kernel/time/tick-sched.c

   1 /*
   2  *  linux/kernel/time/tick-sched.c
   3  *
   4  *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
   5  *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
   6  *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
   7  *
   8  *  No idle tick implementation for low and high resolution timers
   9  *
  10  *  Started by: Thomas Gleixner and Ingo Molnar
  11  *
  12  *  Distribute under GPLv2.
  13  */
  14 #include <linux/cpu.h>
  15 #include <linux/err.h>
  16 #include <linux/hrtimer.h>
  17 #include <linux/interrupt.h>
  18 #include <linux/kernel_stat.h>
  19 #include <linux/percpu.h>
  20 #include <linux/profile.h>
  21 #include <linux/sched.h>
  22 #include <linux/tick.h>
  23
  24 #include <asm/irq_regs.h>
  25
  26 #include "tick-internal.h"
  27
  28 /*
  29  * Per cpu nohz control structure
  30  */
  31 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
  32
  33 /*
  34  * The time, when the last jiffy update happened. Protected by xtime_lock.
  35  */
  36 static ktime_t last_jiffies_update;
  37
  38 struct tick_sched *tick_get_tick_sched(int cpu)
  39 {
  40         return &per_cpu(tick_cpu_sched, cpu);
  41 }
  42
  43 /*
  44  * Must be called with interrupts disabled !
  45  */
  46 static void tick_do_update_jiffies64(ktime_t now)
  47 {
  48         unsigned long ticks = 0;
  49         ktime_t delta;
  50
  51         /* Reevalute with xtime_lock held */
  52         write_seqlock(&xtime_lock);
  53
  54         delta = ktime_sub(now, last_jiffies_update);
  55         if (delta.tv64 >= tick_period.tv64) {
  56
  57                 delta = ktime_sub(delta, tick_period);
  58                 last_jiffies_update = ktime_add(last_jiffies_update,
  59                                                 tick_period);
  60
  61                 /* Slow path for long timeouts */
  62                 if (unlikely(delta.tv64 >= tick_period.tv64)) {
  63                         s64 incr = ktime_to_ns(tick_period);
  64
  65                         ticks = ktime_divns(delta, incr);
  66
  67                         last_jiffies_update = ktime_add_ns(last_jiffies_update,
  68                                                            incr * ticks);
  69                 }
  70                 do_timer(++ticks);
  71         }
  72         write_sequnlock(&xtime_lock);
  73 }
  74
  75 /*
  76  * Initialize and return retrieve the jiffies update.
  77  */
  78 static ktime_t tick_init_jiffy_update(void)
  79 {
  80         ktime_t period;
  81
  82         write_seqlock(&xtime_lock);
  83         /* Did we start the jiffies update yet ? */
  84         if (last_jiffies_update.tv64 == 0)
  85                 last_jiffies_update = tick_next_period;
  86         period = last_jiffies_update;
  87         write_sequnlock(&xtime_lock);
  88         return period;
  89 }
  90
  91 /*
  92  * NOHZ - aka dynamic tick functionality
  93  */
  94 #ifdef CONFIG_NO_HZ
  95 /*
  96  * NO HZ enabled ?
  97  */
  98 static int tick_nohz_enabled __read_mostly  = 1;
  99
 100 /*
 101  * Enable / Disable tickless mode
 102  */
 103 static int __init setup_tick_nohz(char *str)
 104 {
 105         if (!strcmp(str, "off"))
 106                 tick_nohz_enabled = 0;
 107         else if (!strcmp(str, "on"))
 108                 tick_nohz_enabled = 1;
 109         else
 110                 return 0;
 111         return 1;
 112 }
 113
 114 __setup("nohz=", setup_tick_nohz);
 115
 116 /**
 117  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
 118  *
 119  * Called from interrupt entry when the CPU was idle
 120  *
 121  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
 122  * must be updated. Otherwise an interrupt handler could use a stale jiffy
 123  * value. We do this unconditionally on any cpu, as we don't know whether the
 124  * cpu, which has the update task assigned is in a long sleep.
