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, int queued)
  65 {
  66 }
  67
  68 static void set_curr_task_idle(struct rq *rq)
  69 {
  70 }
  71
  72 static 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);
  80 }
  81
  82 static 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);
  97 }
  98
  99 /*
 100  * Simple, special scheduling class for the per-CPU idle tasks:
 101  */
 102 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 #ifdef CONFIG_SMP
 109         .select_task_rq         = select_task_rq_idle,
 110 #endif /* CONFIG_SMP */
 111
 112         .check_preempt_curr     = check_preempt_curr_idle,
 113
 114         .pick_next_task         = pick_next_task_idle,
 115         .put_prev_task          = put_prev_task_idle,
 116
 117 #ifdef CONFIG_SMP
 118         .load_balance           = load_balance_idle,
 119         .move_one_task          = move_one_task_idle,
 120 #endif
 121
 122         .set_curr_task          = set_curr_task_idle,
 123         .task_tick              = task_tick_idle,
 124
 125         .prio_changed           = prio_changed_idle,
 126         .switched_to            = switched_to_idle,
 127
 128         /* no .task_new for idle tasks */
 129 };