Conference Paper

Scheduling Similarity-Constrained Real-Time Tasks.

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
Source: DBLP
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    ABSTRACT: The deferrable scheduling algorithm for fixed priority transactions (DS-FP) (23) is demonstrated to be a very effective approach for minimizing real-time update trans- action workload while maintaining temporal validity of real-time data. This paper examines the schedulability of deferrable scheduling and presents a sufficient condition. While its on-line scheduling overhead is a concern, we pro- pose a hyperperiod based DS-FP approach satisfying the temporal validity constraint with low overhead. The al- gorithm, namely DEferrable Scheduling with Hyperperiod by Schedule Adjustment (DESH-SA), adjusts the DS-FP schedule in an interval so that the adjusted schedule in the interval can be repeated infinitely. Our experiments demon- strate that DESH-SA can reduce scheduling overhead of DS-FP and also achieve update workload near optimal.
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    ABSTRACT: Although the deferrable scheduling algorithm for fixed priority transactions (DS-FP) has been shown to be a very effective approach for minimizing real-time update transaction workload, it suffers from its on-line scheduling overhead. In this work, we propose two extensions of DS-FP to minimize the on-line scheduling overhead. The proposed algorithms produce a hyperperiod from DS-FP so that the schedule generated by repeating the hyperperiod infinitely satisfies the temporal validity constraint of the real-time data. The first algorithm, named DEferrable Scheduling with Hyperperiod by Schedule Construction (DESH-SC), searches the DS-FP schedule for a hyperperiod. The second algorithm, named DEferrable Scheduling with Hyperperiod by Schedule Adjustment (DESH-SA), adjusts the DS-FP schedule in an interval to form a hyperperiod. Our experimental results demonstrate that while both DESH-SC and DESH-SA can reduce the scheduling overhead of DS-FP, DESH-SA outperforms DESH-SC by accommodating significantly more update transactions in the system. Moreover, DESH-SA can also achieve near-optimal update workload.
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    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
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