LXR linux/kernel/sched/stop

   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
  13static int
  14select_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
  20static void
  21check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  22{
  23        /* we're never preempted */
  24}
  25
  26static struct task_struct *
  27pick_next_task_stop(struct rq *rq, struct task_struct *prev)
  28{
  29        struct task_struct *stop = rq->stop;
  30
  31        if (!stop || !stop->on_rq)
  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
  41static void
  42enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  43{
  44        add_nr_running(rq, 1);
  45}
  46
  47static void
  48dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  49{
  50        sub_nr_running(rq, 1);
  51}
  52
  53static void yield_task_stop(struct rq *rq)
  54{
  55        BUG(); /* the stop task should never yield, its pointless. */
  56}
  57
  58static 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
  77static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  78{
  79}
  80
  81static 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
  88static void switched_to_stop(struct rq *rq, struct task_struct *p)
  89{
  90        BUG(); /* its impossible to change to this class */
  91}
  92
  93static void
  94prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  95{
  96        BUG(); /* how!?, what priority? */
  97}
  98
  99static unsigned int
 100get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 101{
 102        return 0;
 103}
 104
 105/*
 106 * Simple, special scheduling class for the per-CPU stop tasks:
 107 */
 108const struct sched_class stop_sched_class = {
 109        .next                   = &dl_sched_class,
 110
 111        .enqueue_task           = enqueue_task_stop,
 112        .dequeue_task           = dequeue_task_stop,
 113        .yield_task             = yield_task_stop,
 114
 115        .check_preempt_curr     = check_preempt_curr_stop,
 116
 117        .pick_next_task         = pick_next_task_stop,
 118        .put_prev_task          = put_prev_task_stop,
 119
 120#ifdef CONFIG_SMP
 121        .select_task_rq         = select_task_rq_stop,
 122#endif
 123
 124        .set_curr_task          = set_curr_task_stop,
 125        .task_tick              = task_tick_stop,
 126
 127        .get_rr_interval        = get_rr_interval_stop,
 128
 129        .prio_changed           = prio_changed_stop,
 130        .switched_to            = switched_to_stop,
 131};
 132