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 select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
  10 {
  11         return task_cpu(p); /* IDLE tasks as never migrated */
  12 }
  13 #endif /* CONFIG_SMP */
  14 /*
  15  * Idle tasks are unconditionally rescheduled:
  16  */
  17 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
  18 {
  19         resched_task(rq->idle);
  20 }
  21
  22 static struct task_struct *pick_next_task_idle(struct rq *rq)
  23 {
  24         schedstat_inc(rq, sched_goidle);
  25         /* adjust the active tasks as we might go into a long sleep */
  26         calc_load_account_active(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  */
  34 static void
  35 dequeue_task_idle(struct rq *rq, struct task_struct *p, int sleep)
  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
  43 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
  44 {
  45 }
  46
  47 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  48 {
  49 }
  50
  51 static void set_curr_task_idle(struct rq *rq)
  52 {
  53 }
  54
  55 static 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
  65 static 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
  82 static 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  */
  90 static 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 };