 125  */
 126 void tick_nohz_update_jiffies(void)
 127 {
 128         int cpu = smp_processor_id();
 129         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 130         unsigned long flags;
 131         ktime_t now;
 132
 133         if (!ts->tick_stopped)
 134                 return;
 135
 136         touch_softlockup_watchdog();
 137
 138         cpu_clear(cpu, nohz_cpu_mask);
 139         now = ktime_get();
 140         ts->idle_waketime = now;
 141
 142         local_irq_save(flags);
 143         tick_do_update_jiffies64(now);
 144         local_irq_restore(flags);
 145 }
 146
 147 void tick_nohz_stop_idle(int cpu)
 148 {
 149         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 150
 151         if (ts->idle_active) {
 152                 ktime_t now, delta;
 153                 now = ktime_get();
 154                 delta = ktime_sub(now, ts->idle_entrytime);
 155                 ts->idle_lastupdate = now;
 156                 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
 157                 ts->idle_active = 0;
 158         }
 159 }
 160
 161 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
 162 {
 163         ktime_t now, delta;
 164
 165         now = ktime_get();
 166         if (ts->idle_active) {
 167                 delta = ktime_sub(now, ts->idle_entrytime);
 168                 ts->idle_lastupdate = now;
 169                 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
 170         }
 171         ts->idle_entrytime = now;
 172         ts->idle_active = 1;
 173         return now;
 174 }
 175
 176 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
 177 {
 178         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 179
 180         *last_update_time = ktime_to_us(ts->idle_lastupdate);
 181         return ktime_to_us(ts->idle_sleeptime);
 182 }
 183
 184 /**
 185  * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
 186  *
 187  * When the next event is more than a tick into the future, stop the idle tick
 188  * Called either from the idle loop or from irq_exit() when an idle period was
 189  * just interrupted by an interrupt which did not cause a reschedule.
 190  */
 191 void tick_nohz_stop_sched_tick(void)
 192 {
 193         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
 194         struct tick_sched *ts;
 195         ktime_t last_update, expires, now;
 196         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
 197         int cpu;
 198
 199         local_irq_save(flags);
 200
 201         cpu = smp_processor_id();
 202         ts = &per_cpu(tick_cpu_sched, cpu);
 203         now = tick_nohz_start_idle(ts);
 204
 205         /*
 206          * If this cpu is offline and it is the one which updates
 207          * jiffies, then give up the assignment and let it be taken by
 208          * the cpu which runs the tick timer next. If we don't drop
 209          * this here the jiffies might be stale and do_timer() never
 210          * invoked.
 211          */
 212         if (unlikely(!cpu_online(cpu))) {
 213                 if (cpu == tick_do_timer_cpu)
 214                         tick_do_timer_cpu = -1;
 215         }
 216
 217         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
 218                 goto end;
 219
 220         if (need_resched())
 221                 goto end;
 222
 223         if (unlikely(local_softirq_pending())) {
 224                 static int ratelimit;
 225
 226                 if (ratelimit < 10) {
 227                         printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
 228                                local_softirq_pending());
 229                         ratelimit++;
 230                 }
 231         }
 232
 233         ts->idle_calls++;
 234         /* Read jiffies and the time when jiffies were updated last */
 235         do {
 236                 seq = read_seqbegin(&xtime_lock);
 237                 last_update = last_jiffies_update;
 238                 last_jiffies = jiffies;
 239         } while (read_seqretry(&xtime_lock, seq));
 240
 241         /* Get the next timer wheel timer */
 242         next_jiffies = get_next_timer_interrupt(last_jiffies);
 243         delta_jiffies = next_jiffies - last_jiffies;
 244
 245         if (rcu_needs_cpu(cpu))
 246                 delta_jiffies = 1;
 247         /*
 248          * Do not stop the tick, if we are only one off
 249          * or if the cpu is required for rcu
 250          */
 251         if (!ts->tick_stopped && delta_jiffies == 1)
 252                 goto out;
 253
 254         /* Schedule the tick, if we are at least one jiffie off */
 255         if ((long)delta_jiffies >= 1) {
 256
 257                 if (delta_jiffies > 1)
 258                         cpu_set(cpu, nohz_cpu_mask);
 259                 /*
 260                  * nohz_stop_sched_tick can be called several times before
 261                  * the nohz_restart_sched_tick is called. This happens when
 262                  * interrupts arrive which do not cause a reschedule. In the
 263                  * first call we save the current tick time, so we can restart
 264                  * the scheduler tick in nohz_restart_sched_tick.
 265                  */
 266                 if (!ts->tick_stopped) {
 267                         if (select_nohz_load_balancer(1)) {
 268                                 /*
 269                                  * sched tick not stopped!
 270                                  */
 271                                 cpu_clear(cpu, nohz_cpu_mask);
 272                                 goto out;
 273                         }
 274
 275                         ts->idle_tick = ts->sched_timer.expires;
 276                         ts->tick_stopped = 1;
 277                         ts->idle_jiffies = last_jiffies;
 278                         rcu_enter_nohz();
 279                 }
 280
 281                 /*
 282                  * If this cpu is the one which updates jiffies, then
 283                  * give up the assignment and let it be taken by the
 284                  * cpu which runs the tick timer next, which might be
 285                  * this cpu as well. If we don't drop this here the
 286                  * jiffies might be stale and do_timer() never
 287                  * invoked.
