Schedulers for BGW Tasks to Guarantee Quality of Service of Embedded Real-Time Systems

International audienceWe present a new task model called BGW for preemptable, periodic task sets, scheduled on a uniprocessor embedded platform. The tasks may be subject to faults and the processor may be overloaded. According to BGW, any Black job has to execute a primary algorithm before deadline, any Grey job may execute either the primary or the backup algorithm and any White job may be discarded. We describe several Earliest Deadline First (EDF) based scheduling frameworks suitable for this model. We also present and discuss the results of experiments that compare the EDF scheduler applied to conventional Liu and Layland task sets to various schedulers applied to BGW task sets. The Quality of Service is observed through metrics including ratio of deadline success, preemption rate, etc

Assessing Molecular Signature for Some Potential Date (Phoenix dactylifera L.) Cultivars from Saudi Arabia, Based on Chloroplast DNA Sequences rpoB and psbA-trnH

Phoenix dactylifera L. (date palm), being economically very important, is widely cultivated in the Middle East and North Africa, having about 400 different cultivars. Assessment of date cultivars under trading and farming is a widely accepted problem owing to lack of a unique molecular signature for specific date cultivars. In the present study, eight different cultivars of dates viz., Khodry, Khalas, Ruthana, Sukkari, Sefri, Segae, Ajwa and Hilali were sequenced for rpoB and psbA-trnH genes and analyzed using bioinformatics tools to establish a cultivar-specific molecular signature. The combined aligned data matrix was of 1147 characters, of which invariable and variable sites were found to be 958 and 173, respectively. The analysis clearly reveals three major groups of these cultivars: (i) Khodary, Sefri, Ajwa, Ruthana and Hilali (58% BS); (ii) Sukkari and Khalas (64% BS); and (iii) Segae. The economically most important cultivar Ajwa showed similarity with Khodary and Sefri (67% BS).The sequences of the date cultivars generated in the present study showed bootstrap values between 38% and 70% so these sequences could be carefully used as molecular signature for potential date cultivars under trading and selection of genuine cultivars at the seedling stage for farming

BGW: New task model for overloaded real time systems: Ordonnancement monoprocesseur

Real-time embedded systems are found in variousapplication domains. They have to offer an increasingnumber of functionalities and to provide the highestQuality of Service despite possible failures due tofaults or processing overloads. In such systems,programs are characterized by upper bounds onfinishing times and the QoS is assessed by the ratio ofsuccessful deadlines. In this thesis, we deal with thisissue. We focus on a uniprocessor architecture in theframework of a firm real-time application that acceptsdeadline missing under some specified limits. Tasksare assumed to be periodic. Our first contribution liesin the proposition of a novel model for tasks which iscalled BGW model. It is drawn from two approachesrespectively known as the skip-over model and theDeadline Mechanism. The first one provides timingfault-tolerance through passive dynamic softwareredundancy with two versions. The second one copeswith transient processing overloads by discardinginstances of the periodic tasks in a controlled andpre-specified way. We give a feasibility test for thismodel. In a second part, we describe the behavior ofdynamic priority schedulers based on EDF (EarliestDeadline First) for BGW task sets. A performanceanalysis is reported which is mainly related to QoSevaluation and measurement of overheads (complexityof the scheduler). The following contribution concernsmore sophisticated schedulers that permit to enhancethe QoS as to improve service balancing.Les systèmes temps-réel embarqués se retrouventdans des domaines d’application très variés :avionique, automobile, environnement, santé, etc. Ilsdoivent offrir un nombre croissant de fonctionnalités etfournir un niveau maximal de Qualité de Service (QdS)et ce, malgré des défaillances liées à l’occurrence defautes ou de surcharges de traitement. Pour ce typede système informatique, la QdS se mesureprincipalement en termes d’échéances respectées carles programmes sont caractérisés par des dates de find’exécution au plus tard. Dans cette thèse, nousconsidérons une architecture monoprocesseur pourune application temps réel dite ferme. La premièrecontribution tient dans la proposition d’un nouveaumodèle de tâche appelé BGW qui permet de spécifierla nature de ses contraintes temporelles. Ce modèleest tiré des deux approches Skip-Over et DeadlineMechanism. La première est dédiée à la gestion dessurcharges de traitement par la perte contrôlée decertaines instances de tâches. La seconde est unetechnique de tolérance aux fautes temporelles baséesur de la redondance logicielle dynamique passiveavec deux versions. Dans une seconde partie, nousproposons de nouveaux ordonnanceurs temps réelbasés sur EDF (Earliest Deadline First) pour destâches BGW. Nous montrons comment maximiser laQdS tout en tenant compte des critères d’équité deservice. Une étude de performance en termes de QdSet d’overheads conforte nos propositions

