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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
11#ifdef CONFIG_SMP
12static int
13select_task_rq_stop(struct task_struct *p, int cpu, int flags)
14{
15 return task_cpu(p); /* stop tasks as never migrate */
16}
17
18static int
19balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
20{
21 return sched_stop_runnable(rq);
22}
23#endif /* CONFIG_SMP */
24
25static void
26check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
27{
28 /* we're never preempted */
29}
30
31static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
32{
33 stop->se.exec_start = rq_clock_task(rq);
34}
35
36static struct task_struct *pick_task_stop(struct rq *rq)
37{
38 if (!sched_stop_runnable(rq))
39 return NULL;
40
41 return rq->stop;
42}
43
44static struct task_struct *pick_next_task_stop(struct rq *rq)
45{
46 struct task_struct *p = pick_task_stop(rq);
47
48 if (p)
49 set_next_task_stop(rq, p, true);
50
51 return p;
52}
53
54static void
55enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
56{
57 add_nr_running(rq, 1);
58}
59
60static void
61dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
62{
63 sub_nr_running(rq, 1);
64}
65
66static void yield_task_stop(struct rq *rq)
67{
68 BUG(); /* the stop task should never yield, its pointless. */
69}
70
71static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
72{
73 struct task_struct *curr = rq->curr;
74 u64 now, delta_exec;
75
76 now = rq_clock_task(rq);
77 delta_exec = now - curr->se.exec_start;
78 if (unlikely((s64)delta_exec < 0))
79 delta_exec = 0;
80
81 schedstat_set(curr->stats.exec_max,
82 max(curr->stats.exec_max, delta_exec));
83
84 update_current_exec_runtime(curr, now, delta_exec);
85}
86
87/*
88 * scheduler tick hitting a task of our scheduling class.
89 *
90 * NOTE: This function can be called remotely by the tick offload that
91 * goes along full dynticks. Therefore no local assumption can be made
92 * and everything must be accessed through the @rq and @curr passed in
93 * parameters.
94 */
95static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
96{
97}
98
99static void switched_to_stop(struct rq *rq, struct task_struct *p)
100{
101 BUG(); /* its impossible to change to this class */
102}
103
104static void
105prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
106{
107 BUG(); /* how!?, what priority? */
108}
109
110static void update_curr_stop(struct rq *rq)
111{
112}
113
114/*
115 * Simple, special scheduling class for the per-CPU stop tasks:
116 */
117DEFINE_SCHED_CLASS(stop) = {
118
119 .enqueue_task = enqueue_task_stop,
120 .dequeue_task = dequeue_task_stop,
121 .yield_task = yield_task_stop,
122
123 .check_preempt_curr = check_preempt_curr_stop,
124
125 .pick_next_task = pick_next_task_stop,
126 .put_prev_task = put_prev_task_stop,
127 .set_next_task = set_next_task_stop,
128
129#ifdef CONFIG_SMP
130 .balance = balance_stop,
131 .pick_task = pick_task_stop,
132 .select_task_rq = select_task_rq_stop,
133 .set_cpus_allowed = set_cpus_allowed_common,
134#endif
135
136 .task_tick = task_tick_stop,
137
138 .prio_changed = prio_changed_stop,
139 .switched_to = switched_to_stop,
140 .update_curr = update_curr_stop,
141};
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
11#ifdef CONFIG_SMP
12static int
13select_task_rq_stop(struct task_struct *p, int cpu, int flags)
14{
15 return task_cpu(p); /* stop tasks as never migrate */
16}
17
18static int
19balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
20{
21 return sched_stop_runnable(rq);
22}
23#endif /* CONFIG_SMP */
24
25static void
26wakeup_preempt_stop(struct rq *rq, struct task_struct *p, int flags)
27{
28 /* we're never preempted */
29}
30
31static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
32{
33 stop->se.exec_start = rq_clock_task(rq);
34}
35
36static struct task_struct *pick_task_stop(struct rq *rq)
37{
38 if (!sched_stop_runnable(rq))
39 return NULL;
40
41 return rq->stop;
42}
43
44static struct task_struct *pick_next_task_stop(struct rq *rq)
45{
46 struct task_struct *p = pick_task_stop(rq);
47
48 if (p)
49 set_next_task_stop(rq, p, true);
50
51 return p;
52}
53
54static void
55enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
56{
57 add_nr_running(rq, 1);
58}
59
60static void
61dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
62{
63 sub_nr_running(rq, 1);
64}
65
66static void yield_task_stop(struct rq *rq)
67{
68 BUG(); /* the stop task should never yield, its pointless. */
69}
70
71static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
72{
73 update_curr_common(rq);
74}
75
76/*
77 * scheduler tick hitting a task of our scheduling class.
78 *
79 * NOTE: This function can be called remotely by the tick offload that
80 * goes along full dynticks. Therefore no local assumption can be made
81 * and everything must be accessed through the @rq and @curr passed in
82 * parameters.
83 */
84static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
85{
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 void update_curr_stop(struct rq *rq)
100{
101}
102
103/*
104 * Simple, special scheduling class for the per-CPU stop tasks:
105 */
106DEFINE_SCHED_CLASS(stop) = {
107
108 .enqueue_task = enqueue_task_stop,
109 .dequeue_task = dequeue_task_stop,
110 .yield_task = yield_task_stop,
111
112 .wakeup_preempt = wakeup_preempt_stop,
113
114 .pick_next_task = pick_next_task_stop,
115 .put_prev_task = put_prev_task_stop,
116 .set_next_task = set_next_task_stop,
117
118#ifdef CONFIG_SMP
119 .balance = balance_stop,
120 .pick_task = pick_task_stop,
121 .select_task_rq = select_task_rq_stop,
122 .set_cpus_allowed = set_cpus_allowed_common,
123#endif
124
125 .task_tick = task_tick_stop,
126
127 .prio_changed = prio_changed_stop,
128 .switched_to = switched_to_stop,
129 .update_curr = update_curr_stop,
130};