面向非易失内存的数据一致性研究综述

在分布式内存系统中,缓存是减少远端内存访问开销的一种有效手段. 然而,单一的缓存一致性保证机制往往不能高效适配不同类型负载的访存特性. 为此,面向分布式异构内存池系统,设计了基于目录和基于广播相结合的混合缓存一致性保证机制. 利用四象限矩阵分析方法,对每个数据对象进行访存模式的判定分析,并为其配置最高效的缓存一致性保证策略,并且可以根据对象访存特征的变化在2 种策略之间动态切换. 实验结果表明,相比使用单一的缓存一致性保证机制,采用可动态配置的混合缓存一致性保证机制可提升分布式异构内存池系统的读和写,性能平均达32.31%和31.20%. 此外,混合的缓存一致性保证机制在客户端数量不断增加时仍然表现出良好的可扩展性.

     

对分布式共享存储中的伪共享的动态控制

分布式共享存储（ＤＳＭ）使得在分布式存储机器上,对显式消息传递编程的需要得到减轻。为降低存储问题延迟,ＤＳＭ系统将数据复制多个拷贝。文中考查了几种用于控制因伪共享问题造成的存储抖动的方法,提出了一种新的存储一致性协议：写者拥有协议,它在运行时检测并消除伪共享。迭代运算中,由于数据在每次迭代中被地存取,写者拥有协议只要消除一次伪共享,所以额外开销非常小。实验数据表明,写者拥有协议通常情况下优于已有的     

分布式共享内存的技术和实现

分布式共享内存结合了布式内存结构与共享存储结构的优点，具有可扩充性、通过性性、方便性，本文论述了在实现ＤＳＭ系统中存在的问题，并讨论了ＤＳＭ系统在软件硬件方面所做的工作和采取的措施。     

以操作系统为中心的存储一致性模型--线程一致性模型

分布共享存储系统为保证程序的正确执行，必须通过存储一致性模型对共享存储访问顺序加以限制，而现有模型在可扩展性和操作系统级实现方面存在不足。结合多线程的特点，提出了一种以操作系统为中心的线程一致性模型，通过并行程序执行过程中线程状态的变化来观察和限制存储访问事件的正确顺序，有利于系统的可扩展性、一致性维护信息获取的方便性和完备性以及操作系统本身的设计和实现。分别从模型的定义、正确性证明、实现方案和性能分析等几个方面展开了论述。     

A Lock-Based Cache Coherence Protocol for Scope Consistency

Directory protocols are widely adopted to maintain cache coherence of distributed shared memory multiprocessors.Although scalable to a certain extent,directory protocols are complex enough to prevent it from being used in very large scale multiprocessors with tens of thousands of nodes.his paper proposes a lock-based cache coherence protocol for scope consistency.In does not rely on directory information to maintain cache coherence.Instead,cache coherence is maintained through requiring the releasing processor of a lock to stroe all write-notices generated in the associated critical section to the lock and the acquiring processor invalidates or updates its locally cached data copies according to the write notices of the lock.To evaluate the performance of the lock-based cache coherence protocol,a software SDM system named JIAJIA is built on network of workstations.Besides the lock-based cache coherence protocol,JIAJIA also characterizes itself with its shared memory organization scheme which combines the physical memories of multiple workstations to form a large shared space.Performance measurements with SPLASH2 program suite and NAS benchmarks indicate that,compared to recent SVM systems such as CVM,higher speedup is achieved by JIAJIA.Besides,JIAJIA can solve large scale problems that cannot be solved by other SVM systems due to memory size limitation.     

DSM系统中内存一致性模型的研究

文章首先回顾了分布式共享存储器（ＤＳＭ）系统中主要的内存一致性协议,重点分析了释放一致性（ＲＣ）模型。在此模型的基础上对其进行了改进,提出了基于动态减少无效副本集的ＲＣ模型。     

A framework for ensuring consistency of Web Services Transactions

For efficiently managing Web Services (WS) transactions which are executed across multiple loosely-coupled autonomous organizations, isolation is commonly relaxed. A Web service operation of a transaction releases locks on its resources once its jobs are completed without waiting for the completions of other operations. However, those early unlocked resources can be seen by other transactions, which can spoil data integrity and cause incorrect outcomes. Existing WS transaction standards do not consider this problem. In this paper, we propose a mechanism to ensure the consistent executions of isolation-relaxing WS transactions. The mechanism effectively detects inconsistent states of transactions with a notion of an end-state dependency and recovers them to consistent states. We also propose a new Web services Transaction Dependency management Protocol (WTDP). WTDP helps organizations manage the WS transactions easily without data inconsistency. WTDP is designed to be compliant with a representative WS transaction standard, the Web Services Transactions specifications, for easy integration into existing WS transaction systems. We prototyped a WTDP-based WS transaction management system to validate our protocol.     