 288                  */
 289                 if (cpu == tick_do_timer_cpu)
 290                         tick_do_timer_cpu = -1;
 291
 292                 ts->idle_sleeps++;
 293
 294                 /*
 295                  * delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that
 296                  * there is no timer pending or at least extremly far
 297                  * into the future (12 days for HZ=1000). In this case
 298                  * we simply stop the tick timer:
 299                  */
 300                 if (unlikely(delta_jiffies >= NEXT_TIMER_MAX_DELTA)) {
 301                         ts->idle_expires.tv64 = KTIME_MAX;
 302                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
 303                                 hrtimer_cancel(&ts->sched_timer);
 304                         goto out;
 305                 }
 306
 307                 /*
 308                  * calculate the expiry time for the next timer wheel
 309                  * timer
 310                  */
 311                 expires = ktime_add_ns(last_update, tick_period.tv64 *
 312                                        delta_jiffies);
 313                 ts->idle_expires = expires;
 314
 315                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
 316                         hrtimer_start(&ts->sched_timer, expires,
 317                                       HRTIMER_MODE_ABS);
 318                         /* Check, if the timer was already in the past */
 319                         if (hrtimer_active(&ts->sched_timer))
 320                                 goto out;
 321                 } else if (!tick_program_event(expires, 0))
 322                                 goto out;
 323                 /*
 324                  * We are past the event already. So we crossed a
 325                  * jiffie boundary. Update jiffies and raise the
 326                  * softirq.
 327                  */
 328                 tick_do_update_jiffies64(ktime_get());
 329                 cpu_clear(cpu, nohz_cpu_mask);
 330         }
 331         raise_softirq_irqoff(TIMER_SOFTIRQ);
 332 out:
 333         ts->next_jiffies = next_jiffies;
 334         ts->last_jiffies = last_jiffies;
 335         ts->sleep_length = ktime_sub(dev->next_event, now);
 336 end:
 337         local_irq_restore(flags);
 338 }
 339
 340 /**
 341  * tick_nohz_get_sleep_length - return the length of the current sleep
 342  *
 343  * Called from power state control code with interrupts disabled
 344  */
 345 ktime_t tick_nohz_get_sleep_length(void)
 346 {
 347         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 348
 349         return ts->sleep_length;
 350 }
 351
 352 /**
 353  * tick_nohz_restart_sched_tick - restart the idle tick from the idle task
 354  *
 355  * Restart the idle tick when the CPU is woken up from idle
 356  */
 357 void tick_nohz_restart_sched_tick(void)
 358 {
 359         int cpu = smp_processor_id();
 360         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 361         unsigned long ticks;
 362         ktime_t now;
 363
 364         local_irq_disable();
 365         tick_nohz_stop_idle(cpu);
 366
 367         if (!ts->tick_stopped) {
 368                 local_irq_enable();
 369                 return;
 370         }
 371
 372         rcu_exit_nohz();
 373
 374         /* Update jiffies first */
 375         select_nohz_load_balancer(0);
 376         now = ktime_get();
 377         tick_do_update_jiffies64(now);
 378         cpu_clear(cpu, nohz_cpu_mask);
 379
 380         /*
 381          * We stopped the tick in idle. Update process times would miss the
 382          * time we slept as update_process_times does only a 1 tick
 383          * accounting. Enforce that this is accounted to idle !
 384          */
 385         ticks = jiffies - ts->idle_jiffies;
 386         /*
 387          * We might be one off. Do not randomly account a huge number of ticks!
