J. Y. T. Leung and M. L. Merrill. A Note on Preemptive Scheduling of Periodic, Real-Time Tasks. Inf. Pro. Letters, 11(3), 1980.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....if and only w . Coffman [2] also showed that any set of asynchronous periodic tasks with period deadlines is feasible if and only if w . The problem of deciding whether a set of asynchronous periodic tasks with pre period deadlines has been proved to be NP hard by Leung and Merrill [9]. Further, Baruah et al. showed that this problem is NP hard in the strong sense [1] Definition 4.1 Let denote the number of jobs of task that must be completely scheduled in k D . It is computed as follows: fCH k D U W k 1 1 7 1 1 7 J Z ....

J.Y.-T. Leung and M.L. Merrill, A Note on Preemptive Scheduling of Periodic, Real-Time Tasks, Information Processing Letters 11(3), 1980.

.... in part by MOST under the National Research Laboratory (NRL) grant 2000 N NL 01 C 136, by Automatic Control Research Center (ACRC) and by the Automation and Systems Research Institute (ASRI) 2 Minsoo Ryu et al. While most real time research has put an emphasis on the periodic task model [15, 2, 12, 3, 14] in which task arrivals and execution times are deterministic, multimedia applications have two distinguishing characteristics. First, processor usage patterns include both periodic and aperiodic tasks. For example, a query for continuous media requires periodic tasks for delivery and processing ....

Leung, J., Merill, M.: A Note on the Preemptive Scheduling of Periodic, Real-Time Tasks. Information Processing Letters (1980), 11(3):115--118

....(for periodic threads) or to their minimum interarrival time (for sporadic threads) Theorem 1. George et al. Non preemptive non idling EDF is optimal. If asynchronous periodic threads are permitted with deadlines not necessarily equal to the periods, then scheduling was shown to be NP hard [7]. However, such cases are the norm in practice and we must deal with them. Therefore, our implementation provides a preemptive non idling EDF scheduler in an attempt to minimize the deadline overruns. Users implementing their own scheduling algorithm within our framework can choose to make their ....

J. Y.-T. Leung, M. L. Merrill, A Note on Preemptive Scheduling of Periodic, Real-Time Tasks, Information Processing Letters, 11(3), 1980.

....designed for the NSWC system. The details of the simulation experiments are given in Section 5. Section 6 concludes the paper. 2. Related Work Many research efforts in the literature concentrate on mapping real time applications on a uniprocessor (e.g. 4, 7, 12, 20, 23, 28, 29, 30, 31, 32, 33, 34, 43, 46] Even though these papers present good schemes to schedule realtime tasks on a uniprocessor, they could not be directly ap sensor actuator non blocking switch Figure 3. The hardware model. All machines have dedicated, full duplex Ethernet connections to a non blocking switch. ....

J. Leung and M. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, Nov. 1980.

....in Section VI, along with the experimental setup and the results for the evaluation of these heuristics. II. Related Work Many research e#orts in the literature concentrate on scheduling real time applications on a processor (e.g. 5] 8] 14] 24] 27] 33] 34] 35] 36] 37] [38], 39] 44] 49] 55] 56] The major ways in which our work di#ers from the works cited above are: a) the system environment of our research is very di#erent from most of the previous research (e.g. multitasking heterogeneous distributed machines capable of round robin scheduling only, and ....

J. Leung and M. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, Nov. 1980.

....their algorithm is applicable only to the periodic task model where tasks have fixed periods, deadlines are equal to periods, and tasks are totally independent of each other. Recent research has made significant enhancements to this model, enhancements which relaxed the original restrictions. In [22] Leung and Merrill showed that a deadline monotonic priority assignment is also optimal where deadlines may be shorter than periods. In [32] Sha et al. presented two protocols which enable tasks to interact via shared resources, while still guaranteeing the tasks deadlines. Most recently, a group ....

