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 sd_flag,int flags)14 select_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
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_next_task_stop(struct rq * rq)37 static struct task_struct *pick_next_task_stop(struct rq *rq)
38 {
39 if (!sched_stop_runnable(rq))
40 return NULL;
41
42 set_next_task_stop(rq, rq->stop, true);
43 return rq->stop;
44 }
45
46 static void
enqueue_task_stop(struct rq * rq,struct task_struct * p,int flags)47 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
48 {
49 add_nr_running(rq, 1);
50 }
51
52 static void
dequeue_task_stop(struct rq * rq,struct task_struct * p,int flags)53 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
54 {
55 sub_nr_running(rq, 1);
56 }
57
yield_task_stop(struct rq * rq)58 static void yield_task_stop(struct rq *rq)
59 {
60 BUG(); /* the stop task should never yield, its pointless. */
61 }
62
put_prev_task_stop(struct rq * rq,struct task_struct * prev)63 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
64 {
65 struct task_struct *curr = rq->curr;
66 u64 delta_exec;
67
68 delta_exec = rq_clock_task(rq) - curr->se.exec_start;
69 if (unlikely((s64)delta_exec < 0))
70 delta_exec = 0;
71
72 schedstat_set(curr->se.statistics.exec_max,
73 max(curr->se.statistics.exec_max, delta_exec));
74
75 curr->se.sum_exec_runtime += delta_exec;
76 account_group_exec_runtime(curr, delta_exec);
77
78 curr->se.exec_start = rq_clock_task(rq);
79 cgroup_account_cputime(curr, delta_exec);
80 }
81
82 /*
83 * scheduler tick hitting a task of our scheduling class.
84 *
85 * NOTE: This function can be called remotely by the tick offload that
86 * goes along full dynticks. Therefore no local assumption can be made
87 * and everything must be accessed through the @rq and @curr passed in
88 * parameters.
89 */
task_tick_stop(struct rq * rq,struct task_struct * curr,int queued)90 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
91 {
92 }
93
switched_to_stop(struct rq * rq,struct task_struct * p)94 static void switched_to_stop(struct rq *rq, struct task_struct *p)
95 {
96 BUG(); /* its impossible to change to this class */
97 }
98
99 static void
prio_changed_stop(struct rq * rq,struct task_struct * p,int oldprio)100 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
101 {
102 BUG(); /* how!?, what priority? */
103 }
104
update_curr_stop(struct rq * rq)105 static void update_curr_stop(struct rq *rq)
106 {
107 }
108
109 /*
110 * Simple, special scheduling class for the per-CPU stop tasks:
111 */
112 const struct sched_class stop_sched_class
113 __section("__stop_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 .set_next_task = set_next_task_stop,
124
125 #ifdef CONFIG_SMP
126 .balance = balance_stop,
127 .select_task_rq = select_task_rq_stop,
128 .set_cpus_allowed = set_cpus_allowed_common,
129 #endif
130
131 .task_tick = task_tick_stop,
132
133 .prio_changed = prio_changed_stop,
134 .switched_to = switched_to_stop,
135 .update_curr = update_curr_stop,
136 };
137