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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/nmi.h>
 15 #include <linux/percpu.h>
 16 #include <linux/profile.h>
 17 #include <linux/sched.h>
 18 #include <linux/module.h>
 19 #include <trace/events/power.h>
 20 
 21 #include <asm/irq_regs.h>
 22 
 23 #include "tick-internal.h"
 24 
 25 /*
 26  * Tick devices
 27  */
 28 DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
 29 /*
 30  * Tick next event: keeps track of the tick time
 31  */
 32 ktime_t tick_next_period;
 33 ktime_t tick_period;
 34 
 35 /*
 36  * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
 37  * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This
 38  * variable has two functions:
 39  *
 40  * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the
 41  *    timekeeping lock all at once. Only the CPU which is assigned to do the
 42  *    update is handling it.
 43  *
 44  * 2) Hand off the duty in the NOHZ idle case by setting the value to
 45  *    TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks
 46  *    at it will take over and keep the time keeping alive.  The handover
 47  *    procedure also covers cpu hotplug.
 48  */
 49 int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
 50 #ifdef CONFIG_NO_HZ_FULL
 51 /*
 52  * tick_do_timer_boot_cpu indicates the boot CPU temporarily owns
 53  * tick_do_timer_cpu and it should be taken over by an eligible secondary
 54  * when one comes online.
 55  */
 56 static int tick_do_timer_boot_cpu __read_mostly = -1;
 57 #endif
 58 
 59 /*
 60  * Debugging: see timer_list.c
 61  */
 62 struct tick_device *tick_get_device(int cpu)
 63 {
 64         return &per_cpu(tick_cpu_device, cpu);
 65 }
 66 
 67 /**
 68  * tick_is_oneshot_available - check for a oneshot capable event device
 69  */
 70 int tick_is_oneshot_available(void)
 71 {
 72         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
 73 
 74         if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
 75                 return 0;
 76         if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
 77                 return 1;
 78         return tick_broadcast_oneshot_available();
 79 }
 80 
 81 /*
 82  * Periodic tick
 83  */
 84 static void tick_periodic(int cpu)
 85 {
 86         if (tick_do_timer_cpu == cpu) {
 87                 raw_spin_lock(&jiffies_lock);
 88                 write_seqcount_begin(&jiffies_seq);
 89 
 90                 /* Keep track of the next tick event */
 91                 tick_next_period = ktime_add(tick_next_period, tick_period);
 92 
 93                 do_timer(1);
 94                 write_seqcount_end(&jiffies_seq);
 95                 raw_spin_unlock(&jiffies_lock);
 96                 update_wall_time();
 97         }
 98 
 99         update_process_times(user_mode(get_irq_regs()));
100         profile_tick(CPU_PROFILING);
101 }
102 
103 /*
104  * Event handler for periodic ticks
105  */
106 void tick_handle_periodic(struct clock_event_device *dev)
107 {
108         int cpu = smp_processor_id();
109         ktime_t next = dev->next_event;
110 
111         tick_periodic(cpu);
112 
113 #if defined(CONFIG_HIGH_RES_TIMERS) || defined(CONFIG_NO_HZ_COMMON)
114         /*
115          * The cpu might have transitioned to HIGHRES or NOHZ mode via
116          * update_process_times() -> run_local_timers() ->
117          * hrtimer_run_queues().
118          */
119         if (dev->event_handler != tick_handle_periodic)
120                 return;
121 #endif
122 
123         if (!clockevent_state_oneshot(dev))
124                 return;
125         for (;;) {
126                 /*
127                  * Setup the next period for devices, which do not have
128                  * periodic mode:
129                  */
130                 next = ktime_add(next, tick_period);
131 
132                 if (!clockevents_program_event(dev, next, false))
133                         return;
134                 /*
135                  * Have to be careful here. If we're in oneshot mode,
136                  * before we call tick_periodic() in a loop, we need
137                  * to be sure we're using a real hardware clocksource.
138                  * Otherwise we could get trapped in an infinite
139                  * loop, as the tick_periodic() increments jiffies,
140                  * which then will increment time, possibly causing
141                  * the loop to trigger again and again.
