中断级别的选择与设置

我们以网卡为例,描述硬件中断级别的选择与设置方法。 网卡是通过IRQ中断通知CPU响应LAN网卡请求的。LAN网卡有权这样操作CPU主要是因为网卡的缓冲区容量有限,如果CPU不能尽快取得这些数据,那么当后续数据进入网卡缓冲区时,就会覆盖当前缓冲器的数据并刷新缓冲区。     

采用轮询机制提高Linux系统的网络性能

目前,Linux操作系统被广泛应用在网络数据包收发系统中。这是因为,Linux采用中断机制来响应外部事件,保证了系统能够合理高效地利用CPU资源。但是,在高负荷网络环境下,大量的CPU资源将会被频繁到达的网卡中断占用,导致系统遭遇性能瓶颈,出现接收活锁1。为了避免在高负荷网络环境下系统性能下降,该文采用轮询机制处理网络数据的收发,而在低负荷网络环境中,仍然采用原有的中断机制。     

一种高速数据包捕获系统的设计与实现

提出一种针对高速光网络环境的数据包捕获平台的设计方案。采用软硬件结合的设计思想,由系统硬件完成数据包的解析和过滤,软件根据硬件解析结果将数据直接向应用进程分发。驱动部分借鉴了零拷贝和循环缓冲区技术,并进行了中断优化以降低数据采集的CPU占用率。     

用中断方式实现监控机串口通信

在计算机系统中,CPU响应外设有三种方法:①查询法:CPU不停地扫描外设,看相应标识位有没有置位,如果有则表明外设已经发送了数据,等待CPU处理。查询法需将进程置于死等状态,会耗费大量CPU资源,仅适合于功能单一,任务量不大的系统。②中断法:当外设发送完数据后产生中断,通知CPU来读取数据。这种方法的效率明显高于查询法,但每次中断CPU都要进行保存断点和恢复断点的操作,如果外设发送数据的间隔小于这一时间,就会造成数据丢失。中断法适合外设通信不太频繁,软件功能较多的情况。③     

无线Mesh网络中节点分级协作缓冲机制研究

在无线Mesh中,由于每个节点缓冲的数据量不同,可能会造成某些节点的缓冲区利用率低,某些节点因为缓冲任务繁重而进行频繁的数据置换操作,从而造成节点存储空间使用不均衡,降低数据缓冲的效率。提出了一种基于节点分级管理的协作缓冲算法,该算法为网络中的每个节点在网络中构造一个分布式缓冲区域,利用该缓冲区域来替代节点本身的缓冲区,通过合理地利用每个节点的存储空间,增加单个节点的数据缓冲能力。理论分析和实验结果表明,该算法可以有效提高数据访问命中率,减少缓冲区数据的置换操作,降低节点的能量消耗。     

基于循环缓冲区的xPC目标串口通信研究

针对半实物仿真中的串口通信要求,提出一种xPC系统下采用CPU中断和软件定时的基于循环缓冲区的串口通信方法,解决了基于S函数的串口模块工作原理设计、硬件中断获取、循环缓冲区设计及参数传递和缓冲区读写操作等关键技术.采用该方法设计了惯性测量单元通信模块,并用三轴转台进行了动态测试,可以实现三路加速度和三路角速率信号的正确...     

缓冲辅助中继网络中的缓冲资源分配方法

随着通信技术和智能终端的发展,移动内容消费出现了明显的增长。人们随时随地享受无线网络带来的多媒体娱乐体验的同时,也给蜂窝网络带来了巨大的压力,尤其是热门视频的重复传输,浪费了网络资源。预存储技术被认为是解决这类问题的有效方法。它是在非高峰时段,将热门视频等预先存储在网络边缘,以缓解高峰时段网络流量的压力。为了给用户提供更好的内容传输效率,预存储技术中基于缓冲辅助的中继网络被提出。由于中继结点缓冲空间有限,当其需要服务多个用户时,有必要对中继结点的缓冲资源进行优化分配。基于此,本文提出了一种中继结点的缓冲资源分配方法。首先,根据中继结点数据到达模型和数据处理模型,以及中继结点能忍受的缓冲区溢出概率,得到中继结点可以贡献出的最大缓冲区比例;接着,根据用户的数据到达模型和数据服务模型,给出用户缓冲区溢出概率与缓冲区比例关系的表达式;然后,建立优化问题,以最小化网络中所有用户缓冲区溢出概率和为目标,给出最优的缓冲区分配方法;最后,仿真结果证实了本文提出的方法比均匀分配法能获得更小的用户缓冲区溢出概率和。     

前后台工作的打印程序

本文的工作是把打印输出安排在后台工作方式,以减少打印机占用CPU的时间,可显著地提高整个系统的效率。具体作法是在内存中开辟一个缓冲区,用以暂时存放要打印输出的数据,系统把要打印的数据送到该缓冲区后就可以转去执行其他操作。真正的将打印数据送至打印机的动作是利用系统的时钟中断来实现的。     

