基于EDF算法的嵌入式Linux实时调度策略

随着Linux广泛应用于嵌入式系统、实时控制等领域,增强Linux内核的实时性变得尤为重要。Linux2.6内核加入了抢占点,可以最大限度地降低内核不可抢占的时间间隔,但嵌入式系统实时性要求较高。本文分析Linux内核的调度策略,指出其应用于实时系统时存在的不足,提出一种改进的的实时调度策略,该策略吸取了最早期限优先调度算法的优点,使内核可以在任何时间被抢占,测试结果表明应用此策略的内核任务响应时间少,从而进一步提高了嵌入式Linux的实时性。     

一种新的嵌入式Linux实时调度算法

针对现有实时调度算法在实时性能上的不足,提出了一种新的实时任务分类调度算法,根据实时任务的到达情况进行分类,划分为周期任务和非周期任务,并对不同类型的实时任务使用不同的改进的实时调度算法.通过实验,证明此算法与现有实时调度算法相比,综合实时性能有了很大程度的提高.     

ASIC设计中一种基于硬件的实时仿真系统

介绍了一种基于硬件的实时仿真系统的设计与实现,它用于带有内嵌ＣＰＵ的专用集成电路的仿真与验证。与软件仿真相比,它具有实时性强、可靠性高等优点。使用硬件实时仿真系统,一方面可以验证目标芯片设计的正确性与可靠性,并确定目标芯片中的一些重要参数;另一方面也为目标芯片中内嵌ＣＰＵ的软件设计构建硬件平台。该设计已应用于智能电话要机控制芯片,并有较强的可移植性。     

基于Xenomai/Linux实时调度算法研究

针对Xenomai／Linux双内核实时操作系统实时调度的单一性,在Xenomai原有的实时调度机制上增加了RM和EDF调度器。经过实验测试表明：新的调度机制增强了系统的灵活性。     

EDF调度算法抢占行为的研究及其改进

通过对采用抢占式EDF算法的嵌入式系统中各实时任务抢占行为的分析,建立了一个周期性任务集的抢占模型,从数学上描述了抢占关系、可调度性、调度开销与实时任务的周期、执行时间、最终期限、启动时间等属性之间的关系.依据该抢占模型,提出了一个改进的抢占式EDF调度算法,通过将基于遗传算法的优化方法离线计算得到的实时任务启动时间作为目标系统的一个调度参数,减少抢占次数,改变抢占关系,从而提高系统的可调度能力和实时性能.最后用实验验证了改进的抢占式EDF调度算法的有效性.     

一种新的基于可配置处理器的异构多核线程级动态调度模型

本文针对基于可配置处理器的异构多核结构,提出一种新的线程级动态调度模型。此类异构多核系统中每个核分别针对某一应用做指令集扩展,调度器通过线程、处理器核以及指令集间的映射关系,动态调度线程至适合的处理器核,从而在没有大幅增加芯片面积的前提下,达到与每个核都具有全扩展指令集相近似的加速比,此外该模型还可以有效减少编程模型的复杂度。     

一种新的基于优先级表的实时调度算法

本文提出了一种新的基于优先级表的实时调度算法,称作截止期—价值密度优先(Deadline - Value Density First)算法,简称DVDF算法.DVDF算法综合考虑了实时任务的截止期和价值密度两个参数,能够更好地适应不同的负载情况.通过使用正常负载和过载情况下的典型数据对算法进行仿真研究表明,这种算法比单纯考虑截止期的EDF(Earliest Deadline First)算法在性能方面有明显的改进,特别是在系统过载的情况下,能够优雅地降级.     

FQLP:ATM网中一种新的实时业务调度算法

 本文提出了基于丢失优先权公平队列(FQLP)调度算法.理论分析和仿真实验表明FQLP调度算法能保证实时业务获得的网络资源不小于预约带宽,为实时业务提供确定的时延上界.FQLP调度算法利用ATM网络中的信元优先权机制,提高了网络资源的利用率.同时FQLP调度策略能保证信元的发送顺序.     

一种适用于宽带无线城域网实时业务的分组调度算法

对宽带无线城域网（WMAN）而言,分组调度算法是保证用户服务质量（QoS）、平衡用户间公平性的关键。在研究比例公平调度算法（PF）算法与修正的最大加权时延优先算法（M-LWDF）的基础上,一种新的适用于宽带无线城域网实时业务的分组调度算法被提出,此算法引入了新的衡量服务队列负载的信息,能够实时地更新状态参数,提高了系统性能。仿真结果表明,此算法在保证系统吞吐量的同时,比M-LWDF算法具有更好的时延特性和公平性。     

实时任务调度器硬件化的设计与实现

硬件化的实时任务调度器使用VHDL语言进行编写,使用组合逻辑电路和时序逻辑电路实现基于优先级的时间片轮转调度算法。由门电路搭建而成的硬件化调度器独立于内核之外,根据连接内核的数量,在编译时进行调整,同时对多个结构相同或不同的内核进行调度。内核只需要执行任务,不需要进行任务调度,以此来减轻对处理器的负担,提升操作系统的实时性和可靠性。     

多功能一体化雷达任务调度算法研究

雷达、电子战、通信等多功能电子系统一体化是雷达的发展方向之一,资源管理与调度技术是一体化雷达的关键技术。针对基于孔径分割实现雷达、电子对抗、通信等多种功能的一体化系统的任务调度问题,对系统任务建模、调度算法设计、算法评价指标进行了探讨。在研究常规相控阵雷达调度策略的基础上,提出了采用多任务并行EDF(Earliest Deadline First)算法来实现系统的自适应调度。最后对比常规多功能雷达的自适应调度进行了仿真比较,且对仿真结果进行了定量分析,结果表明采用多任务并行EDF(MTPEDF)算法的基于孔径分割的一体化雷达系统具有一定的优越性。     

