Kernel support for zero‐loss Internet service restart

Owing to long serving time and huge numbers of clients, Internet services can easily suffer from transient faults. Although restarting a service can solve this problem, information of the on‐line requests will be lost owing to the service restart, which is unacceptable for many commercial or transaction‐based services. In this paper, we propose an approach to achieve the goal of zero‐loss restart for Internet services. Under this approach, a kernel subsystem is responsible for detecting the transient faults, retaining the I/O channels of the service, and managing the service restart flow. In addition, some straightforward modifications to the service should be made to take advantage of the kernel support. To demonstrate the feasibility of our approach, we implemented the subsystem in the Linux kernel. Moreover, we modified a Web server and a CGI program to take advantage of the kernel support. According to the experimental results, our approach incurs little runtime overhead (i.e. less than 3.2%). When the service crashes, it can be restarted quickly (i.e. within 210 μs) with no information loss. Furthermore, the performance impact due to the service crash is small. These results show that the approach can efficiently achieve the goal of zero‐loss restart for Internet services. Copyright © 2006 John Wiley & Sons, Ltd.     

面向绿色云计算的虚拟机迁移推荐

在以节约能源和提高能源利用率为目的的绿色云计算背景下,提出一种基于层次分析法的虚拟机迁移评估模型。该模型通过基于属性聚类的协同过滤方法,针对虚拟机的属性空间进行评分,给出了最佳绿色虚拟机迁移策略的决策方法。通过建立虚拟机任务资源使用率指标体系及两两比较矩阵,采纳五级评分制对虚拟机迁移及任务资源占用进行了评估。实验结果表明,提出的模型和方法能够显著提高云计算集群的能源利用率、节约能源的消耗。该方法对绿色云计算的研究具有重要意义。     

Minimum‐cost virtual machine migration strategy in datacenter

With an explosive growth of the datacenter research, virtual machines migration aiming at optimization of virtual machines placement is a major technology of improving power efficiency and resource utilization in the datacenter. While recent studies have primarily focused on maximizing resource utilization or minimizing migration cost separately, there has been little attention on jointly taking these two objectives into account. In this paper, we present the optimization model taking minimum migration cost and maximum resource utilization with multi‐resources such as storage, bandwidth, CPU, and disk space into account. The optimization of our proposed model is non‐deterministic polynomial‐time hard. According to the model, we present an efficient approximate algorithm based on bin packing algorithm, called MinCost, to resolve our model and obtain a near‐optimal solution. Finally, the simulation results in this paper show that our model and algorithm is efficient. Copyright © 2015 John Wiley & Sons, Ltd.     

面向服务网格的虚拟环境部署运行管理系统

虚拟技术的最新进展为网格计算提供了封装资源的新方式,其封装性、隔离性和安全性能够有效屏蔽底层资源的异构性,根据用户应用需求定制执行环境,更好地适应于网格环境的复杂性和应用的多样性。为了满足当前服务网格的需求发展,基于新的虚拟机技术,研究适合于服务网格的虚拟环境部署运行管理系统,该系统为用户提供可视化、易操作的远程虚拟环境部署和运行管理功能;并实现一个标准的网格服务,结合服务网格平台CROWN,该服务可根据用户应用的特定需求动态透明地部署虚拟执行环境,并根据资源状态自适配调度执行用户任务。并对系统进行了实验分析,实验结果验证了系统的良好可用性和运行性能。     

INTER-VMM:融合虚拟机选择和放置的虚拟机迁移模型

低能量消耗与物理资源的充分利用是绿色云数据中心构造的两个主要目标,需要采用虚拟机迁移模型来完成优化,为此提出了融合虚拟机选择和放置的虚拟机迁移模型INTER-VMM（Interrelation approach in virtual machine migration）。INTER-VMM设计了云数据中心的基于多维物理资源约束的能量消耗模型,是一种将主机负载检测、虚拟机选择及放置结合起来考虑的虚拟机迁移策略。在虚拟机选择中采用HPS（High CPU utilization selection）选择法,选择超负载物理主机上CPU利用率最高的一个虚拟机,让其进入候选迁移虚拟机列表中。在虚拟机放置中采用空间感知分配（Space aware placement, SAP）放置法,考虑了充分利用物理主机空余空间使用效率的方法。仿真结果表明,INTER-VMM比近几年来常见的虚拟机迁移策略具有更好的性能指标,对云服务提供商具有很好的参考价值。     

