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         inc_nr_running(rq);
  38 }
  39
  40 static void
  41 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  42 {
  43         dec_nr_running(rq);
  44 }
  45
  46 static void yield_task_stop(struct rq *rq)
  47 {
  48         BUG(); /* the stop task should never yield, its pointless. */
  49 }
  50
  51 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  52 {
  53 }
  54
  55 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  56 {
  57 }
  58
  59 static void set_curr_task_stop(struct rq *rq)
  60 {
  61 }
  62
  63 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  64 {
  65         BUG(); /* its impossible to change to this class */
  66 }
  67
  68 static void
  69 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  70 {
  71         BUG(); /* how!?, what priority? */
  72 }
  73
  74 static unsigned int
  75 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
  76 {
  77         return 0;
  78 }
  79
  80 /*
  81  * Simple, special scheduling class for the per-CPU stop tasks:
  82  */
  83 static const struct sched_class stop_sched_class = {
  84         .next                   = &rt_sched_class,
  85
  86         .enqueue_task           = enqueue_task_stop,
  87         .dequeue_task           = dequeue_task_stop,
  88         .yield_task             = yield_task_stop,
  89
  90         .check_preempt_curr     = check_preempt_curr_stop,
  91
  92         .pick_next_task         = pick_next_task_stop,
  93         .put_prev_task          = put_prev_task_stop,
  94
  95 #ifdef CONFIG_SMP
  96         .select_task_rq         = select_task_rq_stop,
  97 #endif
  98
  99         .set_curr_task          = set_curr_task_stop,
 100         .task_tick              = task_tick_stop,
 101
 102         .get_rr_interval        = get_rr_interval_stop,
 103
 104         .prio_changed           = prio_changed_stop,
 105         .switched_to            = switched_to_stop,
 106 };