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 cpu, 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 *
  27 pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  28 {
  29         struct task_struct *stop = rq->stop;
  30
  31         if (!stop || !task_on_rq_queued(stop))
  32                 return NULL;
  33
  34         put_prev_task(rq, prev);
  35
  36         stop->se.exec_start = rq_clock_task(rq);
  37
  38         return stop;
  39 }
  40
  41 static void
  42 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  43 {
  44         add_nr_running(rq, 1);
  45 }
  46
  47 static void
  48 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  49 {
  50         sub_nr_running(rq, 1);
  51 }
  52
  53 static void yield_task_stop(struct rq *rq)
  54 {
  55         BUG(); /* the stop task should never yield, its pointless. */
  56 }
  57
  58 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  59 {
  60         struct task_struct *curr = rq->curr;
  61         u64 delta_exec;
  62
  63         delta_exec = rq_clock_task(rq) - curr->se.exec_start;
  64         if (unlikely((s64)delta_exec < 0))
  65                 delta_exec = 0;
  66
  67         schedstat_set(curr->se.statistics.exec_max,
  68                         max(curr->se.statistics.exec_max, delta_exec));
  69
  70         curr->se.sum_exec_runtime += delta_exec;
  71         account_group_exec_runtime(curr, delta_exec);
  72
  73         curr->se.exec_start = rq_clock_task(rq);
  74         cpuacct_charge(curr, delta_exec);
  75 }
  76
  77 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  78 {
  79 }
  80
  81 static void set_curr_task_stop(struct rq *rq)
  82 {
  83         struct task_struct *stop = rq->stop;
  84
  85         stop->se.exec_start = rq_clock_task(rq);
  86 }
  87
  88 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  89 {
  90         BUG(); /* its impossible to change to this class */
  91 }
  92
  93 static void
  94 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  95 {
  96         BUG(); /* how!?, what priority? */
  97 }
  98
  99 static unsigned int
 100 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 101 {
 102         return 0;
 103 }
 104
 105 static void update_curr_stop(struct rq *rq)
 106 {
 107 }
 108
 109 /*
 110  * Simple, special scheduling class for the per-CPU stop tasks:
 111  */
 112 const struct sched_class stop_sched_class = {
 113         .next                   = &dl_sched_class,
 114
 115         .enqueue_task           = enqueue_task_stop,
 116         .dequeue_task           = dequeue_task_stop,
 117         .yield_task             = yield_task_stop,
 118
 119         .check_preempt_curr     = check_preempt_curr_stop,
 120
 121         .pick_next_task         = pick_next_task_stop,
 122         .put_prev_task          = put_prev_task_stop,
 123
 124 #ifdef CONFIG_SMP
 125         .select_task_rq         = select_task_rq_stop,
 126         .set_cpus_allowed       = set_cpus_allowed_common,
 127 #endif
 128
 129         .set_curr_task          = set_curr_task_stop,
 130         .task_tick              = task_tick_stop,
 131
 132         .get_rr_interval        = get_rr_interval_stop,
 133
 134         .prio_changed           = prio_changed_stop,
 135         .switched_to            = switched_to_stop,
 136         .update_curr            = update_curr_stop,
 137 };