idle.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Generic entry points for the idle threads and
  4 * implementation of the idle task scheduling class.
  5 *
  6 * (NOTE: these are not related to SCHED_IDLE batch scheduled
  7 *        tasks which are handled in sched/fair.c )
  8 */
  9#include <linux/cpuidle.h>
 10#include <linux/suspend.h>
 11#include <linux/livepatch.h>
 12#include "sched.h"
 13#include "smp.h"
 14
 15/* Linker adds these: start and end of __cpuidle functions */
 16extern char __cpuidle_text_start[], __cpuidle_text_end[];
 17
 18/**
 19 * sched_idle_set_state - Record idle state for the current CPU.
 20 * @idle_state: State to record.
 21 */
 22void sched_idle_set_state(struct cpuidle_state *idle_state)
 23{
 24	idle_set_state(this_rq(), idle_state);
 25}
 26
 27static int __read_mostly cpu_idle_force_poll;
 28
 29void cpu_idle_poll_ctrl(bool enable)
 30{
 31	if (enable) {
 32		cpu_idle_force_poll++;
 33	} else {
 34		cpu_idle_force_poll--;
 35		WARN_ON_ONCE(cpu_idle_force_poll < 0);
 36	}
 37}
 38
 39#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
 40static int __init cpu_idle_poll_setup(char *__unused)
 41{
 42	cpu_idle_force_poll = 1;
 43
 44	return 1;
 45}
 46__setup("nohlt", cpu_idle_poll_setup);
 47
 48static int __init cpu_idle_nopoll_setup(char *__unused)
 49{
 50	cpu_idle_force_poll = 0;
 51
 52	return 1;
 53}
 54__setup("hlt", cpu_idle_nopoll_setup);
 55#endif /* CONFIG_GENERIC_IDLE_POLL_SETUP */
 56
 57static noinline int __cpuidle cpu_idle_poll(void)
 58{
 59	instrumentation_begin();
 60	trace_cpu_idle(0, smp_processor_id());
 61	stop_critical_timings();
 62	ct_cpuidle_enter();
 63
 64	raw_local_irq_enable();
 65	while (!tif_need_resched() &&
 66	       (cpu_idle_force_poll || tick_check_broadcast_expired()))
 67		cpu_relax();
 68	raw_local_irq_disable();
 69
 70	ct_cpuidle_exit();
 71	start_critical_timings();
 72	trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
 73	local_irq_enable();
 74	instrumentation_end();
 75
 76	return 1;
 77}
 78
 79/* Weak implementations for optional arch specific functions */
 80void __weak arch_cpu_idle_prepare(void) { }
 81void __weak arch_cpu_idle_enter(void) { }
 82void __weak arch_cpu_idle_exit(void) { }
 83void __weak __noreturn arch_cpu_idle_dead(void) { while (1); }
 84void __weak arch_cpu_idle(void)
 85{
 86	cpu_idle_force_poll = 1;
 87}
 88
 89#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE
 90DEFINE_STATIC_KEY_FALSE(arch_needs_tick_broadcast);
 91
 92static inline void cond_tick_broadcast_enter(void)
 93{
 94	if (static_branch_unlikely(&arch_needs_tick_broadcast))
 95		tick_broadcast_enter();
 96}
 97
 98static inline void cond_tick_broadcast_exit(void)
 99{
100	if (static_branch_unlikely(&arch_needs_tick_broadcast))
101		tick_broadcast_exit();
102}
103#else /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE: */
104static inline void cond_tick_broadcast_enter(void) { }
105static inline void cond_tick_broadcast_exit(void) { }
106#endif /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE */
107
108/**
109 * default_idle_call - Default CPU idle routine.
110 *
111 * To use when the cpuidle framework cannot be used.
112 */
113void __cpuidle default_idle_call(void)
114{
115	instrumentation_begin();
116	if (!current_clr_polling_and_test()) {
117		cond_tick_broadcast_enter();
118		trace_cpu_idle(1, smp_processor_id());
119		stop_critical_timings();
120
121		ct_cpuidle_enter();
122		arch_cpu_idle();
123		ct_cpuidle_exit();
124
125		start_critical_timings();
126		trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
127		cond_tick_broadcast_exit();
128	}
129	local_irq_enable();
130	instrumentation_end();
131}
132
133static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
134			       struct cpuidle_device *dev,
135			       u64 max_latency_ns)
136{
137	if (current_clr_polling_and_test())
138		return -EBUSY;
139
140	return cpuidle_enter_s2idle(drv, dev, max_latency_ns);
141}
142
143static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
144		      int next_state)
145{
146	/*
147	 * The idle task must be scheduled, it is pointless to go to idle, just
148	 * update no idle residency and return.
