/* * linux/kernel/time/tick-sched.c * * Copyright(C) 2005-2006, Thomas Gleixner * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner * * No idle tick implementation for low and high resolution timers * * Started by: Thomas Gleixner and Ingo Molnar * * Distribute under GPLv2. */ #include #include #include #include #include #include #include #include #include #include #include "tick-internal.h" /* * Per cpu nohz control structure */ static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); /* * The time, when the last jiffy update happened. Protected by xtime_lock. */ static ktime_t last_jiffies_update; struct tick_sched *tick_get_tick_sched(int cpu) { return &per_cpu(tick_cpu_sched, cpu); } /* * Must be called with interrupts disabled ! */ static void tick_do_update_jiffies64(ktime_t now) { unsigned long ticks = 0; ktime_t delta; /* * Do a quick check without holding xtime_lock: */ delta = ktime_sub(now, last_jiffies_update); if (delta.tv64 < tick_period.tv64) return; /* Reevalute with xtime_lock held */ write_seqlock(&xtime_lock); delta = ktime_sub(now, last_jiffies_update); if (delta.tv64 >= tick_period.tv64) { delta = ktime_sub(delta, tick_period); last_jiffies_update = ktime_add(last_jiffies_update, tick_period); /* Slow path for long timeouts */ if (unlikely(delta.tv64 >= tick_period.tv64)) { s64 incr = ktime_to_ns(tick_period); ticks = ktime_divns(delta, incr); last_jiffies_update = ktime_add_ns(last_jiffies_update, incr * ticks); } do_timer(++ticks); /* Keep the tick_next_period variable up to date */ tick_next_period = ktime_add(last_jiffies_update, tick_period); } write_sequnlock(&xtime_lock); } /* * Initialize and return retrieve the jiffies update. */ static ktime_t tick_init_jiffy_update(void) { ktime_t period; write_seqlock(&xtime_lock); /* Did we start the jiffies update yet ? */ if (last_jiffies_update.tv64 == 0) last_jiffies_update = tick_next_period; period = last_jiffies_update; write_sequnlock(&xtime_lock); return period; } /* * NOHZ - aka dynamic tick functionality */ #ifdef CONFIG_NO_HZ /* * NO HZ enabled ? */ static int tick_nohz_enabled __read_mostly = 1; /* * Enable / Disable tickless mode */ static int __init setup_tick_nohz(char *str) { if (!strcmp(str, "off")) tick_nohz_enabled = 0; else if (!strcmp(str, "on")) tick_nohz_enabled = 1; else return 0; return 1; } __setup("nohz=", setup_tick_nohz); /** * tick_nohz_update_jiffies - update jiffies when idle was interrupted * * Called from interrupt entry when the CPU was idle * * In case the sched_tick was stopped on this CPU, we have to check if jiffies * must be updated. Otherwise an interrupt handler could use a stale jiffy * value. We do this unconditionally on any cpu, as we don't know whether the * cpu, which has the update task assigned is in a long sleep. */ static void tick_nohz_update_jiffies(ktime_t now) { int cpu = smp_processor_id(); struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); unsigned long flags; ts->idle_waketime = now; local_irq_save(flags); tick_do_update_jiffies64(now); local_irq_restore(flags); touch_softlockup_watchdog(); } /* * Updates the per cpu time idle statistics counters */ static void update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) { ktime_t delta; if (ts->idle_active) { delta = ktime_sub(now, ts->idle_entrytime); if (nr_iowait_cpu(cpu) > 0) ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); else ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); ts->idle_entrytime = now; } if (last_update_time) *last_update_time = ktime_to_us(now); } static void tick_nohz_stop_idle(int cpu, ktime_t now) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); update_ts_time_stats(cpu, ts, now, NULL); ts->idle_active = 0; sched_clock_idle_wakeup_event(0); } static ktime_t tick_nohz_start_idle(int cpu, struct tick_sched *ts) { ktime_t now = ktime_get(); ts->idle_entrytime = now; ts->idle_active = 1; sched_clock_idle_sleep_event(); return now; } /** * get_cpu_idle_time_us - get the total idle time of a cpu * @cpu: CPU number to query * @last_update_time: variable to store update time in. Do not update * counters if NULL. * * Return the cummulative idle time (since boot) for a given * CPU, in microseconds. * * This time is measured via accounting rather than sampling, * and is as accurate as ktime_get() is. * * This function returns -1 if NOHZ is not enabled. */ u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); ktime_t now, idle; if (!tick_nohz_enabled) return -1; now = ktime_get(); if (last_update_time) { update_ts_time_stats(cpu, ts, now, last_update_time); idle = ts->idle_sleeptime; } else { if (ts->idle_active && !nr_iowait_cpu(cpu)) { ktime_t delta = ktime_sub(now, ts->idle_entrytime); idle = ktime_add(ts->idle_sleeptime, delta); } else { idle = ts->idle_sleeptime; } } return ktime_to_us(idle); } EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); /** * get_cpu_iowait_time_us - get the total iowait time of a cpu * @cpu: CPU number to query * @last_update_time: variable to store update time in. Do not update * counters if NULL. * * Return the cummulative iowait time (since boot) for a given * CPU, in microseconds. * * This time is measured via accounting rather than sampling, * and is as accurate as ktime_get() is. * * This function returns -1 if NOHZ is not enabled. */ u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); ktime_t now, iowait; if (!tick_nohz_enabled) return -1; now = ktime_get(); if (last_update_time) { update_ts_time_stats(cpu, ts, now, last_update_time); iowait = ts->iowait_sleeptime; } else { if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { ktime_t delta = ktime_sub(now, ts->idle_entrytime); iowait = ktime_add(ts->iowait_sleeptime, delta); } else { iowait = ts->iowait_sleeptime; } } return ktime_to_us(iowait); } EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); static void tick_nohz_stop_sched_tick(struct tick_sched *ts, ktime_t now, int cpu) { unsigned long seq, last_jiffies, next_jiffies, delta_jiffies; ktime_t last_update, expires; struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev; u64 time_delta; /* Read jiffies and the time when jiffies were updated last */ do { seq = read_seqbegin(&xtime_lock); last_update = last_jiffies_update; last_jiffies = jiffies; time_delta = timekeeping_max_deferment(); } while (read_seqretry(&xtime_lock, seq)); if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) || arch_needs_cpu(cpu)) { next_jiffies = last_jiffies + 1; delta_jiffies = 1; } else { /* Get the next timer wheel timer */ next_jiffies = get_next_timer_interrupt(last_jiffies); delta_jiffies = next_jiffies - last_jiffies; } /* * Do not stop the tick, if we are only one off * or if the cpu is required for rcu */ if (!ts->tick_stopped && delta_jiffies == 1) goto out; /* Schedule the tick, if we are at least one jiffie off */ if ((long)delta_jiffies >= 1) { /* * If this cpu is the one which updates jiffies, then * give up the assignment and let it be taken by the * cpu which runs the tick timer next, which might be * this cpu as well. If we don't drop this here the * jiffies might be stale and do_timer() never * invoked. Keep track of the fact that it was the one * which had the do_timer() duty last. If this cpu is * the one which had the do_timer() duty last, we * limit the sleep time to the timekeeping * max_deferement value which we retrieved * above. Otherwise we can sleep as long as we want. */ if (cpu == tick_do_timer_cpu) { tick_do_timer_cpu = TICK_DO_TIMER_NONE; ts->do_timer_last = 1; } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { time_delta = KTIME_MAX; ts->do_timer_last = 0; } else if (!ts->do_timer_last) { time_delta = KTIME_MAX; } /* * calculate the expiry time for the next timer wheel * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals * that there is no timer pending or at least extremely * far into the future (12 days for HZ=1000). In this * case we set the expiry to the end of time. */ if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) { /* * Calculate the time delta for the next timer event. * If the time delta exceeds the maximum time delta * permitted by the current clocksource then adjust * the time delta accordingly to ensure the * clocksource does not wrap. */ time_delta = min_t(u64, time_delta, tick_period.tv64 * delta_jiffies); } if (time_delta < KTIME_MAX) expires = ktime_add_ns(last_update, time_delta); else expires.tv64 = KTIME_MAX; /* Skip reprogram of event if its not changed */ if (ts->tick_stopped && ktime_equal(expires, dev->next_event)) goto out; /* * nohz_stop_sched_tick can be called several times before * the nohz_restart_sched_tick is called. This happens when * interrupts arrive which do not cause a reschedule. In the * first call we save the current tick time, so we can restart * the scheduler tick in nohz_restart_sched_tick. */ if (!ts->tick_stopped) { select_nohz_load_balancer(1); ts->last_tick = hrtimer_get_expires(&ts->sched_timer); ts->tick_stopped = 1; } ts->idle_sleeps++; /* Mark expires */ ts->idle_expires = expires; /* * If