不可抢占式EDF调度算法的可调度性分析

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。     

端到端时间约束的实时任务动态调度算法

在单处理机系统中,由于计算高优先级任务抢占的时间相对比较简单,所以单处理机调度理论取得了长足的进步.提出一个端到端时间约束的实时任务调度算法,当实时任务到达系统时,算法为任务的每个子任务在相应的处理机上预约一定的计算资源,把端到端的多处理机调度问题转换成单处理机调度问题,从而可以利用单处理机调度理论判定实时任务的可调度性.实验表明,该算法明显地提高了CPU利用率和任务接收率.     

EDF调度算法可调度性分析方法的改进研究

任务集的可调度性分析是实时系统研究和应用的关键问题。针对抢占式与不可抢占式EDF(earliest deadline first)调度算法, 分别给出了实时任务集新的可调度性测试条件, 针对任务集为可调度时可以实现快速判定。通过与已有的EDF算法的可调度性判定充要条件相结合, 提出了改进的抢占式与不可抢占式EDF算法的可调度性分析方法。仿真实验表明, 相对现有EDF算法的可调度性分析方法, 所提出的方法能有效提高算法性能。     

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。     

端到端实时CORBA系统调度模型及其可调度性研究

实时CORBA系统中的基本问题是如何合理分配有限的计算资源和通信资源以保证各个实时任务的时间需求。该文以固定优先级方式调度的、周期性任务的硬实时系统为研究对象，提出了端到端实时CORBA系统调度模型，该模型综合考虑了客户端系统的处理、服务对象处理、网络传输等几大主要因素，而且可以描述服务对象间的嵌套调用关系，因而能全面描述实时CORBA系统中客户调用过程。在此基础上，该文基于非连续工作型同步协议，应用时间需求分析方法，研究并提出了该模型的可调度性分析算法。     

CAN总线中改进的EDF调度算法可调度性分析

针对于CAN总线的调度问题,因现有的平均分区EDF调度算法在对于优先级反转问题上收效甚微,从而导致消息缺乏一定的可调度性,故提出一种改进的基于幂函数分区的EDF算法;同时借助量化误差的概念,对该调度算法进行可调度性分析,充分论证了在该调度算法下,消息可调度的判定条件;采用CANoe平台进行实验仿真,对比平均分区EDF调度算法和双幂函数分区EDF调度算法,经试验测试验证了双幂函数分区EDF调度算法的可行性和优越性,改善了消息的最坏响应时间,提高了CAN网络通讯的实时性。     

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。     

全局EDZL实时调度算法的可调度性判定

可调度性判定就是离线验证实时系统中所有任务是否可调度。通过可调度性判定,能够更好地保证实时系统的可靠性。有多种分析方法可用于可调度性判定,得到的结果有所不同。通过分析在多处理器实时系统中全局EDZL算法的任务需求,考虑带入作业和带出作业对处理器资源的需求。引入最大连续忙区间的概念,以确定带入作业的最大个数,得到了多处理器实时系统中全局EDZL算法的可调度性判定算法。实验结果说明了这种方法提高了通过可调度性判定的任务数量,是一种更紧密的可调度性判断方法。     

基于随机模型的软实时系统的任务期望可调度性

本文基于随机模型研究了软实时系统中任务的可调度性特征,提出了期望可调度性的概念. 期望可调度性是与实时任务到达时间t相关的, 因此, 提出的方法能研究任务子集在任意给定时间间隔的可调度性特征. 本文给出了期望可调度性的条件, 如果任务的持续时间满足该条件, 则实时任务具有期望可调度性. 基于理论结果的数值分析与模拟结果是一致的,这表明当软实时系统的负载率小于69%(某些确定性模型提供的)时, 实时任务总是期望可 调度的. 这一结果也表明基于随机模型的期望可调度性方法能为软实时系统的任务可调度性分析提供一个更大的阈值和更好的适应性.     

基于EDF调度算法的端到端延迟保证方法

EDF(EarliestDeadlineFirst)是一种高效的调度算法。为了将其应用于提供端到端延迟保证,提出了一种新的算法JT-EDF(JitterTunableEDF),并证明了所有的端到端EDF调度算法都可以在相同的条件下保证相同的端到端延迟界。     

容错优先级可提升的抢占阈值容错调度算法

基于软件容错模型,提出了允许容错优先级提升的抢占阈值容错调度算法(extended fault-tolerantfixed-priority with preemption threshold,简称FT-FPPT*).该算法能够在抢占式容错调度算法(fault-tolerantfixed-priority preemptive,简称FT-FPP)和抢占阈值容错调度算法(fault-tolerant fixed-priority with preemptionthreshold,简称FT-FPPT)无法提高系统容错能力的情况下,进一步提高系统的容错能力.为了获得系统中任务优先级分配的最佳策略,基于任务最坏响应时间的可调度性分析,提出了一种最优的优先级配置搜索算法(priorityassignment search algorithm,简称PASA).经过深入分析和实验证明,与FT-FPPT算法相比,FT-FPPT*算法能够有效地提高硬实时系统的容错能力.     