 388          */
 389         if (ticks && ticks < LONG_MAX) {
 390                 add_preempt_count(HARDIRQ_OFFSET);
 391                 account_system_time(current, HARDIRQ_OFFSET,
 392                                     jiffies_to_cputime(ticks));
 393                 sub_preempt_count(HARDIRQ_OFFSET);
 394         }
 395
 396         /*
 397          * Cancel the scheduled timer and restore the tick
 398          */
 399         ts->tick_stopped  = 0;
 400         ts->idle_exittime = now;
 401         hrtimer_cancel(&ts->sched_timer);
 402         ts->sched_timer.expires = ts->idle_tick;
 403
 404         while (1) {
 405                 /* Forward the time to expire in the future */
 406                 hrtimer_forward(&ts->sched_timer, now, tick_period);
 407
 408                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
 409                         hrtimer_start(&ts->sched_timer,
 410                                       ts->sched_timer.expires,
 411                                       HRTIMER_MODE_ABS);
 412                         /* Check, if the timer was already in the past */
 413                         if (hrtimer_active(&ts->sched_timer))
 414                                 break;
 415                 } else {
 416                         if (!tick_program_event(ts->sched_timer.expires, 0))
 417                                 break;
 418                 }
 419                 /* Update jiffies and reread time */
 420                 tick_do_update_jiffies64(now);
 421                 now = ktime_get();
 422         }
 423         local_irq_enable();
 424 }
 425
 426 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
 427 {
 428         hrtimer_forward(&ts->sched_timer, now, tick_period);
 429         return tick_program_event(ts->sched_timer.expires, 0);
 430 }
 431
 432 /*
 433  * The nohz low res interrupt handler
 434  */
 435 static void tick_nohz_handler(struct clock_event_device *dev)
 436 {
 437         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 438         struct pt_regs *regs = get_irq_regs();
 439         int cpu = smp_processor_id();
 440         ktime_t now = ktime_get();
 441
 442         dev->next_event.tv64 = KTIME_MAX;
 443
 444         /*
 445          * Check if the do_timer duty was dropped. We don't care about
 446          * concurrency: This happens only when the cpu in charge went
 447          * into a long sleep. If two cpus happen to assign themself to
 448          * this duty, then the jiffies update is still serialized by
 449          * xtime_lock.
 450          */
 451         if (unlikely(tick_do_timer_cpu == -1))
 452                 tick_do_timer_cpu = cpu;
 453
 454         /* Check, if the jiffies need an update */
 455         if (tick_do_timer_cpu == cpu)
 456                 tick_do_update_jiffies64(now);
 457
 458         /*
 459          * When we are idle and the tick is stopped, we have to touch
 460          * the watchdog as we might not schedule for a really long
 461          * time. This happens on complete idle SMP systems while
 462          * waiting on the login prompt. We also increment the "start
 463          * of idle" jiffy stamp so the idle accounting adjustment we
 464          * do when we go busy again does not account too much ticks.
 465          */
 466         if (ts->tick_stopped) {
 467                 touch_softlockup_watchdog();
 468                 ts->idle_jiffies++;
 469         }
 470
 471         update_process_times(user_mode(regs));
 472         profile_tick(CPU_PROFILING);
 473
 474         /* Do not restart, when we are in the idle loop */
 475         if (ts->tick_stopped)
 476                 return;
 477
 478         while (tick_nohz_reprogram(ts, now)) {
 479                 now = ktime_get();
 480                 tick_do_update_jiffies64(now);
 481         }
 482 }
 483
 484 /**
 485  * tick_nohz_switch_to_nohz - switch to nohz mode
 486  */
 487 static void tick_nohz_switch_to_nohz(void)
 488 {
 489         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 490         ktime_t next;
 491
 492         if (!tick_nohz_enabled)
 493                 return;
 494
 495         local_irq_disable();
 496         if (tick_switch_to_oneshot(tick_nohz_handler)) {
 497                 local_irq_enable();
 498                 return;
 499         }
 500
 501         ts->nohz_mode = NOHZ_MODE_LOWRES;
 502
 503         /*
 504          * Recycle the hrtimer in ts, so we can share the
 505          * hrtimer_forward with the highres code.
 506          */
 507         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 508         /* Get the next period */
 509         next = tick_init_jiffy_update();
 510
 511         for (;;) {
 512                 ts->sched_timer.expires = next;
 513                 if (!tick_program_event(next, 0))
 514                         break;
 515                 next = ktime_add(next, tick_period);
 516         }
 517         local_irq_enable();
 518
 519         printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
 520                smp_processor_id());
 521 }
 522
 523 #else
 524
 525 static inline void tick_nohz_switch_to_nohz(void) { }
 526
 527 #endif /* NO_HZ */
 528
 529 /*
 530  * High resolution timer specific code
 531  */
 532 #ifdef CONFIG_HIGH_RES_TIMERS
 533 /*
 534  * We rearm the timer until we get disabled by the idle code.
 535  * Called with interrupts disabled and timer->base->cpu_base->lock held.
