2 * linux/kernel/time/tick-common.c
4 * This file contains the base functions to manage periodic tick
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
11 * This code is licenced under the GPL version 2. For details see
12 * kernel-base/COPYING.
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>
24 #include <asm/irq_regs.h>
26 #include "tick-internal.h"
31 DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
33 * Tick next event: keeps track of the tick time
35 ktime_t tick_next_period;
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:
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.
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.
52 int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
55 * Debugging: see timer_list.c
57 struct tick_device *tick_get_device(int cpu)
59 return &per_cpu(tick_cpu_device, cpu);
63 * tick_is_oneshot_available - check for a oneshot capable event device
65 int tick_is_oneshot_available(void)
67 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
69 if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
71 if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
73 return tick_broadcast_oneshot_available();
79 static void tick_periodic(int cpu)
81 if (tick_do_timer_cpu == cpu) {
82 write_seqlock(&jiffies_lock);
84 /* Keep track of the next tick event */
85 tick_next_period = ktime_add(tick_next_period, tick_period);
88 write_sequnlock(&jiffies_lock);
92 update_process_times(user_mode(get_irq_regs()));
93 profile_tick(CPU_PROFILING);
97 * Event handler for periodic ticks
99 void tick_handle_periodic(struct clock_event_device *dev)
101 int cpu = smp_processor_id();
102 ktime_t next = dev->next_event;
106 #if defined(CONFIG_HIGH_RES_TIMERS) || defined(CONFIG_NO_HZ_COMMON)
108 * The cpu might have transitioned to HIGHRES or NOHZ mode via
109 * update_process_times() -> run_local_timers() ->
110 * hrtimer_run_queues().
112 if (dev->event_handler != tick_handle_periodic)
116 if (!clockevent_state_oneshot(dev))
120 * Setup the next period for devices, which do not have
123 next = ktime_add(next, tick_period);
125 if (!clockevents_program_event(dev, next, false))
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.
136 if (timekeeping_valid_for_hres())
142 * Setup the device for a periodic tick
144 void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
146 tick_set_periodic_handler(dev, broadcast);
148 /* Broadcast setup ? */
149 if (!tick_device_is_functional(dev))
152 if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
153 !tick_broadcast_oneshot_active()) {
154 clockevents_switch_state(dev, CLOCK_EVT_STATE_PERIODIC);
160 seq = read_seqbegin(&jiffies_lock);
161 next = tick_next_period;
162 } while (read_seqretry(&jiffies_lock, seq));
164 clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
167 if (!clockevents_program_event(dev, next, false))
169 next = ktime_add(next, tick_period);
175 * Setup the tick device
177 static void tick_setup_device(struct tick_device *td,
178 struct clock_event_device *newdev, int cpu,
179 const struct cpumask *cpumask)
182 void (*handler)(struct clock_event_device *) = NULL;
185 * First device setup ?
189 * If no cpu took the do_timer update, assign it to
192 if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
193 if (!tick_nohz_full_cpu(cpu))
194 tick_do_timer_cpu = cpu;
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);
202 * Startup in periodic mode first.
204 td->mode = TICKDEV_MODE_PERIODIC;
206 handler = td->evtdev->event_handler;
207 next_event = td->evtdev->next_event;
208 td->evtdev->event_handler = clockevents_handle_noop;
214 * When the device is not per cpu, pin the interrupt to the
217 if (!cpumask_equal(newdev->cpumask, cpumask))
218 irq_set_affinity(newdev->irq, cpumask);
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.
227 if (tick_device_uses_broadcast(newdev, cpu))
230 if (td->mode == TICKDEV_MODE_PERIODIC)
231 tick_setup_periodic(newdev, 0);
233 tick_setup_oneshot(newdev, handler, next_event);
236 void tick_install_replacement(struct clock_event_device *newdev)
238 struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
239 int cpu = smp_processor_id();
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();
247 static bool tick_check_percpu(struct clock_event_device *curdev,
248 struct clock_event_device *newdev, int cpu)
250 if (!cpumask_test_cpu(cpu, newdev->cpumask))
252 if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
254 /* Check if irq affinity can be set */
255 if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
257 /* Prefer an existing cpu local device */
258 if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
263 static bool tick_check_preferred(struct clock_event_device *curdev,
264 struct clock_event_device *newdev)
266 /* Prefer oneshot capable device */
267 if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
268 if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
270 if (tick_oneshot_mode_active())
275 * Use the higher rated one, but prefer a CPU local device with a lower
276 * rating than a non-CPU local device
279 newdev->rating > curdev->rating ||
280 !cpumask_equal(curdev->cpumask, newdev->cpumask);
284 * Check whether the new device is a better fit than curdev. curdev
287 bool tick_check_replacement(struct clock_event_device *curdev,
288 struct clock_event_device *newdev)
290 if (!tick_check_percpu(curdev, newdev, smp_processor_id()))
293 return tick_check_preferred(curdev, newdev);
297 * Check, if the new registered device should be used. Called with
298 * clockevents_lock held and interrupts disabled.
