xref: /openbmc/linux/kernel/time/tick-common.c (revision f5ad1c74)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * This file contains the base functions to manage periodic tick
4  * related events.
5  *
6  * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
7  * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
8  * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
9  */
10 #include <linux/cpu.h>
11 #include <linux/err.h>
12 #include <linux/hrtimer.h>
13 #include <linux/interrupt.h>
14 #include <linux/nmi.h>
15 #include <linux/percpu.h>
16 #include <linux/profile.h>
17 #include <linux/sched.h>
18 #include <linux/module.h>
19 #include <trace/events/power.h>
20 
21 #include <asm/irq_regs.h>
22 
23 #include "tick-internal.h"
24 
25 /*
26  * Tick devices
27  */
28 DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
29 /*
30  * Tick next event: keeps track of the tick time. It's updated by the
31  * CPU which handles the tick and protected by jiffies_lock. There is
32  * no requirement to write hold the jiffies seqcount for it.
33  */
34 ktime_t tick_next_period;
35 
36 /*
37  * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
38  * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This
39  * variable has two functions:
40  *
41  * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the
42  *    timekeeping lock all at once. Only the CPU which is assigned to do the
43  *    update is handling it.
44  *
45  * 2) Hand off the duty in the NOHZ idle case by setting the value to
46  *    TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks
47  *    at it will take over and keep the time keeping alive.  The handover
48  *    procedure also covers cpu hotplug.
49  */
50 int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
51 #ifdef CONFIG_NO_HZ_FULL
52 /*
53  * tick_do_timer_boot_cpu indicates the boot CPU temporarily owns
54  * tick_do_timer_cpu and it should be taken over by an eligible secondary
55  * when one comes online.
56  */
57 static int tick_do_timer_boot_cpu __read_mostly = -1;
58 #endif
59 
60 /*
61  * Debugging: see timer_list.c
62  */
63 struct tick_device *tick_get_device(int cpu)
64 {
65 	return &per_cpu(tick_cpu_device, cpu);
66 }
67 
68 /**
69  * tick_is_oneshot_available - check for a oneshot capable event device
70  */
71 int tick_is_oneshot_available(void)
72 {
73 	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
74 
75 	if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
76 		return 0;
77 	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
78 		return 1;
79 	return tick_broadcast_oneshot_available();
80 }
81 
82 /*
83  * Periodic tick
84  */
85 static void tick_periodic(int cpu)
86 {
87 	if (tick_do_timer_cpu == cpu) {
88 		raw_spin_lock(&jiffies_lock);
89 		write_seqcount_begin(&jiffies_seq);
90 
91 		/* Keep track of the next tick event */
92 		tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);
93 
94 		do_timer(1);
95 		write_seqcount_end(&jiffies_seq);
96 		raw_spin_unlock(&jiffies_lock);
97 		update_wall_time();
98 	}
99 
100 	update_process_times(user_mode(get_irq_regs()));
101 	profile_tick(CPU_PROFILING);
102 }
103 
104 /*
105  * Event handler for periodic ticks
106  */
107 void tick_handle_periodic(struct clock_event_device *dev)
108 {
109 	int cpu = smp_processor_id();
110 	ktime_t next = dev->next_event;
111 
112 	tick_periodic(cpu);
113 
114 #if defined(CONFIG_HIGH_RES_TIMERS) || defined(CONFIG_NO_HZ_COMMON)
115 	/*
116 	 * The cpu might have transitioned to HIGHRES or NOHZ mode via
117 	 * update_process_times() -> run_local_timers() ->
118 	 * hrtimer_run_queues().
119 	 */
120 	if (dev->event_handler != tick_handle_periodic)
121 		return;
122 #endif
123 
124 	if (!clockevent_state_oneshot(dev))
125 		return;
126 	for (;;) {
127 		/*
128 		 * Setup the next period for devices, which do not have
129 		 * periodic mode:
130 		 */
131 		next = ktime_add_ns(next, TICK_NSEC);
132 
133 		if (!clockevents_program_event(dev, next, false))
134 			return;
135 		/*
136 		 * Have to be careful here. If we're in oneshot mode,
137 		 * before we call tick_periodic() in a loop, we need
138 		 * to be sure we're using a real hardware clocksource.
139 		 * Otherwise we could get trapped in an infinite
140 		 * loop, as the tick_periodic() increments jiffies,
141 		 * which then will increment time, possibly causing
142 		 * the loop to trigger again and again.
