This paper presents stride scheduling, a deterministic scheduling technique that efficiently supports the same flexible resource management abstractions introduced by lottery scheduling. Compared to lottery scheduling, stride scheduling achieves significantly improved accuracy over relative throughput rates, with significantly lower response time variability. Stride scheduling implements proportional-share control over processor time and other resources by cross-applying elements of rate-based flow control algorithms designed for networks. We introduce new techniques to support dynamic changes and higher-level resource management abstractions. We also introduce a novel hierarchical stride scheduling algorithm that achieves better throughput accuracy and lower response time variability than prior schemes. Stride scheduling is evaluated using both simulations and prototypes implemented for the Linux kernel.

Most structured design methods claim to address the needs of hard real-time systems. However, few contain abstractions which directly relate to common hard real-time activities, such as periodic or sporadic processes. Furthermore, the methods do not constrain the designer to produce systems which can be analysed for their timing properties. In this paper we present a structured design method called HRT-HOOD (Hard Real-Time Hierarchical Object Oriented Design). HRT-HOOD is an extension of HOOD, and includes object types which enable common hard real-time abstractions to be represented. The method is presented in the context of a hard real-time system life cycle, which enables issues of timeliness and dependability to be addressed much earlier on in the development process. We argue that this will enable dependable real-time systems to be engineered in a more cost effective manner than the current practise, which in effect treats these topics as performance issues. To illustrate our appr...

Scheduling theories for fixed priority scheduling are now sufficiently mature that a genuine engineering approach to the construction of hard real-time systems is possible. In this paper we review recent advances. A flexible computational model is adopted that can accommodate periodic and sporadic activities, different levels of criticality, process interaction and blocking, cooperative scheduling (deferred preemption), release jitter, precedence constrained processes, arbitrary deadlines, deadlines associated with specific events (rather than the end of a task's execution) and offsets. Scheduling tests for these different application characteristics are described. This model can be supported by structured, object oriented or formal development methods. The paper also considers the issues involved in producing safe and predictable kernels to support this computational model.

. This paper describes work in progress at the University of York on worst-case timing analysis of software for hard real-time and safety-critical systems. We are pursuing a programming environment that combines the technologies of program proof and timing analysis. In short, the analytical power afforded by a classical program proof tool is ideal for the high-level analysis of timing properties. The main thrust of our work, then, has been to investigate how these technologies can be integrated to their mutual benefit. This paper describes our current ideas and results in this field. 1. Introduction The need for static timing analysis of software for hard real-time systems is well-known. 1-3 Static timing analysis is important for system design and testing and is a prerequisite for static schedulability analysis. This work is also motivated by the needs of safety-critical systems, and through direct collaboration with industry. During case studies of typical hard real-time and critic...

Real-time systems are those which must execute all tasks within their timing constraints. Due to the catastrophic consequences of missing deadlines of some realtime tasks, fault tolerance is an essential component of such systems. This thesis introduces techniques to enhance the fault tolerance capability of real-time systems by incorporating time redundancy. Time redundancy is essential in ultrareliable real-time systems where correlated faults must be tolerated. It can also be used to detect and tolerate transient faults, which are a majority of the faults in computing systems. This thesis demonstrates how time redundancy can be used in conjunction with hardware and software redundancy to tolerate a variety of faults in real-time systems. This thesis considers several different system and task models, and for each model, presents a schedulability test (a utilization bound or a set of conditions) which guarantees that all tasks in the system will satisfy their timing constraints even ...

ABSTRACT. The scheduling of processes to meet deadlines is a difficult problem often simplified by placing severe restrictions upon the timing characteristics of individual processes. One restriction often introduced is that processes must have deadline equal to period. This paper investigates schedulability tests for sets of periodic processes whose deadlines are permitted to be less than their period. Such a relaxation enables sporadic processes to be directly incorporated without alteration to the process model. Following an introduction outlining the constraints associated with existing scheduling approaches and associated schedulability tests, the deadline-monotonic approach is introduced. New schedulability tests are derived which vary in computational complexity. The tests are shown to be directly applicable to the scheduling of sporadic processes.

Introduction Recent developments in the analysis of fixed-priority preemptive scheduling have made significant enhancements to the models introduced by Lui and Layland in their seminal 1973 paper [33]. These developments, taken together, now represent a body of analysis that forms the basis for an engineering approach to the design, verification, and implementation of hard real-time systems. In this chapter we review much of this analysis in order to support the thesis that safety critical realtime systems can, and should, be built using these techniques. Preemptive priority-based scheduling prescribes a run-time environment in which tasks, with a priority attribute, are dispatched in priority order. Priorities are, essentially, static. Processes are either runnable, in which case they are held on a notional (priority-ordered) run queue; delayed, in which case they are held Sec. 10.1 Introduction 223 on a notional delay queue; or suspended, in which

Recent results in the application of scheduling theory to dependable real-time systems are reviewed. The review takes the form of an analysis of the problems presented by different application requirements and characteristics. Issues covered include uniprocessor and multiprocessor systems, periodic and aperiodic processes, static and dynamic algorithms, transient overloads and resource usage. Protocols that bound and reduce blocking are discussed. A review of specific real-time kernels is also included.

This paper describes the details of, and the experiences gained from, a case study undertaken by the authors on the design and re-implementation of the Olympus Satellite's Attitude and Orbital Control Systems (AOCS). The goal of the study was to demonstrate that real-time systems can be implemented using Ada and its tasking facilities. The system was designed using HRT-HOOD, analysed using Deadline Monotonic Scheduling Analysis, and implemented on a M68020-based system using a modified York compiler and run-time support system (the modifications are compatible with those proposed for Ada 9X). Our results indicate that systems can be designed to have the flexibility given by multi-tasking solutions, and yet still obtain the same levels of guarantees as those given by cyclic executives. 1. Introduction Although Ada 83 has made some inroads into the real-time embedded computer systems market, often these systems are programmed in sequential Ada using cyclic executives. Over the last deca...

A real-time database system (RTDBS) can be defined as a database system where transactions are associated with real-time constraints typically in the form of deadlines. The system must process transactions so as to both meet the deadlines and maintain the data consistency. Previous research effort in this field has been focused on scheduling transactions with soft or firm deadlines under the conventional transaction model and database system architecture which cannot support predictable real#time transaction processing. In this thesis, we provide a framework to realize predictable real-time transaction processing, satisfying both timing and consistency constraints of a real-time database system. First, we classify data objects and transactions found in typical real-time database applications, considering their distinct characteristics and requirements. Each type of real-time data objects has its own correctness criteria, different from the conventional one. Real#time transactions a...