The scheduler’s balancing act of sensing and reacting: a behavioural perspective on scheduling

The scheduler has been extensively studied from the point of view of their schedules, using operations research. However, the scheduler not only fulfils a decision-maker role but also an informational role, responding to requests and disruptions, both from the supply and the demand side. Responding in a timely manner to such requests and disruptions is paramount for the scheduling job. Using a field study with job shadowing of schedulers in a Fortune 500 chemical company, we characterise the scheduler’s workflow in a simulation model; this allows us to discriminate between contextual factors of the scheduler’s job and behavioural factors inherent to them. Furthermore, it explicitly assesses the effect of increasing the frequency sensing of the outer world on responsiveness. Our findings show that the studied schedulers prioritise sensing activities related to checking emails rather than monitoring for disruptions in a decision support system. Thus, we find a higher potential for relative improvement in terms of responding to possible disruptions shown in decision support systems rather than responding to email requests. Moreover, we show that by adjusting email frequency checking and preemption behaviours, it is possible to revert an out of control situation to finite response times.     

多次抢占项目调度问题的混合遗传算法

研究多次抢占式资源受限的项目调度问题，假设任意时间点可作为资源抢占节点且抢占次数不受限制，建立满足多次资源抢占的线性整数规划模型并提出改进遗传算法对其进行求解。为克服遗传算法（GA）局部搜索能力缺陷，在算法中引入禁忌搜索（TS）进一步优化子代。针对性地设计了允许多次抢占的基于工作优先级编码策略以及串行调度方案生成机制。通过测试算例集实验调试算法参数，并以标准算例集（Project Scheduling Problem Library，PSPLIB）对算法进行可行性检验。实验结果表明，资源受限项目调度问题中引入多次抢占机制能有效缩减项目工期，设计的算法对问题求解效果良好。     

基于动态抢占阈值的实时调度

具有抢占阈值的调度算法集非抢占调度和纯抢占调度的特点，既减少了由于过多的随意抢占造成的CPU资源浪费，又保证了一定的任务截止期错失率及CPU资源利用率。已有的工作基本集中于讨论任务集完全给定，任务数、任务的优先级及任务的抢占阈值在调度前已完全确定，而且要求不同的任务具有不同的优先级，提出的具有抢占阈值的调度算法，完全放松了对这些条件的限制，即任务的个数不确定，任务的优先级及其抢占阈值在调度过程中可以动态地变化。最后以常用的LSF调度策略为例，结合动态的抢占阈值进行仿真，仿真结果表明，对于不确定的任务集、任务优先级和抢占阈值，利用具有抢占阈值的动态调度算法，降低了任务截止期错失率、提高了CPU的有效使用率。     

Preemptive Semi-Online Scheduling with Tightly-Grouped Processing Times

This paper investigates a preemptive semi-online scheduling problem on m identical parallel machines where m = 2,3. It is assumed that all jobs have their processing times in between p and rp (p > 0, r≥1). The goal is to minimize the makespan. Best possible algorithms are designed for any r≥1 when m = 2,3.     

改进的最小空闲时间优先调度算法

最小空闲时间优先(least slack first,简称LSF)算法结合任务执行的缓急程度来给任务分配优先级.任务所剩的空闲时间越少,就越需要尽快执行.然而,LSF算法造成任务之间的频繁切换或严重的颠簸现象,增大了系统开销,并限制了其应用.在调度策略中设置抢占阈值可以减少任务之间的切换,但现有的抢占阈值设置方法因受到固定优先级的限制而不适用于LSF算法.为了减轻LSF算法的颠簸现象,基于抢占阈值的思想,提出适用于LSF算法的抢占阈值分配方法,动态地给每个任务配置抢占阈值.任务的抢占阈值是随着任务执行的缓急程度不同而动态地变化的,而且不受任务个数的限制.仿真结果表明,通过对LSF算法的改进,任务之间的切换大大减少,同时降低了任务截止期错失率.该改进型算法对设计和实现实时操作系统具有一定的参考价值.     