J. Leung and M. Merill. A note on the preemptive scheduling of periodic, real-time tasks. Itformatiot Processitg Letters, 11(3):115 118, November 1980.

....the problem is also NP hard. Theorem 2 Given a task set T and an (m,k) pattern for each task in T , the problem of determining whether T is schedulable is NP hard. Proof: Leung and Merrill have shown that checking the feasibility of a periodic task sets with arbitrary initial times is NP hard [14]. For any task set T defined in [14] we can always construct a new task set T with (m,k) constraints such that m i = k i for all 0 i n. The theorem holds because it has been proved in[14] that deciding whether T is schedulable or not is NP hard. 2 In Section 2, we reviewed the deeply red ....

....2 Given a task set T and an (m,k) pattern for each task in T , the problem of determining whether T is schedulable is NP hard. Proof: Leung and Merrill have shown that checking the feasibility of a periodic task sets with arbitrary initial times is NP hard [14] For any task set T defined in [14], we can always construct a new task set T with (m,k) constraints such that m i = k i for all 0 i n. The theorem holds because it has been proved in[14] that deciding whether T is schedulable or not is NP hard. 2 In Section 2, we reviewed the deeply red task set used by the skip over model ....

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J. Y.-T. Leung and M.L.Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, Nov 1980.

....interval, all deadlines for them in this interval are met) in the synchronous case than in the asynchronous one. Indeed, while the length of the feasibility interval for asynchronous systems is approximately twice the least common multiple of the periods of the tasks (and thus of exponential size) [9], it is of pseudo polynomial length for bounded density synchronous systems [1] For multiprocessors platforms, we believe that the point 1 remains valid, however, we shall see that points 2 and 3 do not hold in the multiprocessor case. We shall rst examine the point 2 below; the point 3 will be ....

Leung, J., and Merrill, M. A note on the preemptive scheduling of periodic, real-time tasks. Information Processing Letters 11 (1980), 115{ 118.

....analysis is the process of determining whether all such jobs will indeed complete by their respective deadlines. The problem of designing computationally efficient feasibility analysis algorithms has been extensively studied, particularly in the context of uniprocessor scheduling. For example, [13, 11, 12, 9, 10, 1, 16] have designed feasibilityanalysis algorithms for uniprocessor systems of periodic tasks in a preemptive environment; in [7, 8, 6] feasibilityanalysis of systems of periodic tasks in nonpreemptive environments is considered. While some of the above research has resulted in the discovery of ....

....is considered. While some of the above research has resulted in the discovery of reasonably efficient feasibility analysis algorithms, many of the results obtained have been negative: some basic and important feasibility analysis problems have been proven intractable. For example, it was shown [11, 2] that feasibility analysis is co NP complete in the strong sense for a general class of recurring real time systems the asynchronous arbitrary deadlines periodic task systems (we will define the various task models more precisely in Section 2) However, this is an important problem from a ....

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J. Leung and M. Merrill. A note on the preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11:115--118, 1980.

....real time systems comprised entirely of periodic tasks has been extensively studied, primarily in the context of uniprocessor scheduling the scheduling of real time application systems where all the jobs with hard deadlines are constrained to execute on a single shared processor. For example, [11, 9, 10] have designed scheduling and feasibility analysis algorithms for uniprocessor systems of periodic tasks in a preemptive environment an environment in which a job executing on the processor may be interrupted at any instant and its execution resumed later, with no cost or penalty; in [6] ....

J. Y.-T. Leung and M. L. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, November 1980.

....coincide with the periods and with dynamic priority assignments (initially for synchronous systems, where all the tasks start at the same time, but this restriction was soon relaxed) But the test is only necessary for systems where the deadlines can be less than the periods. Leung and Merrill [6] considered those more general systems where the deadlines may be less than the periods and the tasks do not start their execution at the same instant (i.e. they consider asynchronous systems) and determined a feasibility interval (i.e. a finite interval such that it is sure that no deadline ....

