Nowadays, computer systems are everywhere. From simple portable devices such as watches and MP3 players to large stationary installations that control nuclear power plants, computer systems are now present in all aspects of our modern and every-day life. In about only 70 years, they have completely perturbed our way of life and they reached a so high degree of sophistication that they will be soon capable of driving our cars and cleaning our houses without any human intervention. As computer systems gain in responsibilities, it becomes essential that they provide both safety and reliability. Indeed, a failure in systems such as the anti-lock braking system (ABS) in cars could threaten human lives and generate catastrophic and irreversible consequences. Hence, for many years, researchers have addressed these emerging problems of system safety and reliability which come along with this fulgurant evolution. This thesis provides a general overview of embedded real-time computer systems, i.e., a particular kind of computer system whose number grows daily. We provide the reader with some preliminary knowledge and a good understanding of the concepts that underlie this emerging technology. We focus especially on the theoretical problems related to the real-time issue and briefly summarizes the main solutions, together with their advantages and drawbacks. This brings the reader through all the conceptual layers constituting a computer system, from the software level---the logical part---that specifies both the system behavior and requirements to the hardware level---the physical part---that actually performs the expected treatments and reacts to the environment. In the meanwhile, we introduce the theoretical models that allow researchers for theoretical analyses which ensure that all the system requirements are fulfilled. Finally, we address the energy consumption problem in embedded systems. We describe the various factors of power dissipation in modern technologies and we introduce different solutions to reduce this consumption./Cette thèse se focalise sur un type de systèmes informatiques bien précis appelés “systèmes embarqués temps réel”. Un système est dit “embarqué” lorsqu’il est développé afin de servir un but bien précis. Un téléphone portable est un parfait exemple de système embarqué étant donné que toutes ses fonctionnalités sont rigoureusement définies avant même sa conception. Au contraire, un ordinateur personnel n’est généralement pas considéré comme un système embarqué, les concepteurs ne sachant pas à l’avance à quelles fins il sera utilisé. Une grande partie de ces systèmes embarqués ont des contraintes temporelles très fortes, ce qui les distingue encore plus des ordinateurs grand public. A titre d’exemple, lorsqu’un conducteur de voiture freine brusquement, l’ordinateur de bord déclenche l’application ABS et il est primordial que cette application soit traitée endéans une courte échéance. Autrement dit, cette fonctionnalité ABS doit être traitée prioritairement par rapport aux autres fonctionnalités du véhicule. Ce type de système embarqué est alors dit “temps réel”, dû à ces notions de temps et de priorités entre les applications. La problèmatique posée par les systèmes temps réel est la suivante. Comment déterminer, à tout moment, un ordre d’exécution des différentes fonctionnalités de telle sorte qu’elles soient toutes exécutées entièrement endéans leur échéance ? De plus, avec l’apparition récente des systèmes multiprocesseurs, cette problématique s’est fortement complexifiée, vu que le système doit à présent déterminer quelle fonctionnalité s’exécute à quel moment sur quel processeur afin que toutes les contraintes temporelles soient respectées. Pour finir, ces systèmes embarqués temp réel multiprocesseurs se sont rapidement retrouvés confrontés à un problème de consommation d’énergie. Leur demande en terme de performance (et donc en terme d’énergie) à évolué beaucoup plus rapidement que la capacité des batteries qui les alimentent. Ce problème est actuellement rencontré par de nombreux systèmes, tels que les téléphones portables par exemple. L’objectif de cette thèse est de parcourir les différents composants de tels système embarqués et de proposer des solutions afin de réduire leur consommation d’énergie.

