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TOMOYO Linux Cross Reference
Linux/kernel/time/tick-common.c

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  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  */
 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  */
 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  */
 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  */
 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  */
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  */
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         void (*handler)(struct clock_event_device *) = NULL;
182         ktime_t next_event = 0;
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 = 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 
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 
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 
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  */
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  */
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  */
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  */
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  */
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  */
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  */
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  */
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  */
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  */
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  */
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  */
531 void __init tick_init(void)
532 {
533         tick_broadcast_init();
534         tick_nohz_init();
535 }
536 

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