单调速率及其扩展算法的可调度性判定

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。     

基于RM与EDF的实时混合调度算法研究

通过对实时系统中静态调度算法RM和动态调度算法EDF的研究与分析,针对两种调度算法在实际应用中的问题,提出了一种基于阈值δ的混合调度算法,将RM与EDF调度算法相结合,并从数学角度描述了混合调度算法的可调度性与实时任务的周期、执行时间等属性之间的关系,给出了混合调度算法可调度性的充分必要条件。最后用实验验证了混合调度算法的有效性。     

单调速率调度算法的可调度性分析与仿真

单调速率调度算法是一种经典的周期任务调度算法，在采用单调速率调度算法调度周期任务前对算法的可调度性进行分析和仿真是十分必要的。该文介绍了单调速率调度算法的基本调度规则和可调度的充分必要条件，分别基于Windows平台的多线程机制和实时操作系统SACOS的RMS管理器对单调速率调度算法的可调度性进行仿真，并对仿真结：果进行了评价与分析。仿真结果表明，这两种方法可为单调速率调度算法的可调度性分析提供有益的指导。     

基于时间需求迭代和排队模型的开放式实时系统可调度性分析算法研究

基于RM调度策略和可延期服务器调度的开放式实时系统,以往的可调度性分析算法造成较低资源利用率.结合时间需求分析和服务台休假M/M/1/K排队模型,考虑带宽保留服务器,提出一种高资源利用率的可调度性分析算法,对系统中所有周期任务进行可调度性分析测试.给出其在临界点的响应时间;根据非周期事件到来率和接收缓冲定量分析非周期事件的平均响应时间和事件丢失率.实验表明,提出的可调度性分析方法通过估计任务的响应时间范围,能够在较高资源利用率下,验证多任务系统的可调度性.     

单调速率任务分配算法利用率的界限分析

通过对单调速率任务分配算法调度策略和可调度条件的分析，在多处理器周期任务抢占调度模型基础上，细致刻画了任务分配算法如何分配任务的行为。依据Liu和Layland定理，给出多处理器下任务分配算法的最小RM利用率界的定理。仿真结果表明，分配算法的利用率界是不同特征任务集选择不同分配算法进行任务划分的关键，通过对任务集总利用率与算法利用率界的比较,判断使用该算法对任务集是否可以产生可行分配。     

RM及其扩展可调度性判定算法性能分析

可调度性判定是实时调度算法的关键问题·单调速率算法RM(ratemonotonic)及其扩展是应用广泛的实时调度算法,大量文献讨论了实时任务在这些算法下的可调度性判定,给出了相应的判定算法·但迄今为止,对这些判定算法的性能分析都是理论上的定性分析或者只是少数几种判定算法之间的简单比较,这不利于实时系统的开发·归纳了RM及其扩展的可调度性判定算法,通过测试平台,系统地测试和分析了各算法的性能和适用场合,讨论了各种条件和实现方式对算法性能和可调度性的影响·     

Limited carry-in technique for real-time multi-core scheduling

Schedulability analysis has been widely studied to provide offline timing guarantees for a set of real-time tasks. The so-called limited carry-in technique, which can be orthogonally incorporated into many different multi-core schedulability analysis methods, was originally introduced for Earliest Deadline First (EDF) scheduling to derive a tighter bound on the amount of interference of carry-in jobs at the expense of investigating a pseudo-polynomial number of intervals. This technique has been later adapted for Fixed-Priority (FP) scheduling to obtain the carry-in bound efficiently by examining only one interval, leading to a significant improvement in multi-core schedulability analysis. However, such a successful result has not yet been transferred to any other non-FP scheduling algorithms. Motivated by this, this paper presents a generic limited carry-in technique that is applicable to any work-conserving algorithms. Specifically, this paper derives a carry-in bound in an algorithm-independent manner and demonstrates how to apply the bound to existing non-FP schedulability analysis methods for better schedulability.     

Minimum and maximum utilization bounds for multiprocessor rate monotonic scheduling

The utilization bound for real-time rate monotonic (RM) scheduling on uniprocessors is extended to multiprocessors with partitioning-based scheduling. This allows fast schedulability tests to be performed on multiprocessors and quantifies the influence of key parameters, such as the number of processors and task sizes on the schedulability of the system. The multiprocessor utilization bound is a function of the allocation algorithm, so among all the allocation algorithms there exists at least one allocation algorithm providing the minimum multiprocessor utilization bound, and one allocation algorithm providing the maximum multiprocessor utilization bound. We prove that the multiprocessor utilization bound associated with the allocation heuristic worst fit (WF) coincides with that minimum if we use Liu and Layland's bound (LLB) as the uniprocessor schedulability condition. In addition, we present a class of allocation algorithms sharing the same multiprocessor utilization bound which coincides with the aforementioned maximum using LLB. The heuristics first fit decreasing (FFD) and best fit decreasing (BFD) belong to this class. Thus, not even an optimal allocation algorithm can guarantee a higher multiprocessor utilization bound than that of FFD and BFD using LLB. Finally, the pessimism of the multiprocessor utilization bounds is estimated through extensive simulations.     

