A Quick Look at Scheduling

Notes

• We will discuss scheduling algorithms in the near future
• But for now, we will take a quick look at process management
• And the scheduler, or process scheduler .
• The scheduler keeps a number of queues
  • The ready queue, or processes that are ready to run
  • The wait queue, or processes that need something to run
  • There may be multiple ready queues
  • These are pictured on page 112
• If a system becomes too busy, processes can be swapped out
  • removed from memory and written to disk.
• When the OS removes one process from a core and moves in another it is called a context switch.
  • This occurs when a process is interrupted
    • For I/O
    • For time exceeded
    • For some other reason.
  • The processes context is saved
    • registers
    • Memory management information
    • etc
  • Then the os performs some actions
  • Then a process, possibly the same one, is loaded.
  • And processing continues
  • See Figure 3.6 page 114.
  • Note, in a very real sense, this is not accomplishing anything...
    • So this needs to be as efficient as possible.