Abstract-We study the problem of guaranteeing synchronous message deadlines in token ring networks where the timed to-ken medium access control protocol is employed. Synchronous bandwidth, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous capacities must be properly allocated to individual nodes. We address the issue of appropriate allocation of the synchronous capacities. Several synchronous bandwidth allocation schemes are analyzed in terms of their ability to satisfy deadline constraints of synchronous messages. We show that an inappropriate allocation of the syn-chronous capacities could cause message deadlines to be missed, even if the synchronous traffic is extremely low. We propose

In this paper, we present surplus fair scheduling (SFS), a proportional-share CPU scheduler designed for symmetric multiprocessors. We first show that the infeasibility of certain weight assignments in multiprocessor environments results in unfairness or starvation in many existing proportional-share schedulers. We present a novel weight readjustment algorithm to translate infeasible weight assignments to a set of feasible weights. We show that weight readjustment enables existing proportional-share schedulers to significantly reduce, but not eliminate, the unfairness in their allocations. We then present surplus fair scheduling, a proportional-share scheduler that is designed explicitly for multiprocessor environments. We implement our scheduler in the Linux kernel and demonstrate its efficacy through an experimental evaluation. Our results show that SFS can achieve proportionate allocation, application isolation and good interactive performance, albeit at a slight increase in scheduling overhead. We conclude from our results that a proportionalshare scheduler such as SFS is not only practical but also desirable for server operating systems.

In addition to maintaining database consistency as in conventional databases, real-time database systems must also handle transactions with timing constraints. While transaction response time and throughput are usually used to measure a conventional database system, the percentage of transactions satisfying the deadlines or a time-critical value function is often used to evaluate a real-time database system. Scheduling real-time transactions is far more complex than traditional real-time scheduling in the sense that (1) worst-case execution times are typically hard to estimate, since not only CPU but also I/O requirement isinvolved � and (2) certain aspects of concurrency control may not integrate well with real-time scheduling. In this paper, we rst develop a taxonomy of the underlying design space of concurrency control including the various techniques for achieving serializability and improving performance. This taxonomy provides us with a foundation for addressing the real-time issues. We then consider the integration of concurrency control with realtime requirements. The implications of using run policies to better utilize real-time scheduling in a database environment are examined. Finally, as timing constraints may be more important than data consistency in certain hard real-time database applications, we also discuss several approaches that explore the non-serializable semantics of real-time transactions to meet the hard deadlines. Index terms: concurrency control, real-time databases, real-time scheduling, real-time transactions, serializability, schedulability.

We study the problem of guaranteeing synchronous message deadlines in communication networks where the timed token medium access control protocol is employed. Synchronous capacity, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous capacities must be properly allocated to individual nodes. In this paper, we develop and analyze an optimal synchronous capacity allocation scheme. An optimal scheme can allocate the synchronous capacities in such a way that the synchronous message deadlines are guaranteed if there exists any allocation scheme that can do so. The optimality of the allocation scheme proposed in this paper is formally proved and the bounds for its Worst Case Achievable Utilization are derived. Key Words: Hard Real-Time, Distributed System, FDDI, Timed Token...

Recent results in the application of... this paper. 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 limit and reduce blocking are discussed. Considerations are also given to scheduling Ada tasks.

This thesis develops the Sporadic Server (SS) algorithm for scheduling aperiodic tasks in real-time systems. The SS algorithm is an extension of the rate monotonic algorithm which was designed to schedule periodic tasks. This thesis demonstrates that the SS algorithm is able to guarantee deadlines for hard-deadline aperiodic tasks and provide good responsiveness for soft-deadline aperiodic tasks while avoiding the schedulability penalty and implementation complexity of previous aperiodic service algorithms. It is also proven that the aperiodic servers created by the SS algorithm can be treated as equivalently-sized periodic tasks when assessing schedulability. This allows all the scheduling theories developed for the rate monotonic algorithm to be used to schedule aperiodic tasks. For scheduling aperiodic and periodic tasks that share data, this thesis defines the interactions and schedulability impact of using the SS algorithm with the priority inheritance protocols. For scheduling ha...

Real-time systems are being increasingly used in several applications which are time critical in nature. Fault tolerance is an important requirement of such systems, due to the catastrophic consequences of not tolerating faults. In this paper, we study a scheme that provides fault tolerance through scheduling in real-time multiprocessor systems. We schedule multiple copies of dynamic, aperiodic, non-preemptive tasks in the system, and use two techniques that we call deallocation and overloading to achieve high acceptance ratio (percentage of arriving tasks scheduled by the system). This paper compares the performance of our scheme with that of other fault-tolerant scheduling schemes, and determines how much each of deallocation and overloading affects the acceptance ratio of tasks. The paper also provides a technique that can help real-time system designers determine the number of processors required to provide faulttolerance in dynamic systems. Lastly, a formal model is developed for ...

Real-time scheduling algorithms are usually only available in the kernels of real-time operating systems, and not in more general purpose operating systems, like Unix. For some soft real-time problems, a traditional operating system may be the development platform of choice. This paper addresses methods of emulating real-time scheduling algorithms on top of standard time-share schedulers. We examine (through simulations) three strategies for priority assignment within a traditional multi-tasking environment. The results show that the emulation algorithms are comparable in performance to the real-time algorithms and in some instances outperform them. Keywords: soft real-time, priority assignment, scheduling. 1 Introduction Consider program trading, the use of computer programs to initiate trades in a financial market with little or no human intervention [Voe87]. A financial market (e.g., a stock market) is a complex process whose state is partially captured by variables such a...

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.

In this paper, we consider a storage server architecture for multimedia information systems. While most other works on multimedia storage servers assume on-line disk storage [12, 11, 15, 8, 2], we consider a two-tier storage architecture with a robotic tape library as the vast near-line storage and on-line disks as the front-line storage. Magnetic tapes are cheaper, more robust, and have a larger capacity; hence they are more cost effective for large scale storage systems (e.g., video on demand (VOD) systems [7] may store tens of thousands of videos). We study in details the design issues of the tape subsystem and propose some novel tape scheduling algorithms which give faster response and require less disk buffering. We also study the disk striping policy and the disk space organization in order to fully utilize the throughput of the robotic tape system and to minimize the size of on-line disk storage. 1 Introduction Recent advances in network technologies make it feasible to provi...