1. Extensibility, Safety and Performance in the SPIN Operating System Brian Bershad, Stefan Savage, Przemyslaw Pardyak, Emin Gun Sirer, David Becker, Marc Fiuczynski, Craig Chambers, Susan Eggers Brian BershadStefan SavagePrzemyslaw PardyakEmin Gun SirerDavid BeckerMarc FiuczynskiCraig ChambersSusan Eggers Presented By Ninad Palsule

2. Motivation General purpose OS Specialized OS Application needs a resource control – Ex. DBMS Hard: Support specialization in general purpose OS Kernel User DBMS Data page buffer Log page 1 2 Storage

3. Why it is hard? Ref: Fig from presentation prepared by Author from http://www-spin.cs.washington.edu/

4. SPIN Design Goals – Extensibility Incremental changes – Safety Correctness – Good performance Efficiency

5. SPIN Approach – Language and compiler support – Runtime facility Techniques – Co-location Requires dynamic linking Provides low cost communication – Enforced modularity Modula – 3 Compiler enforce interface between modules Can’t access memory or execute privileged instruction unless access given through interface Modularity enforced by the compiler enables modules – Logical protection domains Dynamic linker resolve code in different logical protection domain – Dynamic call binding System Events

6. Extensibility

7. Extension model Property of Extension – Easy to apply – Transparent – Efficient Dynamically linked to Kernel address space Provide controlled communication between Extension and Base system Extensions defined in terms of Event and Handler

8. Extension model Event raised Dispatcher call guards and handlers Evaluating guards If guard true then call handler Safety issues – Type checking Access Control Denial of service – Runaway handlers – Too many handlers Ref: Fig from paper 2 in Reference

9. Example: System call Ref: From presentation prepared by Author of paper 2.

10. Programmer’s view Ref: From presentation prepared by Author of paper 2.

11. SPIN structure Ref: Fig from presentation prepared by Author from http://www-spin.cs.washington.edu/http://www-spin.cs.washington.edu/

12. Application: Video system components Ref: Fig from Author presentation from http://www-spin.cs.washington.edu/http://www-spin.cs.washington.edu/

13. Safety

14. Modula – 3 support for SPIN Type Safety – Array index checks (static & dynamic) – Pointer-safe casting “VIEW” used to safe cast – Size of input should match with typed structure – Alignment should match Isolation of untrusted code – Terminating untrusted code “EPHEMERAL” procedure tag for killable procedures – Isolating errors in untrusted code Implicit exception for unhandled exception Enforce modularity – Interface, Modules and procedures Automatic storage management

15. Protection model Control set of operations on resource Conventional OS uses Address space as a protection model SPIN – Capabilities – Protection domain

16. Capabilities Implemented using pointers Pointer is a reference to block of memory whose type is declared within interface. Externalized Reference before sending to user space Unforgeable reference to resources (system object and interfaces) Extension reference resources for which they have valid access Interfaces protected to allow different extensions to have different views on services

17. Protection domains Set of accessible names available for execution context Naming and protection interface at level of language – Name ‘c’ is a instance of type ‘Console.T’ Domains can be intersecting or disjoint

18. Domain interface

19. Export/Import domain at run-time Fig from paper [2]

20. Core Services

21. Manages Memory and Processor resources Export interfaces for Extensions Extensible Memory management – Three components: Physical storage, Naming(virtual address) and Translation Extensible thread management – Strands – No state, share processor – Application provide its own thread package – Scheduler runs in Kernel – Checkpoint and Resume events – Block / Unblock Events

22. Performance

23. Methodology Comparative study – SPIN V0.4 – DEC OSF/1 V2.1 (Monolithic OS) – Mach 3.0 (Micro-kernel) Hardware – DEC Alpha 133 MHz AXP 3000/400 workstation, 64 MB RAM, 512 KB unified external cache Tests – Micro benchmarks – End-to-end performance – Networking

24. Micro benchmark – Protected communication NULL procedure call Protected in-kernel : SPIN’s cross domain procedure call Cross Address space call: SPIN’s extension Protected communication overhead in microseconds

25. Micro benchmark: Thread Management overhead

26. Network Latency and Bandwidth

27. End-to-end performance

28. Conclusion It is possible to achieve all three in single OS (Extensibility, Safety and Performance) Extend easily with dynamic linking Use of language and compile with Event facility for safety Communication cost is low Issues – Dispatcher performance? – Does it solve all Safety issues? How do we test correctness? – Language restrictions, changes in Modula - 3

29. References 1. Extensibility, Safety and Performance in the SPIN Operating System Brian Bershad, Stefan Savage, Przemyslaw Pardyak, Emin Gun Sirer, David Becker, Marc Fiuczynski, Craig Chambers, Susan Eggers Brian BershadStefan SavagePrzemyslaw PardyakEmin Gun SirerDavid BeckerMarc FiuczynskiCraig ChambersSusan Eggers 2. Dynamic Binding for an Extensible System, Przemyslaw Pardyak and Brian Bershad 3. Safe Dynamic Linking in an Extensible Operating System, Emin Sirer, Marc Fiucynski, Przemyslaw Pardyak, Brian Bershad 4. Language Support For Extensible Operating System, Wilson Hsieh, Marc Fiuczynski, Charles Garrett, Stefan Savage, David Becker, and Brian Bershad 5. SPIN Operating System web site: Documentation and source code http://www-spin.cs.washington.edu/