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
10/* Linker adds these: start and end of __cpuidle functions */
11extern char __cpuidle_text_start[], __cpuidle_text_end[];
12
13/**
14 * sched_idle_set_state - Record idle state for the current CPU.
15 * @idle_state: State to record.
16 */
17void sched_idle_set_state(struct cpuidle_state *idle_state)
18{
19 idle_set_state(this_rq(), idle_state);
20}
21
22static int __read_mostly cpu_idle_force_poll;
23
24void cpu_idle_poll_ctrl(bool enable)
25{
26 if (enable) {
27 cpu_idle_force_poll++;
28 } else {
29 cpu_idle_force_poll--;
30 WARN_ON_ONCE(cpu_idle_force_poll < 0);
31 }
32}
33
34#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
35static int __init cpu_idle_poll_setup(char *__unused)
36{
37 cpu_idle_force_poll = 1;
38
39 return 1;
40}
41__setup("nohlt", cpu_idle_poll_setup);
42
43static int __init cpu_idle_nopoll_setup(char *__unused)
44{
45 cpu_idle_force_poll = 0;
46
47 return 1;
48}
49__setup("hlt", cpu_idle_nopoll_setup);
50#endif
51
52static noinline int __cpuidle cpu_idle_poll(void)
53{
54 instrumentation_begin();
55 trace_cpu_idle(state: 0, smp_processor_id());
56 stop_critical_timings();
57 ct_cpuidle_enter();
58
59 raw_local_irq_enable();
60 while (!tif_need_resched() &&
61 (cpu_idle_force_poll || tick_check_broadcast_expired()))
62 cpu_relax();
63 raw_local_irq_disable();
64
65 ct_cpuidle_exit();
66 start_critical_timings();
67 trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
68 local_irq_enable();
69 instrumentation_end();
70
71 return 1;
72}
73
74/* Weak implementations for optional arch specific functions */
75void __weak arch_cpu_idle_prepare(void) { }
76void __weak arch_cpu_idle_enter(void) { }
77void __weak arch_cpu_idle_exit(void) { }
78void __weak __noreturn arch_cpu_idle_dead(void) { while (1); }
79void __weak arch_cpu_idle(void)
80{
81 cpu_idle_force_poll = 1;
82}
83
84#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE
85DEFINE_STATIC_KEY_FALSE(arch_needs_tick_broadcast);
86
87static inline void cond_tick_broadcast_enter(void)
88{
89 if (static_branch_unlikely(&arch_needs_tick_broadcast))
90 tick_broadcast_enter();
91}
92
93static inline void cond_tick_broadcast_exit(void)
94{
95 if (static_branch_unlikely(&arch_needs_tick_broadcast))
96 tick_broadcast_exit();
97}
98#else
99static inline void cond_tick_broadcast_enter(void) { }
100static inline void cond_tick_broadcast_exit(void) { }
101#endif
102
103/**
104 * default_idle_call - Default CPU idle routine.
105 *
106 * To use when the cpuidle framework cannot be used.
107 */
108void __cpuidle default_idle_call(void)
109{
110 instrumentation_begin();
111 if (!current_clr_polling_and_test()) {
112 cond_tick_broadcast_enter();
113 trace_cpu_idle(state: 1, smp_processor_id());
114 stop_critical_timings();
115
116 ct_cpuidle_enter();
117 arch_cpu_idle();
118 ct_cpuidle_exit();
119
120 start_critical_timings();
121 trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
122 cond_tick_broadcast_exit();
123 }
124 local_irq_enable();
125 instrumentation_end();
126}
127
128static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
129 struct cpuidle_device *dev)
130{
131 if (current_clr_polling_and_test())
132 return -EBUSY;
133
134 return cpuidle_enter_s2idle(drv, dev);
135}
136
137static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
138 int next_state)
139{
140 /*
141 * The idle task must be scheduled, it is pointless to go to idle, just
142 * update no idle residency and return.
143 */
144 if (current_clr_polling_and_test()) {
145 dev->last_residency_ns = 0;
146 local_irq_enable();
147 return -EBUSY;
148 }
149
150 /*
151 * Enter the idle state previously returned by the governor decision.
