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