453 Works

A Code Policy Guaranteeing Fully Automated Path Analysis

Benedikt Huber & Peter Puschner
Calculating the worst-case execution time (WCET) of real-time tasks is still a tedious job. Programmers are required to provide additional information on the program flow, analyzing subtle, context dependent loop bounds manually. In this paper, we propose to restrict written and generated code to the class of programs with input-data independent loop counters. The proposed policy builds on the ideas of single-path code, but only requires partial input-data independence. It is always possible to find...

Hybrid measurement-based WCET analysis at the source level using object-level traces

Adam Betts, Nicholas Merriam & Guillem Bernat
Hybrid measurement-based approaches to worst-case execution time (WCET) analysis combine measured execution times of small program segments using static analysis of the larger software structure. In order to make the necessary measurements, instrumentation code is added to generate a timestamped trace from the running program. The intrusive presence of this instrumentation code incurs a timing penalty, widely referred to as the probe effect. However, recent years have seen the emergence of trace capability at the...

Toward Precise PLRU Cache Analysis

Daniel Grund & Jan Reineke
Schedulability analysis for hard real-time systems requires bounds on the execution times of its tasks. To obtain useful bounds in the presence of caches, cache analysis is mandatory. The subject-matter of this article is the static analysis of the tree-based PLRU cache replacement policy (pseudo least-recently used), for which the precision of analyses lags behind those of other policies. We introduce the term subtree distance, which is important for the update behavior of PLRU and...

Integrating Abstract Caches with Symbolic Pipeline Analysis

Stephan Wilhelm & Christoph Cullmann
Static worst-case execution time analysis of real-time tasks is based on abstract models that capture the timing behavior of the processor on which the tasks run. For complex processors, task-level execution time bounds are obtained by a state space exploration which involves the abstract model and the program. Partial state space exploration is not sound. Symbolic methods using binary decision diagrams (BDDs) allow for a full state space exploration of the pipeline, thereby maintaining soundness....

Realism in Statistical Analysis of Worst Case Execution Times

David Griffin & Alan Burns
This paper considers the use of Extreme Value Theory (EVT) to model worst-case execution times. In particular it considers the sacrifice that statistical methods make in the realism of their models in order to provide generality and precision, and if the sacrifice of realism can impact the safety of the model. The Gumbel distribution is assessed in terms of its assumption of continuous behaviour and its need for independent and identically distributed data. To ensure...

The Mälardalen WCET Benchmarks: Past, Present And Future

Jan Gustafsson, Adam Betts, Andreas Ermedahl & Björn Lisper
Modelling of real-time systems requires accurate and tight estimates of the Worst-Case Execution Time (WCET) of each task scheduled to run. In the past two decades, two main paradigms have emerged within the field of WCET analysis: static analysis and hybrid measurement-based analysis. These techniques have been succesfully implemented in prototype and commercial toolsets. Yet, comparison among the WCET estimates derived by such tools remains somewhat elusive as it requires a common set of benchmarks...

METAMOC: Modular Execution Time Analysis using Model Checking

Andreas E. Dalsgaard, Mads Chr. Olesen, Martin Toft, René Rydhof Hansen & Kim Guldstrand Larsen
Safe and tight worst-case execution times (WCETs) are important when scheduling hard real-time systems. This paper presents METAMOC, a modular method, based on model checking and static analysis, that determines safe and tight WCETs for programs running on platforms featuring caching and pipelining. The method works by constructing a UPPAAL model of the program being analysed and annotating the model with information from an inter-procedural value analysis. The program model is then combined with a...

Precomputing Memory Locations for Parametric Allocations

Jörg Herter & Sebastian Altmeyer
Current worst-case execution time (WCET) analyses do not support programs using dynamic memory allocation. This is mainly due to the unpredictability of cache performance introduced by standard memory allocators. To overcome this problem, algorithms have been proposed that precompute static allocations for dynamically allocating programs with known numeric bounds on the number and sizes of allocated memory blocks. In this paper, we present a novel algorithm for computing such static allocations that can cope with...