142                  */
143                 if (timekeeping_valid_for_hres())
144                         tick_periodic(cpu);
145         }
146 }
147 
148 /*
149  * Setup the device for a periodic tick
150  */
151 void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
152 {
153         tick_set_periodic_handler(dev, broadcast);
154 
155         /* Broadcast setup ? */
156         if (!tick_device_is_functional(dev))
157                 return;
158 
159         if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
160             !tick_broadcast_oneshot_active()) {
161                 clockevents_switch_state(dev, CLOCK_EVT_STATE_PERIODIC);
162         } else {
163                 unsigned int seq;
164                 ktime_t next;
165 
166                 do {
167                         seq = read_seqcount_begin(&jiffies_seq);
168                         next = tick_next_period;
169                 } while (read_seqcount_retry(&jiffies_seq, seq));
170 
171                 clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
172 
173                 for (;;) {
174                         if (!clockevents_program_event(dev, next, false))
175                                 return;
176                         next = ktime_add(next, tick_period);
177                 }
178         }
179 }
180 
181 #ifdef CONFIG_NO_HZ_FULL
182 static void giveup_do_timer(void *info)
183 {
184         int cpu = *(unsigned int *)info;
185 
186         WARN_ON(tick_do_timer_cpu != smp_processor_id());
187 
188         tick_do_timer_cpu = cpu;
189 }
190 
191 static void tick_take_do_timer_from_boot(void)
192 {
193         int cpu = smp_processor_id();
194         int from = tick_do_timer_boot_cpu;
195 
196         if (from >= 0 && from != cpu)
197                 smp_call_function_single(from, giveup_do_timer, &cpu, 1);
198 }
199 #endif
200 
201 /*
202  * Setup the tick device
203  */
204 static void tick_setup_device(struct tick_device *td,
205                               struct clock_event_device *newdev, int cpu,
206                               const struct cpumask *cpumask)
207 {
208         void (*handler)(struct clock_event_device *) = NULL;
209         ktime_t next_event = 0;
210 
211         /*
212          * First device setup ?
213          */
214         if (!td->evtdev) {
215                 /*
216                  * If no cpu took the do_timer update, assign it to
217                  * this cpu:
218                  */
219                 if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
220                         tick_do_timer_cpu = cpu;
221 
222                         tick_next_period = ktime_get();
223                         tick_period = NSEC_PER_SEC / HZ;
224 #ifdef CONFIG_NO_HZ_FULL
225                         /*
226                          * The boot CPU may be nohz_full, in which case set
227                          * tick_do_timer_boot_cpu so the first housekeeping
228                          * secondary that comes up will take do_timer from
229                          * us.
230                          */
231                         if (tick_nohz_full_cpu(cpu))
232                                 tick_do_timer_boot_cpu = cpu;
233 
234                 } else if (tick_do_timer_boot_cpu != -1 &&
235                                                 !tick_nohz_full_cpu(cpu)) {
236                         tick_take_do_timer_from_boot();
237                         tick_do_timer_boot_cpu = -1;
238                         WARN_ON(tick_do_timer_cpu != cpu);
239 #endif
240                 }
241 
242                 /*
243                  * Startup in periodic mode first.
244                  */
245                 td->mode = TICKDEV_MODE_PERIODIC;
246         } else {
247                 handler = td->evtdev->event_handler;
248                 next_event = td->evtdev->next_event;
249                 td->evtdev->event_handler = clockevents_handle_noop;
250         }
251 
252         td->evtdev = newdev;
253 
254         /*
255          * When the device is not per cpu, pin the interrupt to the
256          * current cpu:
257          */
258         if (!cpumask_equal(newdev->cpumask, cpumask))
259                 irq_set_affinity(newdev->irq, cpumask);
260 
261         /*
262          * When global broadcasting is active, check if the current
263          * device is registered as a placeholder for broadcast mode.
264          * This allows us to handle this x86 misfeature in a generic
265          * way. This function also returns !=0 when we keep the
266          * current active broadcast state for this CPU.
