先进飞机软件实时性能优化与测试算法

阐述了先进飞机电气系统处理机的功能;为了满足先进飞机电气系统处理机的强实时性能,着重探讨了在实时操作系统VxWorks下将电气系统处理机执行软件功能优化为若干任务,并针对普通RMS算法只能对系统中周期任务进行有效调度而不能对系统中的非周期任务进行有效调度的局限,利用分布假设检验改进RMS算法对非周期任务的调度能力,最后定量讨论了系统整个任务集的实时性和可调度性;由实际测试结果可知,该优化算法任务划分合理,可以保证强实时周期、非周期任务满足其时限要求.     

基于动态优先级策略的最优软非周期任务调度算法

周期任务与非周期任务的混合调度是实时调度研究的一个重要方向 通过定义“调度”和“逆调度” ,对实时周期任务集在使用EDF算法调度时的可挪用时间进行分析 ,求出了周期任务集在使用EDF调度时的最大可挪用时间 在此基础上 ,提出用于缩短非周期任务响应时间和周转时间的调度算法———ISA(idlestealingalgorithm) ISA算法充分使用最大可挪用时间 ,在保证周期任务满足最后期限的同时能取得非周期任务的最优响应时间和周转时间 证明了ISA算法的最优性 ,并使用仿真实验进行了性能验证     

基于(m,k)-firm约束规范的混合任务调度算法研究

讨论了在准实时环境下,包括准实时周期任务和准实时非周期任务在内的混合任务调度算法HTSF.HTSF算法是在满足周期任务(m,k)-firm 约束规范的前提下提高非周期任务可调度性,同时合理利用可用空闲时间,提高整个系统的服务质量.HTSF算法给出了非周期任务的可调度性分析方法,同时采用静态调度与动态调度相结合的方法调度周期任务和非周期任务.模拟测试结果显示,系统对非周期任务的接收率比同类相关算法的接收率高.     

实时系统的多任务调度

讨论了实时系统多任务的调度，对速率单调调度算法进行了改进，以便其能应用于具有非周期任务的实时系统，同时对系统的瞬时过载有一定的适应性。最后，给出了系统中任务可调度的条件。     

基于周期虚拟缩减的实时任务调度和分析方法

针对航天器等安全关键系统中实时任务调度和可调度性分析的实际问题, 提出基于任务周期虚拟缩减的可调度性判定方法, 构建SHT (strong-hard task)任务模型对强硬实时任务进行精确描述, 并根据任务时间特性分配优先级. 虚拟化所有强实时任务为一个硬实时任务, 对此硬实时任务周期虚拟缩减并计算出其最差虚拟执行时间, 然后按RMS可调度性判定公式判定. 给出了判定方法的严格证明, 可对包含n个SHT任务的任务集进行快速可调度性判定, 此算法时间复杂度仅为O(n²). 在我国空间站计算机进行了对比验证, 实验表明判定效率优于现有可调度性判定方法, 平均运行时间开销降低了41.8%, 可调度率提高了5.7%.     

面向物联网终端的任务相关性调度策略

对于具有相关性的任务,调度顺序不合理将影响任务的执行时间和实时性。结合物联网终端任务间依赖关系复杂的特点提出了一种利用任务相关性的调度策略。该策略设计了以作业轮询组为主体的任务模型,根据任务时限建立了优先级因子矩阵作为任务调度的凭据,对于周期任务,在每个任务执行完毕后生成,以任务相关性为参数的增量矩阵用以动态修改任务优先级,使前驱任务能优先执行;对于非周期任务采用了构建临时作业轮询组的方式进行抢占调度。测试结果表明,该策略能够有效减少具有相关性的周期任务集执行时间和调度失败次数,缩短非周期任务响应时间。     

基于排队论和时间需求分析法的实时系统时间行为分析*

针对目前广泛使用的固态优先级RMS调度策略,利用时间需求分析算法对系统中所有周期任务进行可调度性分析测试,保证其在临界点仍可以满足时限。利用排队论中的M/M/1/K排队系统,根据非周期事件接收缓冲和可延期服务器定量分析非周期事件的平均响应时间和系统异步事件丢失率,使之符合系统要求。     