实时调度EDZL算法的可调度性判定

针对多处理器实时调度中的EDZL调度算法,利用多任务之间的相互干涉关系,找出与多处理器之间的时间约束条件,提出了一种可调度性判定的方法,并对给出的判定方法进行了证明。给出了一种判定多处理器实时EDZL可调度性的算法,这种方法可在设计多处理器实时系统时使用。     

Feasibility analysis of real-time transactions

The objective of this paper is two-fold: give a survey of response time analysis (RTA), and contribute to schedulability analysis for the real-time transaction model. The RTA is studied under fixed priority policies (FPP), while schedulability analysis assumes an optimal scheduling algorithm (like the deadline driven scheduling algorithm EDF) in a preemptive context on uniprocessor systems. We compare the transaction model to the family of multiframe models, then present the exact, and approximated methods, as well as a tunable method to compute the RTA. Finally we present a new schedulability analysis method and an efficient algorithm to speed up this test.     

Improved multiprocessor global schedulability analysis

A new technique was recently introduced by Bonifaci et al. for the analysis of real-time systems scheduled on multiprocessor platforms by the global Earliest Deadline First (EDF) scheduling algorithm. In this paper, this technique is generalized so that it is applicable to the schedulability analysis of real-time systems scheduled on multiprocessor platforms by any work-conserving algorithm. The resulting analysis technique is applied to obtain a new sufficient global Deadline Monotonic (DM) schedulability test. It is shown that this new test is quantitatively superior to pre-existing DM schedulability analysis tests; in addition, the degree of its deviation from any hypothetical optimal scheduler (that may be clairvoyant) is quantitatively bounded. A new global EDF schedulability test is also proposed here that builds on the results of Bonifaci et al. This new test is shown to be less pessimistic and more widely applicable than the earlier result was, while retaining the strong theoretical properties of the earlier result.     

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。     

Rolling-horizon scheduling for energy constrained distributed real-time embedded systems

Energy-efficient scheduling approaches are critical to battery driven real-time embedded systems. Traditional energy-aware scheduling schemes are mainly based on the individual task scheduling. Consequently, the scheduling space for each task is small, and the schedulability and energy saving are very limited, especially when the system is heavily loaded. To remedy this problem, we propose a novel rolling-horizon (RH) strategy that can be applied to any scheduling algorithm to improve schedulability. In addition, we develop a new energy-efficient adaptive scheduling algorithm (EASA) that can adaptively adjust supply voltages according to the system workload for energy efficiency. Both the RH strategy and EASA algorithm are combined to form our scheduling approach, RH-EASA. Experimental results show that in comparison with some typical traditional scheduling schemes, RH-EASA can achieve significant energy savings while meeting most task deadlines (namely, high schedulability) for distributed real-time embedded systems with dynamic workloads.     

Component-oriented radars with probabilistic timing guarantees

In recent years, many modern phased-array radars are built with commercial off-the-shelf components, and the functions of many hardware components are also reimplemented by software modules. In such systems, radar tasks could be modeled as distributed real-time tasks which require end-to-end deadline guarantees and have precedence constraints. Different from most previous work on either algorithms with restrictions in resource utilization or heuristics without analytical ways for schedulability guarantees, the objective of this paper is to propose a joint real-time scheduling algorithm for both transmitter/receiver and signal processor workloads with an analytical framework for offline probabilistic analysis and online admission control. The strength of our approach is verified by analysis results and a series of experiments based on a real phased-array radar for air defense frigates.     

Low-Power Design for Real-Time Systems

Real-time Systems often are located in the special environments where the power consumption is a big concern. Upon presence of timing constraints, the low power design on the real-time systems has significant impact on the performance as well as the schedulability of the systems. The system developers are facing the challenges for reducing the power consumption and meeting the timing constraints in the real-time systems.This paper represents one of few attempts to address the issue of the low power design on real-time systems. We present two power reduction methods: one is at the software compilation level and the other at the operating system level. Given a real-time program, an inter-instruction power reduction technique is proposed to transform the program to another one with lower power consumption. In addition, a scheduling algorithm for real-time operating systems is proposed to reschedule real-time programs when the execution time of the programs is changed. Therefore, the proposed scheduling algorithm works together with the proposed power reduction technique to make sure all programs meet their deadlines and to improve the system schedulability. We also evaluate the performance of the proposed inter-instruction reduction method by comparing it with the cold scheduling algorithm and show that the proposed method outperforms the cold scheduling algorithm and reduces more energy power.