267          */
268         if (tick_device_uses_broadcast(newdev, cpu))
269                 return;
270 
271         if (td->mode == TICKDEV_MODE_PERIODIC)
272                 tick_setup_periodic(newdev, 0);
273         else
274                 tick_setup_oneshot(newdev, handler, next_event);
275 }
276 
277 void tick_install_replacement(struct clock_event_device *newdev)
278 {
279         struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
280         int cpu = smp_processor_id();
281 
282         clockevents_exchange_device(td->evtdev, newdev);
283         tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
284         if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
285                 tick_oneshot_notify();
286 }
287 
288 static bool tick_check_percpu(struct clock_event_device *curdev,
289                               struct clock_event_device *newdev, int cpu)
290 {
291         if (!cpumask_test_cpu(cpu, newdev->cpumask))
292                 return false;
293         if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
294                 return true;
295         /* Check if irq affinity can be set */
296         if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
297                 return false;
298         /* Prefer an existing cpu local device */
299         if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
300                 return false;
301         return true;
302 }
303 
304 static bool tick_check_preferred(struct clock_event_device *curdev,
305                                  struct clock_event_device *newdev)
306 {
307         /* Prefer oneshot capable device */
308         if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
309                 if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
310                         return false;
311                 if (tick_oneshot_mode_active())
312                         return false;
313         }
314 
315         /*
316          * Use the higher rated one, but prefer a CPU local device with a lower
317          * rating than a non-CPU local device
318          */
319         return !curdev ||
320                 newdev->rating > curdev->rating ||
321                !cpumask_equal(curdev->cpumask, newdev->cpumask);
322 }
323 
324 /*
325  * Check whether the new device is a better fit than curdev. curdev
326  * can be NULL !
327  */
328 bool tick_check_replacement(struct clock_event_device *curdev,
329                             struct clock_event_device *newdev)
330 {
331         if (!tick_check_percpu(curdev, newdev, smp_processor_id()))
332                 return false;
333 
334         return tick_check_preferred(curdev, newdev);
335 }
336 
337 /*
338  * Check, if the new registered device should be used. Called with
339  * clockevents_lock held and interrupts disabled.
340  */
341 void tick_check_new_device(struct clock_event_device *newdev)
342 {
343         struct clock_event_device *curdev;
344         struct tick_device *td;
345         int cpu;
346 
347         cpu = smp_processor_id();
348         td = &per_cpu(tick_cpu_device, cpu);
349         curdev = td->evtdev;
350 
351         /* cpu local device ? */
352         if (!tick_check_percpu(curdev, newdev, cpu))
353                 goto out_bc;
354 
355         /* Preference decision */
356         if (!tick_check_preferred(curdev, newdev))
357                 goto out_bc;
358 
359         if (!try_module_get(newdev->owner))
360                 return;
361 
362         /*
363          * Replace the eventually existing device by the new
364          * device. If the current device is the broadcast device, do
365          * not give it back to the clockevents layer !
366          */
367         if (tick_is_broadcast_device(curdev)) {
368                 clockevents_shutdown(curdev);
369                 curdev = NULL;
370         }
371         clockevents_exchange_device(curdev, newdev);
372         tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
373         if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
374                 tick_oneshot_notify();
375         return;
376 
377 out_bc:
378         /*
379          * Can the new device be used as a broadcast device ?
380          */
381         tick_install_broadcast_device(newdev);
382 }
383 
384 /**
385  * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
386  * @state:      The target state (enter/exit)
387  *
388  * The system enters/leaves a state, where affected devices might stop
389  * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
390  *
391  * Called with interrupts disabled, so clockevents_lock is not
392  * required here because the local clock event device cannot go away
393  * under us.
394  */
395 int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
396 {
397         struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
398 
399         if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))
400                 return 0;
401 
402         return __tick_broadcast_oneshot_control(state);
403 }
404 EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);
405 
406 #ifdef CONFIG_HOTPLUG_CPU
407 /*
408  * Transfer the do_timer job away from a dying cpu.
409  *
410  * Called with interrupts disabled. Not locking required. If
411  * tick_do_timer_cpu is owned by this cpu, nothing can change it.
412  */
413 void tick_handover_do_timer(void)
414 {
415         if (tick_do_timer_cpu == smp_processor_id()) {
416                 int cpu = cpumask_first(cpu_online_mask);
417 
418                 tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
419                         TICK_DO_TIMER_NONE;
420         }
421 }
422 
423 /*
424  * Shutdown an event device on a given cpu:
425  *
426  * This is called on a life CPU, when a CPU is dead. So we cannot
427  * access the hardware device itself.
428  * We just set the mode and remove it from the lists.
429  */
430 void tick_shutdown(unsigned int cpu)
431 {
432         struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
433         struct clock_event_device *dev = td->evtdev;
434 
435         td->mode = TICKDEV_MODE_PERIODIC;
436         if (dev) {
437                 /*
438                  * Prevent that the clock events layer tries to call
439                  * the set mode function!
