linux/kernel/sched_idletask.c
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   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