kernel/sched/stop_task.c

   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
  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         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  */
  85 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  86 {
  87 }
  88
  89 static 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
  96 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  97 {
  98         BUG(); /* its impossible to change to this class */
  99 }
 100
 101 static void
 102 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 103 {
 104         BUG(); /* how!?, what priority? */
 105 }
 106
 107 static unsigned int
 108 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 109 {
 110         return 0;
 111 }
 112
 113 static void update_curr_stop(struct rq *rq)
 114 {
 115 }
 116
 117 /*
 118  * Simple, special scheduling class for the per-CPU stop tasks:
 119  */
 120 const 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 };