虚拟机迁移系统网络连接重定向技术*

针对虚拟机（virtual machine,VM）在不同子网间进行在线迁移时,因网络接入点发生改变而无法继续通信的问题,设计和实现了基于代理移动IP（proxy mobile IP,PMIP）的网络连接重定向系统。当VM迁移到外部子网时,将其看做移动节点,不改变IP地址,通过外部网络和家乡网络之间的双向隧道传输所有来自和发往该VM的网络数据。此方案中跨子网的在线迁移行为对VM以及与VM通信的节点透明。实验证明了该系统可以保证VM较快的网络切换速度和较好的网络通信性能。     

面向QoS保障的虚拟可信服务*

针对服务计算模型中对应用的可信特性支持不足问题,提出面向QoS保障的虚拟可信服务VTS,并依据VTS设计了一种基于反馈控制的自适应QoS保障机制。首先将VTS的QoS保障转换为反馈控制问题,给出一种自适应QoS保障框架,再在此框架下对VTS的QoS维护过程和策略进行建模,设计和实现了相应的动态组建、调节算法和实时评估策略。最后通过仿真实验的结果分析表明,该保障机制能够有效地增强VTS对服务实体运行时的QoS保障能力。     

服务恢复中上下文建模与持久化

服务上下文是实现对用户透明的服务容错以及降低服务恢复代价的关键,然而现有研究缺乏关于服务恢复的上下文分类和表示方法。针对该问题,提出了面向服务恢复的上下文归类、表示和持久化方法。利用一定的应用场景对上下文的使用进行了说明。该方法对服务恢复、等价服务选取中上下文模型的构建提供了可靠的依据。     

A static region‐based compiler for the Dalvik virtual machine

The Dalvik virtual machine (VM) is an integral component used to execute applications in Android, which is one of the leading operating systems for mobile devices. The Dalvik VM is an interpreter and is equipped with a trace‐based just‐in‐time compiler for enhancing the execution performance of frequently executed paths, or traces. However, traces generated by the Dalvik VM can be stopped in a conditional branch or a method call/return, which means that these traces usually have a short lifetime, decreasing the effectiveness of the compiler optimizations applied to them. Furthermore, the just‐in‐time compiler applies only a few simple optimizations because of performance considerations. In this article we present a traces‐to‐region (T2R) framework that extends traces to regions and statically compiles these regions into native binaries so as to improve the execution of Android applications. The T2R framework involves three main stages: (i) the profiling stage, in which the run‐time trace information of an application is extracted; (ii) the compilation stage, in which regions are constructed from the extracted traces and are statically compiled into a native binary; and (iii) the execution stage, in which the compiled binary is loaded into the code cache when the application starts to execute. Experiments performed on an Android tablet demonstrated that the T2R framework was effective in improving the execution performance of applications by 10.5–16.2% and decreasing the size of the code cache by 4.6–28.5%. Copyright © 2015 John Wiley & Sons, Ltd.     

虚拟机快速全系统在线迁移

虚拟机全系统在线迁移对于广域网或者没有共享存储的局域网中的虚拟化平台非常重要.然而,全系统映像一般在几十吉字节(gigabyte, GB)量级,迁移这些数据需占用大量I/O带宽且时间开销很大.快速全系统在线迁移方法具有如下特点:文件系统感知的磁盘同步,利用文件系统的磁盘块分配位图,只拷贝实际使用的磁盘块,显著减少了第1阶段同步的磁盘映像数据量;异或压缩,利用映像数据的自相似性,快速有效地减少了迁移最后两个阶段拷贝的数据量;流水迁移,流水化迁移各个阶段,使得读写映像、压缩解压映像、网络收发各阶段充分并行.实验表明,与传统压缩迁移相比,快速迁移可以减少50%的迁移时间,最好情况和平均情况下,能分别降低21.68%和14.48%的停机时间.在网络带宽受限或虚拟机负载过重等极限条件下,快速迁移同样有效.     