149	 */
150	if (current_clr_polling_and_test()) {
151		dev->last_residency_ns = 0;
152		local_irq_enable();
153		return -EBUSY;
154	}
155
156	/*
157	 * Enter the idle state previously returned by the governor decision.
158	 * This function will block until an interrupt occurs and will take
159	 * care of re-enabling the local interrupts
160	 */
161	return cpuidle_enter(drv, dev, next_state);
162}
163
164static void idle_call_stop_or_retain_tick(bool stop_tick)
165{
166	if (stop_tick || tick_nohz_tick_stopped())
167		tick_nohz_idle_stop_tick();
168	else
169		tick_nohz_idle_retain_tick();
170}
171
172/**
173 * cpuidle_idle_call - the main idle function
174 *
175 * NOTE: no locks or semaphores should be used here
176 *
177 * On architectures that support TIF_POLLING_NRFLAG, is called with polling
178 * set, and it returns with polling set.  If it ever stops polling, it
179 * must clear the polling bit.
180 */
181static void cpuidle_idle_call(bool stop_tick)
182{
183	struct cpuidle_device *dev = cpuidle_get_device();
184	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
185	int next_state, entered_state;
186
187	/*
188	 * Check if the idle task must be rescheduled. If it is the
189	 * case, exit the function after re-enabling the local IRQ.
190	 */
191	if (need_resched()) {
192		local_irq_enable();
193		return;
194	}
195
196	if (cpuidle_not_available(drv, dev)) {
197		idle_call_stop_or_retain_tick(stop_tick);
198
199		default_idle_call();
200		goto exit_idle;
201	}
202
203	/*
204	 * Suspend-to-idle ("s2idle") is a system state in which all user space
205	 * has been frozen, all I/O devices have been suspended and the only
206	 * activity happens here and in interrupts (if any). In that case bypass
207	 * the cpuidle governor and go straight for the deepest idle state
208	 * available.  Possibly also suspend the local tick and the entire
209	 * timekeeping to prevent timer interrupts from kicking us out of idle
210	 * until a proper wakeup interrupt happens.
211	 */
212
213	if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
214		u64 max_latency_ns;
215
216		if (idle_should_enter_s2idle()) {
217			max_latency_ns = cpu_wakeup_latency_qos_limit() *
218					 NSEC_PER_USEC;
219
220			entered_state = call_cpuidle_s2idle(drv, dev,
221							    max_latency_ns);
222			if (entered_state > 0)
223				goto exit_idle;
224		} else {
225			max_latency_ns = dev->forced_idle_latency_limit_ns;
226		}
227
228		tick_nohz_idle_stop_tick();
229
230		next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
231		call_cpuidle(drv, dev, next_state);
232	} else if (drv->state_count > 1) {
233		/*
234		 * stop_tick is expected to be true by default by cpuidle
235		 * governors, which allows them to select idle states with
236		 * target residency above the tick period length.
237		 */
238		stop_tick = true;
239
240		/*
241		 * Ask the cpuidle framework to choose a convenient idle state.
242		 */
243		next_state = cpuidle_select(drv, dev, &stop_tick);
244
245		idle_call_stop_or_retain_tick(stop_tick);
246
247		entered_state = call_cpuidle(drv, dev, next_state);
248		/*
249		 * Give the governor an opportunity to reflect on the outcome
250		 */
251		cpuidle_reflect(dev, entered_state);
252	} else {
253		idle_call_stop_or_retain_tick(stop_tick);
254
255		/*
256		 * If there is only a single idle state (or none), there is
257		 * nothing meaningful for the governor to choose.  Skip the
258		 * governor and always use state 0.
259		 */
260		call_cpuidle(drv, dev, 0);
261	}
262
263exit_idle:
264	__current_set_polling();
265
266	/*
267	 * It is up to the idle functions to re-enable local interrupts
268	 */
269	if (WARN_ON_ONCE(irqs_disabled()))
270		local_irq_enable();
271}
272
273/*
274 * Generic idle loop implementation
275 *
276 * Called with polling cleared.
277 */
278static void do_idle(void)
279{
280	int cpu = smp_processor_id();
281	bool got_tick = false;
282
283	/*
284	 * Check if we need to update blocked load
285	 */
286	nohz_run_idle_balance(cpu);
287
288	/*
289	 * If the arch has a polling bit, we maintain an invariant:
290	 *
291	 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
292	 * rq->idle). This means that, if rq->idle has the polling bit set,
293	 * then setting need_resched is guaranteed to cause the CPU to
294	 * reschedule.