143 		 */
144 		if (timekeeping_valid_for_hres())
145 			tick_periodic(cpu);
146 	}
147 }
148 
149 /*
150  * Setup the device for a periodic tick
151  */
152 void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
153 {
154 	tick_set_periodic_handler(dev, broadcast);
155 
156 	/* Broadcast setup ? */
157 	if (!tick_device_is_functional(dev))
158 		return;
159 
160 	if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
161 	    !tick_broadcast_oneshot_active()) {
162 		clockevents_switch_state(dev, CLOCK_EVT_STATE_PERIODIC);
163 	} else {
164 		unsigned int seq;
165 		ktime_t next;
166 
167 		do {
168 			seq = read_seqcount_begin(&jiffies_seq);
169 			next = tick_next_period;
170 		} while (read_seqcount_retry(&jiffies_seq, seq));
171 
172 		clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
173 
174 		for (;;) {
175 			if (!clockevents_program_event(dev, next, false))
176 				return;
177 			next = ktime_add_ns(next, TICK_NSEC);
178 		}
179 	}
180 }
181 
182 #ifdef CONFIG_NO_HZ_FULL
183 static void giveup_do_timer(void *info)
184 {
185 	int cpu = *(unsigned int *)info;
186 
187 	WARN_ON(tick_do_timer_cpu != smp_processor_id());
188 
189 	tick_do_timer_cpu = cpu;
190 }
191 
192 static void tick_take_do_timer_from_boot(void)
193 {
194 	int cpu = smp_processor_id();
195 	int from = tick_do_timer_boot_cpu;
196 
197 	if (from >= 0 && from != cpu)
198 		smp_call_function_single(from, giveup_do_timer, &cpu, 1);
199 }
200 #endif
201 
202 /*
203  * Setup the tick device
204  */
205 static void tick_setup_device(struct tick_device *td,
206 			      struct clock_event_device *newdev, int cpu,
207 			      const struct cpumask *cpumask)
208 {
209 	void (*handler)(struct clock_event_device *) = NULL;
210 	ktime_t next_event = 0;
211 
212 	/*
213 	 * First device setup ?
214 	 */
215 	if (!td->evtdev) {
216 		/*
217 		 * If no cpu took the do_timer update, assign it to
218 		 * this cpu:
219 		 */
220 		if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
221 			tick_do_timer_cpu = cpu;
222 
223 			tick_next_period = ktime_get();
224 #ifdef CONFIG_NO_HZ_FULL
225 			/*
226 			 * The boot CPU may be nohz_full, in which case set
227 			 * tick_do_timer_boot_cpu so the first housekeeping
228 			 * secondary that comes up will take do_timer from
229 			 * us.
230 			 */
231 			if (tick_nohz_full_cpu(cpu))
232 				tick_do_timer_boot_cpu = cpu;
233 
234 		} else if (tick_do_timer_boot_cpu != -1 &&
235 						!tick_nohz_full_cpu(cpu)) {
236 			tick_take_do_timer_from_boot();
237 			tick_do_timer_boot_cpu = -1;
238 			WARN_ON(tick_do_timer_cpu != cpu);
239 #endif
240 		}
241 
242 		/*
243 		 * Startup in periodic mode first.
244 		 */
245 		td->mode = TICKDEV_MODE_PERIODIC;
246 	} else {
247 		handler = td->evtdev->event_handler;
248 		next_event = td->evtdev->next_event;
249 		td->evtdev->event_handler = clockevents_handle_noop;
250 	}
251 
252 	td->evtdev = newdev;
253 
254 	/*
255 	 * When the device is not per cpu, pin the interrupt to the
256 	 * current cpu:
257 	 */
258 	if (!cpumask_equal(newdev->cpumask, cpumask))
259 		irq_set_affinity(newdev->irq, cpumask);
260 
261 	/*
262 	 * When global broadcasting is active, check if the current
263 	 * device is registered as a placeholder for broadcast mode.
264 	 * This allows us to handle this x86 misfeature in a generic
265 	 * way. This function also returns !=0 when we keep the
266 	 * current active broadcast state for this CPU.
