kernel/sched/stop_task.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include "sched.h"
   3
   4 /*
   5  * stop-task scheduling class.
   6  *
   7  * The stop task is the highest priority task in the system, it preempts
   8  * everything and will be preempted by nothing.
   9  *
  10  * See kernel/stop_machine.c
  11  */
  12
  13 #ifdef CONFIG_SMP
  14 static int
  15 select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags)
  16 {
  17         return task_cpu(p); /* stop tasks as never migrate */
  18 }
  19 #endif /* CONFIG_SMP */
  20
  21 static void
  22 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  23 {
  24         /* we're never preempted */
  25 }
  26
  27 static struct task_struct *
  28 pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  29 {
  30         struct task_struct *stop = rq->stop;
  31
  32         if (!stop || !task_on_rq_queued(stop))
  33                 return NULL;
  34
  35         put_prev_task(rq, prev);
  36
  37         stop->se.exec_start = rq_clock_task(rq);
  38
  39         return stop;
  40 }
  41
  42 static void
  43 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  44 {
  45         add_nr_running(rq, 1);
  46 }
  47
  48 static void
  49 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  50 {
  51         sub_nr_running(rq, 1);
  52 }
  53
  54 static void yield_task_stop(struct rq *rq)
  55 {
  56         BUG(); /* the stop task should never yield, its pointless. */
  57 }
  58
  59 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  60 {
  61         struct task_struct *curr = rq->curr;
  62         u64 delta_exec;
  63
  64         delta_exec = rq_clock_task(rq) - curr->se.exec_start;
  65         if (unlikely((s64)delta_exec < 0))
  66                 delta_exec = 0;
  67
  68         schedstat_set(curr->se.statistics.exec_max,
  69                         max(curr->se.statistics.exec_max, delta_exec));
  70
  71         curr->se.sum_exec_runtime += delta_exec;
  72         account_group_exec_runtime(curr, delta_exec);
  73
  74         curr->se.exec_start = rq_clock_task(rq);
  75         cgroup_account_cputime(curr, delta_exec);
  76 }
  77
  78 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  79 {
  80 }
  81
  82 static void set_curr_task_stop(struct rq *rq)
  83 {
  84         struct task_struct *stop = rq->stop;
  85
  86         stop->se.exec_start = rq_clock_task(rq);
  87 }
  88
  89 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  90 {
  91         BUG(); /* its impossible to change to this class */
  92 }
  93
  94 static void
  95 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  96 {
  97         BUG(); /* how!?, what priority? */
  98 }
  99
 100 static unsigned int
 101 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 102 {
 103         return 0;
 104 }
 105
 106 static void update_curr_stop(struct rq *rq)
 107 {
 108 }
 109
 110 /*
 111  * Simple, special scheduling class for the per-CPU stop tasks:
 112  */
 113 const struct sched_class stop_sched_class = {
 114         .next                   = &dl_sched_class,
 115
 116         .enqueue_task           = enqueue_task_stop,
 117         .dequeue_task           = dequeue_task_stop,
 118         .yield_task             = yield_task_stop,
 119
 120         .check_preempt_curr     = check_preempt_curr_stop,
 121
 122         .pick_next_task         = pick_next_task_stop,
 123         .put_prev_task          = put_prev_task_stop,
 124
 125 #ifdef CONFIG_SMP
 126         .select_task_rq         = select_task_rq_stop,
 127         .set_cpus_allowed       = set_cpus_allowed_common,
 128 #endif
 129
 130         .set_curr_task          = set_curr_task_stop,
 131         .task_tick              = task_tick_stop,
 132
 133         .get_rr_interval        = get_rr_interval_stop,
 134
 135         .prio_changed           = prio_changed_stop,
 136         .switched_to            = switched_to_stop,
 137         .update_curr            = update_curr_stop,
 138 };