基于MPEG4自适应传输编解码系统的研究与实现

文中的流媒体系统包括3个部分:编码部分、流媒体服务器部分和播放器部分。编码部分和播放器部分采用了IBM的ToolkitForMPEG-4SDK.jar开发包。编码部分包括两个工具,实时的MPEG-4制作工具和非实时的MPEG-4制作工具。流媒体服务器部分是在Darwin流媒体服务器的基础上,加入了QoS管理模块,与客户端的QoS模块一起实现质量管理。对Darwin流媒体服务器的RTP打包模块进行了修改,将MPEG-4文件进行特殊形式的打包,并采用“漏桶算法”实现RTP的调度,以适应客户端带宽的需要,最终实现自适应的传输。     

流程工业生产调度与控制集成系统研究

本文根据流程工业生产控制系统的特点,对生产调度和监控系统的集成需求进行了分析,讨论了调度与监控系统的集成策略,建立了一种新型的集成系统模型框架,设计了静态调度器和动态调度器的结构,并从获得工程满意解的实际需求出发,分析了集成系统的约束参数和调度算法,为实现流程工业调度与监控系统的集成提供了一种新方法。     

基于MPEG4自适应传输编解码系统的研究与实现

文中的流媒体系统包括3个部分：编码部分、流媒体服务器部分和播放器部分。编码部分和播放器部分采用了IBM的ToolkirForMPEG-4SDK．jar开发包。编码部分包括两个工具，实时的MPEG-4制作工具和非实时的MPEG-4制作工具。流媒体服务器部分是在Darwin流媒体服务器的基础上，加入了QoS管理模块，与客户端的QoS模块一起实现质量管理。对Darwin流媒体服务器的RTP打包模块进行了修改，将MPEG-4文件进行特殊形式的打包，并采用“漏桶算法”实现RTP的调度，以适应客户端带宽的需要，最终实现自适应的传输。     

基于AHP的Web集群系统负载均衡算法

利用集群技术构建的服务器组在资源利用率上存在较大差异。为此,提出基于层次分析法(AHP)的集群系统负载均衡算法,建立判断矩阵,得到各项评估指标的单项和综合权重。调度器定时接收真实服务器上的4类参数：网络性能,服务器硬件,服务器软件和网络服务类型。根据调度器收到的每一个连接请求,采用动态反馈算法选择负载最小的服务器响应连接请求。实验结果表明,该算法能减少服务器平均响应时间,有效提高集群系统的响应率。     

EDF多任务调度算法在物联网数据监控平台中的应用研究

在基于物联网的数据监控平台中,由于感知层数据采集传感器具有种类繁多、数量庞大的特点,这就要求位于通信层的数据接收服务器必须通过一种完善的多任务调度算法来处理高并发通信,以缓解服务器的通信压力并保持处理的高效性。笔者以物联网数据监控平台为出发点,探究通过引入EDF多任务调度算法来处理高并发通信,对EDF多任务调度算法的算法原理与调度流程进行了深入分析,并通过设计实验论证算法的有效性。     

Linux内核调度器算法研究与性能分析

Linux操作系统正在向嵌入式系统和高端服务器领域发展。提高调度器的调度性能,支持实时应用以及支持多处理器并行性的研究工作显得非常重要。文中对Linux2.4.22和2.6.10两个版本的内核调度器进行比较分析,重点分析了两种调度器的调度算法、调度时机、优先权计算方法和时机以及调度性能。     

Linux内核调度器算法研究与性能分析

Linux操作系统正在向嵌入式系统和高端服务器领域发展。提高调度器的调度性能，支持实时应用以及支持多处理器并行性的研究工作显得非常重要。文中对Linux2．4，22和2．6.10两个版本的内核调度器进行比较分析，重点分析了两种调度器的调度算法、调度时机、优先权计算方法和时机以及调度性能。     

基于Linux虚拟服务器的负载均衡算法

分析Linux虚拟服务器负载均衡调度过程,提出一种基于Linux虚拟服务器的负载均衡算法。该算法结合系统资源类型和服务器权重系数,依据服务器加权负载标准差,进行集群真实服务器负载状况分析,动态调整服务器权重系数,对改进的最小连接数调度算法进行负载均衡调度。测试结果验证了该算法的有效性。     