Implementing hybrid consistency with high-level synchronization operations

Summary.  In recent years, there is a growing tendency to support high-level synchronization operations, such as read-modify-write, FIFO queues and stacks, as part of the programmer’s shared memory model. This paper examines the problem of implementing hybrid consistency with high-level synchronization operations. It is shown that for any implementation of weak consistency, the time required to execute a read-modify-write, a dequeue or a pop operation is Ω(d), where d is the network delay. Following this, an efficient and simple algorithm for providing hybrid consistency that supports most types of high-level synchronization operations and weak read and weak write operations is presented. Weak read and weak write operations are executed instantaneously, while the time required to execute strong operations is O(d). This is within a constant factor of the lower bounds for most of the commonly used types of operations. Received: August 1994 / Accepted: June 1995     

An Asynchronous Protocol for Release Consistent Distributed Shared Memory Systems

Distributed shared memory (DSM) systems provide a simple programming paradigm for networks of workstations, which are gaining popularity due to their cost-effective high computing power. However, DSM systems usually exhibit poor performance due to the large communication delay between the nodes; and a lot of different memory consistency models have been proposed to mask the network delay. In this paper, we propose an asynchronous protocol for the release consistent memory model, which we call an Asynchronous Release Consistency (ARC) protocol. Unlike other protocols where the communication adheres to the synchronous request/receive paradigm, the ARC protocol is asynchronous, such that the necessary pages are broadcast before they are requested. Hence, the network delay can be reduced by proper prefetching of necessary pages. We have also compared the performance of the ARC protocol with the lazy release protocol by running standard benchmark programs; and the experimental results showed that the ARC protocol achieves a performance improvement of up to 29%.     

Weak atomicity for the x86 memory consistency model

We consider the interaction of weakly atomic Software Transactional Memory (STM) providing single global lock atomicity with the x86 memory consistency model. We show that a practical design for such an STM requires that some program behaviour be disallowed, due to the strictness of the x86 memory consistency model in comparison to the language level memory models hitherto considered in weakly atomic STM designs. We present the design and construction of such an STM that disallows races between a transactional read and a non-transactional write. We also report on a practical application of this STM to elide legacy locks in x86 binaries. This allows software transactional memory to be applied without requiring software to be a priori written with awareness of transactional memory and without any restriction on source language or compiler. As an example, we show how a mainstream multiplayer game can use transactional memory with zero changes and 11% overhead over language level transactional memory, which requires over 700 annotations and severely restricts software development.     

虚拟共享存贮器的一种实现策略

本文介绍了虚拟共享存贮器的概念及构成，提出了用动态分布管理者算法构造虚拟共享存贮器的实现策略。     

Delay tolerant lazy release consistency for distributed shared memory in opportunistic networks

Opportunistic networks (ONs) allow mobile wireless devices to interact with one another through a series of opportunistic contacts. While ONs exploit mobility of devices to route messages and distribute information, the intermittent connections among devices make many traditional computer collaboration paradigms, such as distributed shared memory (DSM), very difficult to realize. DSM systems, developed for traditional networks, rely on relatively stable, consistent connections among participating nodes to function properly.We propose a novel delay tolerant lazy release consistency (DTLRC) mechanism for implementing distributed shared memory in opportunistic networks. DTLRC permits mobile devices to remain independently productive while separated, and provides a mechanism for nodes to regain coherence of shared memory if and when they meet again. DTLRC allows applications to utilize the most coherent data available, even in the challenged environments typical to opportunistic networks. Simulations demonstrate that DTLRC is a viable concept for enhancing cooperation among mobile wireless devices in opportunistic networking environment.     

