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
   9 static int
  10 select_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  */
  18 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
  19 {
  20         resched_task(rq->idle);
  21 }
  22
  23 static struct task_struct *pick_next_task_idle(struct rq *rq)
  24 {
  25         schedstat_inc(rq, sched_goidle);
  26         /* adjust the active tasks as we might go into a long sleep */
  27         calc_load_account_active(rq);
  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  */
  35 static void
  36 dequeue_task_idle(struct rq *rq, struct task_struct *p, int sleep)
  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
  44 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
  45 {
  46 }
  47
  48 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  49 {
  50 }
  51
  52 static void set_curr_task_idle(struct rq *rq)
  53 {
  54 }
  55
  56 static void switched_to_idle(struct rq *rq, struct task_struct *p,
  57                              int running)
  58 {
  59         /* Can this actually happen?? */
  60         if (running)
  61                 resched_task(rq->curr);
  62         else
  63                 check_preempt_curr(rq, p, 0);
  64 }
  65
  66 static void prio_changed_idle(struct rq *rq, struct task_struct *p,
  67                               int oldprio, int running)
  68 {
  69         /* This can happen for hot plug CPUS */
  70
  71         /*
  72          * Reschedule if we are currently running on this runqueue and
  73          * our priority decreased, or if we are not currently running on
  74          * this runqueue and our priority is higher than the current's
  75          */
  76         if (running) {
  77                 if (p->prio > oldprio)
  78                         resched_task(rq->curr);
  79         } else
  80                 check_preempt_curr(rq, p, 0);
  81 }
  82
  83 static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
  84 {
  85         return 0;
  86 }
  87
  88 /*
  89  * Simple, special scheduling class for the per-CPU idle tasks:
  90  */
  91 static const struct sched_class idle_sched_class = {
  92         /* .next is NULL */
  93         /* no enqueue/yield_task for idle tasks */
  94
  95         /* dequeue is not valid, we print a debug message there: */
  96         .dequeue_task           = dequeue_task_idle,
  97
  98         .check_preempt_curr     = check_preempt_curr_idle,
  99
 100         .pick_next_task         = pick_next_task_idle,
 101         .put_prev_task          = put_prev_task_idle,
 102
 103 #ifdef CONFIG_SMP
 104         .select_task_rq         = select_task_rq_idle,
 105 #endif
 106
 107         .set_curr_task          = set_curr_task_idle,
 108         .task_tick              = task_tick_idle,
 109
 110         .get_rr_interval        = get_rr_interval_idle,
 111
 112         .prio_changed           = prio_changed_idle,
 113         .switched_to            = switched_to_idle,
 114
 115         /* no .task_new for idle tasks */
 116 };