Expressing and exploiting path conflicts in WCET analysis

Real-Time Systems, 2006

It is advantageous to perform compiler optimizations that attempt to lower the worst-case execution time (WCET) of an embedded application since tasks with lower WCETs are easier to schedule and more likely to meet their deadlines. Compiler writers in recent years have used profile information to detect the frequently executed paths in a program and there has been considerable effort to develop compiler optimizations to improve these paths in order to reduce the average-case execution time (ACET). In this paper, we describe an approach to reduce the WCET by adapting and applying optimizations designed for frequent paths to the worst-case (WC) paths in an application. Instead of profiling to find the frequent paths, our WCET path optimization uses feedback from a timing analyzer to detect the WC paths in a function. Since these path-based optimizations may increase code size, the subsequent effects on the WCET due to these optimizations is measured to ensure that the worst-case path optimizations actually improve the WCET before committing to a code size increase. We evaluate these WC path optimizations and present results showing the decrease in WCET versus the increase in code size.

Deutschsprachige WCET-Tagung

2008

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, runtime properties of these programs. The participants are challenged to solve these problems with their programanalysis tools. Two kinds of problems are defined: WCET problems, which ask for bounds on the execution time of chosen parts (sub programs) of the benchmarks, under given constraints on input data; and flowanalysis problems, which ask for bounds on the number of times certain parts of the benchmark can be executed, again under some constraints. We describe the organization of WCC'08, the benchmark programs, the participating tools, and the general results, successes, and failures. Most participants found WCC'08 to be a useful test of their tools. Unlike the 2006 Challenge, the WCC'08 participants include several tools for the same target (ARM7, LPC2138), and tools that combine measurements and static analysis, as well as pure staticanalysis tools.

11th IEEE Real Time and Embedded Technology and Applications Symposium, 2005

It is advantageous to perform compiler optimizations to lower the WCET of a task since tasks with lower WCETs aree asier to schedule and morel ikely to meet their deadlines. Compiler writersi nr ecent yearsh ave used profile information to detect the frequently executed paths in a programa nd thereh as been muche ffort to develop compiler optimizations to improvet hese paths in order to reduce average-case execution time.I nt his paper we describe our approacht or educe WCET by adapting and applying optimizations designed for frequent paths to the worst-case paths in an application. Our compiler uses feedbackf romo ur timing analyzer to detect the WCET paths through a function that will be subject to aggressive optimizations, reflect subsequent effects on the WCET of the paths due to these optimizations, and to also ensure that the worst-case path optimizations actually improve the WCET beforec ommitting to a code size increase.W e evaluate a number of WC path optimizations and present results showing the decrease in WCET versus the increase in code size.

2006 27th IEEE International Real-Time Systems Symposium (RTSS'06), 2006

Static Worst-Case Execution Time (WCET) analysis is a technique to derive upper bounds for the execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A key component for statically deriving safe and tight WCET bounds is information on the possible program flow through the program. Such flow information can be provided manually by user annotations, or automatically by a flow analysis. To make WCET analysis as simple and safe as possible, it should preferably be automatically derived, with no or very limited user interaction.

Analyzers (SSQSA) is a set of software tools for static analysis that is incorporated in the framework developed to target the common aim-consistent software quality analysis. The main characteristic of all integrated tools is the independency of the input computer language. Language independency is achieved by enriched Concrete Syntax Tree (eCST) that is used as an intermediate representation of the source code. This characteristic gives the tools more generality comparing to the other similar static analyzers. The aim of this paper is to describe an early idea for introducing support for static timing analysis and Worst Case Execution Time (WCET) calculation at code level in SSQSA framework.

Proceedings of the Eighth International Workshop on Object-Oriented Real-Time Dependable Systems, 2003. (WORDS 2003)., 2003

Bounding the Worst Case Execution Time (WCET) of programs is essential for real-time systems. To be able to do WCET calculations, the iteration bounds for loops and recursion must be known. We describe a newly developed prototype tool that calculates these bounds automatically, thereby avoiding the need for manual annotations by the programmer. The analysis is based on an intermediate

2005

Reliable Software Technologies–Ada-Europe 2009, 2009

Knowledge about the Worst-Case Execution-Time (WCET) is of primordial importance in the validation of real-time systems. A WCET estimation must be safe and tight. Tightness in WCET estimation is highly desirable for an efficient utilisation of resources. In order to obtain accurate WCET values, more program execution-history must be accounted for. In this thesis we propose the use of Predicated WCET Analysis which uses constraint-logic programming to model context-sensitive execution-times of program segments. We prove that our predicated analysis is safe and very tight compared to contemporary analysis techniques.

ACM SIGPLAN Notices, 2006

Static Worst-Case Execution Time (WCET) analysis is a technique to derive upper bounds for the execution times of programs. Such bounds are crucial when designing and verifying real-time systems. WCET analysis needs a program flow analysis to derive constraints on the possible execution paths of the analysed program, like iteration bounds for loops and dependences between conditionals.