• Title/Summary/Keyword: Imprecise Task

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Scheduling Algorithm to Minimize Total Error for Imprecise On-Line Tasks

  • Song, Gi-Hyeon
    • Journal of Korea Multimedia Society
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    • v.10 no.12
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    • pp.1741-1751
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    • 2007
  • The imprecise computation technique ensures that all time-critical tasks produce their results before their deadlines by trading off the quality of the results for the computation time requirements of the tasks. In the imprecise computation, most scheduling problems of satisfying both 0/1 constraints and timing constraints, while the total error is minimized, are NP-complete when the optional tasks have arbitrary processing times. In the previous studies, the reasonable strategies of scheduling tasks with the 0/1 constraints on uniprocessors and multiprocessors for minimizing the total error are proposed. But, these algorithms are all off-line algorithms. Then, in the on-line scheduling, NORA(No Off-line tasks and on-line tasks Ready upon Arrival) algorithm can find a schedule with the minimum total error. In NORA algorithm, EDF(Earliest Deadline First) strategy is adopted in the scheduling of optional tasks. On the other hand, for the task system with 0/1 constraints, NORA algorithm may not suitable any more for minimizing total error of the imprecise tasks. Therefore, in this paper, an on-line algorithm is proposed to minimize total error for the imprecise real-time task system with 0/1 constraints. This algorithm is suitable for the imprecise on-line system with 0/1 constraints. Next, to evaluate performance of this algorithm, a series of experiments are done. As a consequence of the performance comparison, it has been concluded that IOSMTE(Imprecise On-line Scheduling to Minimize Total Error) algorithm proposed in this paper outperforms LOF(Longest Optional First) strategy and SOF(Shortest Optional First) strategy for the most cases.

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A deferring strategy to improve schedulability for the imprecise convergence on-line tasks (부정확한 융복합 온라인 태스크들의 스케쥴가능성을 향상시키기 위한 지연 전략)

  • Song, Gi-Hyeon
    • Journal of the Korea Convergence Society
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    • v.12 no.2
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    • pp.15-20
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    • 2021
  • The imprecise real-time scheduling can be used for minimizing the bad effects of timing faults by leaving less important tasks unfinished if necessary when a transient overload occured. In the imprecise scheduling, every time-critical task can be logically decomposed into two tasks : a mandatory task and an optional task. Recently, some studies in this field showed good schedulability performance and minimum total error by deferring the optional tasks. But the schedulability performance of the studies can be shown only when the execution time of each optional task was less than or equal to the execution time of its corresponding mandatory task. Therefore, in this paper, a new deferring strategy is proposed under the reverse execution time restriction to the previous studies. Nevertheless, the strategy produces comparable or superior schedulability performance to the previous studies and can minimize the total error also.

An EDF Based Real-Time Scheduling Algorithm for Imprecise Computation (불확정 계산을 위한 EDF 기반의 실시간 스케줄링 알고리즘)

  • Choi, Hwan-Pil;Kim, Yong-Seok
    • The KIPS Transactions:PartA
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    • v.18A no.4
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    • pp.143-150
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    • 2011
  • This paper presents an EDF based scheduling algorithm for scheduling imprecise computation model where each task consists of mandatory part and optional part. Imprecise computation is useful to manage overload condition. In overload situation, some optional parts should be removed. The proposed DOP algorithm removes optional parts of earlier deadline tasks to enhance flexibly for newly arriving tasks. A simulation result shows that DOP has better performance than other algorithms.

An On-line Algorithm to Search Minimum Total Error for Imprecise Real-time Tasks with 0/1 Constraint

  • Song Gi-Hyeon
    • Journal of Korea Multimedia Society
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    • v.8 no.12
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    • pp.1589-1596
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    • 2005
  • The imprecise real-time system provides flexibility in scheduling time-critical tasks. Most scheduling problems of satisfying both 0/1 constraint and timing constraints, while the total error is minimized, are NP complete when the optional tasks have arbitrary processing times. Liu suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on uniprocessors for minimizing the total error. Song et al suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on multiprocessors for minimizing the total error. But, these algorithms are all off-line algorithms. On the other hand, in the case of on line scheduling, Shih and Liu proposed the NORA algorithm which can find a schedule with the minimum total error for a task system consisting solely of on-line tasks that are ready upon arrival. But, for the task system with 0/1 constraint, it has not been known whether the NORA algorithm can be optimal or not in the sense that it guarantees all mandatory tasks are completed by their deadlines and the total error is minimized. So, this paper suggests an optimal algorithm to search minimum total error for the imprecise on-line real-time task system with 0/1 constraint. Furthermore, the proposed algorithm has the same complexity, O(N log N), as the NORA algorithm, where N is the number of tasks.

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Comparative Analysis on Imprecision Probability Under Several Imprecise Scheduling Schemes in Real Time Systems (실시간 시스템에서 여러 부정확한 스케쥴링 기법하에서의 부정확한 확률에 관한 비교 분석)

  • Ah, Gwl-Im;Koh, Kern
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.19 no.7
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    • pp.1304-1320
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    • 1994
  • There are two computation techniques in real time systems : precise and imprecise computation. The imprecise computation technique is a means to provide scheduling flexibility in real time systems. The studies on imprecise scheduling using queueing theoretical formulation up to data are to explicitly quantify the costs and benifits in trade-off between the average result quality and the average waiting time of tasks. This paper uses two imprecise scheduling schemes and solves the imprecision probability, the probability of any task being imprecise under two imprecise scheduling schemes and analyzes the dependence of the imprecision probability on several parameters os the monotone imprecise system.

