LXR linux/kernel/sched/stop

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * stop-task scheduling class.
   4 *
   5 * The stop task is the highest priority task in the system, it preempts
   6 * everything and will be preempted by nothing.
   7 *
   8 * See kernel/stop_machine.c
   9 */
  10#include "sched.h"
  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, 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
  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        cgroup_account_cputime(curr, delta_exec);
  75}
  76
  77/*
  78 * scheduler tick hitting a task of our scheduling class.
  79 *
  80 * NOTE: This function can be called remotely by the tick offload that
  81 * goes along full dynticks. Therefore no local assumption can be made
  82 * and everything must be accessed through the @rq and @curr passed in
  83 * parameters.
  84 */
  85static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  86{
  87}
  88
  89static void set_curr_task_stop(struct rq *rq)
  90{
  91        struct task_struct *stop = rq->stop;
  92
  93        stop->se.exec_start = rq_clock_task(rq);
  94}
  95
  96static void switched_to_stop(struct rq *rq, struct task_struct *p)
  97{
  98        BUG(); /* its impossible to change to this class */
  99}
 100
 101static void
 102prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 103{
 104        BUG(); /* how!?, what priority? */
 105}
 106
 107static unsigned int
 108get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 109{
 110        return 0;
 111}
 112
 113static void update_curr_stop(struct rq *rq)
 114{
 115}
 116
 117/*
 118 * Simple, special scheduling class for the per-CPU stop tasks:
 119 */
 120const struct sched_class stop_sched_class = {
 121        .next                   = &dl_sched_class,
 122
 123        .enqueue_task           = enqueue_task_stop,
 124        .dequeue_task           = dequeue_task_stop,
 125        .yield_task             = yield_task_stop,
 126
 127        .check_preempt_curr     = check_preempt_curr_stop,
 128
 129        .pick_next_task         = pick_next_task_stop,
 130        .put_prev_task          = put_prev_task_stop,
 131
 132#ifdef CONFIG_SMP
 133        .select_task_rq         = select_task_rq_stop,
 134        .set_cpus_allowed       = set_cpus_allowed_common,
 135#endif
 136
 137        .set_curr_task          = set_curr_task_stop,
 138        .task_tick              = task_tick_stop,
 139
 140        .get_rr_interval        = get_rr_interval_stop,
 141
 142        .prio_changed           = prio_changed_stop,
 143        .switched_to            = switched_to_stop,
 144        .update_curr            = update_curr_stop,
 145};
 146