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  • tick-sched.c 32.05 KiB
    /*
     *  linux/kernel/time/tick-sched.c
     *
     *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
     *  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 <linux/cpu.h>
    #include <linux/err.h>
    #include <linux/hrtimer.h>
    #include <linux/interrupt.h>
    #include <linux/kernel_stat.h>
    #include <linux/percpu.h>
    #include <linux/nmi.h>
    #include <linux/profile.h>
    #include <linux/sched/signal.h>
    #include <linux/sched/clock.h>
    #include <linux/sched/stat.h>
    #include <linux/sched/nohz.h>
    #include <linux/module.h>
    #include <linux/irq_work.h>
    #include <linux/posix-timers.h>
    #include <linux/context_tracking.h>
    #include <linux/mm.h>
    
    #include <asm/irq_regs.h>
    
    #include "tick-internal.h"
    
    #include <trace/events/timer.h>
    
    /*
     * Per-CPU nohz control structure
     */
    static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
    
    struct tick_sched *tick_get_tick_sched(int cpu)
    {
    	return &per_cpu(tick_cpu_sched, cpu);
    }
    
    #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
    /*
     * The time, when the last jiffy update happened. Protected by jiffies_lock.
     */
    static ktime_t last_jiffies_update;
    
    /*
     * 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 jiffies_lock:
    	 */
    	delta = ktime_sub(now, last_jiffies_update);
    	if (delta < tick_period)
    		return;
    
    	/* Reevaluate with jiffies_lock held */
    	write_seqlock(&jiffies_lock);
    
    	delta = ktime_sub(now, last_jiffies_update);
    	if (delta >= tick_period) {
    
    		delta = ktime_sub(delta, tick_period);
    		last_jiffies_update = ktime_add(last_jiffies_update,
    						tick_period);
    
    		/* Slow path for long timeouts */
    		if (unlikely(delta >= tick_period)) {
    			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);
    	} else {
    		write_sequnlock(&jiffies_lock);
    		return;
    	}
    	write_sequnlock(&jiffies_lock);
    	update_wall_time();
    }
    
    /*
     * Initialize and return retrieve the jiffies update.
     */
    static ktime_t tick_init_jiffy_update(void)
    {
    	ktime_t period;
    
    	write_seqlock(&jiffies_lock);
    	/* Did we start the jiffies update yet ? */
    	if (last_jiffies_update == 0)
    		last_jiffies_update = tick_next_period;
    	period = last_jiffies_update;
    	write_sequnlock(&jiffies_lock);
    	return period;
    }
    
    
    static void tick_sched_do_timer(ktime_t now)
    {
    	int cpu = smp_processor_id();
    
    #ifdef CONFIG_NO_HZ_COMMON
    	/*
    	 * 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 themselves to
    	 * this duty, then the jiffies update is still serialized by
    	 * jiffies_lock.
    	 */
    	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
    	    && !tick_nohz_full_cpu(cpu))
    		tick_do_timer_cpu = cpu;
    #endif
    
    	/* Check, if the jiffies need an update */
    	if (tick_do_timer_cpu == cpu)
    		tick_do_update_jiffies64(now);
    }
    
    static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
    {
    #ifdef CONFIG_NO_HZ_COMMON
    	/*
    	 * 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_sched();
    		if (is_idle_task(current))
    			ts->idle_jiffies++;
    		/*
    		 * In case the current tick fired too early past its expected
    		 * expiration, make sure we don't bypass the next clock reprogramming
    		 * to the same deadline.
    		 */
    		ts->next_tick = 0;
    	}
    #endif
    	update_process_times(user_mode(regs));
    	profile_tick(CPU_PROFILING);
    }
    #endif
    
    #ifdef CONFIG_NO_HZ_FULL
    cpumask_var_t tick_nohz_full_mask;
    bool tick_nohz_full_running;
    static atomic_t tick_dep_mask;
    
    static bool check_tick_dependency(atomic_t *dep)
    {
    	int val = atomic_read(dep);
    
    	if (val & TICK_DEP_MASK_POSIX_TIMER) {
    		trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
    		return true;
    	}
    
    	if (val & TICK_DEP_MASK_PERF_EVENTS) {
    		trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
    		return true;
    	}
    
    	if (val & TICK_DEP_MASK_SCHED) {
    		trace_tick_stop(0, TICK_DEP_MASK_SCHED);
    		return true;
    	}
    
    	if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
    		trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
    		return true;
    	}
    
    	return false;
    }
    
    static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
    {
    	lockdep_assert_irqs_disabled();
    
    	if (unlikely(!cpu_online(cpu)))
    		return false;
    
    	if (check_tick_dependency(&tick_dep_mask))
    		return false;
    
    	if (check_tick_dependency(&ts->tick_dep_mask))
    		return false;
    
    	if (check_tick_dependency(&current->tick_dep_mask))
    		return false;
    
    	if (check_tick_dependency(&current->signal->tick_dep_mask))
    		return false;
    
    	return true;
    }
    
    static void nohz_full_kick_func(struct irq_work *work)
    {
    	/* Empty, the tick restart happens on tick_nohz_irq_exit() */
    }
    
    static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
    	.func = nohz_full_kick_func,
    };
    