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A Schedulability Algorithm of Multimedia Real-Time Task Set (멀티미디어 실시간 태스크 집합의 스케쥴가능성 알고리즘)

  • 송기현
    • Journal of the Korea Computer Industry Society
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    • v.2 no.7
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    • pp.923-932
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    • 2001
  • In this paper, An imprecise real-time task sets composed of multimedia datas are generated using several parameters and an algorithm which can analyse schedulability of generated imprecise real-time task sets before execution of this task sets is proposed. Also, The schedulability of task set depends on variation of parameter values which were used during the generation of the task set is studied. As a result of experiment, It isproved that the schedulability of task set is more and more weak as large as execution requirement time of mandatory subtasks and, as many as the number of tasks which can be scheduled at some instant. The schedulabilty analysis algorithm which is presented on this paper is expected to use effectively on QoS service of multimedia datas.

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On-line Schedulability Check Algorithm for Imprecise Real-time Tasks (부정확한 실시간태스크들을 위한 온라인 스케쥴가능성 검사 알고리즘)

  • Gi-Hyeon Song
    • Journal of the Korea Computer Industry Society
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    • v.3 no.9
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    • pp.1167-1176
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    • 2002
  • In a (hard) real-time system, every time-critical task must meet its timing constraint, which is typically specified in terms of its deadline. Many computer systems, such as those for open system environment or multimedia services, need an efficient schedulability test for on-line real-time admission control of new jobs. Although various polynomial time schedulability tests have been proposed, they often fail to decide the schedulability of the system precisely when the system is heavily loaded. Furthermore, the most of previous studies on on-line real-time schedulability tests are concentrated on periodic task applications. Thus, this paper presents an efficient on-line real-time schedulability check algorithm which can be used for imprecise real-time system predictability before dispatching of on-line imprecise real-time task system consisted of aperiodic and preemptive task sets when the system is overloaded.

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Imprecise Computation based Scheduling for QoS Support in Multimedia Systems (멀티미디어 시스템에서 QoS 지원을 위한 불확정계산 기반의 스케줄링)

  • Kim, Tae-Su;Kim, Yong-Seok
    • Proceedings of the IEEK Conference
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    • 2005.11a
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    • pp.995-998
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    • 2005
  • A task in imprecise computation consists of mandatory part and optional part. The optional part can be executed partially and the quality of service is measured by the amount of the execution. Many paper showed that multimedia systems are good applications of imprecise computation. It is important to guarantee QoS which is a critical factor in multimedia systems. Previous works didn't consider QoS and processor slack were assigned randomly to tasks. This paper presented a systemic slack assignment method according to QoS levels of tasks. A simulation result showed that our method can be a good choice for multimedia systems with QoS requirement.

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An Improved Online Algorithm to Minimize Total Error of the Imprecise Tasks with 0/1 Constraint (0/1 제약조건을 갖는 부정확한 태스크들의 총오류를 최소화시키기 위한 개선된 온라인 알고리즘)

  • Song, Gi-Hyeon
    • Journal of KIISE:Computer Systems and Theory
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    • v.34 no.10
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    • pp.493-501
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    • 2007
  • The imprecise real-time system provides flexibility in scheduling time-critical tasks. Most scheduling problems of satisfying both 0/1 constraint and timing constraints, while the total error is minimized, are NP-complete when the optional tasks have arbitrary processing times. Liu suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on uniprocessors for minimizing the total error. Song et at suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on multiprocessors for minimizing the total error. But, these algorithms are all off-line algorithms. In the online scheduling, the NORA algorithm can find a schedule with the minimum total error for the imprecise online task system. In NORA algorithm, EDF strategy is adopted in the optional scheduling. On the other hand, for the task system with 0/1 constraint, EDF_Scheduling may not be optimal in the sense that the total error is minimized. Furthermore, when the optional tasks are scheduled in the ascending order of their required processing times, NORA algorithm which EDF strategy is adopted may not produce minimum total error. Therefore, in this paper, an online algorithm is proposed to minimize total error for the imprecise task system with 0/1 constraint. Then, to compare the performance between the proposed algorithm and NORA algorithm, a series of experiments are performed. As a conseqence of the performance comparison between two algorithms, it has been concluded that the proposed algorithm can produce similar total error to NORA algorithm when the optional tasks are scheduled in the random order of their required processing times but, the proposed algorithm can produce less total error than NORA algorithm especially when the optional tasks are scheduled in the ascending order of their required processing times.

An Efficient Algorithm to Minimize Total Error of the Imprecise Real Time Tasks with 0/1 Constraint (0/1 제약조건을 갖는 부정확한 실시간 태스크들의 총오류를 최소화시키는 효율적인 알고리즘)

  • Song, Gi-Hyeon
    • Journal of the Korea Computer Industry Society
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    • v.7 no.4
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    • pp.309-320
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    • 2006
  • The imprecise real-time system provides flexibility in scheduling time-critical tasks. Most scheduling problems of satisfying both 0/1 constraint and timing constraints, while the total error is minimized, are NP-complete when the optional tasks have arbitrary processing times. Liu suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on uniprocessors for minimizing the total error. Song et al suggested a reasonable strategy of scheduling tasks with the 0/1 constraint on multiprocessors for minimizing the total error. But, these algorithms are all off-line algorithms. In the online scheduling, NORA algorithm can find a schedule with the minimum total error for the imprecise online task system. In the NORA algorithm, the EDF strategy is adopted in the optional scheduling.<중략> The algorithm, proposed in this paper, can be applied to some applications efficiently such as radar tracking, image processing, missile control and so on.

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