桌面式虚拟现实维修训练系统的研究与应用

计算机虚拟现实技术提供一个具有直观感和沉浸感的人机界面,可作为一种用于维修训练的有效工具,但目前的相关研究主要针对沉浸式和增强型虚拟现实,开发成本高且应用性不强。该文提出一种面向对象的桌面式虚拟现实维修训练系统原型,利用面向对象的方法,将基于最优拆卸序列的维修模式运用到系统中。通过某型机械装置的虚拟拆卸,验证了该系统的有效性。     

基于虚拟机部署策略的云平台容错即服务方法

针对如何充分利用云基础架构层资源,满足上层云应用系统租户对应用系统容错的需求多样性和高可靠性要求的问题,提出一种面向租户和云服务提供商的、基于虚拟机部署策略的云平台容错即服务方法。该方法根据租户的特定容错需求适配适合的容错方法及容错级别,据此计算并最优化云服务提供商的收益和资源使用量,在此基础上对提供容错服务的虚拟机进行优化部署,充分利用底层虚拟机资源为租户的云应用系统提供更为可靠的容错服务。实验结果表明,所提方法能够在保障云服务提供商收益的基础上,为多租户云应用系统实现更灵活且可靠性更高的容错服务。     

关节臂式坐标测量机的虚拟样机模型及仿真

基于虚拟样机技术对六自由度关节臂式坐标测量机的测量空间进行研究和仿真,建立了六自由度关节臂式坐标测量机的测量运动学数学模型和虚拟样机模型。在建立起虚拟样机模型之后用图解法对其进行了检验,并将得到的虚拟样机模型与运动学数学模型进行比较验证,结果表明虚拟样机模型能够准确地反映测头位姿,方便有效地进行整个测量空间的运动仿真。正确的虚拟样机模型与测量运动学模型是研究测量机的误差空间分布的必要环节,为下一步工作奠定了研究基础。     

VMBackup: an efficient framework for online virtual machine image backup and recovery

Although deduplication can reduce data volume for backup, it pauses the running system for the purpose of data consistency. This problem becomes severe when the target data are Virtual Machine Image (VMI), the volume of which can scale up to several gigabytes. In this paper, we propose an online framework for VM image backup and recovery, called VMBackup, which comprises three major components: (1) Similarity Retrieval that indexes chunks' fingerprints by its segment id for fast identification, (2) one‐level File‐Index that efficiently tracks file id to its content chunks in a correct order, and (3) Adjacent Storage model that places adjacent chunks of an image in the same disk partition to maximize chunk locality. The experimental results show that (1) the images of one OS serial and the same custom can share high percentage of duplicated contents, (2) variable‐length chunk partitioning is superior to fixed‐length chunk partitioning for deduplication, and (3) VMBackup, in our environment, can provide 8M/s backup throughput and 9.5M/s recovery throughput, which are only 15% and 4% less than storage systems without deduplication. Copyright © 2015 John Wiley & Sons, Ltd.     

可信服务链安全架构研究

针对网络功能虚拟化中服务链的安全性问题,提出一种基于可信计算的安全服务链架构。首先,基于可信计算为网络功能虚拟化架构设置可信管理中心模块,为虚拟网络功能实例的生成、服务链的生成和调整提供可信认证;然后,针对服务链的生成和调整设计了相关安全协议;最后,将HOTP协议引入模型之中,实现了服务链各实例之间的安全认证与安全传输,并支持服务链节点的动态扩充和调整。经过架构仿真分析表明,本安全架构在保证服务链动态性的同时提高了安全性。     

用虚拟目标值和支持向量机直接设计非线性控制器

对于复杂被控对象, 通常采用间接方法设计控制系统. 由于必须首先辨识对象模型, 因此这类方法往往耗时较多. 本文基于虚拟目标值反馈调整(VRFT)方法的思想, 利用支持向量机(SVM), 给出一种非线性控制器直接设计方法. 论文首先分析了VRFT方法与内模控制的关系, 接着给出了基于虚拟目标值(VR)和SVM的非线性控制器的结构和设计步骤. 仿真结果表明, 该方法具有良好的处理非线性和噪声的能力, 并且能消除稳态误差. 与经典基于神经网络(NN)的间接模型参考控制方法相比, 计算量大大降低.     

