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 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
  19 static void
  20 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  21 {
  22         resched_task(rq->curr); /* we preempt everything */
  23 }
  24
  25 static struct task_struct *pick_next_task_stop(struct rq *rq)
  26 {
  27         struct task_struct *stop = rq->stop;
  28
  29         if (stop && stop->state == TASK_RUNNING)
  30                 return stop;
  31
  32         return NULL;
  33 }
  34
  35 static void
  36 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  37 {
  38 }
  39
  40 static void
  41 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  42 {
  43 }
  44
  45 static void yield_task_stop(struct rq *rq)
  46 {
  47         BUG(); /* the stop task should never yield, its pointless. */
  48 }
  49
  50 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  51 {
  52 }
  53
  54 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  55 {
  56 }
  57
  58 static void set_curr_task_stop(struct rq *rq)
  59 {
  60 }
  61
  62 static void switched_to_stop(struct rq *rq, struct task_struct *p,
  63                              int running)
  64 {
  65         BUG(); /* its impossible to change to this class */
  66 }
  67
  68 static void prio_changed_stop(struct rq *rq, struct task_struct *p,
  69                               int oldprio, int running)
  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
 107         /* no .task_new for stop tasks */
 108 };