152 * This function will block until an interrupt occurs and will take
153 * care of re-enabling the local interrupts
154 */
155 return cpuidle_enter(drv, dev, index: next_state);
156}
157
158/**
159 * cpuidle_idle_call - the main idle function
160 *
161 * NOTE: no locks or semaphores should be used here
162 *
163 * On architectures that support TIF_POLLING_NRFLAG, is called with polling
164 * set, and it returns with polling set. If it ever stops polling, it
165 * must clear the polling bit.
166 */
167static void cpuidle_idle_call(void)
168{
169 struct cpuidle_device *dev = cpuidle_get_device();
170 struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
171 int next_state, entered_state;
172
173 /*
174 * Check if the idle task must be rescheduled. If it is the
175 * case, exit the function after re-enabling the local irq.
176 */
177 if (need_resched()) {
178 local_irq_enable();
179 return;
180 }
181
182 /*
183 * The RCU framework needs to be told that we are entering an idle
184 * section, so no more rcu read side critical sections and one more
185 * step to the grace period
186 */
187
188 if (cpuidle_not_available(drv, dev)) {
189 tick_nohz_idle_stop_tick();
190
191 default_idle_call();
192 goto exit_idle;
193 }
194
195 /*
196 * Suspend-to-idle ("s2idle") is a system state in which all user space
197 * has been frozen, all I/O devices have been suspended and the only
198 * activity happens here and in interrupts (if any). In that case bypass
199 * the cpuidle governor and go straight for the deepest idle state
200 * available. Possibly also suspend the local tick and the entire
201 * timekeeping to prevent timer interrupts from kicking us out of idle
202 * until a proper wakeup interrupt happens.
203 */
204
205 if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
206 u64 max_latency_ns;
207
208 if (idle_should_enter_s2idle()) {
209
210 entered_state = call_cpuidle_s2idle(drv, dev);
211 if (entered_state > 0)
212 goto exit_idle;
213
214 max_latency_ns = U64_MAX;
215 } else {
216 max_latency_ns = dev->forced_idle_latency_limit_ns;
217 }
218
219 tick_nohz_idle_stop_tick();
220
221 next_state = cpuidle_find_deepest_state(drv, dev, latency_limit_ns: max_latency_ns);
222 call_cpuidle(drv, dev, next_state);
223 } else {
224 bool stop_tick = true;
225
226 /*
227 * Ask the cpuidle framework to choose a convenient idle state.
228 */
229 next_state = cpuidle_select(drv, dev, stop_tick: &stop_tick);
230
231 if (stop_tick || tick_nohz_tick_stopped())
232 tick_nohz_idle_stop_tick();
233 else
234 tick_nohz_idle_retain_tick();
235
236 entered_state = call_cpuidle(drv, dev, next_state);
237 /*
238 * Give the governor an opportunity to reflect on the outcome
239 */
240 cpuidle_reflect(dev, index: entered_state);
241 }
242
243exit_idle:
244 __current_set_polling();
245
246 /*
247 * It is up to the idle functions to reenable local interrupts
248 */
249 if (WARN_ON_ONCE(irqs_disabled()))
250 local_irq_enable();
251}
252
253/*
254 * Generic idle loop implementation
255 *
256 * Called with polling cleared.
257 */
258static void do_idle(void)
259{
260 int cpu = smp_processor_id();
261
262 /*
263 * Check if we need to update blocked load
264 */
265 nohz_run_idle_balance(cpu);
266
267 /*
268 * If the arch has a polling bit, we maintain an invariant:
269 *
270 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
271 * rq->idle). This means that, if rq->idle has the polling bit set,
272 * then setting need_resched is guaranteed to cause the CPU to
273 * reschedule.
274 */
275
276 __current_set_polling();
277 tick_nohz_idle_enter();
278
279 while (!need_resched()) {
280 rmb();
281
282 /*
283 * Interrupts shouldn't be re-enabled from that point on until
284 * the CPU sleeping instruction is reached. Otherwise an interrupt
285 * may fire and queue a timer that would be ignored until the CPU
286 * wakes from the sleeping instruction. And testing need_resched()
287 * doesn't tell about pending needed timer reprogram.