440                  */
441                 clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);
442                 clockevents_exchange_device(dev, NULL);
443                 dev->event_handler = clockevents_handle_noop;
444                 td->evtdev = NULL;
445         }
446 }
447 #endif
448 
449 /**
450  * tick_suspend_local - Suspend the local tick device
451  *
452  * Called from the local cpu for freeze with interrupts disabled.
453  *
454  * No locks required. Nothing can change the per cpu device.
455  */
456 void tick_suspend_local(void)
457 {
458         struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
459 
460         clockevents_shutdown(td->evtdev);
461 }
462 
463 /**
464  * tick_resume_local - Resume the local tick device
465  *
466  * Called from the local CPU for unfreeze or XEN resume magic.
467  *
468  * No locks required. Nothing can change the per cpu device.
469  */
470 void tick_resume_local(void)
471 {
472         struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
473         bool broadcast = tick_resume_check_broadcast();
474 
475         clockevents_tick_resume(td->evtdev);
476         if (!broadcast) {
477                 if (td->mode == TICKDEV_MODE_PERIODIC)
478                         tick_setup_periodic(td->evtdev, 0);
479                 else
480                         tick_resume_oneshot();
481         }
482 }
483 
484 /**
485  * tick_suspend - Suspend the tick and the broadcast device
486  *
487  * Called from syscore_suspend() via timekeeping_suspend with only one
488  * CPU online and interrupts disabled or from tick_unfreeze() under
489  * tick_freeze_lock.
490  *
491  * No locks required. Nothing can change the per cpu device.
492  */
493 void tick_suspend(void)
494 {
495         tick_suspend_local();
496         tick_suspend_broadcast();
497 }
498 
499 /**
500  * tick_resume - Resume the tick and the broadcast device
501  *
502  * Called from syscore_resume() via timekeeping_resume with only one
503  * CPU online and interrupts disabled.
504  *
505  * No locks required. Nothing can change the per cpu device.
506  */
507 void tick_resume(void)
508 {
509         tick_resume_broadcast();
510         tick_resume_local();
511 }
512 
513 #ifdef CONFIG_SUSPEND
514 static DEFINE_RAW_SPINLOCK(tick_freeze_lock);
515 static unsigned int tick_freeze_depth;
516 
517 /**
518  * tick_freeze - Suspend the local tick and (possibly) timekeeping.
519  *
520  * Check if this is the last online CPU executing the function and if so,
521  * suspend timekeeping.  Otherwise suspend the local tick.
522  *
523  * Call with interrupts disabled.  Must be balanced with %tick_unfreeze().
524  * Interrupts must not be enabled before the subsequent %tick_unfreeze().
525  */
526 void tick_freeze(void)
527 {
528         raw_spin_lock(&tick_freeze_lock);
529 
530         tick_freeze_depth++;
531         if (tick_freeze_depth == num_online_cpus()) {
532                 trace_suspend_resume(TPS("timekeeping_freeze"),
533                                      smp_processor_id(), true);
534                 system_state = SYSTEM_SUSPEND;
535                 sched_clock_suspend();
536                 timekeeping_suspend();
537         } else {
538                 tick_suspend_local();
539         }
540 
541         raw_spin_unlock(&tick_freeze_lock);
542 }
543 
544 /**
545  * tick_unfreeze - Resume the local tick and (possibly) timekeeping.
546  *
547  * Check if this is the first CPU executing the function and if so, resume
548  * timekeeping.  Otherwise resume the local tick.
549  *
550  * Call with interrupts disabled.  Must be balanced with %tick_freeze().
551  * Interrupts must not be enabled after the preceding %tick_freeze().
552  */
553 void tick_unfreeze(void)
554 {
555         raw_spin_lock(&tick_freeze_lock);
556 
557         if (tick_freeze_depth == num_online_cpus()) {
558                 timekeeping_resume();
559                 sched_clock_resume();
560                 system_state = SYSTEM_RUNNING;
561                 trace_suspend_resume(TPS("timekeeping_freeze"),
562                                      smp_processor_id(), false);
563         } else {
564                 touch_softlockup_watchdog();
565                 tick_resume_local();
566         }
567 
568         tick_freeze_depth--;
569 
570         raw_spin_unlock(&tick_freeze_lock);
571 }
572 #endif /* CONFIG_SUSPEND */
573 
574 /**
575  * tick_init - initialize the tick control
576  */
577 void __init tick_init(void)
578 {
579         tick_broadcast_init();
580         tick_nohz_init();
581 }
582 

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