Capacity sharing and stealing in serverbased real-time systems

A dynamic scheduler that supports the coexistence of guaranteed and non-guaranteed bandwidth servers is proposed. Overloads are handled by an efficient reclaiming of residual capacities originated by early completions as well as by allowing reserved capacity stealing of non-guaranteed bandwidth servers. The proposed dynamic budget accounting mechanism ensures that at a particular time the currently executing server is using a residual capacity, its own capacity or is stealing some reserved capacity, eliminating the need of additional server states or unbounded queues. The server to which the budget accounting is going to be performed is dynamically determined at the time instant when a capacity is needed. This paper describes and evaluates the proposed scheduling algorithm, showing that it can efficiently reduce the mean tardiness of periodic jobs. The achieved results become even more significant when tasks’ computation times have a large variance

Combined scheduling of hard and soft real-time tasks in multiprocessor systems

Many complex real-time systems are composed of both hard and soft real-time tasks. Combined scheduling of hard and soft tasks in such systems should satisfy two important goals: (1) maximize the schedulability of soft real-time tasks with no or little impact on the schedulability of hard real-time tasks; (2) minimize the scheduling overhead. In this thesis, we develop two sets of algorithms for the problem, of which the first set allows sacrificing the schedulability of hard tasks and the second set does not. The first set of algorithms is based on a new concept, called task association , by which each soft task is associated with a hard task, whenever possible, in order to minimize the scheduling overhead. The second set has two algorithms, namely, background scheduling and emergency based scheduling. The background scheduling schedules soft tasks in the holes that are present in the schedule considering only the hard tasks. The emergency based scheduling always maintains two schedules (primary schedule and emergency schedule) and switches back and forth between them during the schedule construction process depending on the schedulability of a given hard task. To evaluate the schedulability of the proposed algorithms, extensive simulation studies were conducted and the results show that the proposed algorithms are superior to existing algorithms, in addition to some of them incurring lesser scheduling overhead

Reservation-based mechanisms for Mixed-Criticality Two-Wheeler Instrumentation Clusters

Electronics completely transformed the automotive industry as early vehicles were purely composed by mechanical components but the current reality is quite different. The growing acceptance for embedded electronics devices led to a significant increase in the number of microcontroller-based functions embedded in vehicles. With this increase, customer’s safety concerns raised. To ensure customers safety from the use of Electrical and Electronic (E/E) automotive equipment and systematic failures, Original Equipment Manufacturers (OEMs) and their suppliers must comply with standards such as ISO 26262, the road vehicles functional safety standard. ISO 26262 provides regulations and recommendations for the product development process. When the critical road functionalities are regarded as hard real-time, that shall complete within the defined time boundaries, coexist in an environment with soft and non real-time tasks (e.g., multimedia and connectivity activities) the system designer must use an approach to ensure that no critical activity is jeopardized in order to avoid hazardous events. To cope with the coexistence of activities with different time boundaries and criticality within the same system, this work proposes the implementation of uniprocessor reservation-based mechanisms, namely the Constant Bandwidth Server (CBS) and the Capacity Sharing and Stealing (CSS), in a real-time operating system for scheduling non-critical activities without jeopardizing the apriori guarantee of critical activities. Both schedulers use the concept of server, a task holder where a fraction of the processor bandwidth is reserved for tasks, thus relaxing the need for knowing certain properties of the tasks such as the WCET. Both implementations are detailed and compared through the implementation of task sets where both types of tasks coexist.A eletrónica transformou por completo a indústria automotiva, os primeiros veículos eram puramente compostos por componentes mecânicos, mas atualmente a realidade é significativamente diferente. O aumento da aceitação de dispositivos eletrónicos levou a um crescimento exponencial do número de funções baseadas em microcontroladores embutidos em veículos. E com este aumento, as preocupações relativas à segurança por parte dos clientes aumentaram. Para garantir a segurança de falhas sistemáticas e de falhas provenientes do uso excessivo de componentes Elétricos e Eletrónicos (E/E) de um veículo, tanto os Original Equipment Manufacturers (OEMs) como os seus fornecedores tem que cumprir com standards como por exemplo o ISO 26262, standard referente à segurança funcional de veículos rodoviários. O ISO 26262 apresenta os regulamentos e recomendações presentes em todo o processo de desenvolvimento do produto. Quando as funcionalidades críticas tambem são consideradas como hard real-time, que tem que dar resposta a estimulos externos dentro dos limites temporaris definidos, coexistem no mesmo ambiente com tarefas soft e non real-time (por exemplo, atividades de multimídia e conectividade), o system designer tem que usar abordagens especificas para continuar a garantir que nenhuma atividade hard seja comprometida, evitando assim possiveis consequencias catastróficas. Para fazer face à coexistência de atividades com difrentes niveis de criticalidade e limitações temporais dentro do mesmo sistema, este trabalho propõe a implementação de mecanismos baseados em reservas de partes de utilização do processador, nomeadamente o Constant Bandwidth Server (CBS) e o Capacity Sharing and Stealing (CSS), num sistema operativo de tempo-real para escalonar atividades não críticas sem comprometer a garantia apriori de tarefas criticas. Ambos os escalonadores usam o conceito de servidores dedicados, onde uma fração da largura de banda do processador é reservada para tarefas, relaxando assim a necessidade de conhecer certas propriedades das tarefas, como o WCET. Ambas as implementações são detalhadas e comparadas através da implementação de um conjunto de testes onde os dois tipos de tarefas coexistem

Application of mainstream object relational database to real time database applications in industrial automation

