linux/kernel/sched_stoptask.c
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   1/*
   2 * stop-task scheduling class.
   3 *
   4 * The stop task is the highest priority task in the system, it preempts
   5 * everything and will be preempted by nothing.
   6 *
   7 * See kernel/stop_machine.c
   8 */
   9
  10#ifdef CONFIG_SMP
  11static int
  12select_task_rq_stop(struct rq *rq, struct task_struct *p,
  13                    int sd_flag, int flags)
  14{
  15        return task_cpu(p); /* stop tasks as never migrate */
  16}
  17#endif /* CONFIG_SMP */
  18
  19static void
  20check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  21{
  22        /* we're never preempted */
  23}
  24
  25static struct task_struct *pick_next_task_stop(struct rq *rq)
  26{
  27        struct task_struct *stop = rq->stop;
  28
  29        if (stop && stop->se.on_rq)
  30                return stop;
  31
  32        return NULL;
  33}
  34
  35static void
  36enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  37{
  38}
  39
  40static void
  41dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  42{
  43}
  44
  45static void yield_task_stop(struct rq *rq)
  46{
  47        BUG(); /* the stop task should never yield, its pointless. */
  48}
  49
  50static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  51{
  52}
  53
  54static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  55{
  56}
  57
  58static void set_curr_task_stop(struct rq *rq)
  59{
  60}
  61
  62static void switched_to_stop(struct rq *rq, struct task_struct *p)
  63{
  64        BUG(); /* its impossible to change to this class */
  65}
  66
  67static void
  68prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  69{
  70        BUG(); /* how!?, what priority? */
  71}
  72
  73static unsigned int
  74get_rr_interval_stop(struct rq *rq, struct task_struct *task)
  75{
  76        return 0;
  77}
  78
  79/*
  80 * Simple, special scheduling class for the per-CPU stop tasks:
  81 */
  82static const struct sched_class stop_sched_class = {
  83        .next                   = &rt_sched_class,
  84
  85        .enqueue_task           = enqueue_task_stop,
  86        .dequeue_task           = dequeue_task_stop,
  87        .yield_task             = yield_task_stop,
  88
  89        .check_preempt_curr     = check_preempt_curr_stop,
  90
  91        .pick_next_task         = pick_next_task_stop,
  92        .put_prev_task          = put_prev_task_stop,
  93
  94#ifdef CONFIG_SMP
  95        .select_task_rq         = select_task_rq_stop,
  96#endif
  97
  98        .set_curr_task          = set_curr_task_stop,
  99        .task_tick              = task_tick_stop,
 100
 101        .get_rr_interval        = get_rr_interval_stop,
 102
 103        .prio_changed           = prio_changed_stop,
 104        .switched_to            = switched_to_stop,
 105};
 106