A survey of memory management techniques in virtualized systems

Virtualization technology allows multiple operating systems to share hardware resources of a computer system in an isolated manner. Traditionally, memory is shared by an operating system using segmentation and paging techniques. With virtualization, memory partitioning and management has several new challenges. For isolated and safe execution, hypervisors do not provide direct access to hardware resources. Lack of direct access to the memory management hardware like page tables disqualifies direct usage of virtual memory solutions used on native (non-virtualized) setups. Further, aspects of dual control of the memory resource (by the guest OS and the hypervisor) and lack of semantics regarding memory usage in virtual machines present additional challenges for memory management. This paper surveys different techniques of memory partitioning and management across multiple guest OSs in a virtualized environment.An important goal of virtualization is to increase the physical machine utilization in order to save costs. With varying application demand for memory and diverse memory management policies of the guest OSs, ensuring optimal usage of memory is non-trivial. In this survey, challenges of memory management in virtualized systems, different memory management techniques with their implications, and optimizations to increase memory utilization are discussed in detail.     

实时嵌入式操作系统中核外I/O的实现

传统操作系统核内驱动的I/O结构无法满足嵌入式操作系统的需要，核外I/O技术的实现难点是如何将外部中断从核内引向核外，分析了基于信号机制的核外I/O的实现方法，并提出了一种由系统核心ISR直接跳转到核外驱动程序ISR的核外硬中断方法及其实现方法。     

基于Linux的软件DSM实现

分布式共享存储系统在分布式存储器的基础上构造逻辑上的共享存储模型。提出了在操作系统层实现分布式共享存储的系统框架，并以Linux操作系统为平台介绍了其实现。该系统提供简单的调用接口，并与Linux内存管理框架紧密结合。通过采用合适的DSM一致性协议提高了整体性能。     

一种基于CPLD的I／O总线驱动液晶显示的方法

The paper discusses a new kind of driving the LCD via I/O bus using CPLD and realizing the precise I/O control timing sequence by establishing the corresponding Verilog-HDL model. The results of application show that this solution can not only solve the matching of low-speed device with high-speed bus but also provide the display in-terface during the motherboard debugging process, and also prove that the whole system is reliable and stable.     

Linux系统中网络I/O性能改进方法的研究

选择并设计高效的网络I/O模型是改善服务器性能的关键。该文通过对Linux系统中几种网络I/O模型的分析和研究,提出3种改善网络I/O性能的方法,并讨论这3种方法在Linux系统中的实现技术。实验结果验证了该方案的有效性。     

Improving the I/O performance of intermediate multimedia storage nodes

The data retrieval operations in servers and proxies for Media-on-Demand applications represent a severe bottleneck, because a potentially (very) high number of users concurrently retrieve data with high data rates. In the Intermediate Storage Node Concept (INSTANCE) project, we have developed a new architecture for Media-on-Demand storage nodes that maximizes the number of concurrent clients a single node can support. We avoid the traditional bottlenecks, like copy operations, multiple copies of the same data element in main memory, and checksum calculation in communication protocols, by designing, implementing, and tightly integrating three orthogonal techniques: a zero-copy-one-copy memory architecture, network level framing, and integrated error management. In this paper, we describe the INSTANCE storage node, and present an evaluation of our mechanisms. Our experimental performance results show that the integration of these three techniques in NetBSD at least doubles the number of concurrent clients that a single storage node can serve in our testbed.     

Efficient computation of optimal space-time performance curves for memory hierarchies

The problem of determining the best possible space-time performance for a given program executing in a two-level memory hierarchy for a given access time ratio is known to be computationally expensive. That one often wishes to determine such optimal performance across a broad range of access time ratios changes an expensive computational task into one which is often not feasible. We present a technique by which, given an acceptable error bound, a piecewise linear approximation to the actual space-time vs. access time ratio curve may be efficiently derived. That approximation is shown to deviate from the actual curve by no more than specified by the error bound. Such curves are useful in performance evaluation studies for memory management schemes in which the allocation of real memory is dynamically varied.     

Algorithms for parallel memory,I: Two-level memories

We provide the first optimal algorithms in terms of the number of input/outputs (I/Os) required between internal memory and multiple secondary storage devices for the problems of sorting, FFT, matrix transposition, standard matrix multiplication, and related problems. Our two-level memory model is new and gives a realistic treatmentof parallel block transfer, in which during a single I/O each of theP secondary storage devices can simultaneously transfer a contiguous block ofB records. The model pertains to a large-scale uniprocessor system or parallel multiprocessor system withP disks. In addition, the sorting, FFT, permutation network, and standard matrix multiplication algorithms are typically optimal in terms of the amount of internal processing time. The difficulty in developing optimal algorithms is to cope with the partitioning of memory intoP separate physical devices. Our algorithms' performances can be significantly better than those obtained by the wellknown but nonoptimal technique of disk striping. Our optimal sorting algorithm is randomized, but practical; the probability of using more than times the optimal number of I/Os is exponentially small inl(logl) log(M/B), whereM is the internal memory size.A summarized version of this research was presented at the 22nd Annual ACM Symposium on Theory of Computing, Baltimore, MD, May 1990. This work was done while the first author was at Brown University. Support was provided in part by a National Science Foundation Presidential Young Investigator Award with matching funds from IBM, by NSF Research Grants DCR-8403613 and CCR-9007851, by Army Research Office Grant DAAL03-91-G-0035, and by the Office of Naval Research and the Defense Advanced Research Projects Agency under Contract N00014-91-J-4052 ARPA Order 8225. This work was done in part while the second author was at Brown University supported by a Bellcore graduate fellowship and at Bellcore.     

