Incremental Scheduling of Mixed Workloads in Multimedia Information Servers

In contrast to pure video servers, advanced multimedia applications such as digital libraries or teleteaching exhibit a mixed workload with massive access to conventional, discrete data such as text documents, images and indexes as well as requests for continuous data, like video and audio data. In addition to the service quality guarantees for continuous data requests, quality-conscious applications require that the response time of the discrete data requests stay below some user-tolerance threshold. In this paper, we study the impact of different disk scheduling policies on the service quality for both continuous and discrete data. We provide a framework for describing various policies in terms of few parameters, and we develop a novel policy that is experimentally shown to outperform all other policies.     

混合类型多媒体负载访问存储系统的统计学访问控制算法

混合类型多媒体负载访问存储系统是一个复杂的过程，不同类型的多媒体应用要求存储系统提供不同的服务质量保证．存储系统需要一个有效的访问控制算法，为尽可能多的多媒体应用提供保证服务质量的服务．对混合类型多媒体负载访问存储系统的访问控制问题进行了系统的研究：定义多媒体应用访问存储系统的服务质量参数；建立并发多媒体应用的汇聚负载模型；推导出混合类型多媒体负载的访问控制约束条件；实现相应的统计学访问控制算法．仿真实验的结果表明，新的存储系统访问控制算法是有效的，并具有相当高的精确度．     

基于服务质量需求的存储系统动态优先权调度策略

多媒体应用要求存储系统提供保证服务质量的数据访问服务,响应时间超过延迟上限的访问请求必须小于一定的比例.基于服务质量需求的动态优先权调度策略(QADPS)根据多媒体应用接受存储系统服务的历史信息,计算多媒体应用的服务质量失败距离;并为失败距离较小的多媒体应用分配较高的调度优先权.QADPS根据多媒体应用的不同服务质量需求,实现了有差别的调度：多媒体应用的服务质量需求越严格,它的访问请求被调度的机会越高. QADPS能够在保证服务质量的前提下,支持更多的并发多媒体应用.     

Cello: A Disk Scheduling Framework for Next Generation Operating Systems*

In this paper, we present the Cello disk scheduling framework for meeting the diverse service requirements of applications. Cello employs a two-level disk scheduling architecture, consisting of a class-independent scheduler and a set of class-specific schedulers. The two levels of the framework allocate disk bandwidth at two time-scales: the class-independent scheduler governs the coarse-grain allocation of bandwidth to application classes, while the class-specific schedulers control the fine-grain interleaving of requests. The two levels of the architecture separate application-independent mechanisms from application-specific scheduling policies, and thereby facilitate the co-existence of multiple class-specific schedulers. We demonstrate that Cello is suitable for next generation operating systems since: (i) it aligns the service provided with the application requirements, (ii) it protects application classes from one another, (iii) it is work-conserving and can adapt to changes in work-load, (iv) it minimizes the seek time and rotational latency overhead incurred during access, and (v) it is computationally efficient.     

Deriving Workloads for Performance Testing

An approach is presented to compare the performance of an existing production platform and a proposed replacement architecture. The traditional approach to such a comparison is to develop software for the proposed platform, build the new architecture, and collect performance measurements on both the existing system in production and the new system in the development environment. In this paper we propose a new way to design an application-independent workload for doing such a performance evaluation. We demonstrate the applicability of our approach by describing our experience using it to help an industrial organization determine whether or not a proposed architecture would be adequate to meet their organization's performance requirements.     

网络控制系统中混合调度算法的研究

网络控制系统的性能与信息调度有关,而以往的调度算法大多把时间属性作为确立优先级的依据,无法反映出消息的重要性。该文在最大误差优先算法的基础上,提出以最大优先变化为主,越长时间越低优先级为辅的混合调度算法,丰富了优先级的确立依据。仿真实验结果表明,该混合调度算法能够有效提高控制系统的整体性能。     

一种简单的平滑公平轮转调度算法

根据通用处理器共享的公平排队思想,针对数据包或信元交换,提出了一种将数据流的预订速率作为时隙分配的权值来构建动态调度树的公平轮转调度算法。其主要思路是:当有新数据流到达时,将各数据流按其权值均匀分布到完全二叉树的叶子节点上,在每个时隙开始时轮转调度算法负责从叶子节点中依次取出数据流号,发送该数据流的信元,调度复杂度为O(1)。与其他经典的公平调度算法引比,所提出的公平轮转调度算法实现简单。理论分析和仿真结果都表明,这种简单的平滑公平轮转调度算法(SSFRR)具有良好的公平性,对源端为漏桶控制的数据流能够提供端到端的有界时延,且能够提供基于数据流的QoS保证。     

多性能目标分组调度策略

在高速分组交换网络中,分组调度策略和算法的设计是一个关键问题.由于网络分组调度策略有着多方面性能的要求,如何同时满足多个性能目标是当前的研究难点.基于比例公平性原则,提出了一种分组网络中的比例公平调度策略(proportional fairness scheduling,简称PFS),该调度策略综合考虑了网络效率、用户QoS要求和系统公平性等多维目标,对该策略进行了详细的分析和论证.比例公平调度策略可以广泛应用于分组网络调度策略的设计研究和改进.     

多媒体服务器混合磁盘调度策略

基于多媒体服务器的性能要求，提出了一种自适应的混合磁盘调度策略DRT-window．它既能满足实时请求对实时性的要求，根据实时请求的截止期动态选择窗口大小；又能在其松弛度内尽努力(best-effort)地服务非实时请求，从而减少非实时请求的响应时间。DRT-window采用了两级层次调度方案：第一层为不同类型的请求采用各自适合的调度策略；第二层为混合请求调度嚣，混合调度第一层中的不同类型的请求。通过性能比较和理论证明，表明此混合磁盘调度策略能在保证实时请求无抖动执行的同时，尽量地减少非实时请求的响应时间。     

联合频谱切换调度和QoS重路由的性能优化算法

频谱切换技术可以降低无线传输干扰、优化网络结构,成为无线网络研究的热点。现有频谱切换技术忽视了频谱切换执行顺序对网络性能的影响,无法保证网络在切换过程中的连通性和吞吐量。为了最大化网络吞吐量,提出一新的频谱切换调度问题(SHSTM:Spectrum Handoff Scheduling for Throughput Maximization),并证明SHSTM是NP难问题。为解决SHSTM问题,提出联合频谱切换调度和QoS重路由的跨层优化算法JSHSQ-R。在JSHSQ-R中,频谱切换分多轮执行。为了减少切换延时并保证网络连通性,该算法基于加权最小生成树来确定每轮需要切换的链路,并在切换过程中为数据流进行重路由来满足数据流的QoS需求。在NS2上进行了大量仿真实验,结果表明所提算法能够充分利用无线网状网多接口多信道资源,并能为多流提供较高的网络吞吐量保证。