一种资源优化的双最小均衡Web集群区分服务调度算法

在一种新的Web集群体系结构的基础上,提出了一种资源优化的双最小均衡区分服务调度算法：首先在前端调度器按资源均衡度将Web请求分配到各后台服务器．然后将Web请求的优先级与资源均衡度两个特征参数结合起来,综合设计后台服务器的Web请求调度顺序,为了评估该算法的性能,进行了大量的模拟实验．在与其他著名调度策略如分离式调度的对比结果显示：双最小均衡调度算法使Web请求的效率提高了11％,同时很好地实现了区分服务．证实了资源优化调度策略具有一定的普遍意义．     

基于无服务器边缘计算下的服务负载调度算法

随着边缘计算的不断发展,其在资源管理配置方面逐渐出现相关问题,无服务器计算作为一种新的方式可以有效解决边缘计算的相关问题。然而,无服务器计算不具备在分布式边缘场景中高效处理请求所需服务负载调度的能力,针对这一问题,提出了一种基于无服务器边缘计算的服务负载调度算法(service load scheduling algorithm, SLSA)。SLSA的核心是通过隐式建模充分考虑了动态变化的节点状态、负载调度器放置等影响因素来优化整体时延,然后通过改进的平滑加权轮询调度(smooth weighted round robin, SWRR)算法进行服务调度。经仿真实验分析,SLSA在资源消耗上有着明显下降,同时在单城市场景与多城市场景下均有良好的性能表现,其中在单城市场景中相对于集中式轮询调度(round robin centralized, RRC)算法提升了43.01%,在多城市场景中提升了53.81%。实验结果表明,SLSA可以有效降低资源消耗率并提升性能。     

Scheduling Threads for Low Space Requirement and Good Locality

The running time and memory requirement of a parallel program with dynamic, lightweight threads depends heavily on the underlying thread scheduler. In this paper we present a new asynchronous, space-efficient scheduling algorithm for shared memory machines that combines the low scheduling overheads and good locality of work stealing with the low space requirements of depth-first schedulers. For a nested-parallel program with depth D and serial space requirement S ₁ , we show that the expected space requirement is S ₁ + O(K⋅ p⋅ D) on p processors. Here, K is a user-adjustable runtime parameter, which provides a tradeoff between running time and space requirement. Our algorithm achieves good locality and low scheduling overheads by automatically increasing the granularity of the work scheduled on each processor. We have implemented the new scheduling algorithm in the context of a native, user-level implementation of Posix standard threads or Pthreads, and evaluated its performance using a set of C-based benchmarks that have dynamic or irregular parallelism. We compare the performance of our scheduler with that of two previous schedulers: the thread library's original scheduler (which uses a FIFO queue), and a provably space-efficient depth-first scheduler. At a fine thread granularity, our scheduler outperforms both these previous schedulers, but requires marginally more memory than the depth-first scheduler. We also present simulation results on synthetic benchmarks to compare our scheduler with space-efficient versions of both a work-stealing scheduler and a depth-first scheduler. The results indicate that unlike these previous approaches, the new algorithm covers a range of scheduling granularities and space requirements, and allows the user to trade the space requirement of a program with the scheduling granularity. Received June 11, 2000, and in revised form March 19, 2001, and in final form August 7, 2001. Online publication April 5, 2002.     

An Open Environment for Real-Time Applications

This paper describes an open system architecture that allows independently developed hard real-time applications to run together and supports their reconfiguration at run-time. In the open system, each real-time application is executed by a server. At the lower level, the OS scheduler schedules all the servers on the EDF basis. At the upper level, the server scheduler of each server schedules the ready jobs of the application executed by the server according to the algorithm chosen for the application. The paper describes the two-level CPU scheduling scheme used by the open system and the design and implementation of a uniprocessor open system within the framework of the Windows NT operating system. The implementation consists of three key components: the two-level hierarchical kernel scheduler, common system service providers, and real-time application programming interface.     

Provably Efficient Online Nonclairvoyant Adaptive Scheduling

Multiprocessor scheduling in a shared multiprogramming environment can be structured in two levels, where a kernel-level job scheduler allots processors to jobs and a user-level thread scheduler maps the ready threads of a job onto the allotted processors. We present two provably-efficient two-level scheduling schemes called G-RAD and S-RAD respectively. Both schemes use the same job scheduler RAD for the processor allotments that ensures fair allocation under all levels of workload. In G-RAD, RAD is combined with a greedy thread scheduler suitable for centralized scheduling; in S-RAD, RAD is combined with a work-stealing thread scheduler more suitable for distributed settings. Both G-RAD and S-RAD are non-clairvoyant. Moreover, they provide effective control over the scheduling overhead and ensure efficient utilization of processors. We also analyze the competitiveness of both G-RAD and S-RAD with respect to an optimal clairvoyant scheduler. In terms of makespan, both schemes can achieve O(1)-competitiveness for any set of jobs with arbitrary release time. In terms of mean response time, both schemes are O(1)-competitive for arbitrary batched jobs. To the best of our knowledge, G-RAD and S-RAD are the first non-clairvoyant scheduling algorithms that guarantee provable efficiency, fairness and minimal overhead.     

