SCSI Target Simulator Based on FC and IP Protocols in TH-MSNS

Introduction Storage area networks (SAN)[1] use net-oriented stor- age structures, which separate data processing and data storage with flexible addressing, long-distance, high- speed transfers, and fast I/O performance. SAN are widely used, and have beco…     

LDS脆弱性分析实验环境体系结构研究与实现

支持动态分析的实验环境对于提高大规模分布式的安全性具有重要作用。在分析大规模分布式系统脆弱性分析对实验环境需求的基础上,提出了一种针对大规模分布式系统脆弱性分析的仿真实验环境体系结构,描述了体系结构的实现方法,以及网络拓扑生成与映射、虚实结合的网络仿真等关键技术。并通过实验和示例分析说明实验环境能够有效降低大规模分布式系统脆弱性分析的复杂性,并验证分析结果的准确性。     

面向结构体数据布局优化的高效内存管理

面向结构体数据布局优化的内存池由于自身的使用特点,在传统的内存管理方式下,扩展内存需要移动数据,代价很高。为了避免移动数据,提高内存池性能,该文设计实现了基于共享内存地址映射技术的零数据移动内存管理系统DM3,辅助内存池管理内存。DM3利用POSIX标准编程接口提供的共享内存机制,在用户层操控物理内存到程序虚地址空间的映射,实现高效内存管理。首先,DM3针对结构体数据布局优化的内存使用特点,选择特定地址空间分配,既照顾到内存池扩展需求,又避免影响程序中其他内存请求。其次,在已分配的地址空间不能满足进一步扩展需求时,DM3通过内存地址重映射,实现地址空间转移而避免实际移动数据。通过在多个操作系统上的实验比较了DM3和传统的realloc方式,结果表明:DM3系统性能优越,最高可获得9.76倍加速比。DM3使用POSIX标准实现,具有跨平台移植性和易用性。应用DM3管理内存有效地增加了内存池性能。     

基于NOW的检查点设置与卷回恢复

通过对分布系统卷回恢复过程中出现的主要问题进行讨论，并针对工作站网络系统环境，分析了不同ＣＲＲ技术的优劣。在此基础上，论述了一个并行程序运行回卷恢复与进程迁移系统－ＯｈａＲＭ的设计与实现技术。最后给出了ＣｈａＲＭ系统性能评测结果，并与其他同类系统进行了比较。     

Challenge and Methods of Synchronous Disk I／O

At present, I/O is the performance bottleneck limiting the speed of computer systems. A large number of I/O operations are synchronous read/write operations of only small data blocks. However, reducing the latency of synchronous I/O operation is a non-trivial problem. In this paper, we propose two methods to address this problem. The first method, FastSync, uses a cache disk optimized for write operation via use of a disk-head position prediction algorithm. In this way, disk capacity is traded for synchronous I/O performance. The second method, LND, uses free memory capacity in a network environment as a cache disk for the buffeting of synchronous I/O operation. Data integrity in FastSync is ensured by using a data log on the cache disk, whereas in LND, integrity is ensured by the storage in distributed memory of multiple copies of each data block. Both methods succeed in dramatically increasing the performance of synchronous I/O operation. The performance of LND is limited by the network speed, whereas performance of FastSync is determined mostly by the data block size.     

一种与Bittorrent兼容的流媒体服务系统

在Bittorrent协议和算法的基础上,提出了一种和Bittorrent协议兼容的分段顺序文件下载算法,很好地满足了用户边下载流媒体文件边播放的需求.以该算法为核心,给出了一种以Bittorrent文件下载系统为原型的流媒体服务系统实现.实验结果表明,采用分段顺序下载算法的客户端下载速率有所降低,不过该算法使得流媒体服务系统的负载能力比传统的流媒体服务系统提高了3~4倍,充分体现了P2P技术相对于集中式服务技术的优势.     

基于内存功能划分的并行程序检查点策略研究

目前采用检查点设置技术的并行程序容错系统存在着不能透明处理通信环境变量的缺点,需要在设置检查点之前关闭进程间通信套接字,在恢复之后重新构建,为此提出了基于内存功能划分的通信隔离策略,分离计算模块和通信模块,避免对通信套接字的直接操作,完成了透明的容错功能.实验结果显示此策略对并行检查点系统性能有一定程度的改善,可以降低系统实现的复杂度,提高卷回恢复的可靠性,而且独立于并行系统,具有良好的移植性.     

Class-Based Garbage Collection in Object-Oriented Programming Environments

Many garbage collection algorithms have been proposed, but few address the special needs of long-running server programs. Server applications usually run for years and spawn many threads, so they create and discard thousands of objects. Therefore, efficient garbage collection is especially important for those applications. This paper presents a class-based garbage collector for object-oriented programming environments that classifies objects by their types to achieve better gradualness. Grouping objects of the same type into a group, with a limited type-lock, a mutator cache and the lease protocol will reduce memory fragmentation, which is especially important for the efficiency of long-running server applications. This class-based collector partitions the heap space by type, which provides better concurrency than the traditional mark-sweep collector, and its reusable garbaged object pool also reduces the object allocation overhead. This paper also discusses the implementation details, such as the mutator cache and the lease protocol, and techniques to achieve better accuracy.     

大规模流媒体服务间隔缓存策略的性能预测模型

静态分析模型能在负载固定的情况下预期不同因素对缓存算法性能的影响,为解决该模型在动态负载下预测精度不高的问题,该文结合实际用户访问行为研究,采用负载拟合的方法对此问题进行了探讨,并提出了一种针对变动负载的间隔缓存类算法的动态性能模型。该模型可更准确估算系统实际性能,从而为用户控制等策略提供参考。实验结果表明,静态模型的缓存命中率预测结果比实际高70%以上,而该模型则能适应负载的变动,预测结果与实际结果差别在10%左右。     

Stability Analysis of Runge-Kutta Methods for Delay Integro-Differential Equations

Considering a linear system of delay integro-differential equations with a constant delay whose zero solution is asympototically stable, this paper discusses the stability of numerical methods for the system. The adaptation of Runge-Kutta methods with a Lagrange interpolation procedure was focused on inheriting the asymptotic stability of underlying linear systems. The results show that an A-stable Runge-Kutta method preserves the asympototic stability of underlying linear systems whenever an unconstrained grid is used.