FAST: frequency-aware static timing analysis
Power is a valuable resource in embedded systems as the lifetime of many such systems is constrained by their battery capacity. Recent advances in processor design have added support for dynamic frequency/voltage scaling (DVS) for saving power. Recent work on real-time scheduling focuses on saving power in static as well as dynamic scheduling environments by exploiting idle and slack due to early task completion for DVS of subsequent tasks. These scheduling algorithms rely on a priori knowledge of worst-case execution times (WCET) for each task. They assume that DVS has no effect on the worst-case execution cycles (WCEC) of a task and scale the WCET according to the processor frequency. However, for systems with memory hierarchies, the WCEC typically does not change under DVS due to frequency modulation. Hence, current assumptions used by DVS schemes result in a highly exaggerated WCET. This paper contributes novel techniques for tight and flexible static timing analysis particularly well-suited for dynamic scheduling schemes. The technical contributions are as follows: (1) we assess the problem of changing execution cycles due to scaling techniques. (2) We propose a parametric approach towards bounding the WCET statically with respect to the frequency. Using a parametric model, we can capture the effect of changes in frequency on the WCEC and thus, accurately model the WCET over any frequency range. (3) We discuss design and implementation of the frequency-aware static timing analysis (FAST) tool based on our prior experience with static timing analysis. (4) We demonstrate in experiments that our FAST tool provides safe upper bounds on the WCET, which are tight. The FAST tool allows us to capture the WCET of six benchmarks using equations that overestimate the WCET by less than 1%. FAST equations can also be used to improve existing DVS scheduling schemes to ensure that the effect of frequency scaling on WCET is considered and that the WCET used is not exaggerated. (5) We leverage three DVS scheduling schemes by incorporating FAST into them and by showing that the power consumption further decreases. To the best of our knowledge, this study of DVS effects on timing analysis is unprecedented.

title: Introduction to the special issue
abstract: This special issue of TECS is dedicated to a digest of the best papers for the ACM Conference on Languages, Compilers, and Tools for Embedded Systems 2003 (LCTES’03) with sponsorship from SIGPLAN and, since 2004, also from SIGBED. The conference has matured to one of the top high-quality academic venues on embedded systems with a competitive acceptance rate of 23% in 2003. The conference attracts papers on topics ranging from hardware enhancements of embedded architectures over compilation, system development, and analysis tools to modeling of embedded systems. The four papers presented in this issue are extensions of the authors’ conference contributions. The first paper, Dynamic Coalescing for 16-bit Instructions by Arvind Krishnaswamy and Rajiv Gupta, proposes a minor architectural extension to the ARM processor architecture to allow the native 32-bit ARM instructions to be interspersed with the smaller 16-bit Thumb instructions supported by the processor. The authors use compilation techniques to fold two Thumb instruction into a single equivalent ARM instruction, thereby reducing the number of cycles required for execution. They demonstrate that their technique can result both in performance improvements and potentially reduced energy consumption. The second paper, The Implementation and Evaluation of Dynamic Code Decompression using DISE by Marc L. Corliss, E. Christopher Lewis, and Amir Roth, promotes code compression techniques combined with programmable hardware support for postfetch time decompression using their so-called dynamic instruction stream editing (DISE) technique. Special instructions in the application code can reprogram the DISE engine by specifying patterns and parameters for patterns. Once programmed, instruction fetches consisting of compressed code are expanded upon a match. Benefits of this technique are in a significant reduction in code size, improved performance and, to some extend, lower energy consumption. The third paper, Memory Safety Without Runtime Checks or Garbage Collection by Dinakar Dhurajti, Sumant Kowshik, Vikram Adve, and Chris Lattner, describes a set of methods to ensure memory safety without requiring run-time support or user annotations. The idea is to restrict the C language such that a combination of compilation techniques and type-sensitive pool-based memory allocation ensures safe program execution. As a result, array bound checks and null pointer checks can also be removed without risking to violate program semantics. Experimental results demonstrate the applicability of these techniques to a number of C benchmarks. The fourth paper, Schedulability-Driven Frame Packing for MultiCluster Distributed Embedded Systems by Paul Pop, Eles Petru, and Peng Zebo, focuses on packet scheduling for distributed real-time systems. The authors consider timing constraints on packet delivery across a gateway connecting two distinct processor clusters, one that is connected by an event-triggered network using CSMA and another that is connected by a time-triggered architecture using

