S. Choi, S. Elsharkawy, Bao Trinh, and A. Agrawala. Dynamic Time-Based Scheduling in Hard Real-Time Systems. 1998.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....that of scheduling and dispatching real time tasks running on a network of distributed computing nodes. The major scheduling methodology used is the Dynamic timebased parametric scheduling method initially introduced by M. Saksena et al. [6] and further extended to include periodic tasks by S. Choi [7]. This method uses Fourier Motzkin variable elimination technique [8] in the o line phase to verify the schedulability of the real time task set and calculate a dynamic calendar for dispatching jobs at runtime. The dynamic calendar represents the start time of each job i with two parametric ....

....like jobs start and nish times, whose values are generated at runtime by previously executed jobs. The parametric scheduling method was chosen because it provides hard real time schedulability guarantees, as well as, exibility to manage slack times without a ecting the task set schedulability [7]. 1.3 Outline The rest of this paper is organized as follows. Section 2, summarizes prior work in the areas of hard and distributed real time scheduling. The problem of Distributed Hard Real Time Scheduling is presented in the remainder of the paper s sections. We start by describing the problem ....

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Seonho Choi. Dynamic Time-Based Scheduling for Hard Real-Time Systems. PhD thesis, University of Maryland at College Park, 1997.

....Their strategy is similar to ours, in that they model error rates through processing times, whereas we account for resource variability through execution times. Related modeling approaches have been suggested in [RCGF97] in which both soft and hard preemptive tasks are considered. In both [Cho97] and [Sak94] the Loss of Schedulability phenomenon, discussed in Section x4.3 is mentioned. However, they use the phenomenon to motivate the 49 necessity for parametric scheduling in periodic job sets, with and without interperiod constraints, respectively. Parametric scheduling ( discussed in ....

....constraints ( Appendix xB ) a phenomenon observed when the constraints are arbitrary [HJLL90] In Section x5.6, we shall provide a dual interpretation of their algorithm; this interpretation enables us to design a more efficient and practical online dispatching scheme than the one they provide. Cho97] and [Cho00] extend the results in [GPS95] to handle the case, in which inter period constraints are permitted in the job set. In [WDL91] a dynamic scheduling scheme is presented; however no offline guarantees are provided. Relative separation constraints, but only in restricted forms, are ....

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Seonho Choi. Dynamic Time-based scheduling for Hard Real-Time Systems. PhD thesis, University of Maryland, College Park, jun 1997.

....if there exists a preemptive schedule, then there exists a preemptive schedule using the EDF heuristic. Most manufacturing control systems are inherently periodic in that the same set of tasks repeats at regular intervals [Y. K80, Kor83] Ram90, Foh95] consider preemptive periodic task sets while [Cho97] considers non preemptive task sets. In [Cho00] explicit mention is made of the contrast between time based models such as the ones proposed in [Sak94, SA00d, SA00a] and priority based models, such as the 3 ones proposed in [HKL91, LL73, CC89] The model differences occur primarily as a result ....

....value 7. Attempts to mitigate the effects of variable execution time through worst case assumptions, result in systems that fail at run time [SA00d] Thus, we need a model that explicitly accounts for parameter variability. Sak94, GPS95] proposed a model in which the constraints are standard [SA00a, Cho97] and the execution time of a task is range bound i.e. e 1 can take any value in the range [l 1 ; u 1 ] at run time, l 1 denoting the lower bound and u 1 denoting the upper bound respectively. This model can be represented by restricting the convex set E in x2 to an axis parallel hyper rectangle ....

Seonho Choi. Dynamic Time-based scheduling for Hard Real-Time Systems. PhD thesis, University of Maryland, College Park, jun 1997.

....of each task is presented by two parametric bound functions. A. Mok el al. 4 in [18] presented a method that uses graph representation of tasks and their relative timing constraints to test the schedulability of a real time task set. Dynamic Cyclic Scheduling: Presented by S. Choi et al. in [7, 21]. Extends the parametric scheduling algorithm to periodic tasks with relative timing constraints. The algorithm uses a graph to represent the tasks and their timing constraints. It calculates a cyclic parametric calendar to be used repeatedly to dispatch task instances at run time. 2.2 Distributed ....

S. Choi, S. Elsharkawy, Bao Trinh, and A. Agrawala. Dynamic Time-Based Scheduling in Hard Real-Time Systems. 1998.

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