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
12 static int
select_task_rq_stop(struct task_struct * p,int cpu,int flags)13 select_task_rq_stop(struct task_struct *p, int cpu, int flags)
14 {
15 return task_cpu(p); /* stop tasks as never migrate */
16 }
17
18 static int
balance_stop(struct rq * rq,struct task_struct * prev,struct rq_flags * rf)19 balance_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
25 static void
check_preempt_curr_stop(struct rq * rq,struct task_struct * p,int flags)26 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
27 {
28 /* we're never preempted */
29 }
30
set_next_task_stop(struct rq * rq,struct task_struct * stop,bool first)31 static 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
pick_task_stop(struct rq * rq)36 static 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
pick_next_task_stop(struct rq * rq)44 static 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
54 static void
enqueue_task_stop(struct rq * rq,struct task_struct * p,int flags)55 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
56 {
57 add_nr_running(rq, 1);
58 }
59
60 static void
dequeue_task_stop(struct rq * rq,struct task_struct * p,int flags)61 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
62 {
63 sub_nr_running(rq, 1);
64 }
65
yield_task_stop(struct rq * rq)66 static void yield_task_stop(struct rq *rq)
67 {
68 BUG(); /* the stop task should never yield, its pointless. */
69 }
70
put_prev_task_stop(struct rq * rq,struct task_struct * prev)71 static 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 */
task_tick_stop(struct rq * rq,struct task_struct * curr,int queued)95 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
96 {
97 }
98
switched_to_stop(struct rq * rq,struct task_struct * p)99 static void switched_to_stop(struct rq *rq, struct task_struct *p)
100 {
101 BUG(); /* its impossible to change to this class */
102 }
103
104 static void
prio_changed_stop(struct rq * rq,struct task_struct * p,int oldprio)105 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
106 {
107 BUG(); /* how!?, what priority? */
108 }
109
update_curr_stop(struct rq * rq)110 static void update_curr_stop(struct rq *rq)
111 {
112 }
113
114 /*
115 * Simple, special scheduling class for the per-CPU stop tasks:
116 */
117 DEFINE_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 };
142
