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         spin_unlock_irq(&rq->lock);
  39         printk(KERN_ERR "bad: scheduling from the idle thread!\n");
  40         dump_stack();
  41         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 #ifdef CONFIG_SMP
  49 static unsigned long
  50 load_balance_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
  51                   unsigned long max_load_move,
  52                   struct sched_domain *sd, enum cpu_idle_type idle,
  53                   int *all_pinned, int *this_best_prio)
  54 {
  55         return 0;
  56 }
  57
  58 static int
  59 move_one_task_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
  60                    struct sched_domain *sd, enum cpu_idle_type idle)
  61 {
  62         return 0;
  63 }
  64 #endif
  65
  66 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  67 {
  68 }
  69
  70 static void set_curr_task_idle(struct rq *rq)
  71 {
  72 }
  73
  74 static void switched_to_idle(struct rq *rq, struct task_struct *p,
  75                              int running)
  76 {
  77         /* Can this actually happen?? */
  78         if (running)
  79                 resched_task(rq->curr);
  80         else
  81                 check_preempt_curr(rq, p, 0);
  82 }
  83
  84 static void prio_changed_idle(struct rq *rq, struct task_struct *p,
  85                               int oldprio, int running)
  86 {
  87         /* This can happen for hot plug CPUS */
  88
  89         /*
  90          * Reschedule if we are currently running on this runqueue and
  91          * our priority decreased, or if we are not currently running on
  92          * this runqueue and our priority is higher than the current's
  93          */
  94         if (running) {
  95                 if (p->prio > oldprio)
  96                         resched_task(rq->curr);
  97         } else
  98                 check_preempt_curr(rq, p, 0);
  99 }
 100
 101 unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
 102 {
 103         return 0;
 104 }
 105
 106 /*
 107  * Simple, special scheduling class for the per-CPU idle tasks:
 108  */
 109 static const struct sched_class idle_sched_class = {
 110         /* .next is NULL */
 111         /* no enqueue/yield_task for idle tasks */
 112
 113         /* dequeue is not valid, we print a debug message there: */
 114         .dequeue_task           = dequeue_task_idle,
 115
 116         .check_preempt_curr     = check_preempt_curr_idle,
 117
 118         .pick_next_task         = pick_next_task_idle,
 119         .put_prev_task          = put_prev_task_idle,
 120
 121 #ifdef CONFIG_SMP
 122         .select_task_rq         = select_task_rq_idle,
 123
 124         .load_balance           = load_balance_idle,
 125         .move_one_task          = move_one_task_idle,
 126 #endif
 127
 128         .set_curr_task          = set_curr_task_idle,
 129         .task_tick              = task_tick_idle,
 130
 131         .get_rr_interval        = get_rr_interval_idle,
 132
 133         .prio_changed           = prio_changed_idle,
 134         .switched_to            = switched_to_idle,
 135
 136         /* no .task_new for idle tasks */
 137 };