MVB非周期信息的实时能力分析

MVB的实时能力是基于TCN的列车网络控制系统实时性能的重要保证,详细分析了MVB非周期信息的通信原理和调度流程,对仲裁延迟进行了具体的定义,在研究MVB周期信息和非周期信息带宽占用的基础上,给出了MVB非周期信息的最差情况响应时间.根据非周期信息的各种轮询机制,建立不同优先级的最差情况响应时间计算公式.在此基础上,提出了非周期信息实时能力优化策略,分析表明,该策略有效提高了MVB非周期信息的实时通信能力.     

MVB非周期信息的通信带宽分配策略研究

多功能车辆总线MVB需要传送具有高实时性要求的周期信息和随机到达的非周期信息,合理分配相应信息带宽可以提高整个网络的通信带宽利用率.在分析各类信息特点的基础上,提出了非周期信息通信的两种带宽分配策略.结合MVB非周期信息的调度方法,对两种策略进行了分析研究和性能比较,给出了各种策略的适用范围.     

具有依赖关系的周期任务实时调度方法

随着多核技术在嵌入式领域的快速发展,越来越多的功能被集成在同一个平台上,任务之间的关系越来越复杂.而当前大多数的实时周期任务的调度模型都是不考虑任务之间关系的相互独立的任务模型.文中则针对具有依赖关系的周期任务,提出了一种基于ST(Simple-Tree)的实时周期任务调度模型,通过该模型来维护任务之间的依赖关系.此外,为了有效地提高系统利用率以及降低死限丢失率,文中还提出了可延迟时间越短越优先的调度方法并和RM算法、EDF算法进行仿真实验比较,结果表明该方法具有较高的核利用率和较低的死限丢失率.     

反馈控制实时调度中采样周期的研究

以CPU资源调度为典型应用背景，研究并分析了采样周期对反馈控制实时调度和一般数字控制系统性能影响的差异，通过仿真实验得出采样周期的选择对反馈控制实时调度性能影响规律，提出了采样周期的选择方法。对于平均执行时间难以预测的任务集，提出一种可变采样周期的有效解决方案。     

混合实时事务的延期单调速率调度算法及其可调度性分析

对于含有实时和非实时两部分的混合实时应用,传统的单调速率调度算法(RM)已不再适用.为此,该文引入“混合实时事务”的概念,并针对这类事务提出一种延期单调速率调度算法(DRM);着重分析了DRM算法对混合实时事务的可调度性;进行了实验测试与性能分析比较．结果表明,事务集中混合实时事务占的比例越高,混合事务中非实时子事务占的比例越大,该算法的CPU使用率阈值就越高,且在各种情况下,DRM算法与RM算法相比性能都更优,最低情况也与之一样．     

实时事务调度及静态可调度性分析

在类似闭环控制的硬实时数据库应用环境,实时事务具有一定的静态可预报性,其中实时事务的可调度性分析是维护实时数据库时间正确性的基础.通过利用抢占阈值,提出了一种新的实时事务处理模型,它集成了CPU调度和数据调度,实现离线并发控制,具有单阻塞的特征与好的静态可预测性,并有利于降低事务系统的负载和改善可调度性.进一步由此建立了实时事务的静态可调度性分析模型以及求最优可行调度的整数规划模型,该模型有利于达到实时事务调度的整体优化.     

RTSIM：一种实时调度模拟框架

针对现有的模拟工具无法同时满足实时可调度性分析、调度结果的图表化显示及算法动态可替代性等问题,利用python的Matplotlib库与动态加载技术,提出一种实时调度模拟框架——RTSIM。模拟实时调度算法的调度过程,并验证算法的可调度性是一项较复杂的问题。实验结果表明,RTSIM能够较好地完成对实时调度算法的验证和模拟。     

基于双优先级的实时多任务动态调度

提出了带有非周期服务器的双优先级调度算法.该算法将优先级带宽分为高带、中带和低带3部分.强实时任务实例到达后,优先级设置在低带,经过一段时间后将其优先级提升到高带;软实时任务的优先级设置在中带.分析了强实时任务实例优先级提升时间和任务集的可调度性.     