Earliest Deadline First Scheduling with Active Buffer Management for Real-Time Traffic in the Internet

We studied the problem of QoS guarantee for differentiated services. A two-level hierarchical scheduling framework was deployed to separate QoS metrics. Due to its desirable property of minimizing the maximum packet lateness, the Earliest Deadline First (EDF) scheduling was adopted to provide the in-class scheduling for the time-sensitive traffic. We employed an EDF scheduler combined with an active buffer management scheme (CHOKe) to improve the fairness of resource allocation and to maintain a good delay performance for real-time applications. Simulation results showed that the proposed scheme can achieve a better delay performance and make a more fair bandwidth allocation between the real-time TCP and UDP connections than the First Come First Served (FCFS) scheduling with the drop-tail buffer management which is commonly deployed in traditional IP routers.     

Efficient Scheduling Algorithms for Real-Time Service on WDM Optical Networks

One of the important issues in the design of future generation high-speed networks is the provision of real-time services to different types of traffic with various time constraints. In this paper we study the problem of providing real-time service to hard and soft real-time messages in Wavelength-Division-Multiplexing (WDM) optical networks. We propose a set of scheduling algorithms which prioritize and manage message transmissions in single-hop WDM passive star networks based on specific message time constraints. In particular, we develop time-based priority schemes for scheduling message transmissions in order to increase the real-time performance of a WDM network topology. We formulated an analytical model and conducted extensive discrete-event simulations to evaluate the performance of the proposed algorithms. We compared their performances with that of the state-of-the-art WDM scheduling algorithms which typically do not consider the time constraint of the transmitted messages. This study suggests that when scheduling real-time messages in WDM networks, one has to consider not only the problem of resources allocation in the network but also the problem of sequencing messages based on their time constraints.     

公平调度的分组调度算法设计

针对无线实时多媒体业务应用,该文在算法Exponential rule(Exp)基础上提出了一种增强调度公平性能的Modified Exponential rule(MExp)分组调度算法。通过理论分析和系统级仿真对算法性能进行了分析和验证。     

用于开放式系统的二维优先级实时调度

提出了一种新的用于开放式系统的调度机制,即二维优先级实时调度,它不仅划分任务优先级,还划分调度策略优先级.任务的执行顺序由其调度策略优先级和任务优先级共同决定.它不仅可以解决传统优先级调度机制中机制与调度策略不能相分离的问题,还提高了效率.这种机制中引入的CPU带宽控制策略,可以根据需要实现硬实时、软实时、混合实时不同目标的实时系统,并简化了任务可调度性分析,且可以为不同权限或级别的用户提供不同QoS服务.这种调度架构不仅效率高,而且具有很强的开放性,适用广、易扩展.     

Real-Time Traffic Scheduling and Routing in Packet-Switched Networks Using a Least-Laxity-First Strategy

In this paper, we address the problem of transmission scheduling and buffer management at a switch in a high-speed packet-switched network. Future computer networks are expected to carry bursty real-time multimedia traffic with specific time-delay requirements. We propose a technique to schedule competing packets at a switch in a packet-switched network with two objectives—(i) maximizing the number of packets that would reach their destination before their deadline has been reached (ii) minimizing the number of packets dropped in transit in the network. The method is broadly based on the popular least-laxity heuristic in real-time process scheduling and is combined with buffer management at the switch.     

WiMax终端上行调度算法的研究与设计

在对WiMax终端的不同业务类型调度算法进行分析的基础上,提出了一种有效的上行调度算法实现策略.与传统的基于严格优先级的调度算法相比,本算法在保证各业务QoS参数的基础上,提高了不同业务之间的公平性,使优先级较低的业务也可以获得相应的调度机会.     

Scheduling Real-Time Traffic With Deadlines over a Wireless Channel

Recently, there has been widespread interest in the extension of data networks to the wireless domain. However, scheduling results from the wireline domain do not carry over to wireless systems because wireless channels have unique characteristics not found in wireline channels, namely, limited bandwidth, bursty channel errors and location-dependent channel errors.In this paper, we study the problem of scheduling multiple real-time streams with deadlines, over a shared channel. We show that, in general, unlike the wireline case, the earliest due date (EDD) or shortest time to extinction (STE) policy is not always the optimal policy, even if the channel state is perfectly known and EDD is implemented only over channels in a Good state. Here, optimality is measured with respect to the number of packets lost due to deadline expiry. However, for most values of the channel parameters that are of practical interest, we show through analytical and numerical results that the EDD policy over Good channels is nearly optimal. Finally, through simulations, we also show that by combining this policy with fair scheduling mechanisms would result in scheduling algorithms that provide some degree of isolation between the sources as well as provide a natural way of compensating channels that see prolonged error bursts.     

截止期限约束的实例密集型云服务流调度算法

针对商业云计算中存在大量实例密集型服务流的问题,提出一种新的云环境下两阶段服务流调度算法。该算法先将用户自定义的全局截止期限分配到系统中的每个实例,再将每个实例的截止期限分配到实例中的每个任务中,最后在服务流执行阶段,动态调整后续任务的截止期限,解决了任务可能存在的未能在其截止期限内完成的时间异常问题。CloudSim仿真结果表明,与现有的算法相比,该算法能满足用户定义的截止期限,节约了执行成本,并减少了资源的竞争率,提高了调度的成功率。