Where Does the Time Go in Software DSMs?—Experiences with JIAJIA

1IntroductionSoftwaredistributedsharedmemory(DSM)system,orsharedvirtualmemory(SVM)system,providesanabstractionofsinglesharedspaceontopofthephysicallydistributedmemoriespresentedonnetworkofworkstations.Ithasbeenextensivelystudiedinthepastdecadesinceitcombinestheprogrammabilityofsharedmemorysystemsandscalabilityofdistributedsystems[1].However,theperformancegapbetweensoftwareDSMsystemsandmessagepajssingplatformsremainsexisting,whichpreventstheprevalenceofthesoftwareDSMsystemsgreatly.Ingenera…     

指令级并行编译器的数据预取及优化方法

微处理器芯片的处理能力越来越强,但是,存储器的速度却远远不能与其匹配,造成了整个系统的性能不理想,为解决这个总理２,编译器发展了局部性优化、数据预取等多种技术,文中将介绍一种用于ＩＬＰ（Ｉｎｓｔｒｕｃｔｉｏｎ ｌｅｖ－ｅｌ Ｐａｒａｌｌｅｌｉｓｍ）优化编译器的数据预取技术以及一种利用寄存器堆减少主存访问次数、对程序进行 优化的方法,利用它们可以提高平均存储性能,对科学和工程计算的应用是相当有效的。     

TAUS：A File—Based Software Understanding Tool

A program called TAUS,a Tool for Analyzing and Understanding Software,was developed.It is designed to help the programmer analyze and understand the software interactively.Its aim is to reduce the dependence on human intelligence in software understanding and improve the programmer‘s understanding productivity.The design and implementation of TAUS and its applications are described.     

ARMiner: A Data Mining Tool Based on Association Rules

In this paper,ARM iner,a data mining tool based on association rules,is introduced.Beginning with the system architecture,the characteristics and functions are discussed in details,including data transfer,concept hierarchy generalization,mining rules with negative items and the re-development of the system.An example of the tool‘s application is also shown.Finally,Some issues for future research are presented.     

Large Scattered Data Fitting Based on Radial Basis Functions

Solving large radial basis function （RBF） interpolation problem with non-customized methods is computationally expensive and the matrices that occur are typically badly conditioned. In order to avoid these difficulties, we present a fitting based on radial basis functions satisfying side conditions by least squares, although compared with interpolation the method loses some accuracy, it reduces the computational cost largely. Since the fitting accuracy and the non-singularity of coefficient matrix in normal equation are relevant to the uniformity of chosen centers of the fitted RBE we present a choice method of uniform centers. Numerical results confirm the fitting efficiency.     

移动环境下支持实时事务处理的数据预取

随着移动通信技术的迅速发展,人们提出了新的应用要求:在移动环境下处理实时事务.而移动通信带宽有限性引起较大的数据访问延迟,有时甚至由于网络传输的断接使得事务得不到所需要的数据,数据预取能够很好地解决这个问题.已有的移动环境下数据预取没有考虑到数据的流行性和事务的时间特性.该文分析影响实时事务数据预取的因素,首先考虑数据易变性、活跃性等因素,获得高价值预取数据集合;然后考虑访问预取数据的事务优先级、数据流行性等因素,构造预取数据的选择函数,通过该函数在前面选取的集合中筛选出对满足实时事务截止期更有价值的数据对象进行预取.实验表明,该数据预取策略能降低移动实时事务满足截止期的比率,更好地支持移动实时事务处理.     

一种自适应的数据预取与缓冲算法

在海量数据中进行的直接查找往往耗时巨大,在实际应用中很难满足实时性的需求,因此采用数据预取和缓冲技术实现对查找操作的优化成为实际系统中的重要环节。自适应的数据预取和缓冲算法是通过使用人工智能中的技术来分析用户的查询习惯,从而实现动态的预取策略并对预取的数据进行缓冲,以达到提高查询速度的目的。文章根据不同的数据查询需求提出了两类智能算法以适应不同的应用场合。在实验中分别针对单个用户的历史查询应用和多用户的并发查询应用分别进行了分析,证明了这两类智能算法分别对不同的应用场合拥有较好的性能。     

PostgreSQL数据库预取算法研究

减少磁盘的存取时间是提高数据库性能的关键.本文讨论了PostgreSQL数据库顺序存取的特性,提出了一种PostgreSQL中顺序预取数据块的算法,预取的数据块数目可根据当前存取块之前的顺序存取情况作自适应调整.实验结果表明,该算法能有效地提高磁盘块的平均存取速度.     

