Line data Source code
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 0 : void sched_idle_set_state(struct cpuidle_state *idle_state)
18 : {
19 0 : idle_set_state(this_rq(), idle_state);
20 0 : }
21 :
22 : static int __read_mostly cpu_idle_force_poll;
23 :
24 0 : void cpu_idle_poll_ctrl(bool enable)
25 : {
26 0 : if (enable) {
27 0 : cpu_idle_force_poll++;
28 : } else {
29 0 : cpu_idle_force_poll--;
30 0 : WARN_ON_ONCE(cpu_idle_force_poll < 0);
31 : }
32 0 : }
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 0 : static noinline int __cpuidle cpu_idle_poll(void)
53 : {
54 : instrumentation_begin();
55 0 : trace_cpu_idle(0, smp_processor_id());
56 : stop_critical_timings();
57 : ct_cpuidle_enter();
58 :
59 : raw_local_irq_enable();
60 0 : while (!tif_need_resched() &&
61 0 : (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 0 : trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
68 : local_irq_enable();
69 : instrumentation_end();
70 :
71 0 : return 1;
72 : }
73 :
74 : /* Weak implementations for optional arch specific functions */
75 0 : void __weak arch_cpu_idle_prepare(void) { }
76 0 : void __weak arch_cpu_idle_enter(void) { }
77 0 : void __weak arch_cpu_idle_exit(void) { }
78 0 : void __weak arch_cpu_idle_dead(void) { }
79 0 : void __weak arch_cpu_idle(void)
80 : {
81 0 : cpu_idle_force_poll = 1;
82 0 : }
83 :
84 : /**
85 : * default_idle_call - Default CPU idle routine.
86 : *
87 : * To use when the cpuidle framework cannot be used.
88 : */
89 0 : void __cpuidle default_idle_call(void)
90 : {
91 : instrumentation_begin();
92 : if (!current_clr_polling_and_test()) {
93 0 : trace_cpu_idle(1, smp_processor_id());
94 : stop_critical_timings();
95 :
96 : ct_cpuidle_enter();
97 0 : arch_cpu_idle();
98 : ct_cpuidle_exit();
99 :
100 : start_critical_timings();
101 : trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
102 : }
103 : local_irq_enable();
104 : instrumentation_end();
105 0 : }
106 :
107 : static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
108 : struct cpuidle_device *dev)
109 : {
110 : if (current_clr_polling_and_test())
111 : return -EBUSY;
112 :
113 : return cpuidle_enter_s2idle(drv, dev);
114 : }
115 :
116 : static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
117 : int next_state)
118 : {
119 : /*
120 : * The idle task must be scheduled, it is pointless to go to idle, just
121 : * update no idle residency and return.
122 : */
123 : if (current_clr_polling_and_test()) {
124 : dev->last_residency_ns = 0;
125 : local_irq_enable();
126 : return -EBUSY;
127 : }
128 :
129 : /*
130 : * Enter the idle state previously returned by the governor decision.
131 : * This function will block until an interrupt occurs and will take
132 : * care of re-enabling the local interrupts
133 : */
134 : return cpuidle_enter(drv, dev, next_state);
135 : }
136 :
137 : /**
138 : * cpuidle_idle_call - the main idle function
139 : *
140 : * NOTE: no locks or semaphores should be used here
141 : *
142 : * On architectures that support TIF_POLLING_NRFLAG, is called with polling
143 : * set, and it returns with polling set. If it ever stops polling, it
144 : * must clear the polling bit.
145 : */
146 0 : static void cpuidle_idle_call(void)
147 : {
148 0 : struct cpuidle_device *dev = cpuidle_get_device();
149 0 : struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
150 : int next_state, entered_state;
151 :
152 : /*
153 : * Check if the idle task must be rescheduled. If it is the
154 : * case, exit the function after re-enabling the local irq.
155 : */
156 0 : if (need_resched()) {
157 : local_irq_enable();
158 : return;
159 : }
160 :
161 : /*
162 : * The RCU framework needs to be told that we are entering an idle
163 : * section, so no more rcu read side critical sections and one more
164 : * step to the grace period
165 : */
166 :
167 : if (cpuidle_not_available(drv, dev)) {
168 : tick_nohz_idle_stop_tick();
169 :
170 0 : default_idle_call();
171 : goto exit_idle;
172 : }
173 :
174 : /*
175 : * Suspend-to-idle ("s2idle") is a system state in which all user space
176 : * has been frozen, all I/O devices have been suspended and the only
177 : * activity happens here and in interrupts (if any). In that case bypass
178 : * the cpuidle governor and go straight for the deepest idle state
179 : * available. Possibly also suspend the local tick and the entire
180 : * timekeeping to prevent timer interrupts from kicking us out of idle
181 : * until a proper wakeup interrupt happens.
