一种基于时钟粒度细化的Linux实时化方案

时钟精度直接影响到任务能否被及时响应和调度，作为一个分时系统，Linux的10ms周期性时钟粒度是必要而且合适的．但是实时系统一般都要求微秒级的响应精度，显然Linux的时钟粒度过于粗糙．然而简单地提高时钟频率意味着时钟中断的相应处理过程将占用过多的处理器时间，从而使得整个系统的有效利用率急剧下降．为了改进Linux的实时性能，讨论了基于Linux的实时操作系统RFRTOS中的时钟粒度细化方案．实验结果显示所做改进以不大的代价有效地提高了Linux的时钟精度．     

Linux操作系统实时性分析

随着Linux操作系统在嵌入式实时系统中的广泛应用，有效地提高Linux有限的实时性能是一个重要问题，而Linux内核可抢占调度是实时性能的改进的关键。对Linux内核调度器的工作原理进行了深入分析，并阐述了调度延迟是其实时性不强的原因，然后介绍通过可抢占机制对Linux内核进行改造，测试了改进后的内核的实时性。     

RFRTOS:基于Linux的实时操作系统

随着实时应用领域的逐渐扩大,不仅传统嵌入式系统的需求日益紧迫,而且这种情况也渗透到桌面环境.为了满足国内用户在这方面的广泛需求,基于红旗Linux操作系统,开发了RFRTOS实时操作系统.主要从实时调度策略、内核抢占机制、细粒度定时器几方面讨论了RFRTOS的实时支持.实验结果表明,所作改进有效地提高了Linux的调度精度,满足了软实时方面的需求.     

一种基于Linux操作系统下时钟系统的改进机制

随着Linux操作系统的成功．改进Linux的设计和性能，使其应用于实时领域受到了越来越多人的关注。考虑到Linux目前的时钟粒度仍然粗糙，它将直接影响到整个内核的实时性能．文中提出了一种基于Linux操作系统下时钟系统的改进机制，找出修改时钟系统提高实时性的具体方法。实验结果显示，所作改进以不大的代价有效地提高了Lnux的实时性能。     

Linux核心调度机制的实时改造及应用研究

针对网络多媒体系统的实时应用需求，本文对Linux2．4核心的调度机制进行了改造。通过将弱硬实时调度算法、挪用调度算法、反馈调度算法继承到Linux核心调度机制中，提高了核心的实时性能；最后通过实际应用检验了改造后的Linux系统在处理网络多媒体数据时的实时性能。     

改善Linux核心可抢占性方法的研究与实现

随着开放源码的Linux应用逐渐普及，改进Linux的性能，使其适用于实时领域成为一个极具潜力的发展方向．在参考了与此相关的研究的基础上，该文对改善Linux核心可抢占性的方法提出了3个改进措施：中断管理进程化、改进互斥锁的机制和增加互斥锁协议支持，并在Linux2．2系列的核心上加以实现．试验证明，这些改进达到了减少系统的抢占粒度，提高调度精度的目的。     

RTAI下动态集成的资源预留调度器的设计与实现

近年来基于双内核架构增强Linux操作系统实时性的RTAI(Real-Time Application Interface)在工业控制等硬实时领域得到广泛应用。RTAI通过抢占Linux的执行来保障硬实时性，Linux被抢占的时间依赖于硬实时应用的处理器要求而每次均会有较大不同，导致Linux的执行时间不可预测，从而无法保障软实时应用的服务质量。动态集成的资源预留调度器(Dynamic Integrated Resource Reserved Scheduler，DIRRS)通过增强RTAI调度器使其支持资源预留机制，在Linux实现可动态集成的、基于服务器的调度策略，不但可以保证Linux及其以上的软实时应用，即使在有硬实时任务并发时也能得到处理器资源，而且很容易通过更换不同的服务器内核模块来实现用户自定义的调度策略。     

基于Linux内核的实时调度机制研究及实现

分析了Linux操作系统内核提供的软实时调度机制及其存在的问题，阐述了基于Linux内核构建实时Linux操作系统的技术方案。着重介绍了RTLinux实时内核的结构框架，并对RTLinux的中断处理机制与调度机制进行了设计与实现。     

Linux操作系统实时性分析

随着Linux操作系统在嵌入式实时系统中的广泛应用,有效地提高Linux有限的实时性能是一个重要问题,而Linux内核可抢占调度是实时性能的改进的关键。对Linux内核调度器的工作原理进行了深入分析,并阐述了调度延迟是其实时性不强的原因,然后介绍通过可抢占机制对Linux内核进行改造,测试了改进后的内核的实时性。     

Linux操作系统调度器实时性能的研究和改进

Linux操作系统在嵌入式实时系统中得到了广泛的应用，有效地提高Linux有限的实时性能是一个重要问题，Linux内核调度器实时性能的改进又是其中的关键。该文分析了Linux操作系统调度器的工作机理，指出了影响其实时性能的原因，详细地描述了实时性改进的方案和实现，并给出了改进后的测量结果及评价。     

Deadline scheduling in the Linux kernel

During the last decade, there has been a considerable interest in using Linux in real‐time systems, especially for industrial control. The simple and elegant design of Linux guarantees reliability and very good performance, while its open‐source license allows to modify and change the source code according to the user needs. However, Linux has been designed to be a general‐purpose operating system. Therefore, it presents some issues like unpredictable latencies and limited support for real‐time scheduling. In this paper, we present our experience in the design and implementation of the real‐time scheduler that has been recently included in the Linux kernel. The scheduler is based on the Resource Reservation paradigm, which allows to enforce temporal isolation between the running tasks. We describe the genesis of the project, the challenges we have encountered, the implementation details and the API offered to the programmers. Then, we show the experimental results measured on a real hardware. Copyright © 2015 John Wiley & Sons, Ltd.     

