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, int sync)
  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         spin_unlock_irq(&rq->lock);
  38         printk(KERN_ERR "bad: scheduling from the idle thread!\n");
  39         dump_stack();
  40         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 #ifdef CONFIG_SMP
  48 static unsigned long
  49 load_balance_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
  50                   unsigned long max_load_move,
  51                   struct sched_domain *sd, enum cpu_idle_type idle,
  52                   int *all_pinned, int *this_best_prio)
  53 {
  54         return 0;
  55 }
  56
  57 static int
  58 move_one_task_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
  59                    struct sched_domain *sd, enum cpu_idle_type idle)
  60 {
  61         return 0;
  62 }
  63 #endif
  64
  65 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  66 {
  67 }
  68
  69 static void set_curr_task_idle(struct rq *rq)
  70 {
  71 }
  72
  73 static void switched_to_idle(struct rq *rq, struct task_struct *p,
  74                              int running)
  75 {
  76         /* Can this actually happen?? */
  77         if (running)
  78                 resched_task(rq->curr);
  79         else
  80                 check_preempt_curr(rq, p, 0);
  81 }
  82
  83 static void prio_changed_idle(struct rq *rq, struct task_struct *p,
  84                               int oldprio, int running)
  85 {
  86         /* This can happen for hot plug CPUS */
  87
  88         /*
  89          * Reschedule if we are currently running on this runqueue and
  90          * our priority decreased, or if we are not currently running on
  91          * this runqueue and our priority is higher than the current's
  92          */
  93         if (running) {
  94                 if (p->prio > oldprio)
  95                         resched_task(rq->curr);
  96         } else
  97                 check_preempt_curr(rq, p, 0);
  98 }
  99
 100 /*
 101  * Simple, special scheduling class for the per-CPU idle tasks:
 102  */
 103 static const struct sched_class idle_sched_class = {
 104         /* .next is NULL */
 105         /* no enqueue/yield_task for idle tasks */
 106
 107         /* dequeue is not valid, we print a debug message there: */
 108         .dequeue_task           = dequeue_task_idle,
 109
 110         .check_preempt_curr     = check_preempt_curr_idle,
 111
 112         .pick_next_task         = pick_next_task_idle,
 113         .put_prev_task          = put_prev_task_idle,
 114
 115 #ifdef CONFIG_SMP
 116         .select_task_rq         = select_task_rq_idle,
 117
 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 };