1#include "sched.h"
  2
  3/*
  4 * stop-task scheduling class.
  5 *
  6 * The stop task is the highest priority task in the system, it preempts
  7 * everything and will be preempted by nothing.
  8 *
  9 * See kernel/stop_machine.c
 10 */
 11
 12#ifdef CONFIG_SMP
 13static int
 14select_task_rq_stop(struct task_struct *p, int sd_flag, int flags)
 15{
 16	return task_cpu(p); /* stop tasks as never migrate */
 17}
 18#endif /* CONFIG_SMP */
 19
 20static void
 21check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
 22{
 23	/* we're never preempted */
 24}
 25
 26static struct task_struct *pick_next_task_stop(struct rq *rq)
 27{
 28	struct task_struct *stop = rq->stop;
 29
 30	if (stop && stop->on_rq)
 31		return stop;
 32
 33	return NULL;
 34}
 35
 36static void
 37enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 38{
 39	inc_nr_running(rq);
 40}
 41
 42static void
 43dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 44{
 45	dec_nr_running(rq);
 46}
 47
 48static void yield_task_stop(struct rq *rq)
 49{
 50	BUG(); /* the stop task should never yield, its pointless. */
 51}
 52
 53static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
 54{
 55}
 56
 57static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 58{
 59}
 60
 61static void set_curr_task_stop(struct rq *rq)
 62{
 63}
 64
 65static void switched_to_stop(struct rq *rq, struct task_struct *p)
 66{
 67	BUG(); /* its impossible to change to this class */
 68}
 69
 70static void
 71prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 72{
 73	BUG(); /* how!?, what priority? */
 74}
 75
 76static unsigned int
 77get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 78{
 79	return 0;
 80}
 81
 82/*
 83 * Simple, special scheduling class for the per-CPU stop tasks:
 84 */
 85const struct sched_class stop_sched_class = {
 86	.next			= &rt_sched_class,
 87
 88	.enqueue_task		= enqueue_task_stop,
 89	.dequeue_task		= dequeue_task_stop,
 90	.yield_task		= yield_task_stop,
 91
 92	.check_preempt_curr	= check_preempt_curr_stop,
 93
 94	.pick_next_task		= pick_next_task_stop,
 95	.put_prev_task		= put_prev_task_stop,
 96
 97#ifdef CONFIG_SMP
 98	.select_task_rq		= select_task_rq_stop,
 99#endif
100
101	.set_curr_task          = set_curr_task_stop,
102	.task_tick		= task_tick_stop,
103
104	.get_rr_interval	= get_rr_interval_stop,
105
106	.prio_changed		= prio_changed_stop,
107	.switched_to		= switched_to_stop,
108};