182 : */
183 :
184 : if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
185 : u64 max_latency_ns;
186 :
187 : if (idle_should_enter_s2idle()) {
188 :
189 : entered_state = call_cpuidle_s2idle(drv, dev);
190 : if (entered_state > 0)
191 : goto exit_idle;
192 :
193 : max_latency_ns = U64_MAX;
194 : } else {
195 : max_latency_ns = dev->forced_idle_latency_limit_ns;
196 : }
197 :
198 : tick_nohz_idle_stop_tick();
199 :
200 : next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
201 : call_cpuidle(drv, dev, next_state);
202 : } else {
203 : bool stop_tick = true;
204 :
205 : /*
206 : * Ask the cpuidle framework to choose a convenient idle state.
207 : */
208 : next_state = cpuidle_select(drv, dev, &stop_tick);
209 :
210 : if (stop_tick || tick_nohz_tick_stopped())
211 : tick_nohz_idle_stop_tick();
212 : else
213 : tick_nohz_idle_retain_tick();
214 :
215 : entered_state = call_cpuidle(drv, dev, next_state);
216 : /*
217 : * Give the governor an opportunity to reflect on the outcome
218 : */
219 : cpuidle_reflect(dev, entered_state);
220 : }
221 :
222 : exit_idle:
223 : __current_set_polling();
224 :
225 : /*
226 : * It is up to the idle functions to reenable local interrupts
227 : */
228 0 : if (WARN_ON_ONCE(irqs_disabled()))
229 : local_irq_enable();
230 : }
231 :
232 : /*
233 : * Generic idle loop implementation
234 : *
235 : * Called with polling cleared.
236 : */
237 0 : static void do_idle(void)
238 : {
239 0 : int cpu = smp_processor_id();
240 :
241 : /*
242 : * Check if we need to update blocked load
243 : */
244 0 : nohz_run_idle_balance(cpu);
245 :
246 : /*
247 : * If the arch has a polling bit, we maintain an invariant:
248 : *
249 : * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
250 : * rq->idle). This means that, if rq->idle has the polling bit set,
251 : * then setting need_resched is guaranteed to cause the CPU to
252 : * reschedule.
253 : */
254 :
255 : __current_set_polling();
256 : tick_nohz_idle_enter();
257 :
258 0 : while (!need_resched()) {
259 0 : rmb();
260 :
261 : local_irq_disable();
262 :
263 0 : if (cpu_is_offline(cpu)) {
264 : tick_nohz_idle_stop_tick();
265 : cpuhp_report_idle_dead();
266 : arch_cpu_idle_dead();
267 : }
268 :
269 0 : arch_cpu_idle_enter();
270 : rcu_nocb_flush_deferred_wakeup();
271 :
272 : /*
273 : * In poll mode we reenable interrupts and spin. Also if we
274 : * detected in the wakeup from idle path that the tick
275 : * broadcast device expired for us, we don't want to go deep
276 : * idle as we know that the IPI is going to arrive right away.
277 : */
278 0 : if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
279 : tick_nohz_idle_restart_tick();
280 0 : cpu_idle_poll();
281 : } else {
282 0 : cpuidle_idle_call();
283 : }
284 0 : arch_cpu_idle_exit();
285 : }
286 :
287 : /*
288 : * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
289 : * be set, propagate it into PREEMPT_NEED_RESCHED.
290 : *
291 : * This is required because for polling idle loops we will not have had
292 : * an IPI to fold the state for us.
293 : */
294 : preempt_set_need_resched();
295 : tick_nohz_idle_exit();
296 : __current_clr_polling();
297 :
298 : /*
299 : * We promise to call sched_ttwu_pending() and reschedule if
300 : * need_resched() is set while polling is set. That means that clearing
301 : * polling needs to be visible before doing these things.
302 : */
303 0 : smp_mb__after_atomic();
304 :
305 : /*
306 : * RCU relies on this call to be done outside of an RCU read-side
307 : * critical section.
308 : */
309 : flush_smp_call_function_queue();
310 0 : schedule_idle();
311 :
312 0 : if (unlikely(klp_patch_pending(current)))
313 : klp_update_patch_state(current);
314 0 : }
315 :
316 0 : bool cpu_in_idle(unsigned long pc)
317 : {
318 0 : return pc >= (unsigned long)__cpuidle_text_start &&
319 0 : pc < (unsigned long)__cpuidle_text_end;
320 : }
321 :
322 : struct idle_timer {
323 : struct hrtimer timer;
324 : int done;
325 : };
326 :
327 0 : static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
328 : {
329 0 : struct idle_timer *it = container_of(timer, struct idle_timer, timer);
330 :
331 0 : WRITE_ONCE(it->done, 1);
332 0 : set_tsk_need_resched(current);
333 :
334 0 : return HRTIMER_NORESTART;
335 : }
336 :
337 0 : void play_idle_precise(u64 duration_ns, u64 latency_ns)
338 : {
339 : struct idle_timer it;
340 :
341 : /*
342 : * Only FIFO tasks can disable the tick since they don't need the forced
343 : * preemption.