    /*
     * Kick this CPU if it's full dynticks in order to force it to
     * re-evaluate its dependency on the tick and restart it if necessary.
     * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
     * is NMI safe.
     */
    static void tick_nohz_full_kick(void)
    {
    	if (!tick_nohz_full_cpu(smp_processor_id()))
    		return;
    
    	irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
    }
    
    /*
     * Kick the CPU if it's full dynticks in order to force it to
     * re-evaluate its dependency on the tick and restart it if necessary.
     */
    void tick_nohz_full_kick_cpu(int cpu)
    {
    	if (!tick_nohz_full_cpu(cpu))
    		return;
    
    	irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
    }
    
    /*
     * Kick all full dynticks CPUs in order to force these to re-evaluate
     * their dependency on the tick and restart it if necessary.
     */
    static void tick_nohz_full_kick_all(void)
    {
    	int cpu;
    
    	if (!tick_nohz_full_running)
    		return;
    
    	preempt_disable();
    	for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
    		tick_nohz_full_kick_cpu(cpu);
    	preempt_enable();
    }
    
    static void tick_nohz_dep_set_all(atomic_t *dep,
    				  enum tick_dep_bits bit)
    {
    	int prev;
    
    	prev = atomic_fetch_or(BIT(bit), dep);
    	if (!prev)
    		tick_nohz_full_kick_all();
    }
    
    /*
     * Set a global tick dependency. Used by perf events that rely on freq and
     * by unstable clock.
     */
    void tick_nohz_dep_set(enum tick_dep_bits bit)
    {
    	tick_nohz_dep_set_all(&tick_dep_mask, bit);
    }
    
    void tick_nohz_dep_clear(enum tick_dep_bits bit)
    {
    	atomic_andnot(BIT(bit), &tick_dep_mask);
    }
    
    /*
     * Set per-CPU tick dependency. Used by scheduler and perf events in order to
     * manage events throttling.
     */
    void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
    {
    	int prev;
    	struct tick_sched *ts;
    
    	ts = per_cpu_ptr(&tick_cpu_sched, cpu);
    
    	prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask);
    	if (!prev) {
    		preempt_disable();
    		/* Perf needs local kick that is NMI safe */
    		if (cpu == smp_processor_id()) {
    			tick_nohz_full_kick();
    		} else {
    			/* Remote irq work not NMI-safe */
    			if (!WARN_ON_ONCE(in_nmi()))
    				tick_nohz_full_kick_cpu(cpu);
    		}
    		preempt_enable();
    	}
    }
    
    void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
    {
    	struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
    
    	atomic_andnot(BIT(bit), &ts->tick_dep_mask);
    }
    
    /*
     * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
     * per task timers.
     */
    void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
    {
    	/*
    	 * We could optimize this with just kicking the target running the task
    	 * if that noise matters for nohz full users.
    	 */
    	tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
    }
    
    void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
    {
    	atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
    }
    
    /*
     * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
     * per process timers.
     */
    void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
    {
    	tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
    }
    
    void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
    {
    	atomic_andnot(BIT(bit), &sig->tick_dep_mask);
    }
    
    /*
     * Re-evaluate the need for the tick as we switch the current task.
     * It might need the tick due to per task/process properties:
     * perf events, posix CPU timers, ...
     */
    void __tick_nohz_task_switch(void)
    {
    	unsigned long flags;
    	struct tick_sched *ts;
    
    	local_irq_save(flags);
    
    	if (!tick_nohz_full_cpu(smp_processor_id()))
    		goto out;
    
    	ts = this_cpu_ptr(&tick_cpu_sched);
    
    	if (ts->tick_stopped) {
    		if (atomic_read(&current->tick_dep_mask) ||
    		    atomic_read(&current->signal->tick_dep_mask))
    			tick_nohz_full_kick();
    	}
    out:
    	local_irq_restore(flags);
    }
    