Utilization Bounds for N-Processor Rate Monotone Scheduling with Static Processor Assignment

We consider the schedulability of a set of independent periodic tasks under fixed priority preemptive scheduling on homogeneous multiprocessor systems. Assuming there is no task migration between processors and each processor schedules tasks preemptively according to fixed priorities assigned by the Rate Monotonic policy, the scheduling problem reduces to assigning the set of tasks to disjoint processors in such a way that the Monotonic policy, the scheduling problem reduces to assigning the set of tasks to disjoint processors in such a way that the schedulability of the tasks on each processor can be guaranteed. In this paper we show that the worst case achievable utilization for such systems is between n(2^1/2-1) and (n+1)/(1+2^1/(n+1)), where n stands for the number of processors. The lower bound represents 41 percent of the total system capacity and the upper bound represents 50 to 66 percent depending on n. Practicality of the lower bound is demonstrated by proving it can be achieved using a First Fit scheduling algorithm.     

Rate monotonic schedulability tests using period-dependent conditions

Feasibility and schedulability problems have received considerable attention from the real-time systems research community in recent decades. Since the publication of the Liu and Layland bound, many researchers have tried to improve the schedulability bound of the RM scheduling. The LL bound does not make any assumption on the relationship between any of the task periods. In this paper we consider the relative period ratios in a system. By reducing the difference between the smallest and the second largest virtual period values in a system, we can show that the RM schedulability bound can be improved significantly. This research has also proposed a system design methodology to improve the schedulability of real time system with a fixed system load.

基于改进型统一调度算法改善任务集的可调度性

实时系统要求任务在最差情况下能在其截止时间前获得结果,若超过了其截止时间,也会认为是错误的行为,所以改进任务可调度性分析、提高任务集可调度性尤其重要。统一调度能结合固定优先级调度的优点,防止不必要的抢占,降低资源额外销耗,能够提高任务集合的可调度性;但其任务的可调度性分析方法过于粗糙,影响任务最差响应时间分析的结果,降低了任务集的可调度性。针对存在的问题,基于统一调度,增加任务运行阶段数,重新建立任务模型,并提出通过分配任务抢占阈值、调整运行阶段的抢占阈值与长度,优化任务可容忍阻塞,改善任务集可调度性的算法。最后,实验表明,与统一调度算法及其他算法相比,所提出的调度算法能够有效改善任务集的可调度性。     

一种无抖动的分布式多媒体任务调度算法

在分布式多媒体系统中,资源的管理和分配算法是保证应用的服务质量（ＱｏＳ）的关键问题,而资源管理中,ＱｏＳ协商和确认都和多媒体任务调芳算法有关,任务调度算法是资源管理的重要内容。现有的调度算法ＥＤＦ,ＲＭ,ＤＳｒ适用在分布式多媒体系统中,有局限性。本文基于风车调度模型,提出了一种无抖动调度的逐步消除候选项的并行算法ＤＭＳｒ,能达到分布系统中多媒体任务周期调度的无抖动特点,并讨论了算法的计算复杂度,证     

多处理器EPDFPfair算法的可调度性判定

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。     

EDF统一调度硬实时周期任务和偶发任务的可调度性判定算法

现有的硬实时周期任务和非周期任务的混合调度方法都没有保证非周期任务的实时性,所以不适合调度具有强实时要求的偶发任务.通过分析和计算EDF算法调度偶发任务所占用的空闲时间和挪用时间,以及调度后对空闲时间和最大可挪用时间的影响,提出一种采用EDF算法统一调度硬实时周期任务和偶发任务时的可调度性充分判定算法.最后用仿真实验得出了该算法在不同系统负载下的判定准确率和偶发任务的平均响应时间.     

一种计算混合关键任务响应时间的方法

混合关键系统中不同关键等级的任务在同一个平台运行,任务的可调度性分析更加复杂.基于目前最有效的固定优先级混合关键的调度算法AMC(adaptive mixed criticality),提出了一种任务响应时间分析算法AMC-PM(AMC partition max).该算法将任务最长执行时间(worst case execution time,简称WCET)分成低关键等级态执行时间与高关键等级态执行时间,将这两部分对应的最长响应时间加起来得到总的响应时间上界.通过仿真实验,与已有的AMC响应式分析算法进行比较,结果表明,在任务高关键下最长执行时间较小时,与AMC-rtb相比,AMC-PM能够显著地提高系统的可调度性.同时与AMC-max相比,AMC-PM能够显著降低算法的运行时间.     

