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 select_task_rq_idle(struct task_struct *p, int sync)
  10{
  11        return task_cpu(p); /* IDLE tasks as never migrated */
  12}
  13#endif /* CONFIG_SMP */
  14/*
  15 * Idle tasks are unconditionally rescheduled:
  16 */
  17static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int sync)
  18{
  19        resched_task(rq->idle);
  20}
  21
  22static struct task_struct *pick_next_task_idle(struct rq *rq)
  23{
  24        schedstat_inc(rq, sched_goidle);
  25
  26        return rq->idle;
  27}
  28
  29/*
  30 * It is not legal to sleep in the idle task - print a warning
  31 * message if some code attempts to do it:
  32 */
  33static void
  34dequeue_task_idle(struct rq *rq, struct task_struct *p, int sleep)
  35{
  36        spin_unlock_irq(&rq->lock);
  37        printk(KERN_ERR "bad: scheduling from the idle thread!\n");
  38        dump_stack();
  39        spin_lock_irq(&rq->lock);
  40}
  41
  42static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
  43{
  44}
  45
  46#ifdef CONFIG_SMP
  47static unsigned long
  48load_balance_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
  49                  unsigned long max_load_move,
  50                  struct sched_domain *sd, enum cpu_idle_type idle,
  51                  int *all_pinned, int *this_best_prio)
  52{
  53        return 0;
  54}
  55
  56static int
  57move_one_task_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
  58                   struct sched_domain *sd, enum cpu_idle_type idle)
  59{
  60        return 0;
  61}
  62#endif
  63
  64static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  65{
  66}
  67
  68static void set_curr_task_idle(struct rq *rq)
  69{
  70}
  71
  72static void switched_to_idle(struct rq *rq, struct task_struct *p,
  73                             int running)
  74{
  75        /* Can this actually happen?? */
  76        if (running)
  77                resched_task(rq->curr);
  78        else
  79                check_preempt_curr(rq, p, 0);
  80}
  81
  82static void prio_changed_idle(struct rq *rq, struct task_struct *p,
  83                              int oldprio, int running)
  84{
  85        /* This can happen for hot plug CPUS */
  86
  87        /*
  88         * Reschedule if we are currently running on this runqueue and
  89         * our priority decreased, or if we are not currently running on
  90         * this runqueue and our priority is higher than the current's
  91         */
  92        if (running) {
  93                if (p->prio > oldprio)
  94                        resched_task(rq->curr);
  95        } else
  96                check_preempt_curr(rq, p, 0);
  97}
  98
  99/*
 100 * Simple, special scheduling class for the per-CPU idle tasks:
 101 */
 102static const struct sched_class idle_sched_class = {
 103        /* .next is NULL */
 104        /* no enqueue/yield_task for idle tasks */
 105
 106        /* dequeue is not valid, we print a debug message there: */
 107        .dequeue_task           = dequeue_task_idle,
 108
 109        .check_preempt_curr     = check_preempt_curr_idle,
 110
 111        .pick_next_task         = pick_next_task_idle,
 112        .put_prev_task          = put_prev_task_idle,
 113
 114#ifdef CONFIG_SMP
 115        .select_task_rq         = select_task_rq_idle,
 116
 117        .load_balance           = load_balance_idle,
 118        .move_one_task          = move_one_task_idle,
 119#endif
 120
 121        .set_curr_task          = set_curr_task_idle,
 122        .task_tick              = task_tick_idle,
 123
 124        .prio_changed           = prio_changed_idle,
 125        .switched_to            = switched_to_idle,
 126
 127        /* no .task_new for idle tasks */
 128};
 129