선 요약

| FIFO | min Overhead | poor resp w. vary tasks | optimal resp w. same tasks | | --- | --- | --- | --- | | SJF | | optimal resp | | | RR | | ~SJF w. vary tasks | worst policy w. same tasks |

Process Scheduling

• Process Queue
  • collection of state of all processes
  • ready-to-run processes (run queue / ready queue)
  • blocked processes (wait queue)
    • 하나의 이유마다 하나의 큐 존재 ex. IO queue, sleep queue, …
• Scheduler
  • Long term: job scheduler
    • invoked infrequently (sec~min)
  • Short term: CPU Scheduler
    • invoked frequently (ms)
      • invoked when new ready process is inserted into ready queue ex. on timer interrupt, IO, …
      • then choose order in the queue.
    • must be fast

CPU Scheduler

• Select a Process among the processes in ready queue
• then allocate CPU to process

Process States

running: executing

ready: wating for CPU

waiting: wait for lock

Scheduling When?

• running → waiting (thread_block)
• running → ready (thread_yield)
• waiting → ready (thread_unblock)
• exit

Terminology

• Task of Job: everything
  • ex. mouse click, web request, shell command, …