经典RM调度算法在无人机发动机试车台软件开发中的应用

现代无人机发动机测试项目多、实时性要求高,早期的基于非实时的片上系统不能很好地满足测试要求。本文以某型无人机发动机试车台软件系统实际开发为例,在软件开发中引入了经典RM调度算法,分析了经典RM算法的可调度性判定法则,描述了片上系统任务集设计过程,进行了RM可调度性理论判定。通过对任务集的实际可调度性测试表明：硬件利用率最大可达到93．8％,达到设计指标要求;系统运行稳定可靠,并取得预期效果。     

Laxity dynamics and LLF schedulability analysis on multiprocessor platforms

LLF (Least Laxity First) scheduling, which assigns a higher priority to a task with a smaller laxity, has been known as an optimal preemptive scheduling algorithm on a single processor platform. However, little work has been made to illuminate its characteristics upon multiprocessor platforms. In this paper, we identify the dynamics of laxity from the system??s viewpoint and translate the dynamics into LLF multiprocessor schedulability analysis. More specifically, we first characterize laxity properties under LLF scheduling, focusing on laxity dynamics associated with a deadline miss. These laxity dynamics describe a lower bound, which leads to the deadline miss, on the number of tasks of certain laxity values at certain time instants. This lower bound is significant because it represents invariants for highly dynamic system parameters (laxity values). Since the laxity of a task is dependent of the amount of interference of higher-priority tasks, we can then derive a set of conditions to check whether a given task system can go into the laxity dynamics towards a deadline miss. This way, to the author??s best knowledge, we propose the first LLF multiprocessor schedulability test based on its own laxity properties. We also develop an improved schedulability test that exploits slack values. We mathematically prove that the proposed LLF tests dominate the state-of-the-art EDZL tests. We also present simulation results to evaluate schedulability performance of both the original and improved LLF tests in a quantitative manner.     

长释放时间间隔优先的混合任务调度算法

针对混合任务实时调度的需求和MUF算法的局限性,提出了一种长释放时间间隔优先的混合任务实时调度算法LRIF,该算法除了可对周期性硬实时任务提供调度保证外,同时还可确保非周期性软实时任务的可调度率。论文还提出了LRIF调度算法的可调度性分析方法,并讨论了LRIF调度算法的实现方法。     

A New Approach for Scheduling of Parallelizable Tasks in Real-Time Multiprocessor Systems

In a parallelizable task model, a task can be parallelized and the component tasks can be executed concurrently on multiple processors. We use this parallelism in tasks to meet their deadlines and also obtain better processor utilisation compared to non-parallelized tasks. Non-preemptive parallelizable task scheduling combines the advantages of higher schedulability and lower scheduling overhead offered by the preemptive and non-preemptive task scheduling models, respectively. We propose a new approach to maximize the benefits from task parallelization. It involves checking the schedulability of periodic tasks (if necessary, by parallelizing them) off-line and run-time scheduling of the schedulable periodic tasks together with dynamically arriving aperiodic tasks. To avoid the run-time anomaly that may occur when the actual computation time of a task is less than its worst case computation time, we propose efficient run-time mechanisms.We have carried out extensive simulation to study the effectiveness of the proposed approach by comparing the schedulability offered by it with that of dynamic scheduling using Earliest Deadline First (EDF), and by comparing its storage efficiency with that of the static table-driven approach. We found that the schedulability offered by parallelizable task scheduling is always higher than that of the EDF algorithm for a wide variety of task parameters and the storage overhead incurred by it is less than 3.6% of the static table-driven approach even under heavy task loads.     

Reduction-based schedulability analysis of distributed systems with cycles in the task graph

A significant problem with no simple solutions in current real-time literature is analyzing the end-to-end schedulability of tasks in distributed systems with cycles in the task graph. Prior approaches including network calculus and holistic schedulability analysis work best for acyclic task flows. They involve iterative solutions or offer no solutions at all when flows are non-acyclic. This paper demonstrates the construction of the first generalized closed-form expression for schedulability analysis in distributed task systems with non-acyclic flows. The approach is a significant extension to our previous work on schedulability in Directed Acyclic Graphs. Our main result is a bound on end-to-end delay for a task in a distributed system with non-acyclic task flows. The delay bound allows one of several schedulability tests to be performed. Using the end-to-end delay bound, we extend the delay composition algebra developed for acyclic distributed systems in prior work, to handle loops in the task graph as well. Evaluation shows that the schedulability tests thus constructed are less pessimistic than prior approaches for large distributed systems.