Bounding the Effects of Resource Access Protocols on Cache Behavior

Enrico Mezzetti, Marco Panunzio & Tullio Vardanega
The assumption of task independence has long been consubstantial with the formulation of many schedulability analysis techniques. That assumption is evidently advantageous for the mathematical formulation of the analysis equations, but ill fit to capture the actual behavior of the system. Resource sharing is one of the system design dimensions that break the assumption of task independence. By shaking the very foundations of the real-time analysis theory, the advent of multicore systems has caused resurgence...

Timing Anomalies Reloaded

Gernot Gebhard
Computing tight WCET bounds in the presence of timing anomalies - found in almost any modern hardware architecture - is a major challenge of timing analysis. In this paper, we renew the discussion about timing anomalies, demonstrating that even simple hardware architectures are prone to timing anomalies. We furthermore complete the list of timing-anomalous cache replacement policies, proving that the most-recently-used replacement policy (MRU) also exhibits a domino effect.

WCET 2008 Abstracts Collection -- 8th Intl. Workshop on Worst-Case Execution Time (WCET) Analysis

Raimund Kirner
The workshop on Worst-Case Execution Time Analysis is a satellite event to the annual Euromicro Conference on Real-Time Systems. It brings together people that are interested in all aspects of timing analysis for real-time systems. In the 2008 edition, 13 papers were presented, organized into four sessions: methods for WCET computation, low-level analysis, system-level analysis and flow-analysis. The workshop was also the opportunity to report from the 2007 WCET tool challenge.

Improving the WCET computation time by IPET using control flow graph partitioning

Clément Ballabriga & Hugues Cassé
Implicit Path Enumeration Technique (IPET) is currently largely used to compute Worst Case Execution Time (WCET) by modeling control flow and architecture using integer linear programming (ILP). As precise architecture effects requires a lot of constraints, the super-linear complexity of the ILP solver makes computation times bigger and bigger. In this paper, we propose to split the control flow of the program into smaller parts where a local WCET can be computed faster - as...

A tool for average and worst-case execution time analysis

David Hickey, Diarmuid Early & Michel Schellekens
We have developed a new programming paradigmwhich, for conforming programs, allows the average-case execution time (ACET) to be obtained automatically by a static analysis. This is achieved by tracking the data structures and their distributions that will exist during all possible executions of a program. This new programming paradigm is called MOQA and the tool which performs the static analysis is called Distritrack. In this paper we give an overview of both MOQA and Distritrack....

INFER: Interactive Timing Profiles based on Bayesian Networks

Michael Zolda
We propose an approach for timing analysis of software-based embedded computer systems that builds on the established probabilistic framework of Bayesian networks. We envision an approach where we take (1) an abstract description of the control flow within a piece of software, and (2) a set of run-time traces, which are combined into a Bayesian network that can be seen as an interactive timing profile. The obtained profile can be used by the embedded systems...

Towards Predicated WCET Analysis

Amine Marref & Guillem Bernat
In this paper, we propose the use of constraint logic programming as a way of modeling context-sensitive execution-times of program segments. The context-sensitive constraints are collected automatically through static analysis or measurements. We achieve considerable tightness in comparison to traditional calculation methods that exceeded 20% in some cases during evaluation. The use of constraint-logic programming in our calculations proves to be the right choice when compared to the exponential behaviour recorded by the use of...

WCET 2008 -- Report from the Tool Challenge 2008 -- 8th Intl. Workshop on Worst-Case Execution Time (WCET) Analysis

Niklas Holsti, Jan Gustafsson, Guillem Bernat, Clément Ballabriga, Armelle Bonenfant, Roman Bourgade, Hugues Cassé, Daniel Cordes, Albrecht Kadlec, Raimund Kirner, Jens Knoop, Paul Lokuciejewski, Nicholas Merriam, Marianne De Michiel, Adrian Prantl, Bernhard Rieder, Christine Rochange, Pascal Sainrat & Markus Schordan
Following the successful WCET Tool Challenge in 2006, the second event in this series was organized in 2008, again with support from the ARTIST2 Network of Excellence. The WCET Tool Challenge 2008 (WCC'08) provides benchmark programs and poses a number of "analysis problems" about the dynamic, run-time properties of these programs. The participants are challenged to solve these problems with their program analysis tools. Two kinds of problems are defined: WCET problems, which ask for...