In this thesis, we study temperature-constrained multiprocessor real-time systems, where real-time guarantees must be met without exceeding safe temperature levels within the processors. We focus on Pfair scheduling algorithms, especially ERfair scheduling scheme (a work-conserving extension to Pfair scheduling) as our main multiprocessor real-time scheduling methodology. Then, we study the benefits of simple reactive speed scaling as described in the real-time multiprocessor systems. In this thesis, in support of the temperature-awareness, we extend the applicability of the reactive speed scaling to global scheduling schemes for multiprocessors. We propose temperature-aware scheduling and processor selection schemes motivated by existing (thermally non-optimal) ERfair scheduling in order to reduce thermal stress and therefore increase the processor utilization. Then, we show that the proposed algorithm and reactive scheme can enhance the processor utilization compared with any constant speed scheme on real-time multiprocessor systems. Additionally, we show how the maximum schedulable utilization (MSU) for partitioning heuristics can be determined on the temperature-constrained multiprocessor real-time systems.

abstract: A principal goal of this dissertation is to study stochastic optimization and real-time scheduling in cyber-physical systems (CPSs) ranging from real-time wireless systems to energy systems to distributed control systems. Under this common theme, this dissertation can be broadly organized into three parts based on the system environments. The first part investigates stochastic optimization in real-time wireless systems, with the focus on the deadline-aware scheduling for real-time traffic. The optimal solution to such scheduling problems requires to explicitly taking into account the coupling in the deadline-aware transmissions and stochastic characteristics of the traffic, which involves a dynamic program that is traditionally known to be intractable or computationally expensive to implement. First, real-time scheduling with adaptive network coding over memoryless channels is studied, and a polynomial-time complexity algorithm is developed to characterize the optimal real-time scheduling. Then, real-time scheduling over Markovian channels is investigated, where channel conditions are time-varying and online channel learning is necessary, and the optimal scheduling policies in different traffic regimes are studied. The second part focuses on the stochastic optimization and real-time scheduling involved in energy systems. First, risk-aware scheduling and dispatch for plug-in electric vehicles (EVs) are studied, aiming to jointly optimize the EV charging cost and the risk of the load mismatch between the forecasted and the actual EV loads, due to the random driving activities of EVs. Then, the integration of wind generation at high penetration levels into bulk power grids is considered. Joint optimization of economic dispatch and interruptible load management is investigated using short-term wind farm generation forecast. The third part studies stochastic optimization in distributed control systems under different network environments. First, distributed spectrum access in cognitive radio networks is investigated by using pricing approach, where primary users (PUs) sell the temporarily unused spectrum and secondary users compete via random access for such spectrum opportunities. The optimal pricing strategy for PUs and the corresponding distributed implementation of spectrum access control are developed to maximize the PU's revenue. Then, a systematic study of the nonconvex utility-based power control problem is presented under the physical interference model in ad-hoc networks. Distributed power control schemes are devised to maximize the system utility, by leveraging the extended duality theory and simulated annealing. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

The resource demand on embedded devices is constantly growing. This is caused by the sheer explosion of software based functions in embedded systems, that are growing far faster than the resources of the single-core and multi-core embedded processors. As one of the limitation is the computing power of the processors we need to explore ways to use this resource more efficiently. We identified that during the run-time of the embedded devices the resource demand of the software functions is permanently changing dependent on the device situation. To enable an embedded device to take advantage of this dynamic resource demand, the allocation of the software functions to the processor must be handled by a scheduler that is able to evaluate the resource demand of the software functions in relation to the device situation. This marks a change in embedded devices from static defined software systems to dynamic software systems. Above that we can increase the efficiency even further by extending the approach from a single device to a distributed or networked system (many-core system). However, existing approaches to deal with dynamic resource allocation are focused on individual devices and leave the optimization potential of manycore systems untouched. Our concept will extend the existing Hierarchical Asynchronous Multi-Core Scheduler (HAMS) concept for individual devices to many-core systems. This extension introduces a dynamic situation aware scheduler for many-core systems which take the current workload of all devices and the system-situation into account. With our approach, the resource efficiency of an embedded many-core system can be increased. The following paper will explain the architecture and the expected results of our concept.