295	 */
296
297	__current_set_polling();
298	tick_nohz_idle_enter();
299
300	while (!need_resched()) {
301
302		/*
303		 * Interrupts shouldn't be re-enabled from that point on until
304		 * the CPU sleeping instruction is reached. Otherwise an interrupt
305		 * may fire and queue a timer that would be ignored until the CPU
306		 * wakes from the sleeping instruction. And testing need_resched()
307		 * doesn't tell about pending needed timer reprogram.
308		 *
309		 * Several cases to consider:
310		 *
311		 * - SLEEP-UNTIL-PENDING-INTERRUPT based instructions such as
312		 *   "wfi" or "mwait" are fine because they can be entered with
313		 *   interrupt disabled.
314		 *
315		 * - sti;mwait() couple is fine because the interrupts are
316		 *   re-enabled only upon the execution of mwait, leaving no gap
317		 *   in-between.
318		 *
319		 * - ROLLBACK based idle handlers with the sleeping instruction
320		 *   called with interrupts enabled are NOT fine. In this scheme
321		 *   when the interrupt detects it has interrupted an idle handler,
322		 *   it rolls back to its beginning which performs the
323		 *   need_resched() check before re-executing the sleeping
324		 *   instruction. This can leak a pending needed timer reprogram.
325		 *   If such a scheme is really mandatory due to the lack of an
326		 *   appropriate CPU sleeping instruction, then a FAST-FORWARD
327		 *   must instead be applied: when the interrupt detects it has
328		 *   interrupted an idle handler, it must resume to the end of
329		 *   this idle handler so that the generic idle loop is iterated
330		 *   again to reprogram the tick.
331		 */
332		local_irq_disable();
333
334		if (cpu_is_offline(cpu)) {
335			cpuhp_report_idle_dead();
336			arch_cpu_idle_dead();
337		}
338
339		arch_cpu_idle_enter();
340		rcu_nocb_flush_deferred_wakeup();
341
342		/*
343		 * In poll mode we re-enable interrupts and spin. Also if we
344		 * detected in the wakeup from idle path that the tick
345		 * broadcast device expired for us, we don't want to go deep
346		 * idle as we know that the IPI is going to arrive right away.
347		 */
348		if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
349			tick_nohz_idle_restart_tick();
350			cpu_idle_poll();
351		} else {
352			cpuidle_idle_call(got_tick);
353		}
354		got_tick = tick_nohz_idle_got_tick();
355		arch_cpu_idle_exit();
356	}
357
358	/*
359	 * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
360	 * be set, propagate it into PREEMPT_NEED_RESCHED.
361	 *
362	 * This is required because for polling idle loops we will not have had
363	 * an IPI to fold the state for us.
364	 */
365	preempt_set_need_resched();
366	tick_nohz_idle_exit();
367	__current_clr_polling();
368
369	/*
370	 * We promise to call sched_ttwu_pending() and reschedule if
371	 * need_resched() is set while polling is set. That means that clearing
372	 * polling needs to be visible before doing these things.
373	 */
374	smp_mb__after_atomic();
375
376	/*
377	 * RCU relies on this call to be done outside of an RCU read-side
378	 * critical section.
379	 */
380	flush_smp_call_function_queue();
381	schedule_idle();
382
383	if (unlikely(klp_patch_pending(current)))
384		klp_update_patch_state(current);
385}
386
387bool cpu_in_idle(unsigned long pc)
388{
389	return pc >= (unsigned long)__cpuidle_text_start &&
390		pc < (unsigned long)__cpuidle_text_end;
391}
392
393struct idle_timer {
394	struct hrtimer timer;
395	int done;
396};
397
398static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
399{
400	struct idle_timer *it = container_of(timer, struct idle_timer, timer);
401
402	WRITE_ONCE(it->done, 1);
403	set_tsk_need_resched(current);
404
405	return HRTIMER_NORESTART;
406}
407
408void play_idle_precise(u64 duration_ns, u64 latency_ns)
409{
410	struct idle_timer it;
411
412	/*
413	 * Only FIFO tasks can disable the tick since they don't need the forced
414	 * preemption.
