linux/kernel/sched_idletask.c

/*
 * idle-task scheduling class.
 *
 * (NOTE: these are not related to SCHED_IDLE tasks which are
 *  handled in sched_fair.c)
 */

#ifdef CONFIG_SMP
static int select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
{
	return task_cpu(p); /* IDLE tasks as never migrated */
}
#endif /* CONFIG_SMP */
/*
 * Idle tasks are unconditionally rescheduled:
 */
static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
{
	resched_task(rq->idle);
}

static struct task_struct *pick_next_task_idle(struct rq *rq)
{
	schedstat_inc(rq, sched_goidle);
	/* adjust the active tasks as we might go into a long sleep */
	calc_load_account_active(rq);
	return rq->idle;
}

/*
 * It is not legal to sleep in the idle task - print a warning
 * message if some code attempts to do it:
 */
static void
dequeue_task_idle(struct rq *rq, struct task_struct *p, int sleep)
{
	raw_spin_unlock_irq(&rq->lock);
	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
	dump_stack();
	raw_spin_lock_irq(&rq->lock);
}

static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
{
}

static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
{
}

static void set_curr_task_idle(struct rq *rq)
{
}

static void switched_to_idle(struct rq *rq, struct task_struct *p,
			     int running)
{
	/* Can this actually happen?? */
	if (running)
		resched_task(rq->curr);
	else
		check_preempt_curr(rq, p, 0);
}

static void prio_changed_idle(struct rq *rq, struct task_struct *p,
			      int oldprio, int running)
{
	/* This can happen for hot plug CPUS */

	/*
	 * Reschedule if we are currently running on this runqueue and
	 * our priority decreased, or if we are not currently running on
	 * this runqueue and our priority is higher than the current's
	 */
	if (running) {
		if (p->prio > oldprio)
			resched_task(rq->curr);
	} else
		check_preempt_curr(rq, p, 0);
}

static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
{
	return 0;
}

/*
 * Simple, special scheduling class for the per-CPU idle tasks:
 */
static const struct sched_class idle_sched_class = {
	/* .next is NULL */
	/* no enqueue/yield_task for idle tasks */

	/* dequeue is not valid, we print a debug message there: */
	.dequeue_task		= dequeue_task_idle,

	.check_preempt_curr	= check_preempt_curr_idle,

	.pick_next_task		= pick_next_task_idle,
	.put_prev_task		= put_prev_task_idle,

#ifdef CONFIG_SMP
	.select_task_rq		= select_task_rq_idle,
#endif

	.set_curr_task          = set_curr_task_idle,
	.task_tick		= task_tick_idle,

	.get_rr_interval	= get_rr_interval_idle,

	.prio_changed		= prio_changed_idle,
	.switched_to		= switched_to_idle,

	/* no .task_new for idle tasks */
};