WCET Analysis for Preemptive Scheduling

Sebastian Altmeyer & Gernot Gebhard
Hard real-time systems induce strict constraints on the timing of the task set. Validation of these timing constraints is thus a major challenge during the design of such a system. Whereas the derivation of timing guarantees must already be considered complex if tasks are running to completion, it gets even more complex if tasks are scheduled preemptively -- especially due to caches, deployed to improve the average performance. In this paper we propose a new...

Applying WCET Analysis at Architectural Level

Olivier Gilles & Jérôme Hugues
Real-Time embedded systems must enforce strict timing constraints. In this context, achieving precise Worst Case Execution Time is a prerequisite to apply scheduling analysis and verify system viability. WCET analysis is usually a complex and time-consuming activity. It becomes increasingly complex when one also considers code generation strategies from high-level models. In this paper, we present an experiment made on the coupling of the WCET analysis tool Bound-T and our AADL to code generator OCARINA....

Traces as a Solution to Pessimism and Modeling Costs in WCET Analysis

Jack Whitham & Neil Audsley
WCET analysis models for superscalar out-of-order CPUs generally need to be pessimistic in order to account for a wide range of possible dynamic behavior. CPU hardware modifications could be used to constrain operations to known execution paths called traces, permitting exploitation of instruction level parallelism with guaranteed timing. Previous implementations of traces have used microcode to constrain operations, but other possibilities exist. A new implementation strategy (virtual traces) is introduced here. In this paper the...

Computing time as a program variable: a way around infeasible paths

Niklas Holsti
Conditional branches connect the values of program variables with the execution paths and thus with the execution times, including the worst-case execution time (WCET). Flow analysis aims to discover this connection and represent it as loop bounds and other path constraints. Usually, a specific analysis of the dependencies between branch conditions and assign­ments to variables creates some representation of the feasible paths, for example as IPET execution-count constraints, from which a WCET bound is calculated....

On Composable System Timing, Task Timing, and WCET Analysis

Peter Puschner & Martin Schoeberl
The complexity of hardware and software architectures used in today's embedded systems make a hierarchical, composable timing analysis impossible. This paper describes the source of this complexity in terms of mechanisms and side effects that determine variations in the timing of single tasks and entire applications. Based on these observations, the paper proposes strategies to reduce the complexity. It shows the positive effects of these strategies on the timing of tasks and on WCET analysis.

Towards an Automatic Parametric WCET Analysis

Stefan Bygde & Björn Lisper
Static WCET analysis obtains a safe estimation of the WCET of a program. The timing behaviour of a program depends in many cases on input, and an analysis could take advantage of this information to produce a formula in input variables as estimation of the WCET, rather than a constant. A method to do this was suggested in [12]. We have implemented a working prototype of the method to evaluate its feasibility in practice. We...

TuBound - A Conceptually New Tool for Worst-Case Execution Time Analysis

Adrian Prantl, Markus Schordan & Jens Knoop
TuBound is a conceptually new tool for the worst-case execution time (WCET) analysis of programs. A distinctive feature of TuBound is the seamless integration of a WCET analysis component and of a compiler in a uniform tool. TuBound enables the programmer to provide hints improving the precision of the WCET computation on the high-level program source code, while preserving the advantages of using an optimizing compiler and the accuracy of a WCET analysis performed on...

Towards a Common WCET Annotation Language: Essential Ingredients

Raimund Kirner, Albrecht Kadlec, Adrian Prantl, Markus Schordan & Jens Knoop
Within the last years, ambitions towards the definition of common interfaces and the development of open frameworks have increased the efficiency of research on WCET analysis. The Annotation Language Challenge for WCET analysis has been proposed in line with these ambitions in order to push the development of common interfaces also to the level of annotation languages, which are crucial for the power of WCET analysis tools. In this paper we present a list of...

WCET 2007 Abstracts Collection -- 7th Intl. Workshop on Worst-Case Execution Time (WCET) Analysis

Christine Rochange
The workshop on Worst-Case Execution Time Analysis is a satellite event to the annual Euromicro Conference on Real-Time Systems. It brings together people that are interested in all aspects of timing analysis for real-time systems. In the 2007 edition, 13 papers were presented, organized into four sessions: methods for WCET computation, low-level analysis, system-level analysis and flow-analysis. The workshop was also the opportunity to report from the 2006 WCET tool challenge.

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