针对弱硬实时系统的DRM调度算法

本文在定义支持多级QoS的弱硬实时系统周期任务模型的基础上,提出基于RM调度策略的弱硬实时调度算法DRM,它具备可调度判定不等式,不限定任务的QoS参数模式,并通过在调度的过程中动态调整任务的优先级来反映其紧迫程度.在系统过载时,DRM调度算法可以采用QoS退化机制,在保证紧要任务以及其所要求的最低QoS执行的同时,适当降低某些任务的服务等级,使得更多的任务可以有效运行,以此来提高系统对负载的适应性.最后,本文通过仿真实验,验证了DRM以及QoS退化机制的有效性.     

基于希尔排序的动态优先级调度算法

实时调度策略中,EDF算法应用最为广泛,但其在系统过载的情况下,仅由任务截止期决定任务执行顺序,使得截止期错失率非常高,且系统收益小.近年来,出现了一些改进的EDF算法,综合考虑了时间和执行价值,但未加入能量因素,对于能量有限的系统,充分利用能量是极其重要的.针对这一问题,提出一种基于希尔排序的动态优先级调度算法,在系统过载时,综合考虑任务截止时间、执行价值、消耗能量三种因素确定任务优先级,通过希尔排序算法选出优先级高的任务加入优先调度子集,进行率先调度.实验结果表明,该算法不仅能降低任务截止期错失率,还能提高系统执行收益.     

业务优先级感知的网络流量调度机制

针对网络中业务数据流过大、分布不均匀所造成的网络拥塞,提出一种优先级感知的动态网络流量调度机制.利用令牌桶算法,根据业务优先级的不同为不同业务分配不同速率的令牌,以实现业务优先级的划分;综合考虑业务的优先级及用户节点剩余缓存空间,对不同的业务采取不同的处理方式;同时,以流量到达因素、服务因素及节点缓存为指标定义了一种网络流量调度机制性能指标——分组丢失率.数值结果表明,所提机制可以对网络中业务优先级进行合理的划分,从而有效利用网络资源,预防网络拥塞,提升网络性能,为用户提供更加稳定可靠的网络服务.     

进程调度策略在Linux中的实现

Linux是一个多用户多任务的操作系统。系统上所有运行的东西都可以称作进程。Linux把进程分为实时进程和非实时进程来处理,它采用时间片轮转和可剥夺调度优先级相结合的调度策略。详细介绍了实时进程和非实时进程在Linux不同进程调度中的应用。     

XEN虚拟IO的调度优化

提出一种基于驱动域授权表和优先级加权的虚拟IO调度策略,根据不同客户域与请求资源的差异,得出IO请求的调度优先级,实现虚拟IO调度.实验证明,兼顾不同优先级域的调度策略提高了系统的吞吐率,驱动域授权表机制减少了IO虚拟化中授权与页面映射操作的开销.     

基于负载分类的交换式以太网的实时性研究

为了满足交换式以太网中部分数据的实时性,该文应用网络演算对周期性实时数据和突发性实时数据进行分析,同时对受控类负载采取负载分类的方法,赋以不同优先级并采用静态优先级队列的策略进行调度。仿真结果表明,负载分类的策略有效地将强实时负载任务的延迟控制在一定值内,同时大幅度降低了受控类负载的平均时延,特别是降低了较高优先级受控类负载的时延,从而提高了数据的实时性。     

航空电子核心处理分区优化设计及仿真研究

具有严格实时保障和安全保障的航空电子核心处理系统广泛采用分区管理技术,通过分层调度结构,满足任务时空隔离运行.通过将分区抢占行为看作是一个虚拟周期任务,针对下层调度器分别采用固定优先级和动态优先级两种调度策略,讨论了分区调度设计问题;利用分区任务调度的空闲时间构建分区调度保障条件,给出了满足任务可调度性的分区参数求解表...     

VxWorks多任务网络实时处理软件设计

VxWorks是一种嵌入式实时多任务操作系统,广泛应用于航空航天、通信电子、物联网等领域.多任务软件设计的合理性对嵌入式系统软件的稳定性、可靠性起着重要的作用.对VxWorks网络通信机制以及多任务调度机制进行了分析,介绍了多任务实时软件设计过程中涉及到的任务划分、任务优先级的设置、堆栈大小设置、任务释放等关键问题,结合应用实例给出多任务通信软件设计的步骤和方法,通过试验验证了设计的合理性和可靠性,为基于VxWorks多任务实时处理软件的设计提供了一定的参考.     