Catering to society’s demand for high performance computing, billions of transistors are now integrated on IC chips to deliver unprecedented performances. With increasing transistor density, the power consumption/density is growing exponentially. The increasing power consumption directly translates to the high chip temperature, which not only raises the packaging/cooling costs, but also degrades the performance/reliability and life span of the computing systems. Moreover, high chip temperature also greatly increases the leakage power consumption, which is becoming more and more significant with the continuous scaling of the transistor size. As the semiconductor industry continues to evolve, power and thermal challenges have become the most critical challenges in the design of new generations of computing systems. In this dissertation, we addressed the power/thermal issues from the system-level perspective. Specifically, we sought to employ real-time scheduling methods to optimize the power/thermal efficiency of the real-time computing systems, with leakage/ temperature dependency taken into consideration. In our research, we first explored the fundamental principles on how to employ dynamic voltage scaling (DVS) techniques to reduce the peak operating temperature when running a real-time application on a single core platform. We further proposed a novel real-time scheduling method, “M-Oscillations” to reduce the peak temperature when scheduling a hard real-time periodic task set. We also developed three checking methods to guarantee the feasibility of a periodic real-time schedule under peak temperature constraint. We further extended our research from single core platform to multi-core platform. We investigated the energy estimation problem on the multi-core platforms and developed a light weight and accurate method to calculate the energy consumption for a given voltage schedule on a multi-core platform. Finally, we concluded the dissertation with elaborated discussions of future extensions of our research.

Wurden früher Data-Warehouse-Systeme meist nur zur Datenanalyse für die Entscheidungsunterstützung des Managements eingesetzt, haben sie sich nunmehr zur zentralen Plattform für die integrierte Informationsversorgung eines Unternehmens entwickelt. Dies schließt vor allem auch die Einbindung des Data-Warehouses in operative Prozesse mit ein, für die zum einen sehr aktuelle Daten benötigt werden und zum anderen eine schnelle Anfrageverarbeitung gefordert wird. Daneben existieren jedoch weiterhin klassische Data-Warehouse-Anwendungen, welche hochqualitative und verfeinerte Daten benötigen. Die Anwender eines Data-Warehouse-Systems haben somit verschiedene und zum Teil konfligierende Anforderungen bezüglich der Datenaktualität, der Anfragelatenz und der Datenstabilität. In der vorliegenden Dissertation wurden Methoden und Techniken entwickelt, die diesen Konflikt adressieren und lösen. Die umfassende Zielstellung bestand darin, eine Echtzeit-Data-Warehouse-Architektur zu entwickeln, welche die Informationsversorgung in seiner ganzen Breite -- von historischen bis hin zu aktuellen Daten -- abdecken kann. Zunächst wurde ein Verfahren zur Ablaufplanung kontinuierlicher Aktualisierungsströme erarbeitet. Dieses berücksichtigt die widerstreitenden Anforderungen der Nutzer des Data-Warehouse-Systems und erzeugt bewiesenermaßen optimale Ablaufpläne. Im nächsten Schritt wurde die Ablaufplanung im Kontext mehrstufiger Datenproduktionsprozesse untersucht. Gegenstand der Analyse war insbesondere, unter welchen Bedingungen eine Ablaufplanung in Datenproduktionsprozessen gewinnbringend anwendbar ist. Zur Unterstützung der Analyse komplexer Data-Warehouse-Prozesse wurde eine Visualisierung der Entwicklung der Datenzustände, über die Produktionsprozesse hinweg, vorgeschlagen. Mit dieser steht ein Werkzeug zur Verfügung, mit dem explorativ Datenproduktionsprozesse auf ihr Optimierungspotenzial hin untersucht werden können. Das den operativen Datenänderungen unterworfene Echtzeit-Data-Warehouse-System führt in der Berichtsproduktion zu Inkonsistenzen. Daher wurde eine entkoppelte und für die Anwendung der Berichtsproduktion optimierte Datenschicht erarbeitet. Es wurde weiterhin ein Aggregationskonzept zur Beschleunigung der Anfrageverarbeitung entwickelt. Die Vollständigkeit der Berichtsanfragen wird durch spezielle Anfragetechniken garantiert. Es wurden zwei Data-Warehouse-Fallstudien großer Unternehmen vorgestellt sowie deren spezifische Herausforderungen analysiert. Die in dieser Dissertation entwickelten Konzepte wurden auf ihren Nutzen und ihre Anwendbarkeit in den Praxisszenarien hin überprüft.:1 Einleitung 1 2 Fallstudien 7 2.1 Fallstudie A: UBS AG . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 Unternehmen und Anwendungsdomäne . . . . . . . . . . . . 8 2.1.2 Systemarchitektur . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3 Besonderheiten und Herausforderungen . . . . . . . . . . . . 13 2.2 Fallstudie B: GfK Retail and Technology . . . . . . . . . . . . . . . . 15 2.2.1 Unternehmen und Anwendungsdomäne . . . . . . . . . . . . 15 2.2.2 Systemarchitektur . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2.3 Besonderheiten und Herausforderungen . . . . . . . . . . . . 20 3 Evolution der Data-Warehouse- Systeme und Anforderungsanalyse 23 3.1 Der Data-Warehouse-Begriff und Referenzarchitektur . . . . . . . . . 23 3.1.1 Definition des klassischen Data-Warehouse-Begriffs . . . . . . 23 3.1.2 Referenzarchitektur . . . . . . . . . . . . . . . . . . . . . . . 24 3.2 Situative Datenanalyse . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.2.1 Interaktion zwischen IT und Fachbereich . . . . . . . . . . . 31 3.2.2 Spreadmart-Lösungen . . . . . . . . . . . . . . . . . . . . . . 33 3.2.3 Analytische Mashups und dienstorientierte Architekturen . . 35 3.2.4 Werkzeuge und Methoden im Kostenvergleich . . . . . . . . . 40 3.3 Evolution der Data-Warehouse-Systeme . . . . . . . . . . . . . . . . 40 3.3.1 Nutzung von Data-Warehouse-Systemen . . . . . . . . . . . . 41 3.3.2 Entwicklungsprozess der Hardware- und DBMS-Architekturen 46 3.4 Architektur eines Echtzeit-Data-Warehouse . . . . . . . . . . . . . . 50 3.4.1 Der Echtzeit-Begriff im Data-Warehouse-Umfeld . . . . . . . 50 3.4.2 Architektur eines Echtzeit-Data-Warehouses . . . . . . . . . . 51 3.4.3 Systemmodell . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3.5 Anforderungen an ein Echtzeit-Data-Warehouse . . . . . . . . . . . . 55 3.5.1 Maximierung der Datenaktualität . . . . . . . . . . . . . . . 55 3.5.2 Minimierung der Anfragelatenz . . . . . . . . . . . . . . . . . 56 3.5.3 Erhalt der Datenstabilität . . . . . . . . . . . . . . . . . . . . 57 4 Datenproduktionssteuerung in einstufigen Systemen 59 4.1 Qualitätskriterien und Systemmodell . . . . . . . . . . . . . . . . . . 59 4.1.1 Dienstqualitätskriterien . . . . . . . . . . . . . . . . . . . . . 60 4.1.2 Datenqualitätskriterien . . . . . . . . . . . . . . . . . . . . . 63 4.1.3 Multikriterielle Optimierung . . . . . . . . . . . . . . . . . . 64 4.1.4 Workload- und Systemmodell . . . . . . . . . . . . . . . . . . 66 4.2 Multikriterielle Ablaufplanung . . . . . . . . . . . . . . . . . . . . . 68 4.2.1 Pareto-effiziente Ablaufpläne . . . . . . . . . . . . . . . . . . 68 4.2.2 Abbildung auf das Rucksackproblem . . . . . . . . . . . . . . 71 4.2.3 Lösung mittels dynamischer Programmierung . . . . . . . . . 74 4.3 Dynamische Ablaufplanung zur Laufzeit . . . . . . . . . . . . . . . . 78 4.4 Selektionsbasierte Ausnahmebehandlung . . . . . . . . . . . . . . . . 81 4.5 Evaluierung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.5.1 Experimentierumgebung . . . . . . . . . . . . . . . . . . . . . 84 4.5.2 Leistungsvergleich und Adaptivität . . . . . . . . . . . . . . . 86 4.5.3 Laufzeit- und Speicherkomplexität . . . . . . . . . . . . . . . 87 4.5.4 Änderungsstabilität . . . . . . . . . . . . . . . . . . . . . . . 89 4.6 Zusammenfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5 Bewertung von Ladestrategien in mehrstufigen Datenproduktionsprozessen 5.1 Ablaufplanung in mehrstufigen Datenproduktionsprozessen . . . . . 96 5.1.1 Ladestrategien und Problemstellung . . . . . . . . . . . . . . 97 5.1.2 Evaluierung und Diskussion . . . . . . . . . . . . . . . . . . . 98 5.2 Visualisierung der Datenqualität in mehrstufigen Datenproduktionsprozessen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 5.2.1 Erfassung und Speicherung . . . . . . . . . . . . . . . . . . . 110 5.2.2 Visualisierung der Datenqualität . . . . . . . . . . . . . . . . 111 5.2.3 Prototypische Umsetzung . . . . . . . . . . . . . . . . . . . . 