实现串口接收和发送都使用DMA的方法

单片机串口在嵌入式系统中是很重要的模块,它实现了单片机和外设之间的数据交换。在需要大量频繁进行数据交换的系统中,如何提高数据的高效处理和减少CPU的占用时间显得格外重要。本文介绍了一种实现串口接收和发送都使用DMA的方法,减少对CPU中断的依赖,进而最大程度地减少了CPU占用时间。     

基于混合模式匹配算法的网络入侵检测

为了提升中央处理单元(CPU)和图形处理单元(GPU)协同检测网络入侵的性能,本文提出了一种具有数据包有效载荷长度约束的CPU/GPU混合模式匹配算法(LHPMA)。在分析CPU/GPU混合模式匹配算法(HPMA)的基础上,设计了长度约束分离算法(LBSA)对传入数据包进行提前分类。利用CPU中的预过滤缓冲区对较长数据包进行快速预过滤,结合全匹配缓冲区将较短数据包直接分配给GPU进行全模式匹配,通过减少有效载荷长度的多样性,提升了CPU/GPU协同检测网络入侵的性能。实验结果表明,LHPMA增强了HPMA的处理性能,充分发挥了GPU并行处理较短数据包的优势,并且LHPMA提高了网络入侵检测的吞吐量。     

负载类型相关的Xen虚拟机系统性能模型

针对Xen虚拟机系统执行网络I/O密集型负载时容易耗尽Domain0的CPU资源而过载和执行计算密集型负载时在客户域平均性能与数目之间存在线性规划的问题,提出了两个负载类型相关的性能模型。首先,通过分析Xen虚拟机系统处理网络I/O操作的CPU资源消耗规律,建立了CPU核共享和CPU核隔离两种情况下的客户域网络I/O操作请求次数计算模型;然后,通过分析多个相同客户域并行执行计算密集型负载的平均性能与一个相同客户域执行相同负载的性能表现之间的关系,建立了并行执行计算密集型负载的客户域平均性能分析模型。实验结果表明,两个性能模型能够有效地限制客户域提交的网络I/O操作请求次数以防止Xen虚拟机系统过载,并求解给定资源配置情况下执行计算密集型负载的Xen虚拟机系统客户域伸缩性数目。     

Xen系统中CPU间歇性故障的自适应策略

Xen虚拟化环境没有考虑CPU的间歇性故障带来的影响。基于此,建立模拟CPU间歇性故障的时间模型,在该模型下未修改的Xen系统中的虚拟机会立刻崩溃。提出一种自适应的策略来改进Xen的CPU调度,该策略主动跟踪CPU的状态变化,将发生故障的CPU上的虚拟处理器迁移到可用的其他CPU上。实验结果表明,当CPU间歇性故障频繁发生时,应用该策略可以使虚拟机继续稳定地工作,性能平滑地降低。     

基于Linux系统的高速网络捕包技术研究*

在对Linux系统捕包机制分析的基础上,通过试验详细讨论了高速网络环境下网络捕包的性能瓶颈。针对性能瓶颈给出了NAPI与内存映射机制相结合的改进方案。     

Packet aggregation based network I/O virtualization for cloud computing

Virtualization is a key technology to enable cloud computing. Driver domain based model for network virtualization offers isolation and high levels of flexibility. However, it suffers from poor performance and lacks scalability. In this paper, we evaluate networking performance of virtual machines within Xen. The I/O channel transferring packets between the driver domain and the virtual machines is shown to be the bottleneck. To overcome this limitation, we proposed a packet aggregation based mechanism to transfer packets from the driver domain to the virtual machines. Packet aggregation, combined with an efficient core allocation, allows virtual machines throughput to scale up by 700%, while minimizing both memory and CPU consumption. Besides, aggregation impact on packets delay and jitter remains acceptable. Hence, the proposed I/O virtualization model satisfies infrastructure providers to offer Cloud computing services.     

基于Xen硬件虚拟机的安全通信机制研究

在深入分析Xen硬件虚拟机通信机制和网络安全控制技术的基础上,实现了Xen硬件虚拟机安全通信机制,它在虚拟机监控器上加入了一个安全服务器,同时在虚拟机进行网络通信的关键路径上添加安全检查模块,实现了虚拟机通信的访问控制,提高了虚拟域间通信的安全性。     

Performance of IP-forwarding of Linux hosts with multiple network interfaces

This paper evaluates and compares the performance of IP-packet forwarding of a Linux host equipped with multiple network interface cards (NICs), namely two receiving NICs and one transmitting NIC. We consider a Linux host with SMP (Symmetric Multiprocessing) or multicore multiprocessor (MCMP) architecture. We measure IP forwarding by subjecting an MCMP Linux host to different traffic load conditions of up to 1 Gbps. We used the IXIA hardware traffic generator to generate traffic with fixed- and variable-size packets. At the Linux host, generated packets are forwarded/routed from the two receiving NICs to the transmitting NIC. We consider two NIC affinity modes: (I) both receiving NICs are affinitized (or bound) to two cores of the same processor while the transmitting NIC is affinitized to a core on a separate processor, and (II) the transmitting NIC and one receiving NIC are affinitized to two cores of the same processor while the second receving NIC is affinitized to a core on a separate processor. For each affinity mode, we measure the performance for three packet reception mechanisms: NAPI (New API) with a default budget of 300, NAPI with a budget of 2, and Disable and Enable interrupt handling. The performance is measured and compared in terms of various key performance metrics which include throughput, packet loss, round-trip delay, interrupt rates, and CPU availability.     

