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