Le modèle BGW pour les systèmes temps réel surchargés : Ordonnancement monoprocesseur

Real-time embedded systems are found in various application domains. They have to offer an increasing number of functionalities and to provide the highest Quality of Service despite possible failures due to faults or processing overloads. In such systems, programs are characterized by upper bounds on finishing times and the QoS is assessed by the ratio of successful deadlines. In this thesis, we deal with this issue. We focus on a uniprocessor architecture in the framework of a firm real-time application that accepts deadline missing under some specified limits. Tasks are assumed to be periodic. Our first contribution lies in the proposition of a novel model for tasks which is called BGW model. It is drawn from two approaches respectively known as the skip-over model and the Deadline Mechanism. The first one provides timing fault-tolerance through passive dynamic software redundancy with two versions. The second one copes with transient processing overloads by discarding instances of the periodic tasks in a controlled and pre-specified way. We give a feasibility test for this model. In a second part, we describe the behavior of dynamic priority schedulers based on EDF (Earliest Deadline First) for BGW task sets. A performance analysis is reported which is mainly related to QoS evaluation and measurement of overheads (complexity of the scheduler). The following contribution concerns more sophisticated schedulers that permit to enhance the QoS as to improve service balancing.Les systèmes temps-réel embarqués se retrouvent dans des domaines d’application très variés : avionique, automobile, environnement, santé, etc. Ils doivent offrir un nombre croissant de fonctionnalités et fournir un niveau maximal de Qualité de Service (QdS) et ce, malgré des défaillances liées à l’occurrence de fautes ou de surcharges de traitement. Pour ce type de système informatique, la QdS se mesure principalement en termes d’échéances respectées car les programmes sont caractérisés par des dates de fin d’exécution au plus tard. Dans cette thèse, nous considérons une architecture monoprocesseur pour une application temps réel dite ferme. La première contribution tient dans la proposition d’un nouveau modèle de tâche appelé BGW qui permet de spécifier la nature de ses contraintes temporelles. Ce modèle est tiré des deux approches Skip-Over et Deadline Mechanism. La première est dédiée à la gestion des surcharges de traitement par la perte contrôlée de certaines instances de tâches. La seconde est une technique de tolérance aux fautes temporelles basée sur de la redondance logicielle dynamique passive avec deux versions. Dans une seconde partie, nous proposons de nouveaux ordonnanceurs temps réel basés sur EDF (Earliest Deadline First) pour des tâches BGW. Nous montrons comment maximiser la QdS tout en tenant compte des critères d’équité de service. Une étude de performance en termes de QdS et d’overheads conforte nos propositions

BGW: A Novel QoS Model for Firm Real-time Computing Systems

Abstract—Tasks in a real-time computing systems are commonly periodic. Each job generated by the invocation of a periodic task has normally a deadline constraint by which it must complete its execution in all circumstances. However, the hardware may be subject to failures, faults may be present in software, energy to supply the system may be depleted and the processor may be overloaded transiently. Any of these exceptions involves a situation where it is no longer possible to meet the deadlines of all the jobs in the application. In this paper, we discuss a general model for the application task set that permits the operating system to correctly manage the above emergency situations in accordance with specific parameters statically attached to every task in addition to its classical timing parameters. The model is inspired by the wellknown Deadline Mechanism and Skip-Over model. We introduce the BGW model where each job of any periodic task can get one of the three colours Black, Grey and White. A colour specifies that the job has to imperatively execute the primary version, the job has to execute at least one version among primary and alternate or the job may be discarded. We briefly discuss implementation issues for this new model. I