linux kernel Changes maintained and incorporated into distributions

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Real-Time Garbage Collection

Gencon can provide low pause time GC But the pauses are not predictable

Time-bound work items can potentially fail

Application

Collector

Time

Systems with real-time requirements can fail Unpredictable behavior characteristics

Sufficient time to complete Insufficient time to complete

The metronome garbage collector

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Metronome targets short individual pauses 500us average with 1ms upper bound

However, short pause times arent enough

Need a system that incorporates Short pause times

Time ratios between the application and GC

Application

Collector

Time

0.1ms1ms


This is no better than a full collection!

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Utilization Percentage of time dedicated to the application

in a given window of time

Metronome uses a 10ms sliding windowto measure utilization

Utilization is user selectable via command line


Application

Collector

Time

Application receives a minimum

percentage of time to run10ms

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Utilization is not free!

There are tradeoffsfor higher utilization

Heap size vs.throughput

Finding the right

balance will dependon user andapplication needs

90% 65%

100mb 50mb


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Predictable pause times are not free! There is an impact on throughput

Frequent context switching between applicationand GC threads

Allocation of objects is more complicated Arrays in particular

Tracking of potential hidden objects

Effects of RTSJ overhead are also felt The strength of the system is predictability

The cost of predictability

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100% Java technology MIDI Synthesizer

1 ms (1KHz) timing for MIDI control (GC)44.1KHz for waveform synthesis (Eventrons)

Joint work with Bohm Software

Autonomous Quad Rotor Helicopter100% Java technology, 3ms control loop

Goal is to validate Java technology in a

critical physical control system

Joint work with University of Salzburg

Application Test Beds

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Further Information

IBM JDK home page http://www.ibm.com/developerworks/java/jdk/

IBM support assistant

http://www.ibm.com/software/support/isa/ Early access program

https://www14.software.ibm.com/iwm/web/cc/earlyprog

rams/ibm/java6/ WebSphere Real Time

http://www-306.ibm.com/software/webservers/realtime/

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372007 JavaOneSM Conference | Session TS-2023 |

Q&ATrent Gray-Donald

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TS-2023

Whats Hot in IBMs VirtualMachine for the Java

Platform2007 Edition?Trent Gray-Donald

Java SE JVM Technical LeadIBMwww.ibm.com/java/jdk

TS-2023

Documents