....is not greater than 1 [7, 2] there is no simple way to state that no deadline will ever be missed. It is of course not possible to observe the system, by simulation or response time computations (see [5] till the end of ages. It is possible, however, to determine so called feasibility intervals [6] such that, if we only keep the requests occurring in it and no deadline miss is observed in it, then the system is feasible. We shall here improve (i.e. reduce) the length of the feasibility intervals generally found in the literature for systems with general deadlines, together with the ....

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J. Y.-T. Leung and M. L. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, November 1980.

....or arbitrary deadline systems, being synchronous or not, their feasibility with dynamic schedulers is generally intrinsically exponential in terms of the number of tasks. Again, it may be necessary to determine all the response times on a period which may go up to twice the hyper period [8]. The problem that appears here is that the hyper period grows exponentially (as a function of the biggest period and with the number of tasks) It is why it is important to try to limit the hyper period of real time systems. The paper is structured as follows: section 2 presents our model of ....

.... is periodic from time S n with a period of P (see [4] for details) A feasibility interval for an asynchronous constrained deadline system using the deadline driven scheduler or the least laxity rst algorithm is [O max ; O max 2P [ where O max is the maximal o set (see Leung and Merill [8] for details) moreover the schedule is periodic from O max P , with a period of P . This duration could be laid only to t c 1 P with t c the date of the last acyclic idle slot, calculated on the y (with 1 t c O max P ) Since for the most cases, t c = 1 the simulation duration ....

Leung, J. Y.-T., and Merrill, M. A note on preemptive scheduling of periodic, real-time tasks. Information processing letters 11, 3 (November 1980), 115-118.

....De nition 4 (Refresh Pattern Set) Let the collection of refresh patterns of all Web views in viewbase C be represented as R(C) fr i jr i = hU i ; t i;1 i; 1 6 i 6ng. Then R(C) is the refresh pattern set for C. 3 View Starvation A website refresh system is a real time periodical task systems [1, 7, 10] . Let = f 1 ; 2 ; n g be a set of periodic tasks (a task refers to a refresh query whose execution satis es the refresh request of a Web view) and E i be the amount of computing time required to execute task i , and i be the constant interval between invocations of task i . ....

J. Leung, M. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11:115-118, 1980.

....collected in [7] A non preemptive scheduling policy does not interrupt the execution of any task whereas a preemptive scheduling policy does. Recurring task systems may be periodic or sporadic. Because the base data is updated periodically, we are dealing with the case of a periodic task system [1, 4] where each task makes a request for processor time at regular periodic intervals. For non preemptive scheduling, which is our case, work has been done with inserted idle time allowed or not. Without inserted idle time, when a task has been released, it cannot wait before being scheduled if the ....

J. Leung, M. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11:115-118, 1980.

....that execution of a refresh query must be completed within the interval between two consecutive changes of data source, we may view the refreshing cells as a typical recurring task [15] in real time system that makes repeated requests for processor time. More traditional work can be found in [2, 8, 13, 10]. By utilizing 29 the real time scheduling, we can carefully de ne and analyze the freshness of a website. A similar freshness metric has been de ned in [9] however, their work focus on refreshing a local copy of an autonomous data source (website) instead of the original website. 8 ....

J. Leung, M. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11:115-118, 1980.

.... Secondly, we need construct a suitable scheduling algorithm to eciently schedule the executions of refresh if the given views set is feasible. Recurring task systems may be periodic or sporadic. When the source data is updated periodically, we are dealing with the case of a periodic task system [2, 12, 18] where each task makes a request for processor time at regular periodic intervals. When the source data is updated aperiodically, we are dealing with the case of a sporadic system [11, 15, 18] that is similar with a periodic system except that the request times cannot be predicted. 6.2 View ....