一种基于资源预分配的虚拟机软实时调度方法

虚拟机技术作为云计算的重要技术之一,近年来得到广泛关注,但是由于虚拟机管理层的存在,导致语义鸿沟,使得实时应用程序、并发程序等在虚拟机上的运行性能受到影响。分析和研究了Xen虚拟机管理器的Credit调度算法,针对其在并发调度和软实时调度方面存在的不足,提出了改进调度算法,实现了算法的调度器原型。新的调度算法对软实时虚拟机进行Credit比例预分配,采用动态调度时间片机制,以non-work-conserving方式实现软实时任务周期调度,保障调度周期满足运行周期要求。通过区分并发和非并发软实时虚拟机,采取不同的调度策略,在满足资源利用率的基础上,确保实时任务的顺利运行。测试结果表明,该调度算法在对并发和非并发软实时任务调度上,具有良好的表现,较好满足了软实时应用调度需求。     

Thread prioritization: A thread scheduling mechanism for multiple-context parallel processors

Multiple-context processors provide register resources that allow rapid context switching between several threads as a means of tolerating long communication and synchronization latencies. When scheduling threads on such a processor, we must first decide which threads should have their state loaded into the multiple contexts, and second, which loaded thread is to execute instructions at any given time. In this paper we show that both decisions are important, and that incorrect choices can lead to serious performance degradation. We propose thread prioritization as a means of guiding both levels of scheduling. Each thread has a priority that can change dynamically, and that the scheduler uses to allocate as many computation resources as possible to critical threads. We briefly describe its implementation, and we show simulation performance results for a number of simple benchmarks in which synchronization performance is critical.     

Load balancing to adjust for proximity in some network topologies

Each job scheduler in large decentralized load balancing systems generally must consider whether it is advantageous to offload jobs to remote computation servers when the local load is too high. Although processing power may appear to be available at a very distant server, two problems arise due to the transmission delay between the scheduler and server. Predictably, the response time of the job is adversely affected as the job spends valuable time in transit, but a more subtle problem involves the value, or reliability, of the state information regarding job queues. The longer the delay between scheduler and server, the less a scheduler should value the state information of the server (given that the state changes over time). We examine the performance of schedulers in topologies with different average proximity and show a probabilistic algorithm that allows schedulers to dynamically form efficient clusters in the network.     

集群视频服务平台流媒体监控系统的设计与实现

本文设计了集群视频服务平台流媒体监控系统的分布式体系结构,提出了一种单线程多任务的带宽信息统计策略,以及保证接收信息包顺序的组包算法。测试结果表明,本系统能够快速、稳定地反映集群视频服务平台的性能和提供的服务状况。     

Analysis of task assignment policies in scalable distributedweb-server systems

A distributed multiserver Web site can provide the scalability necessary to keep up with growing client demand at popular sites. Load balancing of these distributed Web-server systems, consisting of multiple, homogeneous Web servers for document retrieval and a Domain Name Server (DNS) for address resolution, opens interesting new problems. In this paper, we investigate the effects of using a more active DNS which, as an atypical centralized scheduler, applies some scheduling strategy in routing the requests to the most suitable Web server. Unlike traditional parallel/distributed systems in which a centralized scheduler has full control of the system, the DNS controls only a very small fraction of the requests reaching the multiserver Web site. This peculiarity, especially in the presence of highly skewed load, makes it very difficult to achieve acceptable load balancing and avoid overloading some Web servers. This paper adapts traditional scheduling algorithms to the DNS, proposes new policies, and examines their impact under different scenarios. Extensive simulation results show the advantage of strategies that make scheduling decisions on the basis of the domain that originates the client requests and limited server state information (e.g., whether a server is overloaded or not). An initially unexpected result is that using detailed server information, especially based on history, does not seem useful in predicting the future load and can often lead to degraded performance     

一个实时CORBA的动态调度服务模型

在实时CORBA中引入调度服务简化了实时应用的开发,但目前实时CORBA1．0所定义的调度服务使用固定优先级调度策略只能适合于一个封闭的CORBA应用系统．本文针对这一局限性,提出了一个基于客户调度器和服务调度器相协作的动态调度服务模型对其进行扩展,使得调度服务可以适用于一个更为开放的实时CORBA系统．