xref: /openbmc/linux/kernel/sched/idle.c (revision cff9b233)
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  */
sched_idle_set_state(struct cpuidle_state * idle_state)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 
cpu_idle_poll_ctrl(bool enable)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
cpu_idle_poll_setup(char * __unused)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 
cpu_idle_nopoll_setup(char * __unused)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 
cpu_idle_poll(void)52 static noinline int __cpuidle cpu_idle_poll(void)
53 {
54 	instrumentation_begin();
55 	trace_cpu_idle(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 */
arch_cpu_idle_prepare(void)75 void __weak arch_cpu_idle_prepare(void) { }
arch_cpu_idle_enter(void)76 void __weak arch_cpu_idle_enter(void) { }
arch_cpu_idle_exit(void)77 void __weak arch_cpu_idle_exit(void) { }
arch_cpu_idle_dead(void)78 void __weak __noreturn arch_cpu_idle_dead(void) { while (1); }
arch_cpu_idle(void)79 void __weak arch_cpu_idle(void)
80 {
81 	cpu_idle_force_poll = 1;
82 }
83 
84 /**
85  * default_idle_call - Default CPU idle routine.
86  *
87  * To use when the cpuidle framework cannot be used.
88  */
default_idle_call(void)89 void __cpuidle default_idle_call(void)
90 {
91 	instrumentation_begin();
92 	if (!current_clr_polling_and_test()) {
93 		trace_cpu_idle(1, smp_processor_id());
94 		stop_critical_timings();
95 
96 		ct_cpuidle_enter();
97 		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 }
106 
call_cpuidle_s2idle(struct cpuidle_driver * drv,struct cpuidle_device * dev)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 
call_cpuidle(struct cpuidle_driver * drv,struct cpuidle_device * dev,int next_state)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  */
cpuidle_idle_call(void)146 static void cpuidle_idle_call(void)
147 {
148 	struct cpuidle_device *dev = cpuidle_get_device();
149 	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 	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 		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 	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  */
do_idle(void)237 static void do_idle(void)
238 {
239 	int cpu = smp_processor_id();
240 
241 	/*
242 	 * Check if we need to update blocked load
243 	 */
244 	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 	while (!need_resched()) {
259 		rmb();
260 
261 		local_irq_disable();
262 
263 		if (cpu_is_offline(cpu)) {
264 			tick_nohz_idle_stop_tick();
265 			cpuhp_report_idle_dead();
266 			arch_cpu_idle_dead();
267 		}
268 
269 		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 		if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
279 			tick_nohz_idle_restart_tick();
280 			cpu_idle_poll();
281 		} else {
282 			cpuidle_idle_call();
283 		}
284 		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 	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 	schedule_idle();
311 
312 	if (unlikely(klp_patch_pending(current)))
313 		klp_update_patch_state(current);
314 }
315 
cpu_in_idle(unsigned long pc)316 bool cpu_in_idle(unsigned long pc)
317 {
318 	return pc >= (unsigned long)__cpuidle_text_start &&
319 		pc < (unsigned long)__cpuidle_text_end;
320 }
321 
322 struct idle_timer {
323 	struct hrtimer timer;
324 	int done;
325 };
326 
idle_inject_timer_fn(struct hrtimer * timer)327 static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
328 {
329 	struct idle_timer *it = container_of(timer, struct idle_timer, timer);
330 
331 	WRITE_ONCE(it->done, 1);
332 	set_tsk_need_resched(current);
333 
334 	return HRTIMER_NORESTART;
335 }
336 
play_idle_precise(u64 duration_ns,u64 latency_ns)337 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 	WARN_ON_ONCE(current->policy != SCHED_FIFO);
346 	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
347 	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
348 	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
349 	WARN_ON_ONCE(!duration_ns);
350 	WARN_ON_ONCE(current->mm);
351 
352 	rcu_sleep_check();
353 	preempt_disable();
354 	current->flags |= PF_IDLE;
355 	cpuidle_use_deepest_state(latency_ns);
356 
357 	it.done = 0;
358 	hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
359 	it.timer.function = idle_inject_timer_fn;
360 	hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
361 		      HRTIMER_MODE_REL_PINNED_HARD);
362 
363 	while (!READ_ONCE(it.done))
364 		do_idle();
365 
366 	cpuidle_use_deepest_state(0);
367 	current->flags &= ~PF_IDLE;
368 
369 	preempt_fold_need_resched();
370 	preempt_enable();
371 }
372 EXPORT_SYMBOL_GPL(play_idle_precise);
373 
cpu_startup_entry(enum cpuhp_state state)374 void cpu_startup_entry(enum cpuhp_state state)
375 {
376 	current->flags |= PF_IDLE;
377 	arch_cpu_idle_prepare();
378 	cpuhp_online_idle(state);
379 	while (1)
380 		do_idle();
381 }
382 
383 /*
384  * idle-task scheduling class.