异构分布式系统混合型实时容错调度算法

基/副版本技术是实现实时分布式系统容错的一个重要手段。提出了一种异构分布式混合型容错模型,该模型与传统的异构分布式实时调度模型相比同时考虑了周期和非周期调度任务。在此基础上给出3种容错调度算法:以可调度性为目的SSA算法、以可靠性为目的RSA算法、以负载均衡性为目的BSA算法。算法能够在异构系统中同时调度具有周期和非周期容错需求的实时任务,且能够保证在异构系统中某节点机失效情况下,实时任务仍然能在截止时间内完成。最后从可调度性、可靠性代价、负载均衡性、周期与非周期任务数及任务周期与粒度J个方面对算法进行了分析。模拟实验结果显示算法各有优缺点,所以在选择调度算法时应该根据异构系统的特点来选择。     

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.     

控制系统中实时任务的动态优化调度算法

提出一种新的调度算法——带有非周期服务器的EDF调度算法.分析了所有任务的可调度性,给出了可调度条件,并给出一种新的周期性任务模型以及主优先级和辅助优先级的概念.它们在保证任务可调度的前提下,对周期性任务的采样频率和控制延时进行优化.仿真结果表明,该算法可以提高周期性任务的采样频率,并降低控制延时,即能优化系统的性能.     

基于RTAI改进的Linux实时调度算法

针对Linux实时内核RTAI的RMS调度算法CPU利用率不高的不足,结合CFS算法能公平对待所有任务的优点,实现一种新的调度算法EIC-CFS（Epoch Increase Control-Completely Fair Scheduler）。实验表明,EIC-CFS算法在负载较高的情况下,CPU的利用率较RMS算法大幅提高,改善了CFS算法因处理器周期自动增长而无法对任务做出实时响应和处理的不足。     

一种满足可靠性和能效的云工作流调度方法

为了同步解决云工作流调度时的失效和高能耗问题,提出一种基于可靠性和能效的工作流调度算法。算法为了在截止时间的QoS约束下最大化系统可靠性并最小化调度能耗,将工作流调度过程划分为四个阶段:计算任务优先级、工作流任务聚簇、截止时间子分配和任务调度。算法在满足执行次序的情况下对任务进行拓扑排序,并以通信代价最小为目标对任务进行聚簇;将截止时间在任务间进行子分割;以合适的频率/电压等级对聚簇后的任务进行调度,在确保可靠性的前提下最小化系统能耗。通过随机任务图和高斯消除任务图进行综合仿真测试,结果表明算法在降低总体能耗和提高工作流调度可靠性方面均优于对比算法。     

应用于实时系统的RMS算法的改进

本文阐述了以PLC为核心的HGJD001实验台电气控制系统，并采用上位计算机实现对实验台运行状态的通讯监测。     

基于命题投影时序逻辑的单调速率调度算法模型检测

提出了基于命题投影时序逻辑(propositional projection temporal logic,简称PPTL)的单调速率调度(rate monotonic scheduling,简称RMS)模型检测方法.该方法使用SPIN模型检测器的系统建模语言PROMELA为任务调度系统建模,使用PPTL描述系统期望的性质,通过SPIN验证系统模型是否满足性质,从而得知一个任务组在RMS下是否可调度.同时,RMS算法控制下的任务调度系统的其他性质也可以得到验证.     

Managing heterogeneous multi-system tasks to support enterprise-wide operations

The computing environment in most medium-sized and large enterprises involves old main-frame based (legacy) applications and systems as well as new workstation-based distributed computing systems. The objective of the METEOR project is to support multi-system workflow applications that automate enterprise operations. This paper deals with the modeling and specification of workflows in such applications. Tasks in our heterogeneous environment can be submitted through different types of interfaces on different processing entities. We first present a computational model for workflows that captures the behavior of both transactional and non-transactional tasks of different types. We then develop two languages for specifying a workflow at different levels of abstraction: the Workflow Specification Language (WFSL) is a declarative rule-based language used to express the application-level interactions between multiple tasks, while the Task Specification Language (TSL) focuses on the issues related to individual tasks. These languages are designed to address the important issues of inter-task dependencies, data formatting, data exchange, error handling, and recovery. The paper also presents an architecture for the workflow management system that supports the model and the languages. Recommended by: Omran Bukhres and e. Kühn     