Timing analysis of the PREEMPT RT Linux kernel

In the theory of real‐time scheduling, tasks are described by mathematical variables, which are used in analytical models in order to prove schedulability of the system. On real‐time Linux, tasks are computer programs, and Linux developers try to lower the latencies caused by the Linux kernel, trying to achieve faster response for the highest‐priority task. Although both seek temporal correctness, they use different abstractions, which end up separating these efforts in two different worlds, making it hard for the Linux practitioners to understand and apply the formally proved models to the Linux kernel and for theoretical researchers to apply the restrictions imposed by Linux for the theoretical models. This paper traces a parallel between the theory of response‐time analysis and the abstractions used in the Linux kernel. The contribution of this paper is threefold. We first identify the PREEMPT RT Linux kernel mechanisms that impact the timing of real‐time tasks and map these impacts to the main abstractions used by the real‐time scheduling theory. Then, we describe a customized trace tool, based on the existing trace infrastructure of the Linux kernel, that allows the measurement of the delays associated with the main abstractions of the real‐time scheduling theory. Finally, we use this customized trace tool to characterize the timing lines resulting from the behavior of the PREEMPT RT Linux kernel. Copyright © 2015 John Wiley & Sons, Ltd.     

嵌入式Linux中调度算法的实现及优化

本文论述实时嵌入式Linux的多任务调度算法实现机制。结合嵌入式操作系统的特点，重点介绍基于优先级驱动嵌入式系统的一种实时调度优化算法的实现机制，讨论如何在GPL下充分利用现有的实时调度算法开发适合嵌入式Linux的优化调度方法，并提出了具体的实现思路。     

ARM Linux中断处理实时性能分析

ARM Linux被广泛地应用于嵌入式系统,但是ARM Linux的实时性能并不尽如人意。该文研究ARM Linux中断处理过程,分析了其实时性能,在Intel PXA255开发板DBPXA255上测试了各种负载情况下中断延迟,并就提高ARM Linux中断处理的实时性能提出建议。     

嵌入式Linux硬实时性的研究与实现

着重论述了增强嵌入式Linux实时性的基本策略，在实际项目中提出并实现了在实时硬件抽象层(RTHAL)的架构下，应用双内核机制使嵌入式Linux支持硬实时性的一种新的方案。     

Measuring and reducing the impact of the operating system kernel on end‐to‐end latencies in synchronous packet switched networks

This paper presents an evaluation of the impact of the so‐called operating system (OS) latencies on the performance of a synchronous network based on global time coordination. The concept of end‐to‐end latency was first defined by extending the concept of latency used to evaluate the performance of real‐time systems and the end‐to‐end latency provided by a general‐purpose OS was measured as a benchmark. Finally, real‐time techniques were used to reduce the worst‐case values of such a latency, showing how a gateway between synchronous and asynchronous networks can be implemented by using commercial‐off‐the‐shelf hardware and a proper software stack (based on a real‐time version of Linux). The use of a real‐time OS is still a nontrivial task, which requires experience and the analysis of the specific application to devise the proper techniques to be applied. This work dissects the problem of OS‐to‐network data transfer (and vice versa) identifying the key sources of latencies and delay jitter, and solving each problem with the application of a proper technique. Copyright © 2011 John Wiley & Sons, Ltd.     

实时音频变调算法的设计与实现

音频变调是在保持旋律和节奏的基础上改变音乐的调性，许多应用都要求实时实现，然而关于实时算法实现的问题还少有文献涉及。改造后的实时变调算法与实现方案通过合理控制CPU时钟和AD／DA时钟的时序关系，不仅能够在两个八度音范围内进行有效的变调，而且能够对实时输入的音频信号进行同步变调输出，在Windows平台上验证实验还表明新方案具有较低的CPU占用率和内存消耗，能够满足实时应用的要求。     

AQuoSA—adaptive quality of service architecture

This paper presents an architecture for quality of service (QoS) control of time‐sensitive applications in multi‐programmed embedded systems. In such systems, tasks must receive appropriate timeliness guarantees from the operating system independently from one another; otherwise, the QoS experienced by the users may decrease. Moreover, fluctuations in time of the workloads make a static partitioning of the central processing unit (CPU) that is neither appropriate nor convenient, whereas an adaptive allocation based on an on‐line monitoring of the application behaviour leads to an optimum design. By combining a resource reservation scheduler and a feedback‐based mechanism, we allow applications to meet their QoS requirements with the minimum possible impact on CPU occupation. We implemented the framework in AQuoSA (Adaptive Quality of Service Architecture (AQuoSA). http://aquosa.sourceforge.net ), a software architecture that runs on top of the Linux kernel. We provide extensive experimental validation of our results and offer an evaluation of the introduced overhead, which is perfectly sustainable in the class of addressed applications. Copyright © 2008 John Wiley & Sons, Ltd.