385  */
386 
387 #ifdef CONFIG_SMP
388 static int
select_task_rq_idle(struct task_struct * p,int cpu,int flags)389 select_task_rq_idle(struct task_struct *p, int cpu, int flags)
390 {
391 	return task_cpu(p); /* IDLE tasks as never migrated */
392 }
393 
394 static int
balance_idle(struct rq * rq,struct task_struct * prev,struct rq_flags * rf)395 balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
396 {
397 	return WARN_ON_ONCE(1);
398 }
399 #endif
400 
401 /*
402  * Idle tasks are unconditionally rescheduled:
403  */
check_preempt_curr_idle(struct rq * rq,struct task_struct * p,int flags)404 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
405 {
406 	resched_curr(rq);
407 }
408 
put_prev_task_idle(struct rq * rq,struct task_struct * prev)409 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
410 {
411 }
412 
set_next_task_idle(struct rq * rq,struct task_struct * next,bool first)413 static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
414 {
415 	update_idle_core(rq);
416 	schedstat_inc(rq->sched_goidle);
417 }
418 
419 #ifdef CONFIG_SMP
pick_task_idle(struct rq * rq)420 static struct task_struct *pick_task_idle(struct rq *rq)
421 {
422 	return rq->idle;
423 }
424 #endif
425 
pick_next_task_idle(struct rq * rq)426 struct task_struct *pick_next_task_idle(struct rq *rq)
427 {
428 	struct task_struct *next = rq->idle;
429 
430 	set_next_task_idle(rq, next, true);
431 
432 	return next;
433 }
434 
435 /*
436  * It is not legal to sleep in the idle task - print a warning
437  * message if some code attempts to do it:
438  */
439 static void
dequeue_task_idle(struct rq * rq,struct task_struct * p,int flags)440 dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
441 {
442 	raw_spin_rq_unlock_irq(rq);
443 	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
444 	dump_stack();
445 	raw_spin_rq_lock_irq(rq);
446 }
447 
448 /*
449  * scheduler tick hitting a task of our scheduling class.
450  *
451  * NOTE: This function can be called remotely by the tick offload that
452  * goes along full dynticks. Therefore no local assumption can be made
453  * and everything must be accessed through the @rq and @curr passed in
454  * parameters.
455  */
task_tick_idle(struct rq * rq,struct task_struct * curr,int queued)456 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
457 {
458 }
459 
switched_to_idle(struct rq * rq,struct task_struct * p)460 static void switched_to_idle(struct rq *rq, struct task_struct *p)
461 {
462 	BUG();
463 }
464 
465 static void
prio_changed_idle(struct rq * rq,struct task_struct * p,int oldprio)466 prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
467 {
468 	BUG();
469 }
470 
update_curr_idle(struct rq * rq)471 static void update_curr_idle(struct rq *rq)
472 {
473 }
474 
475 /*
476  * Simple, special scheduling class for the per-CPU idle tasks:
477  */
478 DEFINE_SCHED_CLASS(idle) = {
479 
480 	/* no enqueue/yield_task for idle tasks */
481 
482 	/* dequeue is not valid, we print a debug message there: */
483 	.dequeue_task		= dequeue_task_idle,
484 
485 	.check_preempt_curr	= check_preempt_curr_idle,
486 
487 	.pick_next_task		= pick_next_task_idle,
488 	.put_prev_task		= put_prev_task_idle,
489 	.set_next_task          = set_next_task_idle,
490 
491 #ifdef CONFIG_SMP
492 	.balance		= balance_idle,
493 	.pick_task		= pick_task_idle,
494 	.select_task_rq		= select_task_rq_idle,
495 	.set_cpus_allowed	= set_cpus_allowed_common,
496 #endif
497 
498 	.task_tick		= task_tick_idle,
499 
500 	.prio_changed		= prio_changed_idle,
501 	.switched_to		= switched_to_idle,
502 	.update_curr		= update_curr_idle,
503 };
504