1 // SPDX-License-Identifier: GPL-2.0-only
3  * Generic entry points for the idle threads and
4  * implementation of the idle task scheduling class.
17  * sched_idle_set_state - Record idle state for the current CPU.
18  * @idle_state: State to record.
32 		cpu_idle_force_poll--;  in cpu_idle_poll_ctrl()
85  * default_idle_call - Default CPU idle routine.
104 		 * rcu_idle_enter() relies on lockdep IRQ state, so switch that  in default_idle_call()
105 		 * last -- this is very similar to the entry code.  in default_idle_call()
135 		return -EBUSY;  in call_cpuidle_s2idle()
144 	 * The idle task must be scheduled, it is pointless to go to idle, just  in call_cpuidle()
145 	 * update no idle residency and return.  in call_cpuidle()
148 		dev->last_residency_ns = 0;  in call_cpuidle()
150 		return -EBUSY;  in call_cpuidle()
154 	 * Enter the idle state previously returned by the governor decision.  in call_cpuidle()
156 	 * care of re-enabling the local interrupts  in call_cpuidle()
162  * cpuidle_idle_call - the main idle function
177 	 * Check if the idle task must be rescheduled. If it is the  in cpuidle_idle_call()
178 	 * case, exit the function after re-enabling the local irq.  in cpuidle_idle_call()
186 	 * The RCU framework needs to be told that we are entering an idle  in cpuidle_idle_call()
199 	 * Suspend-to-idle ("s2idle") is a system state in which all user space  in cpuidle_idle_call()
202 	 * the cpuidle governor and go stratight for the deepest idle state  in cpuidle_idle_call()
204 	 * timekeeping to prevent timer interrupts from kicking us out of idle  in cpuidle_idle_call()
208 	if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {  in cpuidle_idle_call()
219 			max_latency_ns = dev->forced_idle_latency_limit_ns;  in cpuidle_idle_call()
230 		 * Ask the cpuidle framework to choose a convenient idle state.  in cpuidle_idle_call()
250 	 * It is up to the idle functions to reenable local interrupts  in cpuidle_idle_call()
257  * Generic idle loop implementation
267 	 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=  in do_idle()
268 	 * rq->idle). This means that, if rq->idle has the polling bit set,  in do_idle()
291 		 * detected in the wakeup from idle path that the tick  in do_idle()
293 		 * idle as we know that the IPI is going to arrive right away.  in do_idle()
308 	 * This is required because for polling idle loops we will not have had  in do_idle()
309 	 * an IPI to fold the state for us.  in do_idle()
323 	 * RCU relies on this call to be done outside of an RCU read-side  in do_idle()
348 	WRITE_ONCE(it->done, 1);  in idle_inject_timer_fn()
362 	WARN_ON_ONCE(current->policy != SCHED_FIFO);  in play_idle_precise()
363 	WARN_ON_ONCE(current->nr_cpus_allowed != 1);  in play_idle_precise()
364 	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));  in play_idle_precise()
365 	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));  in play_idle_precise()
370 	current->flags |= PF_IDLE;  in play_idle_precise()
383 	current->flags &= ~PF_IDLE;  in play_idle_precise()
390 void cpu_startup_entry(enum cpuhp_state state)  in cpu_startup_entry()  argument
393 	cpuhp_online_idle(state);  in cpu_startup_entry()
399  * idle-task scheduling class.
406 	return task_cpu(p); /* IDLE tasks as never migrated */  in select_task_rq_idle()
417  * Idle tasks are unconditionally rescheduled:
431 	schedstat_inc(rq->sched_goidle);  in set_next_task_idle()
436 	struct task_struct *next = rq->idle;  in pick_next_task_idle()
444  * It is not legal to sleep in the idle task - print a warning
450 	raw_spin_unlock_irq(&rq->lock);  in dequeue_task_idle()
451 	printk(KERN_ERR "bad: scheduling from the idle thread!\n");  in dequeue_task_idle()
453 	raw_spin_lock_irq(&rq->lock);  in dequeue_task_idle()
484  * Simple, special scheduling class for the per-CPU idle tasks:
488 	/* no enqueue/yield_task for idle tasks */