    /* Get the boot-time nohz CPU list from the kernel parameters. */
    void __init tick_nohz_full_setup(cpumask_var_t cpumask)
    {
    	alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
    	cpumask_copy(tick_nohz_full_mask, cpumask);
    	tick_nohz_full_running = true;
    }
    
    static int tick_nohz_cpu_down(unsigned int cpu)
    {
    	/*
    	 * The boot CPU handles housekeeping duty (unbound timers,
    	 * workqueues, timekeeping, ...) on behalf of full dynticks
    	 * CPUs. It must remain online when nohz full is enabled.
    	 */
    	if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
    		return -EBUSY;
    	return 0;
    }
    
    static int tick_nohz_init_all(void)
    {
    	int err = -1;
    
    #ifdef CONFIG_NO_HZ_FULL_ALL
    	if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
    		WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
    		return err;
    	}
    	err = 0;
    	cpumask_setall(tick_nohz_full_mask);
    	tick_nohz_full_running = true;
    #endif
    	return err;
    }
    
    void __init tick_nohz_init(void)
    {
    	int cpu, ret;
    
    	if (!tick_nohz_full_running) {
    		if (tick_nohz_init_all() < 0)
    			return;
    	}
    
    	/*
    	 * Full dynticks uses irq work to drive the tick rescheduling on safe
    	 * locking contexts. But then we need irq work to raise its own
    	 * interrupts to avoid circular dependency on the tick
    	 */
    	if (!arch_irq_work_has_interrupt()) {
    		pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
    		cpumask_clear(tick_nohz_full_mask);
    		tick_nohz_full_running = false;
    		return;
    	}
    
    	cpu = smp_processor_id();
    
    	if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
    		pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
    			cpu);
    		cpumask_clear_cpu(cpu, tick_nohz_full_mask);
    	}
    
    	for_each_cpu(cpu, tick_nohz_full_mask)
    		context_tracking_cpu_set(cpu);
    
    	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
    					"kernel/nohz:predown", NULL,
    					tick_nohz_cpu_down);
    	WARN_ON(ret < 0);
    	pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
    		cpumask_pr_args(tick_nohz_full_mask));
    }
    #endif
    
    /*
     * NOHZ - aka dynamic tick functionality
     */
    #ifdef CONFIG_NO_HZ_COMMON
    /*
     * NO HZ enabled ?
     */
    bool tick_nohz_enabled __read_mostly  = true;
    unsigned long tick_nohz_active  __read_mostly;
    /*
     * Enable / Disable tickless mode
     */
    static int __init setup_tick_nohz(char *str)
    {
    	return (kstrtobool(str, &tick_nohz_enabled) == 0);
    }
    
    __setup("nohz=", setup_tick_nohz);
    
    int tick_nohz_tick_stopped(void)
    {
    	return __this_cpu_read(tick_cpu_sched.tick_stopped);
    }
    
    /**
     * 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)
    {
    	unsigned long flags;
    
    	__this_cpu_write(tick_cpu_sched.idle_waketime, now);
    
    	local_irq_save(flags);
    	tick_do_update_jiffies64(now);
    	local_irq_restore(flags);
    
    	touch_softlockup_watchdog_sched();
    }
    
    /*
     * 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(struct tick_sched *ts, ktime_t now)
    {
    	update_ts_time_stats(smp_processor_id(), ts, now, NULL);
    	ts->idle_active = 0;
    
    	sched_clock_idle_wakeup_event();
    }
    
    static ktime_t tick_nohz_start_idle(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 cumulative 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_active)
    		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 cumulative 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_active)
    		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_restart(struct tick_sched *ts, ktime_t now)
    {
    	hrtimer_cancel(&ts->sched_timer);
    	hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
    
    	/* 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);
    	else
    		tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
    
    	/*
    	 * Reset to make sure next tick stop doesn't get fooled by past
    	 * cached clock deadline.
    	 */
    	ts->next_tick = 0;
    }
    
    static inline bool local_timer_softirq_pending(void)
    {
    	return local_softirq_pending() & TIMER_SOFTIRQ;
    }
    
    static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
    					 ktime_t now, int cpu)
    {
    	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
    	u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
    	unsigned long seq, basejiff;
    	ktime_t	tick;
    
    	/* Read jiffies and the time when jiffies were updated last */
    	do {
    		seq = read_seqbegin(&jiffies_lock);
    		basemono = last_jiffies_update;
    		basejiff = jiffies;
    	} while (read_seqretry(&jiffies_lock, seq));
    	ts->last_jiffies = basejiff;
    