存储模型仿真器的设计与实现

存储一致性问题和高速缓存一致性问题是共享存储并行计算机中两个最关键的问题,通过仿真器对它们进行了量化研究,设计并实现了一个存储模型仿真器MMS．基于MMS仿真了不同并行机结构模型下多种存储一致性模型的行为;针对不同类型的计算问题比较了不同的存储一致性模型,并对实验结果进行了分析;实现了几个不同的高速缓存一致性协议,并比较了它们的性能．     

Super－Object模型：在分布存储器多计算机上实现共享存储器程序设计模式

Ｓｕｐｅｒ－Ｏｂｊｅｃｔ模型提出了一种新的方法，在分布存储器多计算机上实现语言级虚拟共享存储器以支持共享存储器通信模式．Ｓｕｐｅｒ－Ｏｂｊｅｃｔ模型引入新的概念ｓｕｐｅｒ－ｏｂｊｅｃｔ，不同于其它模型，基于ｓｕｐｅｒ－ｏｂｊｅｃｔ，它提出了新的共享数据定位方法，全局地址标识（ｎａｍｅ，ｏｆｆ－ｓｅｔ）．Ｓｕｐｅｒ－Ｏｂｊｅｃｔ模型与Ｆｏｒｔｒａｎ７７结合，我们实现了一个运行时间系统和库调用，支持程序员使用Ｆｏｒｔｒａｎ语言编写并行程序，最后介绍了系统的实现和取得的性能．     

A Platform-Independent Distributed Runtime for Standard Multithreaded Java

JavaSplit is a portable runtime environment for distributed execution of standard multithreaded Java programs. It gains augmented computational power and increased memory capacity by distributing the threads and objects of an application among the available machines. Unlike previous works, which either forfeit Java portability by using a nonstandard Java Virtual Machine (JVM) or compromise transparency by requiring user intervention in making the application suitable for distributed execution, JavaSplit automatically executes standard multithreaded Java on any heterogenous collection of Java-enabled machines. Each machine carries out its part of the computation using nothing but its local standard (unmodified) JVM. Neither the programmer nor the person submitting the program for execution needs to be aware of JavaSplit or its distributed nature. We evaluate the efficiency of JavaSplit on several combinations of operating systems, JVM implementations, and communication hardware.     

一种面向多核DSP的小容量紧耦合快速共享数据池

该文结合片上便笺式存储器(SPM)的结构特点,提出了一种面向异构多核DSP的新型小容量紧耦合共享存储结构——快速共享数据池(FSDP).FSDP在存储层次上与一级Cache平行,可以被访存指令直接访问,采用多体并行的结构、交叉访问模式和基于硬件信号灯的自动同步机制,支持多个DSP核的并行访问与快速的核间数据交换,两核之间交换单个数据只需4拍.该文构建了FSDP的模拟模型,并进行了RTL级设计实现和分析.多种典型测试程序的验证表明,FSDP对于DSP核间细粒度共享数据的传输具有很高的效率,相比同类的VS-SPM结构能够将程序性能提高37%,与传统的共享数据Cache结合使用能够将异构多核DSP的性能提高13%.     

一种应用于网络硬盘存储系统的一致性协议

通常网络硬盘系统会向用户提供高可用性和低延迟的网络服务,并且通过对不同程度上的一致性进行选取,从而寻找可用性、低延迟与一致性这三者的平衡。高一致性意味着系统将会牺牲掉一定的可用性,但低一致性会增加程序设计的难度。为一款网络硬盘系统设计一种一致性协议,使得该网盘可以高效地处理用户对共享目录或文件的移动、删除和重命名等操作,与此同时还能确保共享目录及文件在各个客户端中不会有混乱无序的情况出现。     

基于锁集合的动态数据竞争检测方法

数据竞争使得共享存储程序难于调试．以前大部分针对共享存储程序的动态数据竞争检测工作都是通过维护发生序来实现．这种方法有一个重要缺点，即针对程序的一种输入，对程序的一次执行进行检测，不能检测出所有的可行数据竞争．文中利用存储一致性模型的框架模型，针对域一致性模型提出了增强发生序概念，并依此得出一种基于锁集合的动态数据竞争检测算法，克服了这个问题．在软件DSM系统JIAJIA上的实现获得了很好的性能，应用平均减速比为3．14．利用该方法，在TSP程序中找到了大量的读写数据竞争的情况．     

DSDM:一种基于机群系统的多屏显示接口

利用多个计算机的显示卡和显示屏幕（或外接的投影仪）实现基于机群系统的多屏显示，是一种非常有前途的实现廉价高清晰度显示的技术途径，提出的多屏显示接口为开发多屏显示应用提供了一个多计算机显示内存的统一映像，并同时具有支持并行程度开发的显示同步机制，从而在很大程度上简化了多屏显示应用的模型。