the expiration time == KTIME_MAX, then * in this case we simply stop the tick timer. */ if (unlikely(expires.tv64 == KTIME_MAX)) { if (ts->nohz_mode == NOHZ_MODE_HIGHRES) hrtimer_cancel(&ts->sched_timer); goto out; } if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { hrtimer_start(&ts->sched_timer, expires, HRTIMER_MODE_ABS_PINNED); /* Check, if the timer was already in the past */ if (hrtimer_active(&ts->sched_timer)) goto out; } else if (!tick_program_event(expires, 0)) goto out; /* * We are past the event already. So we crossed a * jiffie boundary. Update jiffies and raise the * softirq. */ tick_do_update_jiffies64(ktime_get()); } raise_softirq_irqoff(TIMER_SOFTIRQ); out: ts->next_jiffies = next_jiffies; ts->last_jiffies = last_jiffies; ts->sleep_length = ktime_sub(dev->next_event, now); } static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) { /* * If this cpu is offline and it is the one which updates * jiffies, then give up the assignment and let it be taken by * the cpu which runs the tick timer next. If we don't drop * this here the jiffies might be stale and do_timer() never * invoked. */ if (unlikely(!cpu_online(cpu))) { if (cpu == tick_do_timer_cpu) tick_do_timer_cpu = TICK_DO_TIMER_NONE; } if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) return false; if (need_resched()) return false; if (unlikely(local_softirq_pending() && cpu_online(cpu))) { static int ratelimit; if (ratelimit < 10) { printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", (unsigned int) local_softirq_pending()); ratelimit++; } return false; } return true; } static void __tick_nohz_idle_enter(struct tick_sched *ts) { ktime_t now; int cpu = smp_processor_id(); now = tick_nohz_start_idle(cpu, ts); if (can_stop_idle_tick(cpu, ts)) { int was_stopped = ts->tick_stopped; ts->idle_calls++; tick_nohz_stop_sched_tick(ts, now, cpu); if (!was_stopped && ts->tick_stopped) ts->idle_jiffies = ts->last_jiffies; } } /** * tick_nohz_idle_enter - stop the idle tick from the idle task * * When the next event is more than a tick into the future, stop the idle tick * Called when we start the idle loop. * * The arch is responsible of calling: * * - rcu_idle_enter() after its last use of RCU before the CPU is put * to sleep. * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. */ void tick_nohz_idle_enter(void) { struct tick_sched *ts; WARN_ON_ONCE(irqs_disabled()); /* * Update the idle state in the scheduler domain hierarchy * when tick_nohz_stop_sched_tick() is called from the idle loop. * State will be updated to busy during the first busy tick after * exiting idle. */ set_cpu_sd_state_idle(); local_irq_disable(); ts = &__get_cpu_var(tick_cpu_sched); /* * set ts->inidle unconditionally. even if the system did not * switch to nohz mode the cpu frequency governers rely on the * update of the idle time accounting in tick_nohz_start_idle(). */ ts->inidle = 1; __tick_nohz_idle_enter(ts); local_irq_enable(); } /** * tick_nohz_irq_exit - update next tick event from interrupt exit * * When an interrupt fires while we are idle and it doesn't cause * a reschedule, it may still add, modify or delete a timer, enqueue * an RCU callback, etc... * So we need to re-calculate and reprogram the next tick event. */ void tick_nohz_irq_exit(void) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); if (!ts->inidle) return; __tick_nohz_idle_enter(ts); } /** * tick_nohz_get_sleep_length - return the length of the current sleep * * Called from power state control code with interrupts disabled */ ktime_t tick_nohz_get_sleep_length(void) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); return ts->sleep_length; } static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) { hrtimer_cancel(&ts->sched_timer); hrtimer_set_expires(&ts->sched_timer, ts->last_tick); while (1) { /* Forward the time to expire in the future */ hrtimer_forward(&ts->sched_timer, now, tick_period); if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED); /* Check, if the timer was already in the past */ if (hrtimer_active(&ts->sched_timer)) break; } else { if (!tick_program_event( hrtimer_get_expires(&ts->sched_timer), 0)) break; } /* Reread time and update jiffies */ now = ktime_get(); tick_do_update_jiffies64(now); } } static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) { /* Update jiffies first */ select_nohz_load_balancer(0); tick_do_update_jiffies64(now); update_cpu_load_nohz(); touch_softlockup_watchdog(); /* * Cancel the scheduled timer and restore the tick */ ts->tick_stopped = 0; ts->idle_exittime = now; tick_nohz_restart(ts, now); } static void tick_nohz_account_idle_ticks(struct tick_sched *ts) { #ifndef CONFIG_VIRT_CPU_ACCOUNTING unsigned long ticks; /* * We stopped the tick in idle. Update process times would miss the * time we slept as update_process_times does only a 1 tick * accounting. Enforce that this is accounted to idle ! */ ticks = jiffies - ts->idle_jiffies; /* * We might be one off. Do not randomly account a huge number of ticks! */ if (ticks && ticks < LONG_MAX) account_idle_ticks(ticks); #endif } /** * tick_nohz_idle_exit - restart the idle tick from the idle task * * Restart the idle tick when the CPU is woken up from idle * This also exit the RCU extended quiescent state. The CPU * can use RCU again after this function is called. */ void tick_nohz_idle_exit(void) { int cpu = smp_processor_id(); struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); ktime_t now; local_irq_disable(); WARN_ON_ONCE(!ts->inidle); ts->inidle = 0; if (ts->idle_active || ts->tick_stopped) now = ktime_get(); if (ts->idle_active) tick_nohz_stop_idle(cpu, now); if (ts->tick_stopped) { tick_nohz_restart_sched_tick(ts, now); tick_nohz_account_idle_ticks(ts); } local_irq_enable(); } static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) { hrtimer_forward(&ts->sched_timer, now, tick_period); return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0); } /* * The nohz low res interrupt handler */ static void tick_nohz_handler(struct clock_event_device *dev) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); struct pt_regs *regs = get_irq_regs(); int cpu = smp_processor_id(); ktime_t now = ktime_get(); dev->next_event.tv64 = KTIME_MAX; /* * Check if the do_timer duty was dropped. We don't care about * concurrency: This happens only when the cpu in charge went * into a long sleep. If two cpus happen to assign themself to * this duty, then the jiffies update is still serialized by * xtime_lock. */ if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) tick_do_timer_cpu = cpu; /* Check, if the jiffies need an update */ if (tick_do_timer_cpu == cpu) tick_do_update_jiffies64(now); /* * When we are idle and the tick is stopped, we have to touch * the watchdog as we might not schedule for a really long * time. This happens on complete idle SMP systems while * waiting on the login prompt. We also increment the "start * of idle" jiffy stamp so the idle accounting adjustment we * do when we go busy again does not account too much ticks. */ if (ts->tick_stopped) { touch_softlockup_watchdog(); ts->idle_jiffies++; } update_process_times(user_mode(regs)); profile_tick(CPU_PROFILING); while (tick_nohz_reprogram(ts, now)) { now = ktime_get(); tick_do_update_jiffies64(now); } } /** * tick_nohz_switch_to_nohz - switch to nohz mode */ static void tick_nohz_switch_to_nohz(void) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); ktime_t next; if (!tick_nohz_enabled) return; local_irq_disable(); if (tick_switch_to_oneshot(tick_nohz_handler)) { local_irq_enable(); return; } ts->nohz_mode = NOHZ_MODE_LOWRES; /* * Recycle the hrtimer in ts, so we can share the * hrtimer_forward with the highres code. */ hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); /* Get the next period */ next = tick_init_jiffy_update(); for (;;) { hrtimer_set_expires(&ts->sched_timer, next); if (!tick_program_event(next, 0)) break; next = ktime_add(next, tick_period); } local_irq_enable(); } /* * When NOHZ is enabled and the tick is stopped, we need to kick the * tick timer from irq_enter() so that the jiffies update is kept * alive during long running softirqs. That's ugly as hell, but * correctness is key even if we need to fix the offending softirq in * the first place. * * Note, this is different to tick_nohz_restart. We just kick the * timer and do not touch the other magic bits which need to be done * when idle is left. */ static void tick_nohz_kick_tick(int cpu, ktime_t now) { #if 0 /* Switch back to 2.6.27 behaviour */ struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); ktime_t delta; /* * Do not touch the tick device, when the next expiry is either * already reached or less/equal than the tick period. */ delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); if (delta.tv64 <= tick_period.tv64) return; tick_nohz_restart(ts, now); #endif } static inline void tick_check_nohz(int cpu) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); ktime_t now; if (!ts->idle_active && !ts->tick_stopped) return; now = ktime_get(); if (ts->idle_active) tick_nohz_stop_idle(cpu, now); if (ts->tick_stopped) { tick_nohz_update_jiffies(now); tick_nohz_kick_tick(cpu, now); } } #else static inline void tick_nohz_switch_to_nohz(void) { } static inline void tick_check_nohz(int cpu) { } #endif /* NO_HZ */ /* * Called from irq_enter to notify about the possible interruption of idle() */ void tick_check_idle(int cpu) { tick_check_oneshot_broadcast(cpu); tick_check_nohz(cpu); } /* * High resolution timer specific code */ #ifdef CONFIG_HIGH_RES_TIMERS /* * We rearm the timer until we get disabled by the idle code. * Called with interrupts disabled and timer->base->cpu_base->lock held. */ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) { struct tick_sched *ts = container_of(timer, struct tick_sched, sched_timer); struct pt_regs *regs = get_irq_regs(); ktime_t now = ktime_get(); int cpu = smp_processor_id(); #ifdef CONFIG_NO_HZ /* * Check if the do_timer duty was dropped. We don't care about * concurrency: This happens only when the cpu in charge went * into a long sleep. If two cpus happen to assign themself to * this duty, then the jiffies update is still serialized by * xtime_lock. */ if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) tick_do_timer_cpu = cpu; #endif /* Check, if the jiffies need an update */ if (tick_do_timer_cpu == cpu) tick_do_update_jiffies64(now); /* * Do not call, when we are not in irq context and have * no valid regs pointer */ if (regs) { /* * When we are idle and the tick is stopped, we have to touch * the watchdog as we might not schedule for a really long * time. This happens on complete idle SMP systems while * waiting on the login prompt. We also increment the "start of * idle" jiffy stamp so the idle accounting adjustment we do * when we go busy again does not account too much ticks. */ if (ts->tick_stopped) { touch_softlockup_watchdog(); if (idle_cpu(cpu)) ts->idle_jiffies++; } update_process_times(user_mode(regs)); profile_tick(CPU_PROFILING); } hrtimer_forward(timer, now, tick_period); return HRTIMER_RESTART; } static int sched_skew_tick; static int __init skew_tick(char *str) { get_option(&str, &sched_skew_tick); return 0; } early_param("skew_tick", skew_tick); /** * tick_setup_sched_timer - setup the tick emulation timer */ void tick_setup_sched_timer(void) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); ktime_t now = ktime_get(); /* * Emulate tick processing via per-CPU hrtimers: */ hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); ts->sched_timer.function = tick_sched_timer; /* Get the next period (per cpu) */ hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); /* Offset the tick to avert xtime_lock contention. */ if (sched_skew_tick) { u64 offset = ktime_to_ns(tick_period) >> 1; do_div(offset, num_possible_cpus()); offset *= smp_processor_id(); hrtimer_add_expires_ns(&ts->sched_timer, offset); } for (;;) { hrtimer_forward(&ts->sched_timer, now, tick_period); hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED); /* Check, if the timer was already in the past */ if (hrtimer_active(&ts->sched_timer)) break; now = ktime_get(); } #ifdef CONFIG_NO_HZ if (tick_nohz_enabled) ts->nohz_mode = NOHZ_MODE_HIGHRES; #endif } #endif /* HIGH_RES_TIMERS */ #if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS void tick_cancel_sched_timer(int cpu) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); # ifdef CONFIG_HIGH_RES_TIMERS if (ts->sched_timer.base) hrtimer_cancel(&ts->sched_timer); # endif ts->nohz_mode = NOHZ_MODE_INACTIVE; } #endif /** * Async notification about clocksource changes */ void tick_clock_notify(void) { int cpu; for_each_possible_cpu(cpu) set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); } /* * Async notification about clock event changes */ void tick_oneshot_notify(void) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); set_bit(0, &ts->check_clocks); } /** * Check, if a change happened, which makes oneshot possible. * * Called cyclic from the hrtimer softirq (driven by the timer * softirq) allow_nohz signals, that we can switch into low-res nohz * mode, because high resolution timers are disabled (either compile * or runtime). */ int tick_check_oneshot_change(int allow_nohz) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); if (!test_and_clear_bit(0, &ts->check_clocks)) return 0; if (ts->nohz_mode != NOHZ_MODE_INACTIVE) return 0; if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) return 0; if (!allow_nohz) return 1; tick_nohz_switch_to_nohz(); return 0; }