Xen虚拟机的虚拟CPU松弛协同调度方法

目前,Xen虚拟机调度算法均采用独立调度虚拟CPU的方式,而没有考虑虚拟机各虚拟CPU之间的协同调度关系,这会使虚拟机各个虚拟CPU之间产生很大的时钟中断数量偏差等问题,从而导致系统不稳定.为了提高系统的稳定性,基于Credit算法提出了一种比RCS(relaxed co-scheduling)算法更松弛的协同调度算法MRCS(more relaxed co-scheduling).该算法采用非抢占式协同调整方法将各个虚拟CPU相对运行的时间间隔控制在同步时间检测的上限门限值Tmax之内,同时利用同步队列中虚拟CPU优化选择调度方法和Credit算法的虚拟CPU动态迁移方法,能够更加及时地协同处理虚拟CPU,并且保证了各个物理CPU的负载均衡,有效地减少客户操作系统与VMM的环境切换次数,降低了系统开销.实验结果证明该方法不但保证了系统的稳定性,而且使系统性能得到一定程度的提升.虚拟机调度算法不仅影响虚拟机的性能,更会影响虚拟机的稳定性,致力于虚拟机调度算法的研究是一项非常有意义的工作.     

Performance evaluation of Web server workloads in Xen‐based virtualized computer system: analytical modeling and experimental validation

Recent developments in the field of virtualization technologies have led to renewed interest in performance evaluation of these systems. Nowadays, maturity of virtualization technology has made a fuss of provisioning IT services to maximize profits, scalability and QoS. This pioneer solution facilitates deployment of datacenter applications and grid and Cloud computing services; however, there are challenges. It is necessary to investigate a trade‐off among overall system performance and revenue and to ensure service‐level agreement of submitted workloads. Although a growing body of literature has investigated virtualization overhead and virtual machines interference, there is still lack of accurate performance evaluation of virtualized systems. In this paper, we present in‐depth performance measurements to evaluate a Xen‐based virtualized Web server. Regarding this experimental study; we support our approach by queuing network modeling. Based on these quantitative and qualitative analyses, we present the results that are important for performance evaluation of consolidated workloads on Xen hypervisor. First, demands of both CPU intensive and disk intensive workloads on CPU and disk are independent from the submitted rate to unprivileged domain when dedicated core(s) are pinned to virtual machines. Second, request response time not only depends on processing time at unprivileged domain but also pertains to amount of flipped pages at Domain 0. Finally, results show that the proposed modeling methodology performs well to predict the QoS parameters in both para‐virtualized and hardware virtual machine modes by knowing the request content size. Copyright © 2015 John Wiley & Sons, Ltd.     

一个基于虚拟机的日志审计和分析系统

SNARE是Linux操作系统的一个日志审计和分析工具,但它容易受到攻击。提出了一个新的方法被用来保护它免受攻击。运用虚拟机监控器的功能,SNARE被移植到运行在虚拟机监控器Xen上的两个虚拟机中,SNARE的两个主要部分——Linux内核补丁和审计后台进程被分隔而分别放入两个被Xen强隔离的虚拟机。Xen提供了两个虚拟机间共享内存的机制,运用这一机制,运行在一个虚拟机上的Linux内核补丁记录并转移审计日志到运行在另一个虚拟机上的审计后台进程。与传统的SNARE相比,新方法使攻击者毁坏或篡改这些日志更加困难。初步的评估表明这个原型是简单而有效的。     

VBMq: pursuit baremetal performance by embracing block I/O parallelism in virtualization

Barely acceptable block I/O performance prevents virtualization from being widely used in the High-Performance Computing field. Although the virtio paravirtual framework brings great I/O performance improvement, there is a sharp performance degradation when accessing high-performance NAND-flash-based devices in the virtual machine due to their data parallel design. The primary cause of this fact is the deficiency of block I/O parallelism in hypervisor, such as KVM and Xen. In this paper, we propose a novel design of block I/O layer for virtualization, named VBMq. VBMq is based on virtio paravirtual I/O model, aiming to solve the block I/O parallelism issue in virtualization. It uses multiple dedicated I/O threads to handle I/O requests in parallel. In the meanwhile, we use polling mechanism to alleviate overheads caused by the frequent context switches of the VM’s notification to and from its hypervisor. Each dedicated I/O thread is assigned to a non-overlapping core to improve performance by avoiding unnecessary scheduling. In addition, we configure CPU affinity to optimize I/O completion for each request. The CPU affinity setting is very helpful to reduce CPU cache miss rate and increase CPU efficiency. The prototype system is based on Linux 4.1 kernel and QEMU 2.3.1. Our measurements show that the proposed method scales graciously in the multi-core environment, and provides performance which is 39.6x better than the baseline at most, and approaches bare-metal performance.