面向对象实时多任务系统的优化实现模型

论文提出了一种基于抢占门限的实时多任务系统的优化实现模型,它同时具有低开销与高可调度性。该模型扩展了固定优先级调度模型,同时通过实现模型中线程数的减少实现了运行时的低开销。文中同时也讨论了互不抢占分组的实现算法及每个任务最大抢占门限的分配算法。     

具有优先级特征的多媒体流的资源管理

本文研究了具有优先级特征的分布式多媒体流的资源管理，提出了一种基于节优先级的资源管理的设计方法，包括资源管理机制，资源管理策略，服务质量（ＱｏＳ）协商调整算法和高优先级节枪占算法，它能够保证稳定的具估优先级特征的多媒体流，能够极大地调度并发的多媒体流，特别是在系统资源不足时，能够最大限度地调度高优先级的多媒体流，并能保证各多媒体流量了的ＱｏＳ。     

一个高分子模拟计算网格的作业管理

高分子模拟计算网格为复杂材料研究人员提供了分子模拟软件、计算资源和信息共享的平台。设计和实现了网格作业管理模块，包括作业的提交、调度和监视，为用户提供了一个透明的网格资源的使用方法。该模块已经成功部署到高分子模拟计算网格系统中，试验结果表明，作业管理为网格用户提供更好的服务质量，实现了对网格资源的优化使用。     

一种不影响任务集合可调度性的优先级映射算法

采用静态优先级调度的实时系统中,当任务个数多于优先级个数时,只能给多个任务分配相同的优先级·现有分配算法增大了高优先级任务的最坏情况响应时间,可能造成任务集合不可调度·利用抢占阈值的调度算法,能在提高任务集合可调度性的同时,使用较少的线程·但所用优先级个数没有减少·提出了一种优先级映射算法———阈值段间映射法(threshold segment mapping,TSM),以及与之配合的事件驱动线程框架·证明了TSM是严格排序的·仿真结果表明,在保证任务集合可调度的前提下,TSM使用了比现有映射算法更少的优先级·     

On Schedulability Analysis of AADL Architecture with Storage Resource Constraint

Embedded systems have been widely applied in real-time automatic control systems, and most of these systems are safety-critical, for example, the engine control systems in an automobile and the avionics in an airplane. It is very important to verify the schedulability of such a real-time embedded system in its early design stages, so as to avoid unexpected loss for the debugging of architecture design problems. However, it has been proved to be a tough challenge to evaluate the schedulability of a Preemptive-Scheduling Real-Time (PSRT) system, especially when the constraints of system resources are taken into consideration. The cache memory built inside the processor is an exclusive-accessing resource shared by all the tasks deployed on the processor. In addition, the Cache-Related Preemption Delay (CRPD) caused by preemptive task scheduling will bring extra time to the execution time for all the tasks. Thus, the CRPD should be taken into consideration when the Worst-Case Execution Time (WCET) of tasks is estimated in a real-time system. A model-based evaluation and verification method of architecture schedulability, which is designed for priority-based PSRT systems, is proposed in this study to make cache resource constrained and CRPD related schedulability evaluation based on the AADL system architecture model. In the first step, the study enhances the property set of AADL storage elements to make it compatible with cache memory properties in a system architecture model. Secondly, the study proposes a set of algorithms to estimate the CRPDs of a task before it is completed; run system schedule simulation and construct the schedule sequence with the constraint of cache resources and CRPDs involved; and make WCET estimation of the tasks in such a CRPD considered, preemptive-scheduling execution sequence. Finally, the methods mentioned above are implemented within a prototype software toolkit, which is designed to make evaluation and verification of system schedulability within CRPD constraints. The toolkit is tested with a use case of aircraft airborne open-architecture intelligent information system. The result shows that, compared with the schedule sequence constructed without cache memory resource constraints, the WCET estimated for most tasks is extended, and the sequence order is changed. In some extreme cases, when CRPD is taken into consideration, some tasks are evaluated to be incompletable. The test shows that the method and algorithms proposed in this study are feasible.