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Linux/kernel/time/tick-common.c

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