schedule()函数详解

schedule主要完成的工作内容如下：
（1）sched_submit_work用于检测当前进程是否有plugged io需要处理，由于当前进程执行schedule后，有可能会进入休眠，所以在休眠之前需要把plugged io处理掉放置死锁。
（2）执行__schedule()这个函数是调度的核心处理函数，当前CPU会选择到下一个合适的进程去执行了。
（3）need_resched()执行到这里时说明当前进程已经被调度器再次执行了，此时要判断是否需要再次执行调度。

static void __sched __schedule(void)
{
struct task_struct *prev, *next;
unsigned long *switch_count;
struct rq *rq;
int cpu;

preempt_disable();
cpu = smp_processor_id();
rq = cpu_rq(cpu);
rcu_note_context_switch();
prev = rq->curr;

schedule_debug(prev);

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

/*
* Make sure that signal_pending_state()->signal_pending() below
* can‘t be reordered with __set_current_state(TASK_INTERRUPTIBLE)
* done by the caller to avoid the race with signal_wake_up().
*/
smp_mb__before_spinlock();
raw_spin_lock_irq(&rq->lock);

rq->clock_skip_update <<= 1; /* promote REQ to ACT */

switch_count = &prev->nivcsw;
if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
if (unlikely(signal_pending_state(prev->state, prev))) {
prev->state = TASK_RUNNING;
} else {
deactivate_task(rq, prev, DEQUEUE_SLEEP);
prev->on_rq = 0;

/*
* If a worker went to sleep, notify and ask workqueue
* whether it wants to wake up a task to maintain
* concurrency.
*/
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);
}
}
switch_count = &prev->nvcsw;
}

if (task_on_rq_queued(prev))
update_rq_clock(rq);

next = pick_next_task(rq, prev);
clear_tsk_need_resched(prev);
clear_preempt_need_resched();
rq->clock_skip_update = 0;

if (likely(prev != next)) {
rq->nr_switches++;
rq->curr = next;
++*switch_count;

rq = context_switch(rq, prev, next); /* unlocks the rq */
cpu = cpu_of(rq);
} else
raw_spin_unlock_irq(&rq->lock);

post_schedule(rq);

sched_preempt_enable_no_resched();
}

schedule()函数详解

原文：https://www.cnblogs.com/ja58/p/14860456.html