engler95exokernel - Exokernel an operating system...

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Exokernel: an operating system architecture for application-level resource management Dawson R. Engler, M. Frans Kaashoek and James O’Toole Jr. M.I.T. Laboratory for Computer Science Cambridge, MA 02139 engler,kaashoek,james @lcs.mit.edu March 24, 1995 Abstract We describe an operating system architecture that securely multiplexes machine resources while permitting an unprece- dented degree of application-specific customization of tradi- tional operating system abstractions. By abstracting physical hardware resources, traditional operating systems have sig- nificantly limited the performance, flexibility, and function- ality of applications. The exokernel architecture removes these limitations by allowing untrusted software to imple- ment traditional operating system abstractions entirely at application-level. We have implemented a prototype exokernel-based sys- tem that includes Aegis, an exokernel, and ExOS, an un- trusted 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. Measure- ments 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 Introduction Operating systems define the interface between applications and physical resources. Unfortunately, this interface can significantly limit the performance and implementation free- dom of applications. This problem arises because the op- erating system abstracts the details of hardware resources to provide a more portable and more full-featured interface than is directly implemented by the hardware. The end result of such a full-featured interface is an approach to resource This work was supported in part by the Advanced Research Projects Agency under contracts N00014-94-1-0985 and by a NSF National Young Investigator Award. management that is strongly centralized. Centralized man- agement can conflict with application needs, limiting both performance and flexibility. We believe these problems can be solved through distributed, application-level , resource management. To this end, we have designed a kernel that se- curely multiplexes machine resources and permits traditional operation system abstractions to be implemented efficiently at application-level, so that they can easily be extended, spe- cialized, or even replaced. Traditionally, operating systems hide information about
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engler95exokernel - Exokernel an operating system...

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