267 	 */
268 	if (tick_device_uses_broadcast(newdev, cpu))
269 		return;
270 
271 	if (td->mode == TICKDEV_MODE_PERIODIC)
272 		tick_setup_periodic(newdev, 0);
273 	else
274 		tick_setup_oneshot(newdev, handler, next_event);
275 }
276 
277 void tick_install_replacement(struct clock_event_device *newdev)
278 {
279 	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
280 	int cpu = smp_processor_id();
281 
282 	clockevents_exchange_device(td->evtdev, newdev);
283 	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
284 	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
285 		tick_oneshot_notify();
286 }
287 
288 static bool tick_check_percpu(struct clock_event_device *curdev,
289 			      struct clock_event_device *newdev, int cpu)
290 {
291 	if (!cpumask_test_cpu(cpu, newdev->cpumask))
292 		return false;
293 	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
294 		return true;
295 	/* Check if irq affinity can be set */
296 	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
297 		return false;
298 	/* Prefer an existing cpu local device */
299 	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
300 		return false;
301 	return true;
302 }
303 
304 static bool tick_check_preferred(struct clock_event_device *curdev,
305 				 struct clock_event_device *newdev)
306 {
307 	/* Prefer oneshot capable device */
308 	if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
309 		if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
310 			return false;
311 		if (tick_oneshot_mode_active())
312 			return false;
313 	}
314 
315 	/*
316 	 * Use the higher rated one, but prefer a CPU local device with a lower
317 	 * rating than a non-CPU local device
318 	 */
319 	return !curdev ||
320 		newdev->rating > curdev->rating ||
321 	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
322 }
323 
324 /*
325  * Check whether the new device is a better fit than curdev. curdev
326  * can be NULL !
327  */
328 bool tick_check_replacement(struct clock_event_device *curdev,
329 			    struct clock_event_device *newdev)
330 {
331 	if (!tick_check_percpu(curdev, newdev, smp_processor_id()))
332 		return false;
333 
334 	return tick_check_preferred(curdev, newdev);
335 }
336 
337 /*
338  * Check, if the new registered device should be used. Called with
339  * clockevents_lock held and interrupts disabled.
340  */
341 void tick_check_new_device(struct clock_event_device *newdev)
342 {
343 	struct clock_event_device *curdev;
344 	struct tick_device *td;
345 	int cpu;
346 
347 	cpu = smp_processor_id();
348 	td = &per_cpu(tick_cpu_device, cpu);
349 	curdev = td->evtdev;
350 
351 	/* cpu local device ? */
352 	if (!tick_check_percpu(curdev, newdev, cpu))
353 		goto out_bc;
354 
355 	/* Preference decision */
356 	if (!tick_check_preferred(curdev, newdev))
357 		goto out_bc;
358 
359 	if (!try_module_get(newdev->owner))
360 		return;
361 
362 	/*
363 	 * Replace the eventually existing device by the new
364 	 * device. If the current device is the broadcast device, do
365 	 * not give it back to the clockevents layer !
366 	 */
367 	if (tick_is_broadcast_device(curdev)) {
368 		clockevents_shutdown(curdev);
369 		curdev = NULL;
370 	}
371 	clockevents_exchange_device(curdev, newdev);
372 	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
373 	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
374 		tick_oneshot_notify();
375 	return;
376 
377 out_bc:
378 	/*
379 	 * Can the new device be used as a broadcast device ?
380 	 */
381 	tick_install_broadcast_device(newdev);
382 }
383 
384 /**
385  * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
386  * @state:	The target state (enter/exit)
387  *
388  * The system enters/leaves a state, where affected devices might stop
389  * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
390  *
391  * Called with interrupts disabled, so clockevents_lock is not
392  * required here because the local clock event device cannot go away
393  * under us.
394  */
395 int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
396 {
397 	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
398 
399 	if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))
400 		return 0;
401 
402 	return __tick_broadcast_oneshot_control(state);
403 }
404 EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);
405 
406 #ifdef CONFIG_HOTPLUG_CPU
407 /*
408  * Transfer the do_timer job away from a dying cpu.
409  *
410  * Called with interrupts disabled. Not locking required. If
411  * tick_do_timer_cpu is owned by this cpu, nothing can change it.
412  */
413 void tick_handover_do_timer(void)
414 {
415 	if (tick_do_timer_cpu == smp_processor_id()) {
416 		int cpu = cpumask_first(cpu_online_mask);
417 
418 		tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
419 			TICK_DO_TIMER_NONE;
420 	}
421 }
422 
423 /*
424  * Shutdown an event device on a given cpu:
425  *
426  * This is called on a life CPU, when a CPU is dead. So we cannot
427  * access the hardware device itself.
428  * We just set the mode and remove it from the lists.
429  */
430 void tick_shutdown(unsigned int cpu)
431 {
432 	struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
433 	struct clock_event_device *dev = td->evtdev;
434 
435 	td->mode = TICKDEV_MODE_PERIODIC;
436 	if (dev) {
437 		/*
438 		 * Prevent that the clock events layer tries to call
439 		 * the set mode function!
