FreeBSD/Linux Kernel Cross Reference
sys/kernel/sched_idletask.c

     /*
      * idle-task scheduling class.
      *
      * (NOTE: these are not related to SCHED_IDLE tasks which are
      *  handled in sched_fair.c)
      */
     
     #ifdef CONFIG_SMP
     static int
    select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
    {
            return task_cpu(p); /* IDLE tasks as never migrated */
    }
    #endif /* CONFIG_SMP */
    /*
     * Idle tasks are unconditionally rescheduled:
     */
    static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
    {
            resched_task(rq->idle);
    }
    
    static struct task_struct *pick_next_task_idle(struct rq *rq)
    {
            schedstat_inc(rq, sched_goidle);
            calc_load_account_idle(rq);
            return rq->idle;
    }
    
    /*
     * It is not legal to sleep in the idle task - print a warning
     * message if some code attempts to do it:
     */
    static void
    dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
    {
            raw_spin_unlock_irq(&rq->lock);
            printk(KERN_ERR "bad: scheduling from the idle thread!\n");
            dump_stack();
            raw_spin_lock_irq(&rq->lock);
    }
    
    static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
    {
    }
    
    static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
    {
    }
    
    static void set_curr_task_idle(struct rq *rq)
    {
    }
    
    static void switched_to_idle(struct rq *rq, struct task_struct *p)
    {
            BUG();
    }
    
    static void
    prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
    {
            BUG();
    }
    
    static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
    {
            return 0;
    }
    
    /*
     * Simple, special scheduling class for the per-CPU idle tasks:
     */
    static const struct sched_class idle_sched_class = {
            /* .next is NULL */
            /* no enqueue/yield_task for idle tasks */
    
            /* dequeue is not valid, we print a debug message there: */
            .dequeue_task           = dequeue_task_idle,
    
            .check_preempt_curr     = check_preempt_curr_idle,
    
            .pick_next_task         = pick_next_task_idle,
            .put_prev_task          = put_prev_task_idle,
    
    #ifdef CONFIG_SMP
            .select_task_rq         = select_task_rq_idle,
    #endif
    
            .set_curr_task          = set_curr_task_idle,
            .task_tick              = task_tick_idle,
    
            .get_rr_interval        = get_rr_interval_idle,
    
            .prio_changed           = prio_changed_idle,
            .switched_to            = switched_to_idle,
    };

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