kernel/sched_stoptask.c

   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
  11 static int
  12 select_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
  18 static void
  19 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  20 {
  21         /* we're never preempted */
  22 }
  23
  24 static 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
  34 static void
  35 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  36 {
  37 }
  38
  39 static void
  40 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  41 {
  42 }
  43
  44 static void yield_task_stop(struct rq *rq)
  45 {
  46         BUG(); /* the stop task should never yield, its pointless. */
  47 }
  48
  49 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  50 {
  51 }
  52
  53 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  54 {
  55 }
  56
  57 static void set_curr_task_stop(struct rq *rq)
  58 {
  59 }
  60
  61 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  62 {
  63         BUG(); /* its impossible to change to this class */
  64 }
  65
  66 static void
  67 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  68 {
  69         BUG(); /* how!?, what priority? */
  70 }
  71
  72 static unsigned int
  73 get_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  */
  81 static 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 };