混合关键系统半划分调度算法研究

混合关键系统是现代嵌入式系统发展的主要趋势之一,其中高关键任务代表紧急度高或者重要程度高的实际任务,往往需要优先保证.为了保证高关键级别任务的执行,当前的混合关键任务调度算法中常常存在对低关键级别任务采用丢弃或者调度不及时的现象,造成在关键级别转换时,任务丢失时限率较大且系统利用率较低.为此,本文在具有双重关键级别的混合关键系统中,对EDF-os半划分调度算法进行改进.首先,在划分阶段,将高关键级别的任务作为固定任务,低关键级别的任务按照利用率使用Worst-Fit策略进行划分.其次,在执行阶段,采用job边界迁移形式,并详细讨论了在不同系统关键级别之下,不同关键级别任务优先级确定的策略,根据优先级对任务进行调度执行.最后,模拟具有双关键级别的多处理器混合关键系统,随机产生任务集进行仿真实验,结果表明,该方法使得低关键级别任务的可执行比例平均提升了14.8%,任务丢失时限率降低了19.7%.     

ATM自愈网的一种恢复调度策略

网络生存性是ATM网络中亟待解决的问题.本文在深入分析ATM中故障恢复机制的基础上,指出在恢复过程中存在着恢复调度问题.针对各种服务对恢复时限的不同要求,提出了一种优先级恢复调度策略,P_-RS策略.经模拟分析显示,该策略可以提高网络的有效恢复率,增强了网络的生存性.     

UbiFOS: A Small Real‐Time Operating System for Embedded Systems

The ubiquitous flexible operating system (UbiFOS) is a real‐time operating system designed for cost‐conscious, low‐power, small to medium‐sized embedded systems such as cellular phones, MP3 players, and wearable computers. It offers efficient real‐time operating system services like multi‐task scheduling, memory management, inter‐task communication and synchronization, and timers while keeping the kernel size to just a few to tens of kilobytes. For flexibility, UbiFOS uses various task scheduling policies such as cyclic time‐slice (round‐robin), priority‐based preemption with round‐robin, priority‐based preemptive, and bitmap. When there are less than 64 tasks, bitmap scheduling is the best policy. The scheduling overhead is under 9 µs on the ARM926EJ processor. UbiFOS also provides the flexibility for user to select from several inter‐task communication techniques according to their applications. We ported UbiFOS on the ARM9‐based DVD player (20 kB), the Calm16‐based MP3 player (under 7 kB), and the ATmega128‐based ubiquitous sensor node (under 6 kB). Also, we adopted the dynamic power management (DPM) scheme. Comparative experimental results show that UbiFOS could save energy up to 30% using DPM.     

A Modified Dynamic Weighted Round Robin Cell Scheduling Algorithm

In this paper, we propose the modified dynamic weighted round robin (MDWRR) cell scheduling algorithm, which guarantees the delay property of real‐time traffic and also efficiently transmits non‐real‐time traffic. The proposed scheduling algorithm is a variation of the dynamic weighted round robin (DWRR) algorithm and guarantees the delay property of real‐time traffic by adding a cell transmission procedure based on delay priority. It also uses a threshold to prevent the cell loss of non‐real‐time traffic that is due to the cell transmission procedure based on delay priority. Though the MDWRR scheduling algorithm may be more complex than the conventional DWRR scheme, considering delay priority minimizes cell delay and decreases the required size of the temporary buffer. The results of our performance study show that the proposed scheduling algorithm has better performance than the conventional DWRR scheme because of the delay guarantee of real‐time traffic.     

Kernel Thread Scheduling in Real‐Time Linux for Wearable Computers

In Linux, real‐time tasks are supported by separating real‐time task priorities from non‐real‐time task priorities. However, this separation of priority ranges may not be effective when real‐time tasks make the system calls that are taken care of by the kernel threads. Thus, Linux is considered a soft real‐time system. Moreover, kernel threads are configured to have static priorities for throughputs. The static assignment of priorities to kernel threads causes trouble for real‐time tasks when real‐time tasks require kernel threads to be invoked to handle the system calls because kernel threads do not discriminate between real‐time and non‐real‐time tasks. We present a dynamic kernel thread scheduling mechanism with weighted average priority inheritance protocol (PIP), a variation of the PIP. The scheduling algorithm assigns proper priorities to kernel threads at runtime by monitoring the activities of user‐level real‐time tasks. Experimental results show that the algorithms can greatly improve the unexpected execution latency of real‐time tasks.     