Efficient implementation of tight response-times for tasks with offsets

Earlier approximate response time analysis (RTA) methods for tasks with offsets (transactional task model) exhibit two major deficiencies: (i) They overestimate the calculated response times resulting in an overly pessimistic result. (ii) They suffer from time complexity problems resulting in an RTA method that may not be applicable in practice. This paper shows how these two problems can be alleviated and combined in one single fast-and-tight RTA method that combines the best of worlds, high precision response times and a fast approximate RTA method. Simulation studies, on randomly generated task sets, show that the response time improvement is significant, typically about 15% tighter response times in 50% of the cases, resulting in about 12% higher admission probability for low priority tasks subjected to admission control. Simulation studies also show that speedups of more than two orders of magnitude, for realistically sized tasks sets, compared to earlier RTA analysis techniques, can be obtained. Other improvements such as Palencia Gutiérrez, González Harbour (Proceedings of the 20th IEEE real-time systems symposium (RTSS), pp. 328–339, 1999), Redell (Technical Report TRITA-MMK 2003:4, Dept. of Machine Design, KTH, 2003) are orthogonal and complementary which means that our method can easily be incorporated also in those methods. Hence, we conclude that the fast-and-tight RTA method presented is the preferred analysis technique when tight response-time estimates are needed, and that we do not need to sacrifice precision for analysis speed; both are obtained with one single method.

An efficient response-time analysis for real-time transactions with fixed priority assignment

In the general context of tasks with offsets (general transactions), only exponential methods are known to calculate the exact worst-case response time (WCRT) of a task. The known pseudo-polynomial techniques give an upper bound of the WCRT. In this paper, we present a new worst-case response-time analysis technique (mixed method) for transactions scheduled by fixed priorities, and executing on a uniprocessor system. This new analysis technique gives a better (i.e. lower) pseudo-polynomial upper bound of the WCRT. The main idea is to combine the principle of exact calculation and the principle of approximation calculation, in order to decrease the pessimism of WCRT analysis, thus allowing improving the upper bound of the response time provided while preserving a pseudo-polynomial complexity. Then we define the Accumulative Monotonic property on which a necessary condition of feasibility is discussed. We also propose, to speed up the exact and mixed analysis, the dominated candidate task concept that allows reducing significantly the number of critical instants to study in an analysis.     

Fault-Tolerant Rate-Monotonic Scheduling

Due to the critical nature of the tasks in hard real-time systems, it is essential that faults be tolerated. In this paper, we present a scheme which can be used to tolerate faults during the execution of preemptive real-time tasks. We describe a recovery scheme which can be used to re-execute tasks in the event of single and multiple transient faults and discuss conditions that must be met by any such recovery scheme. We then extend the original Rate Monotonic Scheduling (RMS) scheme and the exact characterization of RMS to provide tolerance for single and multiple transient faults. We derive schedulability bounds for sets of real-time tasks given the desired level of fault tolerance for each task or subset of tasks. Finally, we analyze and compare those bounds with existing bounds for non-fault-tolerant and other variations of RMS.     

Electromyographic effects of ergonomic modifications in selected meatpacking tasks.

This project evaluated the feasibility of a new method of collection of electromyographic (EMG) data during working conditions in industry, and quantified the effects of specific job modifications on the EMG activity of selected upper extremity muscle groups. Average root mean square (RMS) surface EMG activity, calibrated to force equivalent units, was collected on 20 workers from three pork processing tasks before and after ergonomic modifications to their tasks. Significant reductions in muscle effort were detected in the biceps and/or wrist and finger flexors after modification for two of the three tasks. This EMG measurement technique can be used to objectively validate reduced muscle effort with ergonomic modifications.