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 cpu, 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 *
 27pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct pin_cookie cookie)
 28{
 29	struct task_struct *stop = rq->stop;
 30
 31	if (!stop || !task_on_rq_queued(stop))
 32		return NULL;
 33
 34	put_prev_task(rq, prev);
 35
 36	stop->se.exec_start = rq_clock_task(rq);
 37
 38	return stop;
 39}
 40
 41static void
 42enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 43{
 44	add_nr_running(rq, 1);
 45}
 46
 47static void
 48dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 49{
 50	sub_nr_running(rq, 1);
 51}
 52
 53static void yield_task_stop(struct rq *rq)
 54{
 55	BUG(); /* the stop task should never yield, its pointless. */
 56}
 57
 58static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
 59{
 60	struct task_struct *curr = rq->curr;
 61	u64 delta_exec;
 62
 63	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
 64	if (unlikely((s64)delta_exec < 0))
 65		delta_exec = 0;
 66
 67	schedstat_set(curr->se.statistics.exec_max,
 68			max(curr->se.statistics.exec_max, delta_exec));
 69
 70	curr->se.sum_exec_runtime += delta_exec;
 71	account_group_exec_runtime(curr, delta_exec);
 72
 73	curr->se.exec_start = rq_clock_task(rq);
 74	cpuacct_charge(curr, delta_exec);
 75}
 76
 77static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 78{
 79}
 80
 81static void set_curr_task_stop(struct rq *rq)
 82{
 83	struct task_struct *stop = rq->stop;
 84
 85	stop->se.exec_start = rq_clock_task(rq);
 86}
 87
 88static void switched_to_stop(struct rq *rq, struct task_struct *p)
 89{
 90	BUG(); /* its impossible to change to this class */
 91}
 92
 93static void
 94prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 95{
 96	BUG(); /* how!?, what priority? */
 97}
 98
 99static unsigned int
100get_rr_interval_stop(struct rq *rq, struct task_struct *task)
101{
102	return 0;
103}
104
105static void update_curr_stop(struct rq *rq)
106{
107}
108
109/*
110 * Simple, special scheduling class for the per-CPU stop tasks:
111 */
112const struct sched_class stop_sched_class = {
113	.next			= &dl_sched_class,
114
115	.enqueue_task		= enqueue_task_stop,
116	.dequeue_task		= dequeue_task_stop,
117	.yield_task		= yield_task_stop,
118
119	.check_preempt_curr	= check_preempt_curr_stop,
120
121	.pick_next_task		= pick_next_task_stop,
122	.put_prev_task		= put_prev_task_stop,
123
124#ifdef CONFIG_SMP
125	.select_task_rq		= select_task_rq_stop,
126	.set_cpus_allowed	= set_cpus_allowed_common,
127#endif
128
129	.set_curr_task          = set_curr_task_stop,
130	.task_tick		= task_tick_stop,
131
132	.get_rr_interval	= get_rr_interval_stop,
133
134	.prio_changed		= prio_changed_stop,
135	.switched_to		= switched_to_stop,
136	.update_curr		= update_curr_stop,
137};