root/kernel/time/tick-common.c

DEFINITIONS

1. tick_get_device
2. tick_is_oneshot_available
3. tick_periodic
4. tick_handle_periodic
5. tick_setup_periodic
6. giveup_do_timer
7. tick_take_do_timer_from_boot
8. tick_setup_device
9. tick_install_replacement
10. tick_check_percpu
11. tick_check_preferred
12. tick_check_replacement
13. tick_check_new_device
14. tick_broadcast_oneshot_control
15. tick_handover_do_timer
16. tick_shutdown
17. tick_suspend_local
18. tick_resume_local
19. tick_suspend
20. tick_resume
21. tick_freeze
22. tick_unfreeze
23. tick_init

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