300 void tick_check_new_device(struct clock_event_device *newdev)
302 struct clock_event_device *curdev;
303 struct tick_device *td;
306 cpu = smp_processor_id();
307 td = &per_cpu(tick_cpu_device, cpu);
310 /* cpu local device ? */
311 if (!tick_check_percpu(curdev, newdev, cpu))
314 /* Preference decision */
315 if (!tick_check_preferred(curdev, newdev))
318 if (!try_module_get(newdev->owner))
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 !
326 if (tick_is_broadcast_device(curdev)) {
327 clockevents_shutdown(curdev);
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();
338 * Can the new device be used as a broadcast device ?
340 tick_install_broadcast_device(newdev);
344 * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
345 * @state: The target state (enter/exit)
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.
350 * Called with interrupts disabled, so clockevents_lock is not
351 * required here because the local clock event device cannot go away
354 int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
356 struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
358 if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))
361 return __tick_broadcast_oneshot_control(state);
363 EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);
365 #ifdef CONFIG_HOTPLUG_CPU
367 * Transfer the do_timer job away from a dying cpu.
369 * Called with interrupts disabled. Not locking required. If
370 * tick_do_timer_cpu is owned by this cpu, nothing can change it.
372 void tick_handover_do_timer(void)
374 if (tick_do_timer_cpu == smp_processor_id()) {
375 int cpu = cpumask_first(cpu_online_mask);
377 tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
383 * Shutdown an event device on a given cpu:
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.
389 void tick_shutdown(unsigned int cpu)
391 struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
392 struct clock_event_device *dev = td->evtdev;
394 td->mode = TICKDEV_MODE_PERIODIC;
397 * Prevent that the clock events layer tries to call
398 * the set mode function!
400 clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);
401 clockevents_exchange_device(dev, NULL);
402 dev->event_handler = clockevents_handle_noop;
409 * tick_suspend_local - Suspend the local tick device
411 * Called from the local cpu for freeze with interrupts disabled.
413 * No locks required. Nothing can change the per cpu device.
415 void tick_suspend_local(void)
417 struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
419 clockevents_shutdown(td->evtdev);
423 * tick_resume_local - Resume the local tick device
425 * Called from the local CPU for unfreeze or XEN resume magic.
427 * No locks required. Nothing can change the per cpu device.
429 void tick_resume_local(void)
431 struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
432 bool broadcast = tick_resume_check_broadcast();
434 clockevents_tick_resume(td->evtdev);
436 if (td->mode == TICKDEV_MODE_PERIODIC)
437 tick_setup_periodic(td->evtdev, 0);
439 tick_resume_oneshot();
444 * tick_suspend - Suspend the tick and the broadcast device
446 * Called from syscore_suspend() via timekeeping_suspend with only one
447 * CPU online and interrupts disabled or from tick_unfreeze() under
450 * No locks required. Nothing can change the per cpu device.
452 void tick_suspend(void)
454 tick_suspend_local();
455 tick_suspend_broadcast();
459 * tick_resume - Resume the tick and the broadcast device
461 * Called from syscore_resume() via timekeeping_resume with only one
462 * CPU online and interrupts disabled.
464 * No locks required. Nothing can change the per cpu device.
466 void tick_resume(void)
468 tick_resume_broadcast();
472 #ifdef CONFIG_SUSPEND
473 static DEFINE_RAW_SPINLOCK(tick_freeze_lock);
474 static unsigned int tick_freeze_depth;
477 * tick_freeze - Suspend the local tick and (possibly) timekeeping.
479 * Check if this is the last online CPU executing the function and if so,
480 * suspend timekeeping. Otherwise suspend the local tick.
482 * Call with interrupts disabled. Must be balanced with %tick_unfreeze().
483 * Interrupts must not be enabled before the subsequent %tick_unfreeze().
485 void tick_freeze(void)
487 raw_spin_lock(&tick_freeze_lock);
490 if (tick_freeze_depth == num_online_cpus()) {
491 trace_suspend_resume(TPS("timekeeping_freeze"),
492 smp_processor_id(), true);
493 timekeeping_suspend();
495 tick_suspend_local();
498 raw_spin_unlock(&tick_freeze_lock);
502 * tick_unfreeze - Resume the local tick and (possibly) timekeeping.
504 * Check if this is the first CPU executing the function and if so, resume
505 * timekeeping. Otherwise resume the local tick.
507 * Call with interrupts disabled. Must be balanced with %tick_freeze().
508 * Interrupts must not be enabled after the preceding %tick_freeze().
510 void tick_unfreeze(void)
512 raw_spin_lock(&tick_freeze_lock);
514 if (tick_freeze_depth == num_online_cpus()) {
515 timekeeping_resume();
516 trace_suspend_resume(TPS("timekeeping_freeze"),
517 smp_processor_id(), false);
524 raw_spin_unlock(&tick_freeze_lock);
526 #endif /* CONFIG_SUSPEND */
529 * tick_init - initialize the tick control
531 void __init tick_init(void)
533 tick_broadcast_init();