VoD系统的数据预取及缓冲区动态分配策略

给出了一种基于用户数据消费率的动态数据预取和缓冲区分配策略，并通过构建数据读取函数Ｄａｔａｒｅｎｄ（），实现数据的读取和标准ＶＣＲ控制功能。     

Dynamic Data Prefetching in Home-Based Software DSMs

1 IntroductionSoftware Distributed Shared Memory (DSM) provides the illusion of shared memoryon the top of distributed memory hardware. Most software DSM systems are page-based,using virtual memory protection to trap accesses to shared memory. These systems sufferfrom the high communication and coherence--induced overheads caused by the high levelof implementation and large granularity of coherence. Many techniques, such as multiplewriter protocolll], lazy release consistency[2], and data …     

Supporting flexible data distribution in software DSMs

Page-based software DSM systems suffer from false sharing caused by the large sharing granularity,and only support one-dimension Block or Cyclicblock data distribution schemes,Thus applications running on them will suffer from poor data locality and will be able to exploit parallelism only when using a large number of processors,In this paper.a way towards supporting flexible data distribution(FDD) on software DSM system is presented.Small granularity-tunable blocks,the size of which can be set by compiler or programmer,are used to overlap the working data sets distributed among processors.The FDD was implmented on a software DSM system called JIAJIA.Compared with Block/Cyclic-block distribution schemes used by most DSM systems now,experiments show that the proposed way of flexible data distribution is more effective.The performance of the applications used in the experiments is significantly improved.     

多线程环境下基于多预取点的文件预取

为解决当前Linux内核的预取算法在多线程情况下出现预取误判的问题,依据多线程环境下进程对磁盘文件的访问特点,提出一种基于多预取点的预取算法。在Linux内核原有的预取算法的基础上,结合多线程环境下应用程序对数据的访问模式,在Linux内核的页面缓存层进行了实现。实验和分析表明,在IOzone单线程测试中,该算法和Linux内核原预取算法性能相当;在多线程测试中,读取相同大小的文件,耗时比Linux内核原预取算法至少少1/3。新算法对于提高I/O并行度,从而提高整个计算机系统并行化很有帮助。     

帮助线程预取质量的实时在线评价方法

针对传统静态枚举设置帮助线程控制参数值的繁杂耗时问题,提出了一种帮助线程预取质量的实时在线评价方法。首先,明确了帮助线程的预取服务质量（QoS）的目标;其次,分析了帮助线程预取性能评价的动态指标,对帮助线程预取QoS进行了建模分析;最后,提出一个帮助线程预取的动态自适应调节算法,算法根据程序的阶段行为变化和动态预取获益变化等信息来判断参数值的适用度以及是否需要进行反馈优化,从而实现对预取控制的自适应调节。实验结果表明,应用自适应预取评价算法之后,Mst热点模块的性能提升加速比为1.496,所提出的自适应预取评价方法能够根据程序的动态阶段行为对帮助线程控制参数值作出自适应控制和调节。     

面向链式数据结构的间隔预取策略

由于链式数据结构的存储缺乏空间局部性,导致程序执行过程中对链式数据的访问会发生严重的Cache缺失行为。通过对面向链式结构的线程预取性能分析,研究链式数据结构程序热点循环的计算任务量与访存任务量比例特征对线程预取性能的影响。结合多核处理器平台特点,实现了一种适用于链式数据结构的帮助线程间隔预取方法。实验结果进一步验证了计算任务量与访存任务量比例特征对间隔预取性能的影响,表明间隔预取相比于传统线程预取技术有明显的性能优势。     