实时Petri网及其在任务可调度性分析中的应用

本文描述了一种实时任务可调度性分析工具－实时Petri网,给出了由数据流图向实时Petri网转化的方法,介绍了应用实时Petri网进行可调度性分析折步骤,最后讨论了不可调度的情形和处理方法。     

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%.     

优先级周期性互换的实时调度算法

针对实时多任务调度时低优先级任务的延迟问题,提出了一种优先级周期性互换的静态优先级调度算法。该方法以固定的时间片为周期,对多任务系统中的某两个不同优先级的独立性任务,周期性地互换它们的优先级级别,在保证较高优先级任务的执行时间的前提下,使得较低优先级的任务有机会尽快执行,以缩短其执行过程中的延迟时间。所提方法能有效解决低优先级任务的实时性问题,从而提高实时多任务系统的整体控制性能。     

Real-time load balancing scheduling algorithm for periodic simulation models

A scheduling algorithm is crucial for real-time simulations because it guarantees that each model meets its deadline. Traditional online real-time scheduling algorithms such as Earliest Deadline First (EDF) introduce a high overhead when scheduling a large number of models. In this paper, a new algorithm called time-stepped load balancing (TLS) is proposed to address the real-time execution of a model set in a time-stepped simulation. A load balancing schedule table is generated before a simulation and rebalanced at runtime to dynamically schedule the changed model set. This table is organized by the execution periods of the models and balanced according to the load of each time step. Moreover, the slack time is distributed evenly among the steps to improve the real-time reliability. An extension to the algorithm for a multi-core environment is further studied to address those models with long execution times. Experimental results show that our scheduling algorithm outperforms the classical EDF approach. The highest performance improvement of TLS over EDF reaches 3–4% in terms of saving processor resources, and the jitter is about 4 times less when 90 entities are employed in a typical tank combat simulation scenario.     

Schemes for scheduling control messages by hierarchical protocols

The paper addresses the problem of designing efficient scheduling policies for the transmission of control messages by hierarchical network protocols. Such protocols encounter a tradeoff between the desire to forward a control message across the tree as soon as it is received, and the desire to reduce control traffic. Scheduling problems that arise in this context are defined and discussed. The paper mainly concentrates on minimizing the average extra delay encountered by the control messages under an upper bound on the number of outgoing messages a node can send during a fixed period of time. A polynomial-time algorithm is presented for the off-line version of the problem, and then several efficient on-line heuristics are presented and compared.     

Real-time scheduling of periodic tasks with processing times and deadlines as parametric fuzzy numbers

Task scheduling is very important in real-time systems as it accomplishes the crucial goal of devising a feasible schedule of the tasks. However, the uncertainty associated with the timing constrains of the real-time tasks makes the scheduling problem difficult to formulate. This motivates the use of fuzzy numbers to model task deadlines and completion times. In this paper a method for intuitively defining smooth membership functions (MFs) for deadlines and execution times has been proposed using mixed cubic-exponential Hermite interpolation parametric curves. The effect of changes in parameterized MFs on the task schedulability and task priorities are also reported. A new technique is proposed based on the concept of dynamic slack calculation to make the existing model more practical and realistic. Examples are given to demonstrate the more satisfactory performance of the new technique.     

周期性任务调度的装箱算法

针对基于时间触发的CAN控制系统,给出了确定周期性任务表中的基本周期的两种策略,提出了构造周期性任务调度表的下次适应、降序下次适应、最佳适应和降序最佳适应四种算法,分析了这四种不同算法的时间复杂度和最坏渐近性能比,最后对不同规模下的四种算法进行了仿真比较,结果表明文中给出的四种算法效果均优于经典的一维装箱算法。     

Perfect periodic scheduling for three basic cycles

Periodic scheduling has many attractions for wireless telecommunications. It offers energy saving where equipment can be turned off between transmissions, and high-quality reception through the elimination of jitter, caused by irregularity of reception. However, perfect periodic schedules, in which each (of $n$ ) client is serviced at regular, prespecified intervals, are notoriously difficult to construct. The problem is known to be NP-hard even when service times are identical. This paper focuses on cases of up to three distinct periodicities, with unit service times. Our contribution is to derive a $O(n^4)$ test for the existence of a feasible schedule, and a method of constructing a feasible schedule if one exists, for the given combination of client periodicities. We also indicate why schedules with a higher number of periodicities are unlikely to be useful in practice. This methodology can be used to support perfect periodic scheduling in a wide range in real world settings, including machine maintenance service, wireless mesh networks and various other telecommunication networks transmitting packet size data.     

