kernel/sched/idle_task.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include "sched.h"
   3
   4 /*
   5  * idle-task scheduling class.
   6  *
   7  * (NOTE: these are not related to SCHED_IDLE tasks which are
   8  *  handled in sched/fair.c)
   9  */
  10
  11 #ifdef CONFIG_SMP
  12 static int
  13 select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)
  14 {
  15         return task_cpu(p); /* IDLE tasks as never migrated */
  16 }
  17 #endif /* CONFIG_SMP */
  18
  19 /*
  20  * Idle tasks are unconditionally rescheduled:
  21  */
  22 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
  23 {
  24         resched_curr(rq);
  25 }
  26
  27 static struct task_struct *
  28 pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  29 {
  30         put_prev_task(rq, prev);
  31         update_idle_core(rq);
  32         schedstat_inc(rq->sched_goidle);
  33         return rq->idle;
  34 }
  35
  36 /*
  37  * It is not legal to sleep in the idle task - print a warning
  38  * message if some code attempts to do it:
  39  */
  40 static void
  41 dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
  42 {
  43         raw_spin_unlock_irq(&rq->lock);
  44         printk(KERN_ERR "bad: scheduling from the idle thread!\n");
  45         dump_stack();
  46         raw_spin_lock_irq(&rq->lock);
  47 }
  48
  49 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
  50 {
  51         rq_last_tick_reset(rq);
  52 }
  53
  54 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  55 {
  56 }
  57
  58 static void set_curr_task_idle(struct rq *rq)
  59 {
  60 }
  61
  62 static void switched_to_idle(struct rq *rq, struct task_struct *p)
  63 {
  64         BUG();
  65 }
  66
  67 static void
  68 prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
  69 {
  70         BUG();
  71 }
  72
  73 static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
  74 {
  75         return 0;
  76 }
  77
  78 static void update_curr_idle(struct rq *rq)
  79 {
  80 }
  81
  82 /*
  83  * Simple, special scheduling class for the per-CPU idle tasks:
  84  */
  85 const struct sched_class idle_sched_class = {
  86         /* .next is NULL */
  87         /* no enqueue/yield_task for idle tasks */
  88
  89         /* dequeue is not valid, we print a debug message there: */
  90         .dequeue_task           = dequeue_task_idle,
  91
  92         .check_preempt_curr     = check_preempt_curr_idle,
  93
  94         .pick_next_task         = pick_next_task_idle,
  95         .put_prev_task          = put_prev_task_idle,
  96
  97 #ifdef CONFIG_SMP
  98         .select_task_rq         = select_task_rq_idle,
  99         .set_cpus_allowed       = set_cpus_allowed_common,
 100 #endif
 101
 102         .set_curr_task          = set_curr_task_idle,
 103         .task_tick              = task_tick_idle,
 104
 105         .get_rr_interval        = get_rr_interval_idle,
 106
 107         .prio_changed           = prio_changed_idle,
 108         .switched_to            = switched_to_idle,
 109         .update_curr            = update_curr_idle,
 110 };