114 5.3 Zusammenfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 6 Konsistente Datenanalyse in operativen Datenproduktionsprozessen 119 6.1 Der Reporting-Layer als Basis einer stabilen Berichtsproduktion . . 120 6.1.1 Stabilität durch Entkopplung . . . . . . . . . . . . . . . . . . 120 6.1.2 Vorberechnung von Basisaggregaten . . . . . . . . . . . . . . 121 6.1.3 Vollständigkeitsbestimmung und Nullwertsemantik . . . . . . 125 6.1.4 Datenhaltung . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 6.1.5 Prozess der Anfrageverarbeitung mit Vollständigkeitsbestimmung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 6.1.6 Verwandte Arbeiten und Techniken . . . . . . . . . . . . . . . 127 6.1.7 Evaluierung . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 6.2 Nullwertkomprimierung . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.2.1 Einleitendes Beispiel und Vorbetrachtungen . . . . . . . . . . 134 6.2.2 Nullwertkomprimierung . . . . . . . . . . . . . . . . . . . . . 136 6.2.3 Anfrageverarbeitung auf nullwertkomprimierten Daten . . . . 143 6.2.4 Verwandte Arbeiten und Techniken . . . . . . . . . . . . . . . 146 6.2.5 Evaluierung . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 6.3 Zusammenfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 7 Zusammenfassung und Ausblick 157 Literaturverzeichnis 161 Online-Quellenverzeichnis 169 Abbildungsverzeichnis 173

Une séparation existe de longue date entre les domaines de la compilation et de l'ordonnancement temps-réel. Si ces deux domaines ont le même objectif - la construction d'implantations correctes - la séparation se justifie historiquement par des différences significatives entre les modèles et les méthodes utilisés. Cependant, avec la complexification des applications et du materiel qui les exécute, les problèmes étudiés dans ces deux domaines se confondent désormais largement. Dans cette thèse, nous nous concentrons sur la génération automatique de code pour des systèmes de contrôle embarqué incluant des contraintes complexes (notamment temps-réel). A ces fins, nous défendons l'idée qu'il est profitable de fournir un effort commun de recherche entre ces deux communautés. En adaptant une technique de compilation au problème d'ordonnancement temps réel d'applications sur des architectures multiprocessurs, nous montrons à la fois les difficultés inhérentes à cet effort commun, mais aussi les possibles avancées qu'il porte. En effet, nous montrons que l'adaptation de techniques d'optimisation à de nouveaux objectifs, dans un contexte différent facilite le développement de systèmes de meilleure qualité. Nous proposons d'utiliser les formalismes et langages synchrones comme base formelle commune dans ce travail d'adaptation. Ceux-cis étendent naturellement les modèles classiques utilisés pour l'ordonnancement temps réel (graphes de tâches dépendentes) et la compilation (SSA et graphes de dépendence de données), et fournissent également des techniques efficaces pour la manipulation de structures de contrôle complexes. Nous avons implanté nos résultats dans le compilateur LoPhT. / There is a long standing separation between the fields of compiler construction and real-time scheduling. While both fields have the same objective - the construction of correct implementations – the separation was historically justified by significant differences in the models and methods that were used. Nevertheless, with the ongoing complexification of applications and of the hardware of the execution platforms, the objects and problems studied in these two fields are now largely overlapping. In this thesis, we focus on the automatic code generation for embedded control systems with complex constraints, including hard real-time requirements. To this purpose, we advocate the need for a reconciled research effort between the communities of compilation and real-time systems. By adapting a technique usually used in compilers (software pipelining) to the system-level problem of multiprocessor scheduling of hard real-time applications, we shed light on the difficulties of this unified research effort, but also show how it can lead to real advances. Indeed we explain how adapting techniques for the optimization of new objectives, in a different context, allows us to develop more easily systems of better quality than what was done until now. In this adaptation process, we propose to use synchronous formalisms and languages as a common formal ground. These can be naturally seen as extensions of classical models coming from both real-time scheduling (dependent task graphs) and compilation (single static assignment and data dependency graphs), but also provide powerful techniques for manipulating complex control structures. We implemented our results in the LoPhT compiler.

