Conference: Proceedings of the International Conference on Embedded Systems and Applications, ESA '04 & Proceedings of the International Conference on VLSI, VLSI '04, June 21-24, 2004, Las Vegas, Nevada, USA
[Show abstract][Hide abstract] ABSTRACT: The periodic update transaction model has been used to maintain freshness (or temporal validity) of real-time data. Period and deadline assignment has been the main focus in the past studies such as the More-Less scheme  in which update transactions are guaranteed by the Deadline Monotonic scheduling algorithm  to complete by their deadlines. In this article, we propose a deferrable scheduling algorithm for fixed priority transactions - a novel approach for minimizing update workload while maintaining the temporal validity of real-time data. In contrast to prior work on maintaining data freshness periodically, update transactions follow an aperiodic task model in the deferrable scheduling algorithm. The deferrable scheduling algorithm exploits the semantics of temporal validity constraint of real-time data by judiciously deferring the sampling times of update transaction jobs as late as possible. We present a theoretical estimation of its processor utilization, and a sufficient condition for its schedulability. Our experimental results verify the theoretical estimation of the processor utilization. We demonstrate through the experiments that the deferrable scheduling algorithm is an effective approach, and it significantly outperforms the More-Less scheme in terms of reducing processor workload.
IEEE Transactions on Computers 08/2008; 57(7):952-964. · 1.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The schedulability testing for the deferrable scheduling algorithm for fixed priority transactions (DS-FP) remainsan open problem since its introduction. In this paper, wetake the first step towards investigating necessary and sufficient conditions for the DS-FP schedulability. We propose a necessary and sufficient schedulability condition for the algorithm in discrete time systems, and prove its correctness. Based on this condition, we propose a schedulability test algorithm that is more accurate than the existing test that is only based on a sufficient condition. Our algorithm exploits the fact that there is always a repeating pattern in a DS-FP schedule in discrete time systems. We demonstrate through examples that our schedulability test algorithm outperforms the existing algorithm in terms of accuracy.
[Show abstract][Hide abstract] ABSTRACT: A real-time database is composed of real-time objects whose values remain valid only within their validity intervals. Each object in the database models a real world entity. The freshness of these objects is maintained by update transactions that sample the real world entities. The literature proposes various ways to derive a schedule of transactions that preserves the freshness (also known as absolute consistency) of these objects. But these approaches do not take care of the mutual consistency of the objects, i.e., whether together they represent a logical state of the system. We investigate the problem of checking whether, given an update transaction schedule, a periodic query would be able to read mutually consistent values. We propose solutions for both single- and multiple-query cases in the presence of non-preemptable query executions. Specifically, we first investigate formulas that give the maximal value of mutual gaps among a set of data read at a certain point in time. (A mutual gap for two object values read from the database refers to the difference between the times at which the two objects were updated.) We then propose design approaches to (1) decide the period and relative deadline of a query so that it would guarantee mutual consistency; (2) decide if a given set of queries with relative deadlines and periods can guarantee mutual consistency. Finally, we suggest ways of reducing the complexity of our proposed approaches for both harmonic periods and general cases
Proceedings of the 27th IEEE Real-Time Systems Symposium (RTSS 2006), 5-8 December 2006, Rio de Janeiro, Brazil; 01/2006
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.