A clustering-based prefetching scheme on a Web cache environment

Web prefetching is an attractive solution to reduce the network resources consumed by Web services as well as the access latencies perceived by Web users. Unlike Web caching, which exploits the temporal locality, Web prefetching utilizes the spatial locality of Web objects. Specifically, Web prefetching fetches objects that are likely to be accessed in the near future and stores them in advance. In this context, a sophisticated combination of these two techniques may cause significant improvements on the performance of the Web infrastructure. Considering that there have been several caching policies proposed in the past, the challenge is to extend them by using data mining techniques. In this paper, we present a clustering-based prefetching scheme where a graph-based clustering algorithm identifies clusters of “correlated” Web pages based on the users’ access patterns. This scheme can be integrated easily into a Web proxy server, improving its performance. Through a simulation environment, using a real data set, we show that the proposed integrated framework is robust and effective in improving the performance of the Web caching environment.     

Web访问流的局部性特征建模

网络访问流的局部性特征包括时间局部性和空间局部性,利用数学建模方法研究局部性特征对于缓存和预取系统的设计及性能提高具有重要的作用.通过分析和讨论,利用信息熵和变异系数建立了网络流量局部性特征新的度量方法,信息熵比Zipf定律更能反映访问流的时间局部性,变异系数则解决了访问流的相同文档间的空间局部性建模问题.实验和分析表明,这些参数能较好地描述网络访问流的局部性特征且易于使用.     

Performance bounds for concurrent software with rendezvous

Synchronous message-passing communication, or rendezvous, occurring between software tasks can have a significant effect on system performance. The rendezvous style of communication is coming into wider use in programming languages and operating systems for parallel and distributed environments. Understanding the performance implications of this style of inter-task communication is becoming a matter of practical importance. The dual nature of a task which acts both like a customer as well as a server, makes the performance analysis of rendezvous-based multitasking systems quite different from the analysis of the other queueing systems with known results. This research focuses on rendezvous-based systems in which the execution behavior of the software has a nondeterministic component of a very general nature which may for example be the manifestation of a data dependent behavior. Based on a model called the Stochastic Rendezvous Network the computation of bounds on task throughputs for multitasking systems characterized by rendezvous style communication is presented. Although the behavior of tasks is called stochastic, it is very general and the results are valid for general distributions of computation times and the number of messages generated by tasks. The inter-relationship among task throughputs, however, makes it difficult to extract the bounds in closed analytic form. The notion of a feasible throughput region which encloses the set of feasible tasks throughputs and captures the inter-relationship among the behavior of tasks is introduced. Variations of this basic bounding approach that are useful in the context of different types of multitasking systems are considered in the article. For example, a novel technique based on interval arithmetic is proposed for the computation of numerical values for the bounds. The applicability of the bounds and their tightness are analyzed through case studies. Issues such as the inter-relationship between the software architecture and system performance, and the effect of processor contention on the performance bounds are discussed.     

软件事务内存的动态竞争管理策略

软件事务内存是为了简化并行程序设计而出现的一种新的程序设计技术.为了降低软件事务内存系统中事务冲突的发生频率以提升系统整体性能,提出了一种新的基于动态控制和队列调度的竞争管理策略.定义了竞争强度的概念和系统总体框架,并在此基础上给出了利用运行时反馈信息动态调节竞争强度的方法.同时给出了事务序列化的设计方法与实现中应注意的问题,通过将冲突概率大的事务序列化以达到避免相同冲突再次发生的目的.结合常用的基准数据结构,对模型和算法进行了实验,最后结果表明了算法的正确性和有效性.     

申威处理器硬件数据预取技术的实现

硬件数据预取技术可以有效提升处理器的访存性能,是申威处理器性能优化过程中亟需突破的一项技术。硬件开销和处理器架构的制约是硬件预取技术实现中的主要难点。借鉴学术界对硬件预取技术的研究成果和工业界的应用现状,紧密结合申威处理器的结构特点,研究了申威处理器硬件预取技术的实现方法。以流预取为例,在处理器核心面积增加0.97%的情况下,硬件预取技术的应用可以将目前申威处理器的整数性能平均提升5.17%,最高提升28.88%;浮点性能平均提升6.39%,最高提升30.11%。