传感器网络的任务双效节能调度研究

能源供应有限性是局限传感器网络的性能和存活寿命的重要因素,本文从传感器网络节点的任务调度出发,提出动态能量管理DPM和动态电压/频率调节DV/FS的双效处理器节能调度算法,即DV/FS-RM和DV/FS-EDF调度算法;在DPM动态控制空闲任务进入休眠的同时,在保证节点的实时性的前提下,通过DV/FS-RM或DV/FS-EDF算法降低处理器频率,达到更好的节能效果.实验显示,该节能任务调度算法使以电池为能源的传感器网络节点的生存期成倍地延长.     

基于模糊流感知的动态优先公平调度算法

为适应网络的动态性,提高调度公平性和资源效率,流感知优先公平调度机制需要动态的多业务区分转发。与链路负载状态相关的模糊流感知能够实现路径上的一致性业务区分,而基于模糊流感知的动态优先公平调度算法通过调整优先队列负载门限在流式流和弹性流之间实现转发优先权的动态交替,在链路轻载时实现不同流间的相对公平调度,在链路重载时则强调实时业务的绝对优先权以保证其时延要求。算法公平性分析和仿真计算显示提出算法的动态区分转发通过适度增加优先业务队长能够大幅度提高弹性流的接纳率,具有较高的链路平均吞吐量和资源效率。     

Delay constrained uplink scheduling policy for rtPS/ertPS service in IEEE 802.16e BWA systems

WiMAX is a promising broadband wireless networking technology and is expected to take the place of broadband access solutions such as DSL and cable. Owing to its superior support in mobility, it is expected to provide integrated voice and data service to realize broadband mobile computing. In order to reach better quality‐of‐service (QoS) requirements for real‐time applications, the IEEE 802.16e standard defines five different services among traffic categories with different multimedia requirements. However, the problem of choosing the right set of medium access control parameters and packet scheduling policy to provide strict QoS guaranteed in IEEE 802.16e Broadband Wireless Access (BWA) systems remains unsolved and left as an open issue. In this paper, we propose a novel polling‐based uplink packet scheduling policy for real‐time Polling Service and extended real‐time Polling Service (rtPS/ertPS) traffic to support real‐time applications, with strict delay requirements, such as variable bit rate (VBR) traffic in IEEE 802.16e BWA systems. The proposed transmit‐permission policy can derive sufficient conditions such that all the rtPS/ertPS sources satisfy their time constraints to provide deterministic QoS guarantees. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design provides a good quality performance in the IEEE 802.16e BWA systems. Copyright © 2008 John Wiley & Sons, Ltd.     

一种改进的具有区分功能的无线局域网MAC机制

文章探讨了IEEE802.11MAC的信道分配机制,提出了一个改进的具有区分功能的MAC机制RDCF/P(RevisedDCF/Priority)。新机制引入了优先级的区分,根据优先级的不同设定不同的最大传输时间,让高优先级站点和流不仅得到长的服务时间,并优先得到信道使用权,且引入补偿门槛,减少了信道的冲突和空闲等待时间。通过理论分析和实验仿真可以得出,新机制有着好的QOS性能。     

Temperature-Aware Task Allocation and Scheduling for Embedded Multiprocessor Systems-on-Chip (MPSoC) Design

Temperature affects not only the performance but also the power, reliability, and cost of the embedded system. This paper proposes a temperature-aware task allocation and scheduling algorithm for MPSoC embedded systems. Thermal-aware heuristics are developed, and a temperature-aware floorplanning tool is used to reduce the peak temperature and achieve a thermally even distribution while meeting real time constraints. The paper investigates both power-aware and thermal-aware approaches to the task allocation and scheduling. The experimental results show that the thermal-aware approach outperforms the power-aware schemes in terms of maximal and average temperature reductions. To the best of our knowledge, this is the first MPSoC task allocation and scheduling algorithm that takes temperature into consideration.

---

     

基于实时业务挤占的OFDMA系统的无线资源分配方案

为了在实时业务和非实时业务共享无线资源的场景中增加系统吞吐量,该文提出了一种基于实时业务挤占的无线资源分配方法,该方案首先实施统一调度,然后进行实时业务挤占过程。在保证对实时业务服务的情况下,实时业务挤占的无线资源分配方案提高了多用户分集效果,增加了系统的吞吐量。理论和仿真分析表明,与已有的传统的实时业务和非实时业务共享无线资源的调度方案相比,该方案能够提供更高的系统吞吐量和频谱效率。在实际应用中,该方案具有一定的可行性和可操作性。