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 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  */
  17 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p)
  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
  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  */
  33 static void
  34 dequeue_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
  42 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
  43 {
  44 }
  45
  46 #ifdef CONFIG_SMP
  47 static unsigned long
  48 load_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
  56 static int
  57 move_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
  64 static void task_tick_idle(struct rq *rq, struct task_struct *curr)
  65 {
  66 }
  67
  68 static void set_curr_task_idle(struct rq *rq)
  69 {
  70 }
  71
  72 /*
  73  * Simple, special scheduling class for the per-CPU idle tasks:
  74  */
  75 const 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 #ifdef CONFIG_SMP
  82         .select_task_rq         = select_task_rq_idle,
  83 #endif /* CONFIG_SMP */
  84
  85         .check_preempt_curr     = check_preempt_curr_idle,
  86
  87         .pick_next_task         = pick_next_task_idle,
  88         .put_prev_task          = put_prev_task_idle,
  89
  90 #ifdef CONFIG_SMP
  91         .load_balance           = load_balance_idle,
  92         .move_one_task          = move_one_task_idle,
  93 #endif
  94
  95         .set_curr_task          = set_curr_task_idle,
  96         .task_tick              = task_tick_idle,
  97         /* no .task_new for idle tasks */
  98 };