WCET Analysis for a Java Processor - Aalborg Universitetpeople.cs.aau.dk/~bt/DAT5E07/petur3.pdf ·...

WCET Analysis for a Java Processor

Martin Schoberl Rasmus Pedersen

Presenter: Petur Olsen

October 25, 2007

IntroductionJOP Processor

AnalysisEvaluationConclusion

AuthorsArticle

Authors

Martin Schoberl

Ph.D. at Vienna University

Creator of JOP processor

Rasmus Pedersen

Department of Informatics at Copenhagen Business School

Embedded systems, WCET analysis, real-time systems

2/29 Schoberl, Pedersen WCET Analysis for a Java Processor



AuthorsArticle

Article

Published

Proceedings of the 4th international workshop on Javatechnologies for real-time and embedded systems

ACM Press 2006




AuthorsArticle

General Idea

Analyze Java source code and class files

Calculate WCET (in clock cycles)

Translate into actual WCET (in (milli)seconds)

Time predictable Java processor (JOP)




AuthorsArticle

Contributions

Actual WCET analysis

High level and low level(incl. memory access and cache control)

Analysis tool called WCA




AuthorsArticle

Outline

1 JOP Processor

2 Analysis

3 Evaluation

4 Conclusion




OverviewCache

Overview

Stack computer

RISC stack architecture

Translates Java bytecode into microcode

Three stage pipeline (fourth stage)

No timing anomalies (e.g. branch prediction)

New caching features




OverviewCache

Overview

Regular cache

Focus on average case execution time

Difficult to analyze

JOP cache

Focus on analyzability

No data cache

Stack cache

Method cache




OverviewCache

Stack Cache

Stack for (currently executing) method

Swapped on method invoke and return

Size is known ⇒ time is bounded

Requires stack flush for thread switch




OverviewCache

Method Cache

Short methods

Simple branching (internal and relative)

Cache for entire method body

Swapped on invocation and return

Three types:

Single methodTwo methodsVariable block cache




DecidabilityHigh-Level WCET AnalysisLow-Level WCET AnalysisCache Analysis

Decidability

WCET analysis is undecidable

Making it decidable:1 No recursion2 No dynamic class loading3 Known upper bounds for loops





High-Level

Calculate clock cycles from source code

Loop bounds extracted

CFG of basic blocks

ILP to calculate clock cycles





Example

public static int loop(boolean b, int val) {for (int i=0; i<10; i++) {

if (b) {for (int j=0; j<3; j++) {

val ∗= val;}

} else {for (int j=0; j<7; j++) {

val += val;}

}}return val;

}





Example





Example

public static int loop(boolean b, int val) {for (int i=0; i<10; i++) {

if (b) {for (int j=0; j<3; j++) {

val ∗= val;}

} else {for (int j=0; j<7; j++) {

val += val;}

}}return val;

}





Dynamic Methods





Low-Level

Basic bytecodes

Bytecodes in Java

Native Methods

Memory Access





Memory Access

Instructions

Object oriented instructions

Array access

Invoke instructions

Access time

Access time more than one cycle

rws for read access

wws for write access





Memory Access

tldc2 w = 17 +

{rws − 2 : rws > 20 : rws ≤ 2

+

{rws − 1 : rws > 10 : rws ≤ 1





Overview

Contains entire method bodies

Misses centered on invocations





Example





Example





Dual Block




Evaluation

Evaluation

Cannot measure WCET

Measurement as test

Two real-life benchmarks




Evaluation

Benchmarks




ContributionsFuture WorkArticle

Contributions

WCET analysis

Minor changes to the language

Time predictable processor

Good performance

Good estimation (with correct development)





Future Work

Variable block cache

Integration into IDE (Eclipse)

Graphical representation of path on CFG

Better aid in development





Article

Well written

Simple

Important contributions

Many references

Good article


Questions?

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WCET Analysis for a Java Processor - Aalborg Universitetpeople.cs.aau.dk/~bt/DAT5E07/petur3.pdf ·...

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