Preference-oriented fixed-priority scheduling for periodic real-time tasks

Traditionally, real-time scheduling algorithms prioritize tasks solely based on their timing parameters and cannot effectively handle tasks that have different execution preferences. In this paper, for a set of periodic real-time tasks running on a single processor, where some tasks are preferably executed as soon as possible (ASAP) and others as late as possible (ALAP), we investigate Preference-Oriented Fixed-Priority (POFP) scheduling techniques. First, based on Audsley’s Optimal Priority Assignment (OPA), we study a Preference Priority Assignment (PPA) scheme that attempts to assign ALAP (ASAP) tasks lower (higher) priorities, whenever possible. Then, by considering the non-work-conserving strategy, we exploit the promotion times of ALAP tasks and devise an online dual-queue based POFP scheduling algorithm. Basically, with the objective of fulfilling the execution preferences of all tasks, the POFP scheduler retains ALAP tasks in the delay queue until their promotion times while putting ASAP tasks into the ready queue right after their arrivals. In addition, to further expedite (delay) the executions of ASAP (ALAP) tasks using system slack, runtime techniques based on dummy and wrapper tasks are investigated. The proposed schemes are evaluated through extensive simulations. The results show that, compared to the classical fixed-priority Rate Monotonic Scheduling (RMS) algorithm, the proposed priority assignment scheme and POFP scheduler can achieve significant improvement in terms of fulfilling the execution preferences of both ASAP and ALAP tasks, which can be further enhanced at runtime with the wrapper-task based slack management technique.     

On periodic resource scheduling for continuous-media databases

The Enhanced Pay-Per-View (EPPV) model for providing continuous-media services associates with each continuous-media clip a display frequency that depends on the clip's popularity. The aim is to increase the number of clients that can be serviced concurrently beyond the capacity limitations of available resources, while guaranteeing a constraint on the response time. This is achieved by sharing periodic continuous-media streams among multiple clients. The EPPV model offers a number of advantages over other data-sharing schemes (e.g., batching), which make it more attractive to large-scale service providers. In this paper, we provide a comprehensive study of the resource-scheduling problems associated with supporting EPPV for continuous-media clips with (possibly) different display rates, frequencies, and lengths. Our main objective is to maximize the amount of disk bandwidth that is effectively scheduled under the given data layout and storage constraints. Our formulation gives rise to -hard combinatorial optimization problems that fall within the realm of hard real-time scheduling theory. Given the intractability of the problems, we propose novel heuristic solutions with polynomial-time complexity. We also present preliminary experimental results for the average case behavior of the proposed scheduling schemes and examine how they compare to each other under different workloads. A major contribution of our work is the introduction of a robust scheduling framework that, we believe, can provide solutions for a variety of realistic EPPV resource-scheduling scenarios, as well as any scheduling problem involving regular, periodic use of a shared resource. Based on this framework, we propose various interesting research directions for extending the results presented in this paper. Received June 9, 1998 / Accepted October 13, 1998     

多功能车辆总线周期扫描表优化设计

针对参与通信的各周期信息特点设计优化的多功能车辆总线周期扫描表对提高列车通信网络的实时性能具有重要作用;标准推荐的周期轮询算法存在周期信息分布不均匀,带宽利用率相差较大的问题,在对周期扫描表的优化设计方法进行深入研究后,提出基于模拟退火算法的优化方案。建立了周期信息通信模型,详细阐述了通信抖动的概念并对其进行了定义。给出了优化目标函数并采用模拟退火算法进行求解,对算法的几个关键步骤进行了设计,并采用改进策略提高了模拟退火算法效率。通过实例仿真证明该算法实现了周期信息在整个宏周期范围内的均匀分布,优化了周期扫描表的构造。