We describe an operating system architecture that securely multiplexes machine resources while permitting an unprecedented degree of application-specific customization of traditional operating system abstractions. By abstracting physical hardware resources, traditional operating systems have significantly limited the performance, flexibility, and functionality of applications. The exokernel architecture removes these limitations by allowing untrusted software to implement traditional operating system abstractions entirely at application-level. We have implemented a prototype exokernel-based system that includes Aegis, an exokernel, and ExOS, an untrusted application-level operating system. Aegis defines the low-level interface to machine resources. Applications can allocate and use machine resources, efficiently handle events, and participate in resource revocation. Measurements show that most primitive Aegis operations are 10–100 times faster than Ultrix,a mature monolithic UNIX operating system. ExOS implements processes, virtual memory, and inter-process communication abstractions entirely within a library. Measurements show that ExOS’s application-level virtual memory and IPC primitives are 5–50 times faster than Ultrix’s primitives. These results demonstrate that the exokernel operating system design is practical and offers an excellent combination of performance and flexibility. 1

The V distributed System was developed at Stanford University as part of a research project to explore issues in distributed systems. Aspects of the design suggest important directions for the design of future operating systems and communication systems.

This dissertation shows that operating systems can provide fundamental services an order of magnitude more efficiently than traditional implementations. It describes the implementation of a new operating system kernel, Synthesis, that achieves this level of performance. The Synthesis kernel combines several new techniques to provide high performance without sacrificing the expressive power or security of the system. The new ideas include: ffl Run-time code synthesis --- a systematic way of creating executable machine code at runtime to optimize frequently-used kernel routines --- queues, buffers, context switchers, interrupt handlers, and system call dispatchers --- for specific situations, greatly reducing their execution time. ffl Fine-grain scheduling --- a new process-scheduling technique based on the idea of feedback that performs frequent scheduling actions and policy adjustments (at submillisecond intervals) resulting in an adaptive, self-tuning system that can support real-ti...

We assert that in order to perform well, a shared-memory multiprocessor inter-process communication (IPC) facility must avoid a) accessing any shared data, and b) acquiring any locks. In addition, such a multiprocessor IPC facility must preserve the locality and concurrency of the applications themselves so that the high performance of the IPC facility can be fully exploited. In this paper we describe the design and implementation of a new shared-memory multiprocessor IPC facility that in the common case internally requires no accesses to shared data and no locking. In addition, the model of IPC we support and our implementation ensure that local resources are made available to the server to allow it to exploit any locality and concurrency available in the service. To the best of our knowledge, this is the first IPC subsystem with these attributes. The performance data we present demonstrates that the endto -end performance of our multiprocessor IPC facility is competitive with the fas...

The Design and Implementation of a Prototype Exokernel Operating System

This paper describes the design and the prototype implementation of the Muse operating system

In message based systems, interprocess communication (IPC) is a central facility. If the IPC part is ineffective in such a system, it will decrease the performance and response time. By implementing the IPC facility in hardware, the administration (scheduling, message handling, time-out supervising etc.), is reduced on the CPU , which leads to more time left for the application and a more deterministic time behaviour. This paper describes an hardware implementation of asynchronous IPC in an RTU based architecture. RTU is a hardware implementation of a real-time kernel for uniprocessor and multiprocessor systems. In addition, our implementation of IPC supports message priority, priority inheritance on message arrival , and task timeout on message send/receive. An increased performance and message flow, in a message intense system, can be realized by implementing IPC functions in an RTU architecture. 1. Introduction Different methods have been used to improve IPC e.g. using registers [...

There is a demand for ever more powerful computing facilities, and for the ability to improve the power of those that are already owned, without the need to replace machines. This thesis examines a method of meeting these demands by the development of a scalable computing facility - one that can be built from as many processors as needed, and which can have more added whenever there is a need to increase the power available. The approach taken is to provide a scalable operating system, called Wisdom, that will run on a scalable architecture, a network of point to point connected processors. This thesis details the issues in, requirements of, and problems with building such an operating system. The lessons of research in the field of distributed operating systems, and other specialist work in appropriate areas are used to develop a model which provides the necessary support for a usable scalable system. The model so derived consists of three degrees of transparency: interconnection tran...

This paper gives a survey of all common transparent distributed systems. We distinguish between Distributed File Systems (DFS) and Distributed Operating Systems (DOS). Our overview is focussed on systems providing at least access or location transparency. The paper is organized as follows: The introduction offers definitions of the features of each transparent distributed system as well as the services it is able to provide. We also propose a catalog of criteria that enables us to compare different systems independently of implementation done. The main entries we make are heterogeneity of the system's environment, communication strategy, as well as naming and security issues. Finally, we examine the reliability and availability of the separate systems and the way these issues are achieved. The following section consists of the survey. The description of each system is organized as follows: First, we introduce the main goal the system was developed for, the classification of th...

a research project to explore issues in distributed systems. Aspects ‘of the design suggest important directions for the design of future operating systems and communication systems. DAVID R. CHERITON The V distributed system is an operating system designed for a cluster of computer workstations connected by a high-performance network. The system is structured as a relatively small “distributed ” kernel, a set of service modules, various run-time libraries and a set of commands, as shown in Figure 1. The kernel is distributed in that a separate copy of the kernel executes on each participating network node yet the separate copies cooperate to provide a single system abstraction of processes in address spaces communicating using a base set of communication primitives. The existence of multiple