title: 2006 WCET Preface - Proceedings of the 6th Intl. Workshop on Worst-Case Execution Time Analysis (WCET'06)
abstract: On the 4th of July, 2006, the 6th International Workshop onWorst-Case Execution Time Analysis (WCET'06) 
was held in Dresden, Germany, co-located with the 18th Euromicro International Conference on Real-Time 
Systems (ECRTS'06), both with support of Euromicro Technical Committee. The goal of the workshop was 
to bring together people from academia, tool vendors and users in industry that are interested in all aspects 
of timing analysis for real-time systems. The workshop provided a relaxed forum to present and discuss 
new ideas, new research directions, and to review current trends in this area. The workshop was based on 
short presentations that should encourage discussion by the attendees.

title: MOLAR: adaptive runtime support for high-end computing operating and runtime systems
abstract: MOLAR is a multi-institutional research effort that concentrates on adaptive, reliable, and efficient operating and runtime system (OS/R) solutions for ultra-scale high-end scientific computing on the next generation of supercomputers. This research addresses the challenges outlined in FAST-OS (forum to address scalable technology for runtime and operating systems) and HECRTF (high-end computing revitalization task force) activities by exploring the use of advanced monitoring and adaptation to improve application performance and predictability of system interruptions, and by advancing computer reliability, availability and serviceability (RAS) management systems to work cooperatively with the OS/R to identify and preemptively resolve system issues. This paper describes recent research of the MOLAR team in advancing RAS for high-end computing OS/Rs.

title: Proactive process-level live migration in HPC environments
abstract: As the number of nodes in high-performance computing environments keeps increasing, faults are becoming common place. Reactive fault tolerance (FT) often does not scale due to massive I/O requirements and relies on manual job resubmission. This work complements reactive with proactive FT at the process level. Through health monitoring, a subset of node failures can be anticipated when one's health deteriorates. A novel process-level live migration mechanism supports continued execution of applications during much of processes migration. This scheme is integrated into an MPI execution environment to transparently sustain health-inflicted node failures, which eradicates the need to restart and requeue MPI jobs. Experiments indicate that 1-6.5 seconds of prior warning are required to successfully trigger live process migration while similar operating system virtualization mechanisms require 13-24 seconds. This self-healing approach complements reactive FT by nearly cutting the number of checkpoints in half when 70% of the faults are handled proactively.

title: Improving WCET by optimizing worst-case paths
abstract: It is advantageous to perform compiler optimizations to lower the WCET of a task 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 much effort to develop compiler optimizations to improve these paths in order to reduce average-case execution time. In this paper we describe our approach to reduce WCET by adapting and applying optimizations designed for frequent paths to the worst-case paths in an application. Our compiler uses feedback from our 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 before committing to a code size increase. We evaluate a number of WC path optimizations and present results showing the decrease in WCET versus the increase in code size.

title: Penumbra: an Eclipse plugin for introductory programming
abstract: Eclipse is a full-featured and easily extensible integrated development environment. As such, it has grown to include a large degree of functionality that may be overwhelming to the novice programmer. Nevertheless, we believe Eclipse is an environment that students of programming will come to find useful and empowering once they become familiar with it. The trick is easing them into using Eclipse without them feeling overwhelmed at the outset. Penumbra is an Eclipse plug-in developed at Purdue University for use in our introductory programming classes. It is intended to ease the transition to use of the full-featured functionality of Eclipse. Penumbra presents an Eclipse perspective that hides all but the basic actions of Eclipse's existing Java perspective, while packaging elements of other perspectives (e.g., the CVS perspective) into simpler actions that ease the downloading and turn-in of programming assignments, and adding new code views inspired by other environments for introductory programmers. Our experiences using Eclipse with a small group of introductory programming students in the Spring of 2003 have guided the development of Penumbra, which is now being rolled out for general use by the full class of 230 students in the Fall of 2003.