 536  */
 537 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
 538 {
 539         struct tick_sched *ts =
 540                 container_of(timer, struct tick_sched, sched_timer);
 541         struct pt_regs *regs = get_irq_regs();
 542         ktime_t now = ktime_get();
 543         int cpu = smp_processor_id();
 544
 545 #ifdef CONFIG_NO_HZ
 546         /*
 547          * Check if the do_timer duty was dropped. We don't care about
 548          * concurrency: This happens only when the cpu in charge went
 549          * into a long sleep. If two cpus happen to assign themself to
 550          * this duty, then the jiffies update is still serialized by
 551          * xtime_lock.
 552          */
 553         if (unlikely(tick_do_timer_cpu == -1))
 554                 tick_do_timer_cpu = cpu;
 555 #endif
 556
 557         /* Check, if the jiffies need an update */
 558         if (tick_do_timer_cpu == cpu)
 559                 tick_do_update_jiffies64(now);
 560
 561         /*
 562          * Do not call, when we are not in irq context and have
 563          * no valid regs pointer
 564          */
 565         if (regs) {
 566                 /*
 567                  * When we are idle and the tick is stopped, we have to touch
 568                  * the watchdog as we might not schedule for a really long
 569                  * time. This happens on complete idle SMP systems while
 570                  * waiting on the login prompt. We also increment the "start of
 571                  * idle" jiffy stamp so the idle accounting adjustment we do
 572                  * when we go busy again does not account too much ticks.
 573                  */
 574                 if (ts->tick_stopped) {
 575                         touch_softlockup_watchdog();
 576                         ts->idle_jiffies++;
 577                 }
 578                 update_process_times(user_mode(regs));
 579                 profile_tick(CPU_PROFILING);
 580         }
 581
 582         /* Do not restart, when we are in the idle loop */
 583         if (ts->tick_stopped)
 584                 return HRTIMER_NORESTART;
 585
 586         hrtimer_forward(timer, now, tick_period);
 587
 588         return HRTIMER_RESTART;
 589 }
 590
 591 /**
 592  * tick_setup_sched_timer - setup the tick emulation timer
 593  */
 594 void tick_setup_sched_timer(void)
 595 {
 596         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 597         ktime_t now = ktime_get();
 598         u64 offset;
 599
 600         /*
 601          * Emulate tick processing via per-CPU hrtimers:
 602          */
 603         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 604         ts->sched_timer.function = tick_sched_timer;
 605         ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
 606
 607         /* Get the next period (per cpu) */
 608         ts->sched_timer.expires = tick_init_jiffy_update();
 609         offset = ktime_to_ns(tick_period) >> 1;
 610         do_div(offset, num_possible_cpus());
 611         offset *= smp_processor_id();
 612         ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);
 613
 614         for (;;) {
 615                 hrtimer_forward(&ts->sched_timer, now, tick_period);
 616                 hrtimer_start(&ts->sched_timer, ts->sched_timer.expires,
 617                               HRTIMER_MODE_ABS);
 618                 /* Check, if the timer was already in the past */
 619                 if (hrtimer_active(&ts->sched_timer))
 620                         break;
 621                 now = ktime_get();
 622         }
 623
 624 #ifdef CONFIG_NO_HZ
 625         if (tick_nohz_enabled)
 626                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
 627 #endif
 628 }
 629
 630 void tick_cancel_sched_timer(int cpu)
 631 {
 632         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 633
 634         if (ts->sched_timer.base)
 635                 hrtimer_cancel(&ts->sched_timer);
 636
 637         ts->nohz_mode = NOHZ_MODE_INACTIVE;
 638 }
 639 #endif /* HIGH_RES_TIMERS */
 640
 641 /**
 642  * Async notification about clocksource changes
 643  */
 644 void tick_clock_notify(void)
 645 {
 646         int cpu;
 647
 648         for_each_possible_cpu(cpu)
 649                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
 650 }
 651
 652 /*
 653  * Async notification about clock event changes
 654  */
 655 void tick_oneshot_notify(void)
 656 {
 657         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 658
 659         set_bit(0, &ts->check_clocks);
 660 }
 661
 662 /**
 663  * Check, if a change happened, which makes oneshot possible.
 664  *
 665  * Called cyclic from the hrtimer softirq (driven by the timer
 666  * softirq) allow_nohz signals, that we can switch into low-res nohz
 667  * mode, because high resolution timers are disabled (either compile
 668  * or runtime).
 669  */
 670 int tick_check_oneshot_change(int allow_nohz)
 671 {
 672         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 673
 674         if (!test_and_clear_bit(0, &ts->check_clocks))
 675                 return 0;
 676
 677         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
 678                 return 0;
 679
 680         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
 681                 return 0;
 682
 683         if (!allow_nohz)
 684                 return 1;
 685
 686         tick_nohz_switch_to_nohz();
 687         return 0;
 688 }