Linux 2.6.36版本内核分析之schedule()

最新推荐文章于 2023-07-07 19:30:57 发布

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#内核 #Linux #schedule

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本文详细分析了Linux 2.6.36内核中的schedule()函数，该函数是内核调度的主要实现，负责进程的切换。文章通过讲解schedule()函数的内部流程，包括获取当前CPU、处理中断、判断进程状态、选择下一个进程等步骤，揭示了Linux内核如何维持系统的并发执行和资源分配。

/*
* schedule() is the main scheduler function.调度主函数，又称主调度
*/
asmlinkage void__schedschedule(void)
{
    struct task_struct *prev, *next;//prev:换出进程标识符，next:换入进程标识符
    unsigned long *switch_count;//对prev的进程切换进行计数
    struct rq *rq;//运行队列
    int cpu;//CPU号

need_resched:
preempt_disable();//关中断
cpu = smp_processor_id();//获取执行prev进程的cpu号
rq = cpu_rq(cpu);//获取cpu号所代表的CPU的运行队列
rcu_note_context_switch(cpu);//
prev = rq->curr;//获取运行队列中当前指向的进程，也是即将被换出的进程，进程状态是什么？

release_kernel_lock(prev);//释放大内核锁
need_resched_nonpreemptible:

schedule_debug(prev);

if (sched_feat(HRTICK))
hrtick_clear(rq);

raw_spin_lock_irq(&rq->lock);
clear_tsk_need_resched(prev);

switch_count = &prev->nivcsw;
if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
  if (unlikely(signal_pending_state(prev->state, prev))) {
   prev->state = TASK_RUNNING;
  } else {
   /*
    * If a worker is going to sleep, notify and
    * ask workqueue whether it wants to wake up a
    * task to maintain concurrency. If so, wake
    * up the task.
    */
   if (prev->flags & PF_WQ_WORKER) {
    struct task_struct *to_wakeup;

    to_wakeup = wq_worker_sleeping(prev, cpu);
    if (to_wakeup)
     try_to_wake_up_local(to_wakeup);
   }
   deactivate_task(rq, prev, DEQUEUE_SLEEP);
  }
  switch_count = &prev->nvcsw;
}

pre_schedule(rq, prev);

if (unlikely(!rq->nr_running))
idle_balance(cpu, rq);

put_prev_task(rq, prev);
next = pick_next_task(rq);

if (likely(prev != next)) {
sched_info_switch(prev, next);
perf_event_task_sched_out(prev, next);

  rq->nr_switches++;
  rq->curr = next;
  ++*switch_count;

  context_switch(rq, prev, next); /* unlocks the rq */
  /*
   * The context switch have flipped the stack from under us
   * and restored the local variables which were saved when
   * this task called schedule() in the past. prev == current
   * is still correct, but it can be moved to another cpu/rq.
   */
  cpu = smp_processor_id();
  rq = cpu_rq(cpu);
} else
  raw_spin_unlock_irq(&rq->lock);

post_schedule(rq);

if (unlikely(reacquire_kernel_lock(prev)))
goto need_resched_nonpreemptible;

preempt_enable_no_resched();
if (need_resched())
goto need_resched;
}