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)
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#endif
127
128	.set_curr_task          = set_curr_task_stop,
129	.task_tick		= task_tick_stop,
130
131	.get_rr_interval	= get_rr_interval_stop,
132
133	.prio_changed		= prio_changed_stop,
134	.switched_to		= switched_to_stop,
135	.update_curr		= update_curr_stop,
136};
137