CS533 Concepts of Operating Systems

Class 12

Micro-kernels (or Extensibility via Hardware-Based

Protection)

CS533 - Concepts of Operating Systems 2

Questions

What is the motivation for modular operating systems?

o Does this imply modules with hardware protection?o .. and what do I mean by hardware protection for modules?

What is the motivation for using hardware protection at module boundaries?

o Does this imply message passing across module boundaries?

o … what other alternatives do you have?

What is the motivation for using message-passing for inter-module communication?

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Questions

What is the structure of a pure emulation library-based OS above a micro-kernel?

o How are system calls handled?

What is the structure of a single-server based OS above a micro-kernel?

o How are system calls handled?

What is the structure of a multi-server based OS above a micro-kernel?

o How are system calls handled?

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Questions

What are the main sources of overhead in micro-kernel based OSs compared to monolithic OSs?

How does L4 address these overheads?o Do these optimizations completely solve the problem?

What is the difference between L4 IPC and a protected control transfer (PCT)?

o Would you expect a lot of difference in performance following extreme optimization of both?

What minimal abstractions should a kernel provide?

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Questions

What is extensibility and how does micro-kernel-based OS structure help?

o What other approaches are there?

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Reminder

Take a look at the Liedtke paper from SOSP’93 Presenters, start working your talk early! Don’t leave it to the last minute! You can’t

expect to do an adequate job if you do it the night before.

Send me a draft of your slides early enough that I have some time to work with you