Typically, a real-time system consists of a controlling system (i.e., a computer) and a controlled system (i.e., the environment). Real-time systems are those systems where correctness depends on two aspects: i) the logical result of computation and, ii) the time in which results are produced. It is essential to guarantee meeting timing constraints for this kind of systems to operate correctly. Missing deadlines in many cases -- in so-called hard real-time systems -- is associated with economic loss or loss of human lives and must be avoided under all circumstances. On the other hand, there is a trend towards consolidating software functions onto fewer processors in different domains such as automotive systems and avionics with the aim of reducing costs and complexity. Hence, applications with different levels of criticality that used to run in isolation now start sharing processors. As a result, there is a need for techniques that allow designing such mixed-criticality (MC) systems -- i.e., real-time systems combining different levels of criticality -- and, at the same time, complying with certification requirements in the different domains. In this research, we study the problem of scheduling MC tasks under EDF (Earliest Deadline First) and propose new approaches to improve scheduling techniques. In particular, we consider that a mix of low-criticality (LO) and high-criticality (HI) tasks are scheduled on one processor. While LO tasks can be modeled by minimum inter-arrival time, deadline, and worst-case execution time (WCET), HI tasks are characterized by two WCET parameters: an optimistic and a conservative one. Basically, the system operates in two modes: LO and HI mode. In LO mode, HI tasks run for no longer than their optimistic execution budgets and are scheduled together with the LO tasks. The system switches to HI mode when one or more HI tasks run for more than their conservative execution budgets. In this case, LO tasks are immediately discarded so as to be able of accommodating the increase in HI execution demand. We propose an exact test for mixed-criticality EDF, which increases efficiency and reliability when compared with the existing approaches from the literature. On this basis, we further derive approximated tests with less complexity and, hence, a reduced running time that makes them more suitable for online checks.:Contents 1. Introduction 1 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2. Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Structure of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Concepts, Models and Assumptions 7 2.1. Real-Time Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1. Tasks Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2. Scheduling Policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.1. Feasibility versus Schedulability . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2. Schedulability Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3. Mixed-Criticality Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.4. Basic Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.5. The Earliest Deadline First Algorithm . . . . . . . . . . . . . . . . . . . . . . 13 2.5.1. EDF-VD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.5.2. Mixed-Criticality EDF . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.5.3. Demand Bound Function . . . . . . . . . . . . . . . . . . . . . . . . . 16 3. Related Work 17 3.1. Uniprocessor Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1.1. Uniprocessor Scheduling Based on EDF . . . . . . . . . . . . . . . . . 18 3.2. Multiprocessor Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2.1. Multiprocessor Scheduling Based on EDF . . . . . . . . . . . . . . . . 20 4. Introducing Utilization Caps 23 4.1. Introducing Utilization Caps . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.1.1. Fixed utilization caps . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 4.1.2. Optimized utilization caps . