Linux 2.6.36版本内核分析之schedule()
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/*
* 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;
}
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