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.
14  * sched_idle_set_state - Record idle state for the current CPU.
29 		cpu_idle_force_poll--;  in cpu_idle_poll_ctrl()
104  * default_idle_call - Default CPU idle routine.
132 		return -EBUSY;  in call_cpuidle_s2idle()
141 	 * The idle task must be scheduled, it is pointless to go to idle, just  in call_cpuidle()
142 	 * update no idle residency and return.  in call_cpuidle()
145 		dev->last_residency_ns = 0;  in call_cpuidle()
147 		return -EBUSY;  in call_cpuidle()
151 	 * Enter the idle state previously returned by the governor decision.  in call_cpuidle()
153 	 * care of re-enabling the local interrupts  in call_cpuidle()
159  * cpuidle_idle_call - the main idle function
161  * NOTE: no locks or semaphores should be used here
174 	 * Check if the idle task must be rescheduled. If it is the  in cpuidle_idle_call()
175 	 * case, exit the function after re-enabling the local IRQ.  in cpuidle_idle_call()
190 	 * Suspend-to-idle ("s2idle") is a system state in which all user space  in cpuidle_idle_call()
193 	 * the cpuidle governor and go straight for the deepest idle state  in cpuidle_idle_call()
195 	 * timekeeping to prevent timer interrupts from kicking us out of idle  in cpuidle_idle_call()
199 	if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {  in cpuidle_idle_call()
210 			max_latency_ns = dev->forced_idle_latency_limit_ns;  in cpuidle_idle_call()
221 		 * Ask the cpuidle framework to choose a convenient idle state.  in cpuidle_idle_call()
241 	 * It is up to the idle functions to re-enable local interrupts  in cpuidle_idle_call()
248  * Generic idle loop implementation
264 	 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=  in do_idle()
265 	 * rq->idle). This means that, if rq->idle has the polling bit set,  in do_idle()
276 		 * Interrupts shouldn't be re-enabled from that point on until  in do_idle()
284 		 * - SLEEP-UNTIL-PENDING-INTERRUPT based instructions such as  in do_idle()
288 		 * - sti;mwait() couple is fine because the interrupts are  in do_idle()
289 		 *   re-enabled only upon the execution of mwait, leaving no gap  in do_idle()
290 		 *   in-between.  in do_idle()
292 		 * - ROLLBACK based idle handlers with the sleeping instruction  in do_idle()
294 		 *   when the interrupt detects it has interrupted an idle handler,  in do_idle()
296 		 *   need_resched() check before re-executing the sleeping  in do_idle()
299 		 *   appropriate CPU sleeping instruction, then a FAST-FORWARD  in do_idle()
301 		 *   interrupted an idle handler, it must resume to the end of  in do_idle()
302 		 *   this idle handler so that the generic idle loop is iterated  in do_idle()
316 		 * In poll mode we re-enable interrupts and spin. Also if we  in do_idle()
317 		 * detected in the wakeup from idle path that the tick  in do_idle()
319 		 * idle as we know that the IPI is going to arrive right away.  in do_idle()
334 	 * This is required because for polling idle loops we will not have had  in do_idle()
349 	 * RCU relies on this call to be done outside of an RCU read-side  in do_idle()
374 	WRITE_ONCE(it->done, 1);  in idle_inject_timer_fn()
388 	WARN_ON_ONCE(current->policy != SCHED_FIFO);  in play_idle_precise()
389 	WARN_ON_ONCE(current->nr_cpus_allowed != 1);  in play_idle_precise()
390 	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));  in play_idle_precise()
391 	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));  in play_idle_precise()
393 	WARN_ON_ONCE(current->mm);  in play_idle_precise()
397 	current->flags |= PF_IDLE;  in play_idle_precise()
410 	current->flags &= ~PF_IDLE;  in play_idle_precise()
419 	current->flags |= PF_IDLE;  in cpu_startup_entry()
427  * idle-task scheduling class.
434 	return task_cpu(p); /* IDLE tasks as never migrated */  in select_task_rq_idle()
445  * Idle tasks are unconditionally rescheduled:
462 	schedstat_inc(rq->sched_goidle);  in set_next_task_idle()
463 	next->se.exec_start = rq_clock_task(rq);  in set_next_task_idle()
469 	return rq->idle;  in pick_task_idle()
473  * It is not legal to sleep in the idle task - print a warning
480 	printk(KERN_ERR "bad: scheduling from the idle thread!\n");  in dequeue_task_idle()
490  * goes along full dynticks. Therefore no local assumption can be made
514  * Simple, special scheduling class for the per-CPU idle tasks:
516 DEFINE_SCHED_CLASS(idle) = {
518 	/* no enqueue/yield_task for idle tasks */