1 // SPDX-License-Identifier: GPL-2.0
2 #include "sched.h"
3
4 /*
5 * idle-task scheduling class.
6 *
7 * (NOTE: these are not related to SCHED_IDLE tasks which are
8 * handled in sched/fair.c)
9 */
10
11 #ifdef CONFIG_SMP
12 static int
select_task_rq_idle(struct task_struct * p,int cpu,int sd_flag,int flags,int sibling_count_hint)13 select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags,
14 int sibling_count_hint)
15 {
16 return task_cpu(p); /* IDLE tasks as never migrated */
17 }
18 #endif /* CONFIG_SMP */
19
20 /*
21 * Idle tasks are unconditionally rescheduled:
22 */
check_preempt_curr_idle(struct rq * rq,struct task_struct * p,int flags)23 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
24 {
25 resched_curr(rq);
26 }
27
28 static struct task_struct *
pick_next_task_idle(struct rq * rq,struct task_struct * prev,struct rq_flags * rf)29 pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
30 {
31 put_prev_task(rq, prev);
32 update_idle_core(rq);
33 schedstat_inc(rq->sched_goidle);
34 return rq->idle;
35 }
36
37 /*
38 * It is not legal to sleep in the idle task - print a warning
39 * message if some code attempts to do it:
40 */
41 static void
dequeue_task_idle(struct rq * rq,struct task_struct * p,int flags)42 dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
43 {
44 raw_spin_unlock_irq(&rq->lock);
45 printk(KERN_ERR "bad: scheduling from the idle thread!\n");
46 dump_stack();
47 raw_spin_lock_irq(&rq->lock);
48 }
49
put_prev_task_idle(struct rq * rq,struct task_struct * prev)50 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
51 {
52 rq_last_tick_reset(rq);
53 }
54
task_tick_idle(struct rq * rq,struct task_struct * curr,int queued)55 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
56 {
57 }
58
set_curr_task_idle(struct rq * rq)59 static void set_curr_task_idle(struct rq *rq)
60 {
61 }
62
switched_to_idle(struct rq * rq,struct task_struct * p)63 static void switched_to_idle(struct rq *rq, struct task_struct *p)
64 {
65 BUG();
66 }
67
68 static void
prio_changed_idle(struct rq * rq,struct task_struct * p,int oldprio)69 prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
70 {
71 BUG();
72 }
73
get_rr_interval_idle(struct rq * rq,struct task_struct * task)74 static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
75 {
76 return 0;
77 }
78
update_curr_idle(struct rq * rq)79 static void update_curr_idle(struct rq *rq)
80 {
81 }
82
83 /*
84 * Simple, special scheduling class for the per-CPU idle tasks:
85 */
86 const struct sched_class idle_sched_class = {
87 /* .next is NULL */
88 /* no enqueue/yield_task for idle tasks */
89
90 /* dequeue is not valid, we print a debug message there: */
91 .dequeue_task = dequeue_task_idle,
92
93 .check_preempt_curr = check_preempt_curr_idle,
94
95 .pick_next_task = pick_next_task_idle,
96 .put_prev_task = put_prev_task_idle,
97
98 #ifdef CONFIG_SMP
99 .select_task_rq = select_task_rq_idle,
100 .set_cpus_allowed = set_cpus_allowed_common,
101 #endif
102
103 .set_curr_task = set_curr_task_idle,
104 .task_tick = task_tick_idle,
105
106 .get_rr_interval = get_rr_interval_idle,
107
108 .prio_changed = prio_changed_idle,
109 .switched_to = switched_to_idle,
110 .update_curr = update_curr_idle,
111 };
112