Linux内核schedule函数分析

Linux内核schedule函数分析

asmlinkage void schedule(void)
{
 task_t *prev, *next;
 runqueue_t *rq;
 prio_array_t *array;
 struct list_head *queue;
 int idx;

 #判断是否调度发生在中断上下文，如果是就出错;在ＬＩＮＵＸ的中断中是不允许发生调度的

 if (unlikely(in_interrupt()))   
  BUG();

need_resched:

 preempt_disable();
 prev = current;
 rq = this_rq();

 release_kernel_lock(prev, smp_processor_id());
 prepare_arch_schedule(prev);
 prev->sleep_timestamp = jiffies;
 spin_lock_irq(&rq->lock);

 
 if (unlikely(preempt_get_count() & PREEMPT_ACTIVE))
  goto pick_next_task;

 switch (prev->state) {
 case TASK_INTERRUPTIBLE:
  if (unlikely(signal_pending(prev))) {
   prev->state = TASK_RUNNING;
   break;
  }
 default:
  deactivate_task(prev, rq);
 case TASK_RUNNING:
  ;
 }
pick_next_task:
 if (unlikely(!rq->nr_running)) {
#if CONFIG_SMP
  load_balance(rq, 1);
  if (rq->nr_running)
   goto pick_next_task;
#endif
  next = rq->idle;
  rq->expired_timestamp = 0;
  goto switch_tasks;
 }

 array = rq->active;
 if (unlikely(!array->nr_active)) {
 
  rq->active = rq->expired;
  rq->expired = array;
  array = rq->active;
  rq->expired_timestamp = 0;
 }

 idx = sched_find_first_bit(array->bitmap);
 queue = array->queue + idx;
 next = list_entry(queue->next, task_t, run_list);

switch_tasks:
 prefetch(next);
 clear_tsk_need_resched(prev);

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

  TRACE_SCHEDCHANGE(prev, next);

  prev = context_switch(prev, next);
  barrier();
  rq = this_rq();
  finish_arch_switch(rq);
 } else
  spin_unlock_irq(&rq->lock);
 finish_arch_schedule(prev);

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