Root/kernel/sched_idletask.c

1/*
2 * idle-task scheduling class.
3 *
4 * (NOTE: these are not related to SCHED_IDLE tasks which are
5 * handled in sched_fair.c)
6 */
7
8#ifdef CONFIG_SMP
9static int
10select_task_rq_idle(struct rq *rq, struct task_struct *p, int sd_flag, int flags)
11{
12    return task_cpu(p); /* IDLE tasks as never migrated */
13}
14#endif /* CONFIG_SMP */
15/*
16 * Idle tasks are unconditionally rescheduled:
17 */
18static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
19{
20    resched_task(rq->idle);
21}
22
23static struct task_struct *pick_next_task_idle(struct rq *rq)
24{
25    schedstat_inc(rq, sched_goidle);
26    calc_load_account_idle(rq);
27    return rq->idle;
28}
29
30/*
31 * It is not legal to sleep in the idle task - print a warning
32 * message if some code attempts to do it:
33 */
34static void
35dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
36{
37    raw_spin_unlock_irq(&rq->lock);
38    printk(KERN_ERR "bad: scheduling from the idle thread!\n");
39    dump_stack();
40    raw_spin_lock_irq(&rq->lock);
41}
42
43static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
44{
45}
46
47static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
48{
49}
50
51static void set_curr_task_idle(struct rq *rq)
52{
53}
54
55static void switched_to_idle(struct rq *rq, struct task_struct *p,
56                 int running)
57{
58    /* Can this actually happen?? */
59    if (running)
60        resched_task(rq->curr);
61    else
62        check_preempt_curr(rq, p, 0);
63}
64
65static void prio_changed_idle(struct rq *rq, struct task_struct *p,
66                  int oldprio, int running)
67{
68    /* This can happen for hot plug CPUS */
69
70    /*
71     * Reschedule if we are currently running on this runqueue and
72     * our priority decreased, or if we are not currently running on
73     * this runqueue and our priority is higher than the current's
74     */
75    if (running) {
76        if (p->prio > oldprio)
77            resched_task(rq->curr);
78    } else
79        check_preempt_curr(rq, p, 0);
80}
81
82static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
83{
84    return 0;
85}
86
87/*
88 * Simple, special scheduling class for the per-CPU idle tasks:
89 */
90static const struct sched_class idle_sched_class = {
91    /* .next is NULL */
92    /* no enqueue/yield_task for idle tasks */
93
94    /* dequeue is not valid, we print a debug message there: */
95    .dequeue_task = dequeue_task_idle,
96
97    .check_preempt_curr = check_preempt_curr_idle,
98
99    .pick_next_task = pick_next_task_idle,
100    .put_prev_task = put_prev_task_idle,
101
102#ifdef CONFIG_SMP
103    .select_task_rq = select_task_rq_idle,
104#endif
105
106    .set_curr_task = set_curr_task_idle,
107    .task_tick = task_tick_idle,
108
109    .get_rr_interval = get_rr_interval_idle,
110
111    .prio_changed = prio_changed_idle,
112    .switched_to = switched_to_idle,
113
114    /* no .task_new for idle tasks */
115};
116

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