288 *
289 * Several cases to consider:
290 *
291 * - SLEEP-UNTIL-PENDING-INTERRUPT based instructions such as
292 * "wfi" or "mwait" are fine because they can be entered with
293 * interrupt disabled.
294 *
295 * - sti;mwait() couple is fine because the interrupts are
296 * re-enabled only upon the execution of mwait, leaving no gap
297 * in-between.
298 *
299 * - ROLLBACK based idle handlers with the sleeping instruction
300 * called with interrupts enabled are NOT fine. In this scheme
301 * when the interrupt detects it has interrupted an idle handler,
302 * it rolls back to its beginning which performs the
303 * need_resched() check before re-executing the sleeping
304 * instruction. This can leak a pending needed timer reprogram.
305 * If such a scheme is really mandatory due to the lack of an
306 * appropriate CPU sleeping instruction, then a FAST-FORWARD
307 * must instead be applied: when the interrupt detects it has
308 * interrupted an idle handler, it must resume to the end of
309 * this idle handler so that the generic idle loop is iterated
310 * again to reprogram the tick.
311 */
312 local_irq_disable();
313
314 if (cpu_is_offline(cpu)) {
315 cpuhp_report_idle_dead();
316 arch_cpu_idle_dead();
317 }
318
319 arch_cpu_idle_enter();
320 rcu_nocb_flush_deferred_wakeup();
321
322 /*
323 * In poll mode we reenable interrupts and spin. Also if we
324 * detected in the wakeup from idle path that the tick
325 * broadcast device expired for us, we don't want to go deep
326 * idle as we know that the IPI is going to arrive right away.
327 */
328 if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
329 tick_nohz_idle_restart_tick();
330 cpu_idle_poll();
331 } else {
332 cpuidle_idle_call();
333 }
334 arch_cpu_idle_exit();
335 }
336
337 /*
338 * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
339 * be set, propagate it into PREEMPT_NEED_RESCHED.
340 *
341 * This is required because for polling idle loops we will not have had
342 * an IPI to fold the state for us.
343 */
344 preempt_set_need_resched();
345 tick_nohz_idle_exit();
346 __current_clr_polling();
347
348 /*
349 * We promise to call sched_ttwu_pending() and reschedule if
350 * need_resched() is set while polling is set. That means that clearing
351 * polling needs to be visible before doing these things.
352 */
353 smp_mb__after_atomic();
354
355 /*
356 * RCU relies on this call to be done outside of an RCU read-side
357 * critical section.
358 */
359 flush_smp_call_function_queue();
360 schedule_idle();
361
362 if (unlikely(klp_patch_pending(current)))
363 klp_update_patch_state(current);
364}
365
366bool cpu_in_idle(unsigned long pc)
367{
368 return pc >= (unsigned long)__cpuidle_text_start &&
369 pc < (unsigned long)__cpuidle_text_end;
370}
371
372struct idle_timer {
373 struct hrtimer timer;
374 int done;
375};
376
377static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
378{
379 struct idle_timer *it = container_of(timer, struct idle_timer, timer);
380
381 WRITE_ONCE(it->done, 1);
382 set_tsk_need_resched(current);
383
384 return HRTIMER_NORESTART;
385}
386
387void play_idle_precise(u64 duration_ns, u64 latency_ns)
388{
389 struct idle_timer it;
390
391 /*
392 * Only FIFO tasks can disable the tick since they don't need the forced
393 * preemption.
