kernel/sched/stop_task.c

   1 #include "sched.h"
   2
   3 /*
   4  * stop-task scheduling class.
   5  *
   6  * The stop task is the highest priority task in the system, it preempts
   7  * everything and will be preempted by nothing.
   8  *
   9  * See kernel/stop_machine.c
  10  */
  11
  12 #ifdef CONFIG_SMP
  13 static int
  14 select_task_rq_stop(struct task_struct *p, int sd_flag, int flags)
  15 {
  16         return task_cpu(p); /* stop tasks as never migrate */
  17 }
  18 #endif /* CONFIG_SMP */
  19
  20 static void
  21 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  22 {
  23         /* we're never preempted */
  24 }
  25
  26 static struct task_struct *pick_next_task_stop(struct rq *rq)
  27 {
  28         struct task_struct *stop = rq->stop;
  29
  30         if (stop && stop->on_rq)
  31                 return stop;
  32
  33         return NULL;
  34 }
  35
  36 static void
  37 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  38 {
  39         inc_nr_running(rq);
  40 }
  41
  42 static void
  43 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  44 {
  45         dec_nr_running(rq);
  46 }
  47
  48 static void yield_task_stop(struct rq *rq)
  49 {
  50         BUG(); /* the stop task should never yield, its pointless. */
  51 }
  52
  53 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  54 {
  55 }
  56
  57 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  58 {
  59 }
  60
  61 static void set_curr_task_stop(struct rq *rq)
  62 {
  63 }
  64
  65 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  66 {
  67         BUG(); /* its impossible to change to this class */
  68 }
  69
  70 static void
  71 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  72 {
  73         BUG(); /* how!?, what priority? */
  74 }
  75
  76 static unsigned int
  77 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
  78 {
  79         return 0;
  80 }
  81
  82 /*
  83  * Simple, special scheduling class for the per-CPU stop tasks:
  84  */
  85 const struct sched_class stop_sched_class = {
  86         .next                   = &rt_sched_class,
  87
  88         .enqueue_task           = enqueue_task_stop,
  89         .dequeue_task           = dequeue_task_stop,
  90         .yield_task             = yield_task_stop,
  91
  92         .check_preempt_curr     = check_preempt_curr_stop,
  93
  94         .pick_next_task         = pick_next_task_stop,
  95         .put_prev_task          = put_prev_task_stop,
  96
  97 #ifdef CONFIG_SMP
  98         .select_task_rq         = select_task_rq_stop,
  99 #endif
 100
 101         .set_curr_task          = set_curr_task_stop,
 102         .task_tick              = task_tick_stop,
 103
 104         .get_rr_interval        = get_rr_interval_stop,
 105
 106         .prio_changed           = prio_changed_stop,
 107         .switched_to            = switched_to_stop,
 108 };