344 : */
345 0 : WARN_ON_ONCE(current->policy != SCHED_FIFO);
346 0 : WARN_ON_ONCE(current->nr_cpus_allowed != 1);
347 0 : WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
348 0 : WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
349 0 : WARN_ON_ONCE(!duration_ns);
350 0 : WARN_ON_ONCE(current->mm);
351 :
352 : rcu_sleep_check();
353 0 : preempt_disable();
354 0 : current->flags |= PF_IDLE;
355 0 : cpuidle_use_deepest_state(latency_ns);
356 :
357 0 : it.done = 0;
358 0 : hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
359 0 : it.timer.function = idle_inject_timer_fn;
360 0 : hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
361 : HRTIMER_MODE_REL_PINNED_HARD);
362 :
363 0 : while (!READ_ONCE(it.done))
364 0 : do_idle();
365 :
366 0 : cpuidle_use_deepest_state(0);
367 0 : current->flags &= ~PF_IDLE;
368 :
369 : preempt_fold_need_resched();
370 0 : preempt_enable();
371 0 : }
372 : EXPORT_SYMBOL_GPL(play_idle_precise);
373 :
374 0 : void cpu_startup_entry(enum cpuhp_state state)
375 : {
376 0 : arch_cpu_idle_prepare();
377 0 : cpuhp_online_idle(state);
378 : while (1)
379 0 : do_idle();
380 : }
381 :
382 : /*
383 : * idle-task scheduling class.
384 : */
385 :
386 : #ifdef CONFIG_SMP
387 : static int
388 : select_task_rq_idle(struct task_struct *p, int cpu, int flags)
389 : {
390 : return task_cpu(p); /* IDLE tasks as never migrated */
391 : }
392 :
393 : static int
394 : balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
395 : {
396 : return WARN_ON_ONCE(1);
397 : }
398 : #endif
399 :
400 : /*
401 : * Idle tasks are unconditionally rescheduled:
402 : */
403 0 : static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
404 : {
405 0 : resched_curr(rq);
406 0 : }
407 :
408 2 : static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
409 : {
410 2 : }
411 :
412 0 : static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
413 : {
414 1 : update_idle_core(rq);
415 : schedstat_inc(rq->sched_goidle);
416 0 : }
417 :
418 : #ifdef CONFIG_SMP
419 : static struct task_struct *pick_task_idle(struct rq *rq)
420 : {
421 : return rq->idle;
422 : }
423 : #endif
424 :
425 1 : struct task_struct *pick_next_task_idle(struct rq *rq)
426 : {
427 1 : struct task_struct *next = rq->idle;
428 :
429 1 : set_next_task_idle(rq, next, true);
430 :
431 1 : return next;
432 : }
433 :
434 : /*
435 : * It is not legal to sleep in the idle task - print a warning
436 : * message if some code attempts to do it:
437 : */
438 : static void
439 0 : dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
440 : {
441 0 : raw_spin_rq_unlock_irq(rq);
442 0 : printk(KERN_ERR "bad: scheduling from the idle thread!\n");
443 0 : dump_stack();
444 0 : raw_spin_rq_lock_irq(rq);
445 0 : }
446 :
447 : /*
448 : * scheduler tick hitting a task of our scheduling class.
449 : *
450 : * NOTE: This function can be called remotely by the tick offload that
451 : * goes along full dynticks. Therefore no local assumption can be made
452 : * and everything must be accessed through the @rq and @curr passed in
453 : * parameters.
454 : */
455 4 : static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
456 : {
457 4 : }
458 :
459 0 : static void switched_to_idle(struct rq *rq, struct task_struct *p)
460 : {
461 0 : BUG();
462 : }
463 :
464 : static void
465 0 : prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
466 : {
467 0 : BUG();
468 : }
469 :
470 0 : static void update_curr_idle(struct rq *rq)
471 : {
472 0 : }
473 :
474 : /*
475 : * Simple, special scheduling class for the per-CPU idle tasks:
476 : */
477 : DEFINE_SCHED_CLASS(idle) = {
478 :
479 : /* no enqueue/yield_task for idle tasks */
480 :
481 : /* dequeue is not valid, we print a debug message there: */
482 : .dequeue_task = dequeue_task_idle,
483 :
484 : .check_preempt_curr = check_preempt_curr_idle,
485 :
486 : .pick_next_task = pick_next_task_idle,
487 : .put_prev_task = put_prev_task_idle,
488 : .set_next_task = set_next_task_idle,
489 :
490 : #ifdef CONFIG_SMP
491 : .balance = balance_idle,
492 : .pick_task = pick_task_idle,
493 : .select_task_rq = select_task_rq_idle,
494 : .set_cpus_allowed = set_cpus_allowed_common,
495 : #endif
496 :
497 : .task_tick = task_tick_idle,
498 :
499 : .prio_changed = prio_changed_idle,
500 : .switched_to = switched_to_idle,
501 : .update_curr = update_curr_idle,
502 : };
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