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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * stop-task scheduling class.
4 *
5 * The stop task is the highest priority task in the system, it preempts
6 * everything and will be preempted by nothing.
7 *
8 * See kernel/stop_machine.c
9 */
10#include "sched.h"
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
19static int
20balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
21{
22 return sched_stop_runnable(rq);
23}
24#endif /* CONFIG_SMP */
25
26static void
27check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
28{
29 /* we're never preempted */
30}
31
32static void set_next_task_stop(struct rq *rq, struct task_struct *stop)
33{
34 stop->se.exec_start = rq_clock_task(rq);
35}
36
37static struct task_struct *
38pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
39{
40 WARN_ON_ONCE(prev || rf);
41
42 if (!sched_stop_runnable(rq))
43 return NULL;
44
45 set_next_task_stop(rq, rq->stop);
46 return rq->stop;
47}
48
49static void
50enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
51{
52 add_nr_running(rq, 1);
53}
54
55static void
56dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
57{
58 sub_nr_running(rq, 1);
59}
60
61static void yield_task_stop(struct rq *rq)
62{
63 BUG(); /* the stop task should never yield, its pointless. */
64}
65
66static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
67{
68 struct task_struct *curr = rq->curr;
69 u64 delta_exec;
70
71 delta_exec = rq_clock_task(rq) - curr->se.exec_start;
72 if (unlikely((s64)delta_exec < 0))
73 delta_exec = 0;
74
75 schedstat_set(curr->se.statistics.exec_max,
76 max(curr->se.statistics.exec_max, delta_exec));
77
78 curr->se.sum_exec_runtime += delta_exec;
79 account_group_exec_runtime(curr, delta_exec);
80
81 curr->se.exec_start = rq_clock_task(rq);
82 cgroup_account_cputime(curr, delta_exec);
83}
84
85/*
86 * scheduler tick hitting a task of our scheduling class.
87 *
88 * NOTE: This function can be called remotely by the tick offload that
89 * goes along full dynticks. Therefore no local assumption can be made
90 * and everything must be accessed through the @rq and @curr passed in
91 * parameters.
92 */
93static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
94{
95}
96
97static void switched_to_stop(struct rq *rq, struct task_struct *p)
98{
99 BUG(); /* its impossible to change to this class */
100}
101
102static void
103prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
104{
105 BUG(); /* how!?, what priority? */
106}
107
108static unsigned int
109get_rr_interval_stop(struct rq *rq, struct task_struct *task)
110{
111 return 0;
112}
113
114static void update_curr_stop(struct rq *rq)
115{
116}
117
118/*
119 * Simple, special scheduling class for the per-CPU stop tasks:
120 */
121const struct sched_class stop_sched_class = {
122 .next = &dl_sched_class,
123
124 .enqueue_task = enqueue_task_stop,
125 .dequeue_task = dequeue_task_stop,
126 .yield_task = yield_task_stop,
127
128 .check_preempt_curr = check_preempt_curr_stop,
129
130 .pick_next_task = pick_next_task_stop,
131 .put_prev_task = put_prev_task_stop,
132 .set_next_task = set_next_task_stop,
133
134#ifdef CONFIG_SMP
135 .balance = balance_stop,
136 .select_task_rq = select_task_rq_stop,
137 .set_cpus_allowed = set_cpus_allowed_common,
138#endif
139
140 .task_tick = task_tick_stop,
141
142 .get_rr_interval = get_rr_interval_stop,
143
144 .prio_changed = prio_changed_stop,
145 .switched_to = switched_to_stop,
146 .update_curr = update_curr_stop,
147};
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};