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 */ |
11 | extern 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 | */ |
17 | void sched_idle_set_state(struct cpuidle_state *idle_state) |
18 | { |
19 | idle_set_state(this_rq(), idle_state); |
20 | } |
21 | |
22 | static int __read_mostly cpu_idle_force_poll; |
23 | |
24 | void 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 |
35 | static 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 | |
43 | static 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 | |
52 | static 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 */ |
75 | void __weak arch_cpu_idle_prepare(void) { } |
76 | void __weak arch_cpu_idle_enter(void) { } |
77 | void __weak arch_cpu_idle_exit(void) { } |
78 | void __weak __noreturn arch_cpu_idle_dead(void) { while (1); } |
79 | void __weak arch_cpu_idle(void) |
80 | { |
81 | cpu_idle_force_poll = 1; |
82 | } |
83 | |
84 | #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST_IDLE |
85 | DEFINE_STATIC_KEY_FALSE(arch_needs_tick_broadcast); |
86 | |
87 | static inline void cond_tick_broadcast_enter(void) |
88 | { |
89 | if (static_branch_unlikely(&arch_needs_tick_broadcast)) |
90 | tick_broadcast_enter(); |
91 | } |
92 | |
93 | static inline void cond_tick_broadcast_exit(void) |
94 | { |
95 | if (static_branch_unlikely(&arch_needs_tick_broadcast)) |
96 | tick_broadcast_exit(); |
97 | } |
98 | #else |
99 | static inline void cond_tick_broadcast_enter(void) { } |
100 | static 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 | */ |
108 | void __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 | |
128 | static 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 | |
137 | static 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 | */ |
167 | static 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 | |
243 | exit_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 | */ |
258 | static 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 | |
366 | bool cpu_in_idle(unsigned long pc) |
367 | { |
368 | return pc >= (unsigned long)__cpuidle_text_start && |
369 | pc < (unsigned long)__cpuidle_text_end; |
370 | } |
371 | |
372 | struct idle_timer { |
373 | struct hrtimer timer; |
374 | int done; |
375 | }; |
376 | |
377 | static 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 | |
387 | void 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 | } |
422 | EXPORT_SYMBOL_GPL(play_idle_precise); |
423 | |
424 | void 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 |
438 | static int |
439 | select_task_rq_idle(struct task_struct *p, int cpu, int flags) |
440 | { |
441 | return task_cpu(p); /* IDLE tasks as never migrated */ |
442 | } |
443 | |
444 | static int |
445 | balance_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 | */ |
454 | static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags) |
455 | { |
456 | resched_curr(rq); |
457 | } |
458 | |
459 | static void put_prev_task_idle(struct rq *rq, struct task_struct *prev) |
460 | { |
461 | } |
462 | |
463 | static 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 |
470 | static struct task_struct *pick_task_idle(struct rq *rq) |
471 | { |
472 | return rq->idle; |
473 | } |
474 | #endif |
475 | |
476 | struct 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 | */ |
489 | static void |
490 | dequeue_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 | */ |
506 | static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued) |
507 | { |
508 | } |
509 | |
510 | static void switched_to_idle(struct rq *rq, struct task_struct *p) |
511 | { |
512 | BUG(); |
513 | } |
514 | |
515 | static void |
516 | prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio) |
517 | { |
518 | BUG(); |
519 | } |
520 | |
521 | static void update_curr_idle(struct rq *rq) |
522 | { |
523 | } |
524 | |
525 | /* |
526 | * Simple, special scheduling class for the per-CPU idle tasks: |
527 | */ |
528 | DEFINE_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 | |