440 		 */
441 		clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);
442 		clockevents_exchange_device(dev, NULL);
443 		dev->event_handler = clockevents_handle_noop;
444 		td->evtdev = NULL;
445 	}
446 }
447 #endif
448 
449 /**
450  * tick_suspend_local - Suspend the local tick device
451  *
452  * Called from the local cpu for freeze with interrupts disabled.
453  *
454  * No locks required. Nothing can change the per cpu device.
455  */
456 void tick_suspend_local(void)
457 {
458 	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
459 
460 	clockevents_shutdown(td->evtdev);
461 }
462 
463 /**
464  * tick_resume_local - Resume the local tick device
465  *
466  * Called from the local CPU for unfreeze or XEN resume magic.
467  *
468  * No locks required. Nothing can change the per cpu device.
469  */
470 void tick_resume_local(void)
471 {
472 	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
473 	bool broadcast = tick_resume_check_broadcast();
474 
475 	clockevents_tick_resume(td->evtdev);
476 	if (!broadcast) {
477 		if (td->mode == TICKDEV_MODE_PERIODIC)
478 			tick_setup_periodic(td->evtdev, 0);
479 		else
480 			tick_resume_oneshot();
481 	}
482 }
483 
484 /**
485  * tick_suspend - Suspend the tick and the broadcast device
486  *
487  * Called from syscore_suspend() via timekeeping_suspend with only one
488  * CPU online and interrupts disabled or from tick_unfreeze() under
489  * tick_freeze_lock.
490  *
491  * No locks required. Nothing can change the per cpu device.
492  */
493 void tick_suspend(void)
494 {
495 	tick_suspend_local();
496 	tick_suspend_broadcast();
497 }
498 
499 /**
500  * tick_resume - Resume the tick and the broadcast device
501  *
502  * Called from syscore_resume() via timekeeping_resume with only one
503  * CPU online and interrupts disabled.
504  *
505  * No locks required. Nothing can change the per cpu device.
506  */
507 void tick_resume(void)
508 {
509 	tick_resume_broadcast();
510 	tick_resume_local();
511 }
512 
513 #ifdef CONFIG_SUSPEND
514 static DEFINE_RAW_SPINLOCK(tick_freeze_lock);
515 static unsigned int tick_freeze_depth;
516 
517 /**
518  * tick_freeze - Suspend the local tick and (possibly) timekeeping.
519  *
520  * Check if this is the last online CPU executing the function and if so,
521  * suspend timekeeping.  Otherwise suspend the local tick.
522  *
523  * Call with interrupts disabled.  Must be balanced with %tick_unfreeze().
524  * Interrupts must not be enabled before the subsequent %tick_unfreeze().
525  */
526 void tick_freeze(void)
527 {
528 	raw_spin_lock(&tick_freeze_lock);
529 
530 	tick_freeze_depth++;
531 	if (tick_freeze_depth == num_online_cpus()) {
532 		trace_suspend_resume(TPS("timekeeping_freeze"),
533 				     smp_processor_id(), true);
534 		system_state = SYSTEM_SUSPEND;
535 		sched_clock_suspend();
536 		timekeeping_suspend();
537 	} else {
538 		tick_suspend_local();
539 	}
540 
541 	raw_spin_unlock(&tick_freeze_lock);
542 }
543 
544 /**
545  * tick_unfreeze - Resume the local tick and (possibly) timekeeping.
546  *
547  * Check if this is the first CPU executing the function and if so, resume
548  * timekeeping.  Otherwise resume the local tick.
549  *
550  * Call with interrupts disabled.  Must be balanced with %tick_freeze().
551  * Interrupts must not be enabled after the preceding %tick_freeze().
552  */
553 void tick_unfreeze(void)
554 {
555 	raw_spin_lock(&tick_freeze_lock);
556 
557 	if (tick_freeze_depth == num_online_cpus()) {
558 		timekeeping_resume();
559 		sched_clock_resume();
560 		system_state = SYSTEM_RUNNING;
561 		trace_suspend_resume(TPS("timekeeping_freeze"),
562 				     smp_processor_id(), false);
563 	} else {
564 		touch_softlockup_watchdog();
565 		tick_resume_local();
566 	}
567 
568 	tick_freeze_depth--;
569 
570 	raw_spin_unlock(&tick_freeze_lock);
571 }
572 #endif /* CONFIG_SUSPEND */
573 
574 /**
575  * tick_init - initialize the tick control
576  */
577 void __init tick_init(void)
578 {
579 	tick_broadcast_init();
580 	tick_nohz_init();
581 }
582