Linux下的Input子系统

Input子系统属于Linux系统下字符类驱动系统,现在Android、X-windows、Qt等众多应用于Linux系统中键盘、鼠标、触摸屏等输入设备的支持都通过、或越来越多倾向于标准的Input子系统．基于现况本文首先从Input_dev层,InputCore层和EventHandler层介绍Input输入子系统的实现框架,然后通过4x4矩阵按键在Input子系统中的实现以及用户在应用层通过Input子系统提供的接口函数对按键操作来查看具体的键值和按键状态．测试结果表明,Input子系统里的按键驱动稳定高效通用性强．     

并行文件系统Lustre细粒度I/O性能优化

并行文件系统Lustre粗粒度I/O性能良好,细粒度I/O性能相对粗粒度I/O比较低下,因此优化细粒度I/O性能成为提高系统整体I/O性能的关键问题。在研究和分析了Lustre的I/O访问模式、细粒度I/O服务流程和页面替换算法等方面后,提出了细粒度优先（Fine Grained First,FGF）LRU算法。在OST端及Client端的页高速缓存中最大程度地保留细粒度I/O的页面,降低细粒度I/O引起的页面下沉速度,延长细粒度I/O页面在主存中的时间,进而减少对磁盘的访问次数,降低磁盘访问开销。通过对实验数据的对比和分析,验证了FGF-LRU算法的有效性。在不影响粗粒度I/O性能的情况下,提高了细粒度I/O性能,最终实现提高系统整体I/O性能。     

PC汇编语言的I/O问题

PC汇编语言没有提供任何I／O手段，给汇编语言的教学和开发造成极大的困难。本文给出了一套I／O工具，功能强大，用法简单，便于记忆，能满足教学和开发工作的需要。     

Linux I/O调度算法分析与研究

研究表明,好的磁盘调度算法可以明显优化磁盘的I/O性能,Linux提供四种调度算法可供选择。基于Linux 2.6.32内核源码,研究Noop、Deadline、Anticipatory、CFQ四种磁盘调度算法的基本原理和特点,分析每种算法的优缺点,这对系统管理员针对不同类型的应用场景来调整优化I/O调度算法有着重要意义。     

在操作系统实现指令对文件的直接寻址

1.引言在计算机系统中,进程的数据存储在内部存储器和外部存储设备上,但操作系统并不允许进程直接访问这两种资源,允许进程直接访问的是另外两个逻辑上的数据存储模型:逻辑空间和文件。逻辑空间是物理存储器的抽象,通过为每个进程构造各自独立的逻辑空间,操作系统不仅实现了各个进程之间数据的相互隔离,而且很方便地实现了存储保护、存储扩充、存储共享等功能。可以这样说,现代操作系统中的存储管理,就是围绕如何构造和维护进程的逻辑空间而展开的。     

分布式多计算机系统中的存储扩充问题及其解决办法

在大规模分布式多计算机系统中,内外存之间容量的差距正在减小,这极大地影响了操作系统中存储管理的设计和实现。操作系统设计得必须解决在外存存量不足的情况下如何实施存储扩充。提出了指令对文件直接寻址的概念及其实现方法,并分析了指令对文件直接寻址如何解决了这个问题。     

Linux内核支持服务质量的改进

分布实时计算平台存在着服务质量（QoS）问题,选择Linux系统并对其进行QoS扩展来解决这一问题。总结出Linux进程管理策略与机制分离的重要设计风格,来建立支持QoS要求的实时调度器,从而不需要修改应用就能满足应用的QoS需求。然后选择EDF实时调度算法作为扩展目标,引入了“预留”对象这一数据结构,在Linux进程间共享QoS,建立了支持QoS的新的Linux核心,更好地满足了实时系统的QoS需求。     

MROS-68K,a memory resident operating system,for MC68000

The operating system described has been designed and implemented for use in dedicated one-purpose applications, typically in real tihe. Specific attention has been paid to flexible intertask contkol. In the first installation the application system was the steering and controlling of large hydraulic devices. Typical subtasks involved were measuring, coordinate transformations, control, teaching and following robotic paths and evaluating daily material transfkrs. As a programming effort, developing the operating system was fairly reasonable being of the order of three or four months for one person, including design, coding, testing and documentation.     

可编程序控制器应用中节省输入输出通道的方法

主要介绍了在使用可编程序控制器时,节省输入输出通道的实用方法和实例,从而达到节约成本、优化设计的目的。     

Linux系统中按字节显示文件内容的方法

本文给出Linux系统中按字节显示文件内容的实现方法。对于给定的文件，所显示的格式中包括当前字符到文首的偏移量、各字节的ASCII码的16进制值及其对应的字符(对于非可打印字符，显示成圈点“．”)。利用此方法。可方便地查看文件(特别是非文本文件)的字节构成。例如，可分析某些带结构的数据文件．如BMP位图文件等。     

Linux下高性能网络I/O解决方案分析

Linux下网络I/O的高性能,主要指当Socket文件描述符上有大量事件发生时,系统可以快速响应,且其处理能力具有可扩展性.以往,人们都是使用select()或poll()来实现,但实践表明,随着文件描述符的增多,这两个系统调用的性能会显著下降.本文将讨论一种实现机制更高效、扩展性更好的解决方案:使用epoll(),并通过实验证明其高效性.     

Sinking型和Sourcing型数字信号I/O接口应用

当为控制系统选择数字信号输入/输出模块的接口类型时,正确理解Sinking Current(灌电流)和Sourcing Current(拉电流)的概念是非常重要的。讨论数字信号输入/输出接口/连接电路时会经常使用这些术语,在设计与负载连接的电路时,除了考虑电压、电流、功率等匹配外,更要注意灌电流型和拉电流型DI/O的区别,以使得连接电路更合理、可靠,逻辑表达更清楚和正确。