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 task_struct *p, int sd_flag, int flags)
  13{
  14        return task_cpu(p); /* stop tasks as never migrate */
  15}
  16#endif /* CONFIG_SMP */
  17
  18static void
  19check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  20{
  21        /* we're never preempted */
  22}
  23
  24static struct task_struct *pick_next_task_stop(struct rq *rq)
  25{
  26        struct task_struct *stop = rq->stop;
  27
  28        if (stop && stop->on_rq)
  29                return stop;
  30
  31        return NULL;
  32}
  33
  34static void
  35enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  36{
  37}
  38
  39static void
  40dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  41{
  42}
  43
  44static void yield_task_stop(struct rq *rq)
  45{
  46        BUG(); /* the stop task should never yield, its pointless. */
  47}
  48
  49static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  50{
  51}
  52
  53static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  54{
  55}
  56
  57static void set_curr_task_stop(struct rq *rq)
  58{
  59}
  60
  61static void switched_to_stop(struct rq *rq, struct task_struct *p)
  62{
  63        BUG(); /* its impossible to change to this class */
  64}
  65
  66static void
  67prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  68{
  69        BUG(); /* how!?, what priority? */
  70}
  71
  72static unsigned int
  73get_rr_interval_stop(struct rq *rq, struct task_struct *task)
  74{
  75        return 0;
  76}
  77
  78/*
  79 * Simple, special scheduling class for the per-CPU stop tasks:
  80 */
  81static const struct sched_class stop_sched_class = {
  82        .next                   = &rt_sched_class,
  83
  84        .enqueue_task           = enqueue_task_stop,
  85        .dequeue_task           = dequeue_task_stop,
  86        .yield_task             = yield_task_stop,
  87
  88        .check_preempt_curr     = check_preempt_curr_stop,
  89
  90        .pick_next_task         = pick_next_task_stop,
  91        .put_prev_task          = put_prev_task_stop,
  92
  93#ifdef CONFIG_SMP
  94        .select_task_rq         = select_task_rq_stop,
  95#endif
  96
  97        .set_curr_task          = set_curr_task_stop,
  98        .task_tick              = task_tick_stop,
  99
 100        .get_rr_interval        = get_rr_interval_stop,
 101
 102        .prio_changed           = prio_changed_stop,
 103        .switched_to            = switched_to_stop,
 104};
 105
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