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.2. Findings of this Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5. Bounding Execution Demand under Mixed-Criticality EDF 29 5.1. Bounding Execution Demand . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 5.2. Analytical Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 5.2.1. The GREEDY Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . 35 5.2.2. The ECDF Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.3. Finding Valid xi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 5.4. Findings of this Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 6. Approximating Execution Demand Bounds 41 6.1. Applying Approximation Techniques . . . . . . . . . . . . . . . . . . . . . . . 41 6.2. Devi’s Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 6.2.1. Per-task deadline scaling . . . . . . . . . . . . . . . . . . . . . . . . . . 42 6.2.2. Uniform deadline scaling . . . . . . . . . . . . . . . . . . . . . . . . . . 44 6.2.3. Complexity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 6.3. Findings of this Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 7. Evaluation and Results 49 7.1. Mixed-Criticality EDF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.2. Obtaining Test Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.2.1. The Case Di = Ti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.2.2. The Case Di ≤ Ti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 7.3. Weighted schedulability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 7.4. Algorithms in this Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . 51 7.4.1. The EDF-VD and DEDF-VD Algorithms . . . . . . . . . . . . . . . . 51 7.4.2. The GREEDY algorithm . . . . . . . . . . . . . . . . . . . . . . . . . 52 7.4.3. The ECDF algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 7.5. Evaluation of Utilization Caps . . . . . . . . . . . . . . . . . . . . . . . . . . 53 7.5.1. 10 tasks per task set . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 7.5.2. 20 tasks per task set . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 7.5.3. 50 tasks per task set . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 7.5.4. Comparison of runtime . . . . . . . . . . . . . . . . . . . . . . . . . . 59 7.6. Evaluation of Execution Demand Bounds . . . . . . . . . . . . . . . . . . . . 61 7.6.1. Comparison for sets of 10 tasks . . . . . . . . . . . . . . . . . . . . . . 61 7.6.2. Comparison for sets of 20 tasks . . . . . . . . . . . . . . . . . . . . . . 64 7.7. Evaluation of Approximation Techniques . . . . . . . . . . . . . . . . . . . . . 67 7.7.1. Schedulability curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 7.7.2. Weighted schedulability . . . . . . . . . . . . . . . . . . . . . . . . . . 69 7.7.3. Comparison of runtime . . . . . . . . . . . . . . . . . . . . . . . . . . 72 7.8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 8. Conclusion and Future Work 77 8.1. Outlook/Future Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Bibliography 83 A. Introduction 91 A.1. Multiple Levels of Criticality . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 A.1.1. Ordered mode switches . . . . . . . . . . . . . . . . . . . . . . . . . . 91 A.1.2. Unordered mode switches . . . . . . . . . . . . . . . . . . . . . . . . . 93 B. Evaluation and Results 95 B.1. Uniform Distribution for Task Periods . . . . . . . . . . . . . . . . . . . . . . 95

In this dissertation, we consider timeliness and energy optimization in battery-powered, mobile embedded real-time systems. We focus on real-time systems that operate in environments with dynamically uncertain properties, including context-dependent activity execution times and arbitrary activity arrival patterns. We consider an application model where activities are subject to time/utility function (or TUF) time constraints, mutual exclusion constraints on concurrent sharing of non-CPU resources, timeliness requirements including assurances on individual activity timeliness behavior, and system-level energy consumption requirements including a non-exhaustable energy budget. To account for uncertainties in activity properties in dynamic systems, we stochastically describe activity execution demands, and describe activity arrival