415	 */
416	WARN_ON_ONCE(current->policy != SCHED_FIFO);
417	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
418	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
419	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
420	WARN_ON_ONCE(!duration_ns);
421	WARN_ON_ONCE(current->mm);
422
423	rcu_sleep_check();
424	preempt_disable();
425	current->flags |= PF_IDLE;
426	cpuidle_use_deepest_state(latency_ns);
427
428	it.done = 0;
429	hrtimer_setup_on_stack(&it.timer, idle_inject_timer_fn, CLOCK_MONOTONIC,
430			       HRTIMER_MODE_REL_HARD);
431	hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
432		      HRTIMER_MODE_REL_PINNED_HARD);
433
434	while (!READ_ONCE(it.done))
435		do_idle();
436
437	cpuidle_use_deepest_state(0);
438	current->flags &= ~PF_IDLE;
439
440	preempt_fold_need_resched();
441	preempt_enable();
442}
443EXPORT_SYMBOL_GPL(play_idle_precise);
444
445void cpu_startup_entry(enum cpuhp_state state)
446{
447	current->flags |= PF_IDLE;
448	arch_cpu_idle_prepare();
449	cpuhp_online_idle(state);
450	while (1)
451		do_idle();
452}
453
454/*
455 * idle-task scheduling class.
456 */
457
458static int
459select_task_rq_idle(struct task_struct *p, int cpu, int flags)
460{
461	return task_cpu(p); /* IDLE tasks as never migrated */
462}
463
464static int
465balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
466{
467	return WARN_ON_ONCE(1);
468}
469
470/*
471 * Idle tasks are unconditionally rescheduled:
472 */
473static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags)
474{
475	resched_curr(rq);
476}
477
478static void update_curr_idle(struct rq *rq);
479
480static void put_prev_task_idle(struct rq *rq, struct task_struct *prev, struct task_struct *next)
481{
482	update_curr_idle(rq);
483	scx_update_idle(rq, false, true);
484}
485
486static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
487{
488	update_idle_core(rq);
489	scx_update_idle(rq, true, true);
490	schedstat_inc(rq->sched_goidle);
491	next->se.exec_start = rq_clock_task(rq);
492
493	/*
494	 * rq is about to be idle, check if we need to update the
495	 * lost_idle_time of clock_pelt
496	 */
497	update_idle_rq_clock_pelt(rq);
498}
499
500struct task_struct *pick_task_idle(struct rq *rq, struct rq_flags *rf)
501{
502	scx_update_idle(rq, true, false);
503	return rq->idle;
504}
505
506/*
507 * It is not legal to sleep in the idle task - print a warning
508 * message if some code attempts to do it:
509 */
510static bool
511dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
512{
513	raw_spin_rq_unlock_irq(rq);
514	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
515	dump_stack();
516	raw_spin_rq_lock_irq(rq);
517	return true;
518}
519
520/*
521 * scheduler tick hitting a task of our scheduling class.
522 *
523 * NOTE: This function can be called remotely by the tick offload that
524 * goes along full dynticks. Therefore no local assumption can be made
525 * and everything must be accessed through the @rq and @curr passed in
526 * parameters.
527 */
528static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
529{
530	update_curr_idle(rq);
531}
532
533static void switching_to_idle(struct rq *rq, struct task_struct *p)
534{
535	BUG();
536}
537
538static void
539prio_changed_idle(struct rq *rq, struct task_struct *p, u64 oldprio)
540{
541	if (p->prio == oldprio)
542		return;
543
544	BUG();
545}
546
547static void update_curr_idle(struct rq *rq)
548{
549	struct sched_entity *se = &rq->idle->se;
550	u64 now = rq_clock_task(rq);
551	s64 delta_exec;
552
553	delta_exec = now - se->exec_start;
554	if (unlikely(delta_exec <= 0))
555		return;
556
557	se->exec_start = now;
558
559	dl_server_update_idle(&rq->fair_server, delta_exec);
560}
561
562/*
563 * Simple, special scheduling class for the per-CPU idle tasks:
564 */
565DEFINE_SCHED_CLASS(idle) = {
566
567	.queue_mask		= 0,
568
569	/* no enqueue/yield_task for idle tasks */
570
571	/* dequeue is not valid, we print a debug message there: */
572	.dequeue_task		= dequeue_task_idle,
573
574	.wakeup_preempt		= wakeup_preempt_idle,
575
576	.pick_task		= pick_task_idle,
577	.put_prev_task		= put_prev_task_idle,
578	.set_next_task          = set_next_task_idle,
579
580	.balance		= balance_idle,
581	.select_task_rq		= select_task_rq_idle,
582	.set_cpus_allowed	= set_cpus_allowed_common,
583
584	.task_tick		= task_tick_idle,
585
586	.prio_changed		= prio_changed_idle,
587	.switching_to		= switching_to_idle,
588	.update_curr		= update_curr_idle,
589};