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