1. CS533 Concepts of Operating Systems Class 5 System Structuring using Layers & Micro-Kernel Based OSs

2. CS533 - Concepts of Operating Systems 2 Questions  Why is performance a problem in process-per-layer or even thread-per-layer mappings of specifications to implementations? o What are the costs of crossing layer boundaries?  If data is not passed across layer boundaries in buffers, how is it passed in Swift? o How is inter-task communication within a multi-task module implemented in Swift?

3. CS533 - Concepts of Operating Systems 3 Questions  What do “up” and “down” mean in the context of Swift upcalls and downcalls? o Why is arming required in upcalling, but not in downcalling? o Why is upcalling more perilous than downcalling?  When is it better to use upcalls than downcalls?  Should you always pass data among tasks on the stack? o How do you decide what work must be done immediately and what to queue for later? If you queue it for later, where should you store the state?

4. CS533 - Concepts of Operating Systems 4 Questions  Are upcalls part of a thread-based or event-based programming model?  Is arming stack-ripping? o Does it leave state for a future call-back?  How does Swift implement protection?  What safety rules (conventions) are used in Swift?

5. 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?

6. Questions  What are the main sources of overhead in micro- kernel based OSs compared to monolithic OSs?  What minimal abstractions should a kernel provide?

7. 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?

8. Questions  What is extensibility and how does micro-kernel- based OS structure help? o What other approaches are there?