共查询到17条相似文献,搜索用时 140 毫秒
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单调速率及其扩展算法的可调度性判定 总被引:34,自引:6,他引:28
任务可调度性判定是实时系统调度理论研究的核心问题.单调速率(RM)算法是实时调度的重要算法,自其提出以来已被广泛研究.然而到目前为止,尚缺乏专题性的文章来系统而深入地探讨RM及其扩展算法的可调度性判定,以及各种现实条件和实现方式(包括任务调度的时间开销和任务同步问题等)对可调度性的影响.围绕RM算法下的可调度性判定问题,由浅入深,系统性地讨论各种不同假设和实现方式对可调度性的影响,具体为下述3大类问题:(1)理想的RM算法下的可调度性判定的CPU利用率最小上界最小及可调度的充分必要条件;(2)考虑调度时间开销情况下的可调度性判定条件;(3)优先级反转协议及其对可调度性的影响.给除了具体实例来叙述上述问题,并从算法复杂度和可检测率两方面比较各种算法的优劣。 相似文献
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针对多处理器实时调度中的最早伪时限优先(EPDF)Pfair算法,分析了EPDF算法在M个处理器平台上的可调度利用率约束,根据基于利用率的充分可调度性判定,提出了一种改进的可调度性判定方法。这种方法可以得到更多的可调度任务集,从而使得满足判定的强实时系统和使用tie-breaking规则困难的动态任务系统的调度有较小的开销。实验结果表明,改进的可调度性判定方法增加了判为可调度的任务集数量,具有较好的性能。 相似文献
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实时系统中调度算法起着重要的作用.单调速率调度算法(rate monotonic algorithm,RM)是一种被 广泛使用的调度算法,并且已被证明是一种最佳的静态优先级算法.传统的RM算法忽略上下文切换需要消耗的时间,针对此问题,提出了一种延迟抢占的改进方法.该方法考虑了上下文切换消耗时间对调度算法的影响,可以减少... 相似文献
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针对多处理器实时调度中的固定优先级(FP)调度算法,提出了一种改进的可调度性判定方法。引入Baruah的最早截止期优先(EDF)窗口分析框架,将高优先级任务带入作业的最大数量限定为m-1(m为处理器个数),进而对任务的干涉上界进行重新界定,并由此得到一个更加紧密的可调度性判定充分条件。仿真实验结果表明,该方法增加了通过判定任务集的数量,体现出更优的可调度判定性能。 相似文献
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静态优先级调度在实时系统中得到了广泛应用.然而,静态优先级调度受到系统支持的优先级个数的限制.当任务的个数大于优先级个数时,需要将多个任务映射到同一个优先级.针对优先级个数有限的情况,给出了在截止期限大于周期时任务可调度的充分必要条件,并提出了基于有限优先级的静态优先级分配算法(AGP).AGP算法对于基本任务集合是最优的静态优先级分配算法.其最优性表现在,所需的优先级个数最小,并且若采用AGP算法不可调度某个任务集,则采用其他静态优先级分配算法也不可调度该任务集.模拟结果表明,AGP算法的可调度性要远远大于常量法.AGP算法对于解决在嵌入式实时系统中任务的优先级分配问题具有重要意义. 相似文献
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The current literature of fixed-priority scheduling algorithms relies on sufficient tests to determine if a set of mixed-criticality sporadic tasks is schedulable on a single processor. The drawback of these safe tests is their pessimism, a matter that could be solved if an exact schedulability analysis is used. However, because of the non-deterministic behavior of tasks in the mentioned setups, exact quantification of worst-case response times, needed for the test, is a difficult problem; more precisely, such a quantification needs evaluation of enormous sequences of job executions. The core problem is thus to merge such sequences to make the analysis practical. This paper, for the first time, gives an algorithm for exact worst-case response time characterization of mixed-criticality sporadic real-time tasks executing according to a given fixed-priority scheduler. We use a set of techniques which carefully consider the task properties and their relation to the worst scenarios to prune the analysis state space. We also show an interesting result that if an exact schedulability test is used, the Audsley’s optimal priority assignment algorithm is not applicable to the mixed-criticality case. Accordingly, we need new priority assignment algorithms to work with the exact test; we give a simple task priority assignment algorithm to this aim. The performance of the proposed exact test (in terms of time complexity) is examined and the effectiveness of some heuristic priority assignment algorithms using the test (in terms of the ratio of task sets which are deemed schedulable) are compared. 相似文献
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不可抢占式EDF调度算法的可调度性分析 总被引:4,自引:1,他引:4
沈卓炜 《计算机工程与应用》2006,42(9):10-12,29
现有的不可抢占式EDF调度算法的可调度性分析判定条件限定实时任务的截止期必须等于其周期,限制了它的使用范围。论文突破这一限制,提出了更具一般性的可调度性分析判定充要条件。通过对可调度性判定充要条件的分析,提出了基于不可抢占式EDF调度算法的周期性实时系统可调度性分析算法。 相似文献
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在通信、雷达、导航以及各种消费类电子产品等民用和军事领域,嵌入式实时调度已逐渐成为电子电气系统的控制核心。针对同优先级任务使用FIFO调度的静态优先级系统,使用反例指出给定同优先级任务初始执行顺序的前提下,Katcher可调度判定条件的必要性不成立,提出并解析证明了FP可调度的充要条件。随机实验表明,对于高利用率下任务间执行时间差异较大的情况,约有15%的可调度任务集会被Katcher条件错判为不可调度。进一步的仿真和实例分析表明,Liu、Lehoczky、Bini等提出的条件不能判定相同优先级的情况,Katcher条件的必要性不成立,论文提到的条件能够正确判定任务集的可调度性。提出方法为实时系统调度的顶层设计提供了快速离线工具。 相似文献
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Nasro Min-Allah Samee U. Khan Xiuli Wang Albert Y. Zomaya 《Journal of Parallel and Distributed Computing》2013
The feasibility problem of periodic tasks under fixed priority systems has always been a critical research issue in real-time systems and a number of feasibility tests have been proposed to guarantee the timing requirements of real-time systems. These tests can be broadly classified into: (a) inexact and (b) exact tests. The inexact tests are applied to the task sets that present lower utilization, while the exact tests become inevitable when system utilization is high. The exact tests can be further classified into: (a) Scheduling Points Tests (SPT) and (b) Response Time Tests (RTT). The SPT analyze task set feasibility at the arrival times while the RTT utilize fixed-point techniques to determine task feasibility. All of the available exact feasibility tests, whichever class it belongs to, share pseudo-polynomial complexity. Therefore, the aforementioned tests become impractical for online systems. Currently, both SPT and RTT employ the Highest Priority First (HPF) approach, which determines the system feasibility by testing the schedulability of individual tasks in the decreasing order of priority. In contrast, this work exploits the Lowest Priority First (LPF) alternative which is an aggressive solution based on the observation that the system infeasibility is primarily due to the lower priority tasks and not because of the higher priority tasks. For the average case analysis, our technique demonstrates promising results. Moreover, in the worst case scenario our solution is no inferior to the existing state of the art alternatives. We compare our proposed technique with the existing tests: (a) by counting the number of scheduling points used by a test that belongs to the SPT, (b) by counting the number of inner-most loops executed by an algorithm for the RTT, and (c) by measuring the actual running time of the existing alternatives. 相似文献