A feedback scheduler for real-time controller tasks

The problem studied in this paper is how to distribute computing resources over a set of real-time control loops in order to optimize the total control performance. Two subproblems are investigated: how the control performance depends on the sampling interval, and how a recursive resource allocation optimization routine can be designed. Linear quadratic cost functions are used as performance indicators. Expressions for calculating their dependence on the sampling interval are given. An optimization routine, called a feedback scheduler, that uses these expressions is designed.     

HEARS: A heterogeneous energy-aware real-time scheduler

Developing energy-efficient schedulers for real-time heterogeneous platforms executing periodic tasks is an onerous as well as a computationally challenging problem. As a result, today we are confronting a scarcity of real-time energy-aware scheduling techniques which are applicable to heterogeneous platforms. Hence, this research proposes a heuristic strategy called, HEARS, for DVFS enabled energy-aware scheduling of a set of periodic tasks executing on a heterogeneous multicore system having an arbitrary number of core types. The presented scheme first applies deadline-partitioning to acquire a set of distinct time-intervals called frames. At any frame boundary, the following two-phase hierarchical operation is applied to obtain schedule for the next frame: First, it computes execution requirements for each task on every processing core of the platform. For any task, its execution requirement on a core within a frame depends upon the following criteria: (i) Length of the ensuing frame, (ii) Total execution requirements of the instance of the task on different cores (as a single task may have different execution requirement on different cores) and, (iii) Deadline of the instance of the task. Next, it simultaneously allocates each task on one or more cores and selects operating frequencies for the concerned cores such that the total execution demand of all the allocated tasks are satisfied as well as there is minimum change in energy consumption for the system. Experimental results show that our proposed strategy is not only able to achieve appreciable energy savings with respect to state-of-the-art MaxMin (2% to 37% on average) but also enables significant improvement in resource utilization (as high as 57%).     

Design and implementation of contractual based real-time scheduler for multimedia streaming proxy server

In nowadays World Wide Web topology, it is not difficult to find the presence of proxy servers. They reduce network traffic through the cut down of repetitive information. However, traditional proxy server does not support multimedia streaming. One of the reasons is that general scheduling strategy adopted by most of the traditional proxy servers does not provide real-time support to multimedia services. Based on the concept of contractual scheduling, we have developed a proxy server that supports real-time multimedia applications. Moreover, we developed the group scheduling mechanism to enable processing power transfer between tasks that can hardly be achieved by traditional schedulers. They result in a substantially improved performance particularly when both time-constrained and non-time-constrained processes coexist within the proxy server. In this paper, the design and implementation of this proxy server and the proposed scheduler are detailed. Wai-Kong Cheuk received the B.Eng. (Hons.) and M. Phil. degrees in 1996 and 2001, respectively, from the Hong Kong Polytechnic University, where he is currently pursuing the Ph.D. degree. His main research interests include distributed operating systems and video streaming. Tai-Chiu Hsung (M'93) received the B.Eng. (Hons.) and Ph.D. degrees in electronic and information engineering in 1993 and 1998, respectively, from the Hong Kong Polytechnic University, Hong Kong. In 1999, he joined the Hong Kong Polytechnic University as a Research Fellow. His research interests include wavelet theory and applications, tomography, and fast algorithms. Dr. Hsung is also a member of IEE. Daniel Pak-Kong Lun (M'91) received his B.Sc. (Hons.) degree from the University of Essex, Essex, U.K., and the Ph.D. degree from the Hong Kong Polytechnic University, Hung Hom, Hong Kong, in 1988 and 1991, respectively. He is currently an Associate Professor and the Associate Head of the Department of Electronic and Information Engineering, the Hong Kong Polytechnic University. His research interests include digital signal processing, wavelets, multimedia technology, and Internet technology. Dr. Lun was the Secretary, Treasurer, Vice-Chairman, and Chairman of the IEEE Hong Kong Chapter of Signal Processing in 1994, 1995–1996, 1997–1998, 1999–2000, respectively. He was the Finance Chair of 2003 IEEE International Conference on Acoustics, Speech and Signal Processing, held in Hong Kong, in April 2003. He is a Chartered Engineer and a Corporate member of the IEE.     

