1/*
  2 * stop-task scheduling class.
  3 *
  4 * The stop task is the highest priority task in the system, it preempts
  5 * everything and will be preempted by nothing.
  6 *
  7 * See kernel/stop_machine.c
  8 */
  9
 10#ifdef CONFIG_SMP
 11static int
 12select_task_rq_stop(struct task_struct *p, int sd_flag, int flags)
 13{
 14	return task_cpu(p); /* stop tasks as never migrate */
 15}
 16#endif /* CONFIG_SMP */
 17
 18static void
 19check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
 20{
 21	/* we're never preempted */
 22}
 23
 24static struct task_struct *pick_next_task_stop(struct rq *rq)
 25{
 26	struct task_struct *stop = rq->stop;
 27
 28	if (stop && stop->on_rq)
 29		return stop;
 30
 31	return NULL;
 32}
 33
 34static void
 35enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 36{
 37}
 38
 39static void
 40dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 41{
 42}
 43
 44static void yield_task_stop(struct rq *rq)
 45{
 46	BUG(); /* the stop task should never yield, its pointless. */
 47}
 48
 49static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
 50{
 51}
 52
 53static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 54{
 55}
 56
 57static void set_curr_task_stop(struct rq *rq)
 58{
 59}
 60
 61static void switched_to_stop(struct rq *rq, struct task_struct *p)
 62{
 63	BUG(); /* its impossible to change to this class */
 64}
 65
 66static void
 67prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 68{
 69	BUG(); /* how!?, what priority? */
 70}
 71
 72static unsigned int
 73get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 74{
 75	return 0;
 76}
 77
 78/*
 79 * Simple, special scheduling class for the per-CPU stop tasks:
 80 */
 81static const struct sched_class stop_sched_class = {
 82	.next			= &rt_sched_class,
 83
 84	.enqueue_task		= enqueue_task_stop,
 85	.dequeue_task		= dequeue_task_stop,
 86	.yield_task		= yield_task_stop,
 87
 88	.check_preempt_curr	= check_preempt_curr_stop,
 89
 90	.pick_next_task		= pick_next_task_stop,
 91	.put_prev_task		= put_prev_task_stop,
 92
 93#ifdef CONFIG_SMP
 94	.select_task_rq		= select_task_rq_stop,
 95#endif
 96
 97	.set_curr_task          = set_curr_task_stop,
 98	.task_tick		= task_tick_stop,
 99
100	.get_rr_interval	= get_rr_interval_stop,
101
102	.prio_changed		= prio_changed_stop,
103	.switched_to		= switched_to_stop,
104};