Layered virtual machine migration algorithm for network resource balancing in cloud computing

Due to the increasing sizes of cloud data centers, the number of virtual machines (VMs) and applications rises quickly. The rapid growth of large scale Internet services results in unbalanced load of network resource. The bandwidth utilization rate of some physical hosts is too high, and this causes network congestion. This paper presents a layered VM migration algorithm (LVMM). At first, the algorithm will divide the cloud data center into several regions according to the bandwidth utilization rate of the hosts. Then we balance the load of network resource of each region by VM migrations, and ultimately achieve the load balance of network resource in the cloud data center. Through simulation experiments in different environments, it is proved that the LVMMalgorithm can effectively balance the load of network resource in cloud computing.     

Development of a decision support system for service delivery

Most traditional service delivery models were developed to solve single objective problems. While the disaster recovery task usually needed the consideration of multiple objectives (e.g. the total waiting time, the total weighted time of travelling, the fairness of resource distribution). Therefore, the traditional models can't completely support the disaster recovery task. In the real world, the assignments of service delivery are always performed by the vehicle dispatchers or truck drivers based on their experiences. However, the intuitive assignment methods are lacking a mathematic basis. They may be efficient but not necessarily effective. In order to provide an efficient and effective decision support system, this study has focused on the general expression of performances for service delivery and modifies the traditional delivery models by rule-inference techniques. The objective of this paper is to describe how a decision support system has been developed to achieve the performance requirement in emergency service delivery tasks, while traditional routing algorithms are modified and software techniques are utilized under a PC-based environment. Furthermore, some directions for future improvement are proposed.     

Internet操作题虚拟实验环境搭建及自动阅卷研究

针对计算机基础Internet操作题实验教学中,使用真实操作环境难以检验学生结果,提出Internet操作题虚拟实验环境的搭建和在虚拟环境下进行自动阅卷的方法。在服务器端,通过程序调用IIS相关功能自动生成WEB虚拟目录,调用小型绿色免费服务器软件,自动生成大批量FTP、邮件账号信息和FTP、邮件虚拟目录,并自动启动相关服务,实现一键完成Internet主要操作题型服务器端虚拟环境的搭建。在客户端中通过客户端程序自动设置Outlook Express账号,实现完整实验操作环境的搭建。在自动阅卷方面重点介绍接收邮件的自动阅卷方法,其它题型也简单介绍了自动阅卷采用的方法和技术。     

Efficient support for content‐aware request distribution and persistent connection in Web clusters

To support Web clusters with efficient dispatching mechanisms and policies, we propose a light‐weight TCP connection transfer mechanism, TCP Rebuilding, and use it to develop a content‐aware request dispatching platform, LVS‐CAD, in which the request dispatcher can extract and analyze the content in requests and then dispatch each request by its content or type of service requested. To efficiently support HTTP/1.1 persistent connection in Web clusters, request scheduling should be performed per request rather than per connection. Consequently, multiple TCP Rebuilding, as an extension to normal TCP Rebuilding, is proposed and implemented. On this platform, we also devise fast TCP module handshaking to process the handshaking between clients and the request dispatcher in the IP layer instead of in the TCP layer for faster response times. Furthermore, we also propose content‐aware request distribution policies that consider cache locality and various types of costs for dispatching requests in this platform, which makes the resourceutilization of Web servers more effective. Experimental results of a practical implementation on Linux show that the proposed system, mechanisms, and policies can effectively improve the performance of Web clusters. Copyright © 2007 John Wiley & Sons, Ltd.