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
13 static int
select_task_rq_stop(struct task_struct * p,int cpu,int flags)14 select_task_rq_stop(struct task_struct *p, int cpu, int flags)
15 {
16 return task_cpu(p); /* stop tasks as never migrate */
17 }
18
19 static int
balance_stop(struct rq * rq,struct task_struct * prev,struct rq_flags * rf)20 balance_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
26 static void
check_preempt_curr_stop(struct rq * rq,struct task_struct * p,int flags)27 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
28 {
29 /* we're never preempted */
30 }
31
set_next_task_stop(struct rq * rq,struct task_struct * stop,bool first)32 static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
33 {
34 stop->se.exec_start = rq_clock_task(rq);
35 }
36
pick_task_stop(struct rq * rq)37 static struct task_struct *pick_task_stop(struct rq *rq)
38 {
39 if (!sched_stop_runnable(rq))
40 return NULL;
41
42 return rq->stop;
43 }
44
pick_next_task_stop(struct rq * rq)45 static struct task_struct *pick_next_task_stop(struct rq *rq)
46 {
47 struct task_struct *p = pick_task_stop(rq);
48
49 if (p)
50 set_next_task_stop(rq, p, true);
51
52 return p;
53 }
54
55 static void
enqueue_task_stop(struct rq * rq,struct task_struct * p,int flags)56 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
57 {
58 add_nr_running(rq, 1);
59 }
60
61 static void
dequeue_task_stop(struct rq * rq,struct task_struct * p,int flags)62 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
63 {
64 sub_nr_running(rq, 1);
65 }
66
yield_task_stop(struct rq * rq)67 static void yield_task_stop(struct rq *rq)
68 {
69 BUG(); /* the stop task should never yield, its pointless. */
70 }
71
put_prev_task_stop(struct rq * rq,struct task_struct * prev)72 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
73 {
74 struct task_struct *curr = rq->curr;
75 u64 delta_exec;
76
77 delta_exec = rq_clock_task(rq) - curr->se.exec_start;
78 if (unlikely((s64)delta_exec < 0))
79 delta_exec = 0;
80
81 schedstat_set(curr->se.statistics.exec_max,
82 max(curr->se.statistics.exec_max, delta_exec));
83
84 curr->se.sum_exec_runtime += delta_exec;
85 account_group_exec_runtime(curr, delta_exec);
86
87 curr->se.exec_start = rq_clock_task(rq);
88 cgroup_account_cputime(curr, delta_exec);
89 }
90
91 /*
92 * scheduler tick hitting a task of our scheduling class.
93 *
94 * NOTE: This function can be called remotely by the tick offload that
95 * goes along full dynticks. Therefore no local assumption can be made
96 * and everything must be accessed through the @rq and @curr passed in
97 * parameters.
98 */
task_tick_stop(struct rq * rq,struct task_struct * curr,int queued)99 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
100 {
101 }
102
switched_to_stop(struct rq * rq,struct task_struct * p)103 static void switched_to_stop(struct rq *rq, struct task_struct *p)
104 {
105 BUG(); /* its impossible to change to this class */
106 }
107
108 static void
prio_changed_stop(struct rq * rq,struct task_struct * p,int oldprio)109 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
110 {
111 BUG(); /* how!?, what priority? */
112 }
113
update_curr_stop(struct rq * rq)114 static void update_curr_stop(struct rq *rq)
115 {
116 }
117
118 /*
119 * Simple, special scheduling class for the per-CPU stop tasks:
120 */
121 DEFINE_SCHED_CLASS(stop) = {
122
123 .enqueue_task = enqueue_task_stop,
124 .dequeue_task = dequeue_task_stop,
125 .yield_task = yield_task_stop,
126
127 .check_preempt_curr = check_preempt_curr_stop,
128
129 .pick_next_task = pick_next_task_stop,
130 .put_prev_task = put_prev_task_stop,
131 .set_next_task = set_next_task_stop,
132
133 #ifdef CONFIG_SMP
134 .balance = balance_stop,
135 .pick_task = pick_task_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 .prio_changed = prio_changed_stop,
143 .switched_to = switched_to_stop,
144 .update_curr = update_curr_stop,
145 };
146
