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                 stop->se.exec_start = rq->clock_task;
  30                 return stop;
  31         }
  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         struct task_struct *curr = rq->curr;
  56         u64 delta_exec;
  57
  58         delta_exec = rq->clock_task - curr->se.exec_start;
  59         if (unlikely((s64)delta_exec < 0))
  60                 delta_exec = 0;
  61
  62         schedstat_set(curr->se.statistics.exec_max,
  63                         max(curr->se.statistics.exec_max, delta_exec));
  64
  65         curr->se.sum_exec_runtime += delta_exec;
  66         account_group_exec_runtime(curr, delta_exec);
  67
  68         curr->se.exec_start = rq->clock_task;
  69         cpuacct_charge(curr, delta_exec);
  70 }
  71
  72 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  73 {
  74 }
  75
  76 static void set_curr_task_stop(struct rq *rq)
  77 {
  78         struct task_struct *stop = rq->stop;
  79
  80         stop->se.exec_start = rq->clock_task;
  81 }
  82
  83 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  84 {
  85         BUG(); /* its impossible to change to this class */
  86 }
  87
  88 static void
  89 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  90 {
  91         BUG(); /* how!?, what priority? */
  92 }
  93
  94 static unsigned int
  95 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
  96 {
  97         return 0;
  98 }
  99
 100 /*
 101  * Simple, special scheduling class for the per-CPU stop tasks:
 102  */
 103 static const struct sched_class stop_sched_class = {
 104         .next                   = &rt_sched_class,
 105
 106         .enqueue_task           = enqueue_task_stop,
 107         .dequeue_task           = dequeue_task_stop,
 108         .yield_task             = yield_task_stop,
 109
 110         .check_preempt_curr     = check_preempt_curr_stop,
 111
 112         .pick_next_task         = pick_next_task_stop,
 113         .put_prev_task          = put_prev_task_stop,
 114
 115 #ifdef CONFIG_SMP
 116         .select_task_rq         = select_task_rq_stop,
 117 #endif
 118
 119         .set_curr_task          = set_curr_task_stop,
 120         .task_tick              = task_tick_stop,
 121
 122         .get_rr_interval        = get_rr_interval_stop,
 123
 124         .prio_changed           = prio_changed_stop,
 125         .switched_to            = switched_to_stop,
 126 };