This thesis examines the proposition that because of recent huge increases in processing power, disk and memory capacities the commercial mainstream object relational databases may now be a viable option to replace dedicated real-time databases in industrial automation. The benefits are lower product cost, greater availability of trained manpower for development and maintenance and lower risks due to larger installed base and larger number of platforms supported. The issues considered in testing this proposition were performance, ability to mimic critical real-time database features, replication of the real-time database application development and administration tools and finally the low overhead high speed, real-time data compression facility available in real-time databases. An efficient yet simple real-time compression algorithm was developed for use with relational databases and benchmarked. Extensive comparative benchmarking has been done to convincingly prove the proposition. The results overwhelmingly show, that for a majority of industrial real-time database applications, the performance offered by a commercial object relational database on a current platform are more than adequate

Using hierarchical scheduling to support soft real-time applications in general-purpose operating systems

Journal ArticleThe CPU schedulers in general-purpose operating systems are designed to provide fast response time for interactive applications and high throughput for batch applications. The heuristics used to achieve these goals do not lend themselves to scheduling real-time applications, nor do they meet other scheduling requirements such as coordinating scheduling across several processors or machines, or enforcing isolation between applications, users, and administrative domains. Extending the scheduling subsystems of general-purpose operating systems in an ad hoc manner is time consuming and requires considerable expertise as well as source code to the operating system. Furthermore, once extended, the new scheduler may be as inflexible as the original. The thesis of this dissertation is that extending a general-purpose operating system with a general, heterogeneous scheduling hierarchy is feasible and useful. A hierarchy of schedulers generalizes the role of CPU schedulers by allowing them to schedule other schedulers in addition to scheduling threads. A general, heterogeneous scheduling hierarchy is one that allows arbitrary (or nearly arbitrary) scheduling algorithms throughout the hierarchy. In contrast, most of the previous work on hierarchical scheduling has imposed restrictions on the schedulers used in part or all of the hierarchy. This dissertation describes the Hierarchical Loadable Scheduler (HLS) architecture, which permits schedulers to be dynamically composed in the kernel of a general-purpose operating system. The most important characteristics of HLS, and the ones that distinguish it from previous work, are that it has demonstrated that a hierarchy of nearly arbitrary schedulers can be efficiently implemented in a general-purpose operating system, and that the behavior of a hierarchy of soft real-time schedulers can be reasoned about in order to provide guaranteed scheduling behavior to application threads. The flexibility afforded by HLS permits scheduling behavior to be tailored to meet complex requirements without encumbering users who have modest requirements with the performance and administrative costs of a complex scheduler. Contributions of this dissertation include the following. (1) The design, prototype implementation, and performance evaluation of HLS in Windows 2000. (2) A system of guarantees for scheduler composition that permits reasoning about the scheduling behavior of a hierarchy of soft real-time schedulers. Guarantees assure users that application requirements can be met throughout the lifetime of the application, and also provide application developers with a model of CPU allocation to which they can program. (3) The design, implementation, and evaluation of two augmented CPU reservation schedulers, which provide increase scheduling predictability when low-level operating system activity steals time from applications

A framework for flexible scheduling in real-time middleware

The traditional vehicle for the deployment of a real-time system has been a real-time operating system (RTOS). In recent years another programming approach has increasingly found its way into the real-time systems domain: the use of middleware. Examples are the so called pervasive systems (embedded, interactive but not mobile), and ubiquitous systems (embedded, interactive and mobile), e.g. hand-held devices. These tend to be dynamic systems that often exhibit a need for flexible scheduling because of their operating requirement; or their execution environment. Thus, today there is a true need in many realtime applications for more flexible scheduling than what is currently the stateof- prac'tice. By flexible scheduling we mean the ability of the program execution platform to provide a range of scheduling policies, all the way from hard real-time to soft real-time policies, from which an application can choose one most suited to its needs. Furthermore, some applications may need to be scheduled by one policy while others may need a different policy, e.g. fi'Ced priority or earliest deadline first (EDF) for hard real-time tasks, least slack time first (LST) or shortest remaining time for soft real-time tasks. It would be difficult for the middleware to expect this functionality from the RTOS. This would require a fine balance to be struck in the RTOS between flexibility and usability, and many years will probably pass until such approaches become mainstream and usable. 'This thesis maintains that this flexibility can be introduced into the middleware. It presents a viable solution to introducing flexible scheduling in real-time program execution middleware in the form of a flexible scheduling framework. Such a framework allows use of the same program execution middleware for a variety of applications - soft, firm and hard. In particular, the framework allows different scheduling policies to co-exist in the system and their tasks to share common resources. The thesis describes tlle framework's protocol, examines the different types of scheduling policies that can be supported, tests its correctness through the use of a model checker and evaluates the proposed framework by measuring its execution cost overhead. The framework is deemed appropriate for the types of real-time applications that need the services of flexible scheduling

Integrated Scheduling of Multimedia and Hard Real-Time Tasks

An integrated platform which is capable of meeting the requirements of both traditional real-time control processing and multimedia processing has enormous potential for accommodating various kinds of new applications. However, except for the simplest of situations, few, if any, research or commercial systems successfully provide architectural and OS mechanisms which can efficiently support both hard real-time computation and multimedia soft real-time computation. In this paper, we propose a multimedia server executing on multiprocessor real-time operating systems to provide different classes of guarantee to support both types of processing. The multimedia server supports multiple periodic multimedia streams with a capability for graceful QoS degradation during system overload. In this paper we (i) discuss realistic system implementation issues on the SGI IRIX/REACT/PRO operating system, (ii) develop several multimedia server scheduling algorithms, and (iii) present a performance evalu..