面向服务的网格调度组件的设计与实现

针对当前网格调度体制的研究仅从功能需求、执行过程方面进行描述,尚未对调度过程中的接口和交互协议进行定义,缺乏对语义支持的现状。结合语义Web服务技术,从实现角度讨论服务网格环境下的调度机制。从分析服务调度过程入手,讨论服务网格中动态调度系统的组成、系统架构及实现技术,初步设计和实现能够完成服务网格中调度需求的服务调度组件——G-Sched,并以模拟网络化虚拟制造作为应用示例来验证所提出方法的可行性和有效性。     

A QoS-enhanced intelligent stochastic real-time packet scheduler for multimedia IP traffic

A re-configurable, QoS-enhanced intelligent stochastic real-time optimal fair packet scheduler, QUEST, for IP routers is proposed and investigated. The objective is to maximize the system QoS subject to the constraint that the processor utilization is kept at 100%. All past work on router schedulers for multimedia traffic were of earlier generation, in that they focused on maximizing utilization whereas being QoS-aware but without explicitly maximizing the QoS. Keeping utilization fixed at nearly 100%, QoS is dynamically maximized, thus moving to the next generation. QUEST’s other unique advantages are three-fold. First, it solves the challenging problem of starvation for low priority processes; second, it solves the major bottleneck of Earliest Deadline First scheduler’s failure at heavy traffic loads. Finally, QUEST offers the benefit of arbitrarily pre-programming the process utilization ratio. Three classes of multimedia IP traffic, namely, VoIP, IPTV and HTTP have been considered. Two most important QoS metrics, namely, packet loss rate (PLR) and mean waiting time, are addressed. All claims are supported by discrete event and Monte Carlo simulations. The proposed scheduler outperforms benchmark schedulers and offers 37% improvement in packet loss rate and 23% improvement in mean waiting time over the best competing current scheduler Accuracy-aware EDF. The proposed scheduler was validated in a test-bed platform of a NetFPGA® router and results were observed with Paessler® PRTG network monitor.

     

A Distributed Error Recovery Technique and Its Implementation and Application on UNIX

This paper presents a checkpoint setting techniqute to eliminate domino effect in backward recovery in disttributed systems,which is very efficient,powerful,widely applicable and easy to be implememted,Besides theoretical analysis,an implementation on UNIX system and a package for software fault-tolerance are introduced.Then the problems of checkpoint management and process termination are discussed.     

Tolerating permanent and transient value faults

Transmission faults allow us to reason about permanent and transient value faults in a uniform way. However, all existing solutions to consensus in this model are either in the synchronous system, or require strong conditions for termination, that exclude the case where all messages of a process can be corrupted. In this paper we introduce eventual consistency in order to overcome this limitation. Eventual consistency denotes the existence of rounds in which processes receive the same set of messages. We show how eventually consistent rounds can be simulated from eventually synchronous rounds, and how eventually consistent rounds can be used to solve consensus. Depending on the nature and number of permanent and transient transmission faults, we obtain different conditions on $n$ , the number of processes, in order to solve consensus in our weak model.     

平面阴影算法研究与实现

阴影对提升图形的真实感具有重要意义。探讨了平面阴影生成算法，针对平面阴影算法在实际应用中的缺点，利用OpenGL的模板缓冲技术实现阴影裁剪，利用基于截锥体的裁剪矩阵消除假影和反影现象，并利用OpenGL累积缓冲技术实现软阴影。较好解决了平面阴影算法的缺点，程序计算量小、效率高，图形的真实感和场景的可视化效果得以提升，达到良好的效果。     

MPLS恢复模型的仿真与实现

根据MPLS故障恢复机制的原理,采用功能强大的网络仿真软件NS-2作为工具,讨论了近年来网络研究的必然趋势--利用容错技术构造高可靠网络系统.通过原理模拟出一种MPLS网络的Global恢复模型,结合平均无故障时间和恢复时间等来验证该模型在网络发生故障时,依旧能保证系统的可靠性和可用性.通过延迟、吞吐量等仿真数据得出,采用适当的压缩算法能够加速数据在网络上的传送,在保证网络传输的稳定性和可靠性的同时,可供其它同类网络故障恢复仿真参考,也可以直接应用到实际网络中.     

工业无线传感器网络节点通信中的瞬时故障恢复

无线传感器网络在工业领域应用广泛,由于电磁干扰、电源突然中断、软件突发错误等瞬时故障导致系统失效,影响系统安全,其控制和恢复在涉及安全的领域越发得到重视。考虑到瞬时故障在网络的多个层次可能都有发生,提出了一种三层故障处理机制,在芯片级采用硬件逻辑调整、在节点级采用重传和跳频、在系统级采用冗余路由等措施进行故障控制和恢复。实验结果表明,采用三层故障处理机制后,网络的丢包率和端对端的时延有效降低,节点通信的可靠性和安全性得到有效的提高。     

网络化控制系统瞬时故障恢复和安全控制研究综述

鉴于瞬时故障是导致控制系统事故的主要故障形式,瞬时故障恢复是保证系统安全的重要手段,首先,介绍了当前通过主动冗余和基于系统模型分析进行瞬时故障恢复的方法;然后,综述这些技术在网络化控制系统的通信网络、网络节点、系统层面瞬时故障恢复和安全控制中的应用研究;最后,对网络化控制系统瞬时故障恢复和安全控制方法的发展趋势进行了展望.     

