Operating System Architecture for Incredibly Diverse Devices

1. Operating System Architecture for Incredibly Diverse Devices David Culler http://www.cs.berkeley.edu/~culler U.C. Berkeley Expeditions Meeting 8/16/1999

2. Massive Cluster Clusters Gigabit Ethernet Server Scalable, Available Internet Services Client Info. appliances Away from the ‘average’ Device Expeditions Diverse OS

3. Convergence at the Extremes • Powerful Services on “Small” Devices • massive computing and storage in the infrastructure • active adaptation of form and content “along the way” • Extremes more alike that either is to the middle • More specialized in function • Communication centric design • wide range of networking options • Federated System of Many Many Systems • Hands-off operation, mgmt, development • High Reliability, Availability • Scalability • Power and space limited • simplicity • They have to “work or die!” Expeditions Diverse OS

4. Body of Work in the Very Large • Academic: metacomputing, computational grid • Glunix (UCB), Globus(ANL), Legion (UVA), IPG (NASA), Harness, NetSolve, Snipe (UTK), EMOP, Apples, Cactus, Meta-Chaos, ... • Commercial • LSF Expeditions Diverse OS

5. Dominant thrust: Glue over big OS • Nodes a full OS and Institutional structure • accounts, authentication, resources, execution, storage, policy • User constructs a personal virtual machine spanning numerous, potentially diverse resources • mapping from uniform metasystem mechanisms to site specific mechanism • naming, authentication, transparent execution, storage, scheduling • uniform, multiprotocol communication mechanism • “Many nodes in a net”, not “Unix on Steroids” • mgmt is fundamental problem, but still unadressed Expeditions Diverse OS

6. And in the small... • Academic • microkernels, Exokernel, OSKit, ucLinux, ELKS, • Commercial • PalmOS, PSION, GeoWorks, WinCE, Inferno, QNX, VxWorks, javaos, chorusOS, BeOS, • jini, corba, dcom, ... => tracks the 80386 • when it becomes ~ 1990 PC Unix will run on it Expeditions Diverse OS

7. Small OS Dominant thrust • Unix on a diet + real time seasoning • Microkernel finally works on small devices • ability to remove components (modularity) + fault boundaries more important than performance • legacy applications less dominant Expeditions Diverse OS

8. Design Issues for “Small Device OS” • Managing address spaces • Thread scheduling • IP stack • Windowing System • Device drivers • File system • Applications Programming Interface • Power management Expeditions Diverse OS

9. Core Questions • What are the principles of design for tiny operating systems? • How are they different from a desktop or server? • Where should we look for ideas and experience? • How can operating systems be made radically simpler? • How should we proceed with the investigation? Expeditions Diverse OS

10. 1st Stab at Principles for Simple OS • Communication is fundamental • treated as part of the hardware. No comm is like no power • you don’t bring up the device then “configure comm.” • hands off: a direct “user interface” is the exception not the norm • typical device has a network on one side + sensor/actuators on the other • buttons and display a special case • all deployment, development, configuration, mgmt, programming, is through the communication interface • schedule data movement, not arbitrary threads of computation • constant self-checking and telemetry • rely on the infrastructure for hard stuff Expeditions Diverse OS

11. other places to look for ideas • Operating systems that are not called “operating systems” • eg: modern disk controller • event scheduler handling stream of commands from network link, controlling complex array of sensors and actuators, performing sophisticated calculations to determine what and when (scheduling and caching) as well as transforming data on the fly • automatic connection, enumeration, configuration • but several simplifying assumptions must be removed Complex array of Sensors and actuators Network link: - EIDE, SCSI - FCAL, SSA - USB, 1394 - ??? Expeditions Diverse OS

12. OS as little more than FSM • Primary focus is scheduling discrete chunks of data movement • not general thread scheduling and unlimited memory management • there may be a bounded amount of work to xform or check data • Commands are an event stream merged with sensor/actuator events • General thread must be compiled to sequence of bounded atomic transactions • spagetti part of an application is configuring the flows • steady-state is straight-forward event processing + signaling unusual events • Simplify network-based debug and mgmt Expeditions Diverse OS

13. Adaptation in Flows • View data transfers as continuous flows • plumbing as programming model • reservoirs provide slack • trade bandwidth for robustness • Natural form of adaptation • ex: faster consumer gets more data • flow equations provide goal, simple error bounds, and react • performance availability Expeditions Diverse OS

14. Example: streaming output • Events associated with particular configuration of reservoirs and flows drive operation scheduling • hard to effect through queue management and priorities of threads High water mark => stop input low water mark => start input Expeditions Diverse OS

15. 2 10 10 10 10 5 5 5 5 5 5 5 5 7 3 7 1 1 3 8 8 8 8 Availability => Performance availability Expeditions Diverse OS

16. Key Extensions • active elements in the protocol hierarchy • intermittent connection • narrow interface with commitment • Pilot --- RMI Proxy --- Ninja Service Prototype • device OS = protocol engine Alternative: Comm = Location independent Access to shared storage • Key Concepts from Parallel Architecture • hierarchical composition of cache-coherence protocols + consistency models • natural framework for adaptation (pull what you touch) Expeditions Diverse OS

17. How to proceed? • A lot of experience to be gained from the chopped desktop OS efforts • same time-to-mkt benefit research prototype • brings many small, interesting devices on line • bring Universal Computing Lab on-line (IRDA + 802.11) • and from meta-OS efforts • Build simulation environment for bottom-up development • currently exploring UCLA GloMo simulator • Develop ‘always-on’ networking component for expedition testbed • Deploy for unusual new devices • smart boulders -> pebbles -> dust Expeditions Diverse OS