J. Leung, M. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11:115-118, 1980.

....real time systems comprised entirely of periodic tasks has been extensively studied, primarily in the context of uniprocessor scheduling the scheduling of real time application systems where all the jobs with hard deadlines are constrained to execute on a single shared processor. For example, [12, 10, 11] have designed scheduling and feasibility analysis algorithms for uniprocessor systems of periodic tasks in a preemptive environment an environment in which a job executing on the processor may be interrupted at any instant and its execution resumed later, with no cost or penalty; in [7] ....

J. Y.-T. Leung and M. L. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, November 1980.

.... The study of scheduling theory has recently become a rapidly expanding area of research (see, e.g. Bla87] One specific area of scheduling theory which has been studied for a number of years involves preemptive scheduling of periodic, real time task systems with deadlines [LL73,Lab74,LM80, LM81,LW82, Leu89] A task system consists of a finite number of tasks, eachofwhich is released at regular periodic intervals. In general, the initial release of individual tasks may occur at different times. Each time a task is released, it This work was supported in part by National Science ....

....later time, or if we are considering a multiprocessor environment, resumed by a different processor. However, we require that no single task be simultaneously scheduled on more than one processor. There is no penalty associated with a preemption. In most of the work done in the past (e.g. LL73, LM80, LM81, LW82, Leu89] the parameters to the problems havenotbeen restricted to integer values, and preemptions havebeenallowed at any time. Furthermore, in schedules constructed byseveral algorithms in the literature, preemptions may occur at noninteger time values even if all start times, ....

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J. Leung and M. Merrill. A note on preemptivescheduling of periodic, real-time tasks. Information Processing Letters, 11:115--118, 1980.

.... seems to currently be enjoying a renaissance. Hardreal time scheduling problems may concern either fixed duration tasks or recurring tasks that must be completed within a certain time frame. The problems most studied within the recurring category involve periodically recurring tasks [LL73, LM80, LM81, LW82,Mok83, BHR90]. Aperiodically or sporadically recurring tasks have also been studied [Mok83, LSS87, HL88,SLS88, JAM90,SSL89] but currently seem less understood. The main focus of this paper concerns feasibility testing with respect to sporadic task systems (i.e. testing whether a sporadic task system is ....

....a processor schedule for any periodic task system that can be scheduled. If the system cannot be scheduled the algorithm will eventually miss a deadline. Dertouzos [Der74] subsequently extended this to obtain a deadline algorithm that is optimal for sporadic task systems. Leung Merrill [LM80] then derived a feasibility test for periodic task systems by showing that a periodic task system is not feasible iff the deadline algorithm of Liu Layland and Labetoulle fails to schedule the system through a predetermined number of time units. Prior to our (this) work, no complete feasibility ....

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J. Leung and M. Merrill. A note on the preemptive scheduling of periodic, real-time tasks. Information Processing Letters,11:115-- 118, 1980.

....per slot scheduled. The third result is a fast scheduling algorithm based on pinwheel scheduling. 1 Introduction Hard real time systems are systems of tasks where missing a single deadline may have disastrous consequences. Such systems have been the focus of much study over the past twentyyears [13,11,9,12,14,1, 10, 7, 17, 8]. Sporadic tasks in a hard real time environment were introduced by Mok [14] to model a computer responding to external events in a way that is consistent with hard real time systems. They are typically characterized by three positiveintegers e, d, and p, with e d and e p. Two requests for ....

J. Leung and M. Merrill. A note on the preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11:115--118, 1980.

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J. Y. T. Leung and M. L. Merrill. A Note on Preemptive Scheduling of Periodic, Real-Time Tasks. Inf. Pro. Letters, 11(3), 1980.

No context found.

J. Leung and M. Merrill. A note on the preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11:115--118, 1980.

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J. Y.-T. Leung and M.L.Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, Nov 1980.

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Joseph Y.-T. Leung and M. L. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115--118, November 1980.

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J. Y. -T. Leung and M. L. Merrill. A note on preemptive scheduling of periodic, real-time tasks. Information Processing Letters, 11(3):115-118, November 1980.

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