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Operating Systems CSE 411. Revision and final thoughts Dec. 15 2006 - Lecture 33 Instructor: Bhuvan Urgaonkar. What did we learn?. What is an operating system A piece of software that runs on a computer (kernel) Privileged mode Direct access to all hardware (device drivers)

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operating systems cse 411

Operating SystemsCSE 411

Revision and final thoughts

Dec. 15 2006 - Lecture 33

Instructor: Bhuvan Urgaonkar

what did we learn
What did we learn?
  • What is an operating system
    • A piece of software that runs on a computer (kernel)
    • Privileged mode
      • Direct access to all hardware (device drivers)
    • Resource allocation
      • Efficiency
      • Fairness
      • Contention resolution (e.g., synchronization)
    • Protection and isolation
    • (Easy/Agreed upon) interface to programmers
      • Hides several hardware details and heterogeneity
what did we learn1
What did we learn?
  • Relation between hardware/architecture and operating system design
    • Impact of hardware characteristics on OS design
      • Good example was disk management versus memory management
    • How hardware designers and architects assist OS designers
      • Example - Atomic operations
    • What should the hardware do versus what should the OS do
what did we learn2
What did we learn?
  • Important architectural features
    • Interrupts: I/O devices, passage of time (scheduling)
    • Exceptions: Request services from OS
  • Related OS abstraction
    • Signals: Inter-process communication, asynchronous handling of special events by OS and programs
what did we learn3
What did we learn?
  • Key abstractions provided by the OS
    • Process
      • Related: threads, address space/virtual memory
    • File
      • Related: device files
what did we learn4
What did we learn?
  • CPU management
    • Process, thread, kernel control paths
      • User-level threads
      • Kernels are usually multi-threaded
    • Scheduling
      • Work conservation
      • Proportional-share, reservation-based
    • Synchronization
      • Mutual exclusion
      • Semaphores
    • Deadlocks
    • Multi-processors have special scheduling and synchronization considerations
what did we learn5
What did we learn?
  • Memory management
    • Virtual memory
      • Current memory technology: RAM
      • Fragmentation: internal and external
      • Paging
      • Page table, TLB
      • Page replacement
      • Swap space: Extension of RAM
    • Caching and buffering in RAM for I/O devices
    • Sharing memory
      • Memory mapping, CoW
    • Relation between memory manager and CPU scheduler
      • Under memory pressure, VMM can become the de-facto CPU scheduler
      • VMM needs to be designed with fairness and performance in mind
what did we learn6
What did we learn?
  • I/O management
    • Hardware characteristics, DMA
    • Close look at disk management
      • Disk characteristics
      • Disk scheduling
        • Multiple locations where scheduling occurs
      • File systems
        • Data layout
        • Virtual File systems
        • Traditional file systems
        • Emerging file system: CAS
      • Emerging systems based on Flash
cross cutting concerns principles
Cross-cutting concerns/principles
  • Caching and buffering
  • Fairness and isolation
  • Design for average/frequent case
  • Virtualization
    • VMM, VFS, system calls, multi-programming
  • Multiplexing of resources
    • Over-commitment of resources
  • Accounting and monitoring
research goals
Research goals
  • Traditional
    • Performance
    • Fairness
    • Isolation
  • Increasingly important
    • Power
    • Manageability
      • Self-* properties
    • Change management
    • Accountability and security
operating systems topics we didn t cover
Operating systems topics we didn’t cover
  • Traditional OS topics
    • OS externals (311)
    • System bootstrap
    • Synchronization: Monitors
    • Deadlocks: Banker’s algorithm
    • File systems: Log-structured file systems
  • Multimedia systems
  • Real-time systems
  • Distributed systems (Chapters 16-18)
what do we make of this
What do we make of this?
  • Debatable and controversial arguments
  • I would like to believe that the new OS papers graph doesn’t indicate the death of OS research
    • Research has moved on to other aspects, taken newer forms
    • Similar phenomenon are seen in other fields
    • Can you give any examples?
  • I feel the focus and scope of OS research has changed
    • More on distributed systems, embedded systems
    • Issues other than performance
where do we go from here what s happening now
Where do we go from here/ what’s happening now?
  • Sensors and embedded devices
  • Highly distributed systems
    • P2P networks, grids
  • Mobile computing
    • Ubiquitous computing
  • Virtual machines
    • Multiple operating systems on a single computer!
  • Data centers
    • Green computing
final exam
Final exam
  • 2 hour
  • Open-notes, open-book
  • Easier than the mid-terms
  • Do the final quiz carefully
    • Still not up, but will be sometime tomorrow
  • Only topics covered in lectures
  • Tentative structure
    • 8 Short questions (2-3 sentences each): 40%
    • 3 longer design/essay questions: 60%, one each on:
      • CPU scheduling/synchronization
      • Memory management
      • Disk management / file systems