A fault-tolerant real-time multiprocessor with a built-in recovery mechanism

The architecture of a fault-tolerant multiprocessor with a rollback recovery mechanism is described. Fault-tolerance is attained owing to restarts of faulty processes of computations or their definite parts after detecting failures. An error occurring during the interaction of some processes leads to the multistep reconstruction of the entire computational process. An estimate of the efficiency of the proposed fault-tolerant technology is given.Translated from Kibernetika i Sistemnyi Analiz, No. 5, pp. 169–176, September–October 2004.     

改进的实时反走样透视阴影图算法及实现

为解决透视阴影图算法中,物体被非线性比例导致愈加明显的自阴影或表面波纹现象,提出一种基于GPU的实时反走样透视阴影图改进算法。该算法结合透视阴影图算法以及D.Weiskopf的dual depth layers算法,通过采用GPU深度剥离技术采样场景的双层深度值信息,并引入自适应偏移量zbias来计算场景的深度偏移量。该算法采用C语言实现,同时使用GPU顶点渲染器和像素渲染器编程有效避免程序复杂度。实验结果表明,该改进算法较好解决了透视阴影图的自阴影问题,提高了渲染阴影质量。     

多核对分区操作系统影响研究

分区操作系统是综合化航空电子领域中的核心技术。随着单核性能极限的到来,处理器结构向着多核发展。将两者结合起来,在多核分区操作系统的基础上研究分析多核处理器结构为分区操作系统带来的影响。经分析实验数据得出多核处理器结构在多核处理器中共享Cache结构和内核中临界资源并发访问两方面对分区操作系统产生影响。     

RTAI下动态集成的资源预留调度器的设计与实现

近年来基于双内核架构增强Linux操作系统实时性的RTAI(Real-Time Application Interface)在工业控制等硬实时领域得到广泛应用。RTAI通过抢占Linux的执行来保障硬实时性,Linux被抢占的时间依赖于硬实时应用的处理器要求而每次均会有较大不同,导致Linux的执行时间不可预测,从而无法保障软实时应用的服务质量。动态集成的资源预留调度器(Dynamic Integrated Resource Reserved Scheduler,DIRRS)通过增强RTAI调度器使其支持资源预留机制,在Linux实现可动态集成的、基于服务器的调度策略,不但可以保证Linux及其以上的软实时应用,即使在有硬实时任务并发时也能得到处理器资源,而且很容易通过更换不同的服务器内核模块来实现用户自定义的调度策略。     

A decentralized multichannel length transformation algorithm and its parallel implementation for real-time ECG monitoring.

Multichannel algorithms have been developed for more accurate analysis of electrocardiograms (ECGs). Their benefit is the ability to use the information contained in all simultaneously acquired channels. In this paper we present a multichannel version of a nonsyntactic algorithm, based on length transformation. The proposed algorithm uses a decentralized schema for combining the results derived from each individual lead, instead of a global/centralized one (a spatial vector approach). Its performance was evaluated using the CSE database and real ECGs acquired by a 12-lead cardiograph. The results are also compared with previous-single-channel and multichannel-versions of the algorithm, showing a better performance. Since a multichannel algorithm is always a time-consuming task, it is rarely used in real-time monitoring systems. Motivated by this observation, we designed a parallel implementation of the proposed algorithm and tested its ability to be used in such systems.     

Cost analysis of recovery block scheme and its implementation issues

In this paper, a cost analysis of recovery block scheme has been presented. This study provides us the selection criterion for alternates and the software granularity under perfect acceptance tests. Two performance evaluation measures: a) cost-reliability index (CRI); b) cost of failure (COF) are studied and compared. CRI is shown to be a move restricted measure than COF. An experimental study has been carried out to supplement the analysis. Efficient placement of recovery blocks and the design of alternates has been discussed with reference to real-time applications.This work has been carried out under contract DOT-RC-92031.     

A flexible real-time scheduling abstraction: design and implementation

An evolution is happening in the way that operating systems support the real-time requirements of their applications. The need to run real-time applications such as multimedia in the same environment as complex non-real-time servers and applications has motivated much interest in restructuring existing operating systems. Many issues related to thread scheduling and synchronization have been investigated. However, little consideration has been given to the flexibility and modularity required in the support of application-level scheduling needs, although it is well known that application requirements are diverse. In this paper, we describe a real-time scheduling abstraction which provides modularity and flexibility to the scheduling support of operating systems. Our design has been implemented using the Mach 3.0 kernel and a locally developed multiprocessor kernel (the r-kernel) as development platforms. © 1997 John Wiley & Sons, Ltd.     

实时交互式三维脸部表情动画研究及其实现

根据人脸的生理结构特点,使用分块造型技术进行脸部建模,提出了一个基于"脸型特征"和"五官特征"的参数化肌肉模型,通过模型上控制顶点的属性值来控制脸部形成不同的表情,并利用MAYA MEL语言实现了一个实时交互操作界面.这使得对脸部表情的研究更加方便、灵活,建模及其动画化也更加逼真、实用.