PART 1PART 1 COMPUTER HARDWARECOMPUTER HARDWARE CHAPTER 2 COMPUTER OPERATING CHAPTER 2 COMPUTER OPERATING SYSTEMSYSTEM 2-5 A CACHING MODEL OF OPERATING SYSTEM KERNEL FUNCTIONALITY2-5 A CACHING MODEL OF OPERATING SYSTEMKERNEL FUNCTIONALITYMain Point Insufficiencies of micro-kernels in operatingsystem Introduction to an alternative approach to kernet design on a caching modelKEYWORDScaching model 高速缓存模型micro-kernel 微内核monolithic 单块（片）的virtual memory system 虚拟存储系统copy-on-write 按写拷贝domain-specific 特定域resource allocation 资源分配 random access 随机访问 sequential access 顺序访问resource management 资源管理failure 故障，失效application module 应用模块server 服务器active object 活动对象address space 地址空间thread 线程Inter-Process Communication (IPC) 进程间通信mapping 映像，镜像descriptor 描述符page frame 页面帧supervisor-level 管理层programming interface 编程接口emulator 仿真器 Micro-kernels to date have not provided compelling advantages over the conventional monolithic operating system kernel for several reasons.First, micro-kernels are larger than desired because of the complications of a modern virtual memory system (such as the copy-on-write facility), the need to support many different hardware devices, and complex optimizations in communication facilities, all of which have been handled inside most micro-kernels. 1 原因状语原因状语原因状语非限定性定语从句Moreover, performance problems have tended to force services originally implemented on top of a micro-kernel back into the kernel, increasing its size. 2Second, micro-kernel do not support domain-specific resource allocation policies any better than monolithic kernels, an increasingly important issues with sophisticated applications and application systems. 3 For example, the standard page-replacement policies of UNIX-like operating systems perform poorly for applications with random or定语结果状语比较同位语sequential access. Placement of conventional operating system kernel services in a micro-kernel-based does not generally give the applications any more control because the server is a fixed protected system service. 4 Adding a variety of resource management policies to the micro-kernel fails to achieve the efficiency that application-specific knowledge allows and increases the kernel size and complexity. 5 宾语补语原因状语从句主语谓语原因状语从句Finally, micro-kernels are bloated with exception-handling mechanisms for the failure and unusual cases that can arise with the hardware and with other server and application modules. 6 For example, the potential page-in exception conditions with external pagers introduces complications into machine.原因状语定语从句原因状语?1 List three reasons that micro-kernels have not provided compeling advantages over the conventional monolithic operating kernel ?In this paper, we present an alternative approach to kernel design based on a caching model, as realized in the V+ Cache Kernel. The V+ Cache Kernel caches the active objects associated with the basic operating system facilities, namely the address spaces and threads associated with virtual memory, scheduling and IPC. In contrast to conventional micro-kernel design, it does not fully implement all the functionality associated with address spaces and threads. Instead, it relies on higher-level application 方式状语同位语kernels to provide the management functions required for a complete implementation, including the loading and write-back of these objects to and from the Cache Kernel. 7 For example, on a page fault, the application kernel associated with the faulting thread loads a new page mapping descriptor into the Cache Kernel as part of a cached address space object. This new descriptor may cause another page mapping descriptor to be written back to another application kernel to make space for the new descriptor. 状语宾语补语Because the application kernel selects the physical page frame to use, it fully controls physical page selection, the page replacement policy and paging I/O The following sections argue that this caching model reduces supervisor-level complexity, provides application control of resource management and provides application control over exception conditions and recovery, addressing the problems with micro kernel designs to date (including a micro-kernel that we developed previously). 8原因状语从句宾语宾语宾语宾语从句谓语谓语谓语状语The next section describes the Cache Kernel programming interface, illustrating its use by describing how an emulator application kernel would use this interface to implement standard UNIX-like services. 9 Section 3 describes how sophisticated applications can use this interface directly by execu