Scheduler

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Task State

stateDiagram-v2
    R: running
    S: sleeping
    D: disk sleep
    T: stopped
    t: tracing stop
    X: dead
    Z: zombie
    P: parked
    I: idle

    R --> S: schedule_timeout()
    R --> D: Wait for Disk I/O
    R --> T: SIGTSTP
    R --> t: gdb/strace
    S --> R: wake_up_process()
    D --> R: I/O Completed
    T --> R: SIGCONT
    T --> t: gdb/strace
    T --> Z: SIGKILL But Sth Wrong with Its Parent
    R --> Z: Exit But Sth Wrong with Its Parent
    t --> T: Quit gdb

Notes:

  • disk sleep 也就是 uninterruptible sleep 状态
  • zombie 状态的进程在 ps 中被标记为 <defunct>
  • 正常的空闲用户进程一般是 sleeping 状态，空闲的 kthread 是 idle 状态

内核中和调度相关的 APIs

  • signed long __sched shedule_timeout_interruptible(signed long timeout);

    • 调用者 task 开始睡眠直到超时

  • wait_event_timeout(wq_head, condition, timeout)

    • wq_head: 正在等待的一个队列 waitqueue, 每次 wq_head 被唤醒， condition 都会被检查一次

其它

  • static inline int signal_pending(struct task_struct *)
    • 检查当前 task 是否有信号处理，返回非 0 表示有信号需要处理

References