394 */
395 WARN_ON_ONCE(current->policy != SCHED_FIFO);
396 WARN_ON_ONCE(current->nr_cpus_allowed != 1);
397 WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
398 WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
399 WARN_ON_ONCE(!duration_ns);
400 WARN_ON_ONCE(current->mm);
401
402 rcu_sleep_check();
403 preempt_disable();
404 current->flags |= PF_IDLE;
405 cpuidle_use_deepest_state(latency_limit_ns: latency_ns);
406
407 it.done = 0;
408 hrtimer_init_on_stack(timer: &it.timer, CLOCK_MONOTONIC, mode: HRTIMER_MODE_REL_HARD);
409 it.timer.function = idle_inject_timer_fn;
410 hrtimer_start(timer: &it.timer, tim: ns_to_ktime(ns: duration_ns),
411 mode: HRTIMER_MODE_REL_PINNED_HARD);
412
413 while (!READ_ONCE(it.done))
414 do_idle();
415
416 cpuidle_use_deepest_state(latency_limit_ns: 0);
417 current->flags &= ~PF_IDLE;
418
419 preempt_fold_need_resched();
420 preempt_enable();
421}
422EXPORT_SYMBOL_GPL(play_idle_precise);
423
424void cpu_startup_entry(enum cpuhp_state state)
425{
426 current->flags |= PF_IDLE;
427 arch_cpu_idle_prepare();
428 cpuhp_online_idle(state);
429 while (1)
430 do_idle();
431}
432
433/*
434 * idle-task scheduling class.
435 */
436
437#ifdef CONFIG_SMP
438static int
439select_task_rq_idle(struct task_struct *p, int cpu, int flags)
440{
441 return task_cpu(p); /* IDLE tasks as never migrated */
442}
443
444static int
445balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
446{
447 return WARN_ON_ONCE(1);
448}
449#endif
450
451/*
452 * Idle tasks are unconditionally rescheduled:
453 */
454static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags)
455{
456 resched_curr(rq);
457}
458
459static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
460{
461}
462
463static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
464{
465 update_idle_core(rq);
466 schedstat_inc(rq->sched_goidle);
467}
468
469#ifdef CONFIG_SMP
470static struct task_struct *pick_task_idle(struct rq *rq)
471{
472 return rq->idle;
473}
474#endif
475
476struct task_struct *pick_next_task_idle(struct rq *rq)
477{
478 struct task_struct *next = rq->idle;
479
480 set_next_task_idle(rq, next, first: true);
481
482 return next;
483}
484
485/*
486 * It is not legal to sleep in the idle task - print a warning
487 * message if some code attempts to do it:
488 */
489static void
490dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
491{
492 raw_spin_rq_unlock_irq(rq);
493 printk(KERN_ERR "bad: scheduling from the idle thread!\n");
494 dump_stack();
495 raw_spin_rq_lock_irq(rq);
496}
497
498/*
499 * scheduler tick hitting a task of our scheduling class.
500 *
501 * NOTE: This function can be called remotely by the tick offload that
502 * goes along full dynticks. Therefore no local assumption can be made
503 * and everything must be accessed through the @rq and @curr passed in
504 * parameters.
505 */
506static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
507{
508}
509
510static void switched_to_idle(struct rq *rq, struct task_struct *p)
511{
512 BUG();
513}
514
515static void
516prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
517{
518 BUG();
519}
520
521static void update_curr_idle(struct rq *rq)
522{
523}
524
525/*
526 * Simple, special scheduling class for the per-CPU idle tasks:
527 */
528DEFINE_SCHED_CLASS(idle) = {
529
530 /* no enqueue/yield_task for idle tasks */
531
532 /* dequeue is not valid, we print a debug message there: */
533 .dequeue_task = dequeue_task_idle,
534
535 .wakeup_preempt = wakeup_preempt_idle,
536
537 .pick_next_task = pick_next_task_idle,
538 .put_prev_task = put_prev_task_idle,
539 .set_next_task = set_next_task_idle,
540
541#ifdef CONFIG_SMP
542 .balance = balance_idle,
543 .pick_task = pick_task_idle,
544 .select_task_rq = select_task_rq_idle,
545 .set_cpus_allowed = set_cpus_allowed_common,
546#endif
547
548 .task_tick = task_tick_idle,
549
550 .prio_changed = prio_changed_idle,
551 .switched_to = switched_to_idle,
552 .update_curr = update_curr_idle,
553};
554

source code of linux/kernel/sched/idle.c