behaviors using the unimodal arbitrary arrival model, which allows unbounded arrival frequencies. We consider the scheduling optimality criteria of: (1) probabilistically satisfying lower bounds on individual activities' maximal timeliness utilities, and (2) maximizing system-level energy efficiency, while ensuring that the system's energy consumption never exhausts the energy budget and resource mutual exclusion constraints are satisfied. For this multi-criteria scheduling problem, we present a DVS (dynamic voltage scaling)-based, real-time scheduling algorithm called the Energy-Bounded Utility Accrual Algorithm (or EBUA). Since the scheduling problem is NP-hard, EBUA heuristically (and dynamically) allocates CPU cycles to activities, computes activity schedules, and scales CPU voltage and frequency with a polynomial-time cost. If activities' cumulative execution demands exceed the available CPU time or may exhaust the system's energy budget, the algorithm defers and rejects jobs in a controlled fashion, minimizing system-level energy consumption and maximizing total accrued utility. We analytically establish several properties of EBUA. We prove that the algorithm never exhausts the specified energy budget. Further, we establish EBUA's timeliness optimality during under-loads, freedom from deadlocks, and correctness in mutually exclusive resource sharing. In particular, we prove that the algorithm's timeliness behavior subsumes the optimal timeliness behavior of deadline scheduling as a special case, and identify the conditions under which lower bounds on individual activity utilities are satisfied. In addition, we upper bound the time needed for mutually exclusively accessing shared resources under EBUA. We conduct experimental studies by simulating the algorithm on the DVS-enabled AMD k6 processor model, and by implementing it on QNX Neutrino 6.2.1 RTOS. Our experimental results validate our analytical results. Further, they confirm EBUA's superiority over other energy-efficient real-time scheduling algorithms on timeliness and energy consumption behaviors. / Ph. D.

In this dissertation, we consider scheduling distributed soft real-time tasks in unreliable (e.g., those with arbitrary node and network failures) and untrustworthy systems (e.g., those with Byzantine node behaviors). We present a distributed real-time scheduling algorithm called Gamma. Gamma considers a distributed (i.e., multi-node) task model where tasks are subject to Time/Utility Function (or TUF) end-to-end time constraints, and the scheduling optimality criterion of maximizing the total accrued utility. The algorithm makes three novel contributions. First, Gamma uses gossip for reliably propagating task scheduling parameters and for discovering task execution nodes. Second, Gamma achieves distributed real-time mutual exclusion in unreliable environments. Third, the algorithm guards against potential disruption of message propagation due to Byzantine attacks using a mechanism called Launcher-Attacker-Infective-Susceptible-Immunized-Removed-Consumer (or LAISIRC). By doing so, the algorithm schedules tasks with probabilistic termination-time satisfactions, despite system unreliability and untrustworthiness. We analytically establish several timeliness and non-timeliness properties of the algorithm including probabilistic end-to-end task termination time satisfactions, optimality of message overheads, mutual exclusion guarantees, and the mathematical model of the LAISIRC mechanism. We conducted simulation-based experimental studies and compared Gamma with its competitors. Our experimental studies reveal that Gamma's scheduling algorithm accrues greater utility and satisfies a greater number of deadlines than do competitor algorithms (e.g., HVDF) by as much as 47% and 45%, respectively. LAISIRC is more tolerant to Byzantine attacks than competitor protocols (e.g., Path Verification) by obtaining as much as 28% higher correctness ratio. Gamma's mutual exclusion algorithm accrues greater utility than do competitor algorithms (e.g., EDF-Sigma) by as much as 25%. Further, we implemented the basic Gamma algorithm in the Emulab/ChronOS 250-node testbed, and measured the algorithm's performance. Our implementation measurements validate our theoretical analysis and the algorithm's effectiveness and robustness. / Ph. D.