LXR linux/kernel/sched

   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
   9static 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 */
  17static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
  18{
  19        resched_task(rq->idle);
  20}
  21
  22static 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 */
  34static void
  35dequeue_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
  43static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
  44{
  45}
  46
  47#ifdef CONFIG_SMP
  48static unsigned long
  49load_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
  57static int
  58move_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
  65static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  66{
  67}
  68
  69static void set_curr_task_idle(struct rq *rq)
  70{
  71}
  72
  73static 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
  83static 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
 100unsigned int get_rr_interval_idle(struct task_struct *task)
 101{
 102        return 0;
 103}
 104
 105/*
 106 * Simple, special scheduling class for the per-CPU idle tasks:
 107 */
 108static const struct sched_class idle_sched_class = {
 109        /* .next is NULL */
 110        /* no enqueue/yield_task for idle tasks */
 111
 112        /* dequeue is not valid, we print a debug message there: */
 113        .dequeue_task           = dequeue_task_idle,
 114
 115        .check_preempt_curr     = check_preempt_curr_idle,
 116
 117        .pick_next_task         = pick_next_task_idle,
 118        .put_prev_task          = put_prev_task_idle,
 119
 120#ifdef CONFIG_SMP
 121        .select_task_rq         = select_task_rq_idle,
 122
 123        .load_balance           = load_balance_idle,
 124        .move_one_task          = move_one_task_idle,
 125#endif
 126
 127        .set_curr_task          = set_curr_task_idle,
 128        .task_tick              = task_tick_idle,
 129
 130        .get_rr_interval        = get_rr_interval_idle,
 131
 132        .prio_changed           = prio_changed_idle,
 133        .switched_to            = switched_to_idle,
 134
 135        /* no .task_new for idle tasks */
 136};
 137