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