    	/*
    	 * Keep the periodic tick, when RCU, architecture or irq_work
    	 * requests it.
    	 * Aside of that check whether the local timer softirq is
    	 * pending. If so its a bad idea to call get_next_timer_interrupt()
    	 * because there is an already expired timer, so it will request
    	 * immeditate expiry, which rearms the hardware timer with a
    	 * minimal delta which brings us back to this place
    	 * immediately. Lather, rinse and repeat...
    	 */
    	if (rcu_needs_cpu(basemono, &next_rcu) || arch_needs_cpu() ||
    	    irq_work_needs_cpu() || local_timer_softirq_pending()) {
    		next_tick = basemono + TICK_NSEC;
    	} else {
    		/*
    		 * Get the next pending timer. If high resolution
    		 * timers are enabled this only takes the timer wheel
    		 * timers into account. If high resolution timers are
    		 * disabled this also looks at the next expiring
    		 * hrtimer.
    		 */
    		next_tmr = get_next_timer_interrupt(basejiff, basemono);
    		ts->next_timer = next_tmr;
    		/* Take the next rcu event into account */
    		next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
    	}
    
    	/*
    	 * If the tick is due in the next period, keep it ticking or
    	 * force prod the timer.
    	 */
    	delta = next_tick - basemono;
    	if (delta <= (u64)TICK_NSEC) {
    		/*
    		 * Tell the timer code that the base is not idle, i.e. undo
    		 * the effect of get_next_timer_interrupt():
    		 */
    		timer_clear_idle();
    		/*
    		 * We've not stopped the tick yet, and there's a timer in the
    		 * next period, so no point in stopping it either, bail.
    		 */
    		if (!ts->tick_stopped) {
    			tick = 0;
    			goto out;
    		}
    	}
    
    	/*
    	 * 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_deferment value.
    	 * Otherwise we can sleep as long as we want.
    	 */
    	delta = timekeeping_max_deferment();
    	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) {
    		delta = KTIME_MAX;
    		ts->do_timer_last = 0;
    	} else if (!ts->do_timer_last) {
    		delta = KTIME_MAX;
    	}
    
    #ifdef CONFIG_NO_HZ_FULL
    	/* Limit the tick delta to the maximum scheduler deferment */
    	if (!ts->inidle)
    		delta = min(delta, scheduler_tick_max_deferment());
    #endif
    
    	/* Calculate the next expiry time */
    	if (delta < (KTIME_MAX - basemono))
    		expires = basemono + delta;
    	else
    		expires = KTIME_MAX;
    
    	expires = min_t(u64, expires, next_tick);
    	tick = expires;
    
    	/* Skip reprogram of event if its not changed */
    	if (ts->tick_stopped && (expires == ts->next_tick)) {
    		/* Sanity check: make sure clockevent is actually programmed */
    		if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer))
    			goto out;
    
    		WARN_ON_ONCE(1);
    		printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n",
    			    basemono, ts->next_tick, dev->next_event,
    			    hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer));
    	}
    
    	/*
    	 * 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) {
    		calc_load_nohz_start();
    		cpu_load_update_nohz_start();
    		quiet_vmstat();
    
    		ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
    		ts->tick_stopped = 1;
    		trace_tick_stop(1, TICK_DEP_MASK_NONE);
    	}
    
    	ts->next_tick = tick;
    
    	/*
    	 * If the expiration time == KTIME_MAX, then we simply stop
    	 * the tick timer.
    	 */
    	if (unlikely(expires == KTIME_MAX)) {
    		if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
    			hrtimer_cancel(&ts->sched_timer);
    		goto out;
    	}
    
    	hrtimer_set_expires(&ts->sched_timer, tick);
    
    	if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
    		hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
    	else
    		tick_program_event(tick, 1);
    out:
    	/*
    	 * Update the estimated sleep length until the next timer
    	 * (not only the tick).
    	 */
    	ts->sleep_length = ktime_sub(dev->next_event, now);
    	return tick;
    }
    
    static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
    {
    	/* Update jiffies first */
    	tick_do_update_jiffies64(now);
    	cpu_load_update_nohz_stop();
    
    	/*
    	 * Clear the timer idle flag, so we avoid IPIs on remote queueing and
    	 * the clock forward checks in the enqueue path:
    	 */
    	timer_clear_idle();
    
    	calc_load_nohz_stop();
    	touch_softlockup_watchdog_sched();
    	/*
    	 * 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_full_update_tick(struct tick_sched *ts)
    {
    #ifdef CONFIG_NO_HZ_FULL
    	int cpu = smp_processor_id();
    
    	if (!tick_nohz_full_cpu(cpu))
    		return;
    
    	if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
    		return;
    
    	if (can_stop_full_tick(cpu, ts))
    		tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
    	else if (ts->tick_stopped)
    		tick_nohz_restart_sched_tick(ts, ktime_get());
    #endif
    }
    
    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;
    		/*
    		 * Make sure the CPU doesn't get fooled by obsolete tick
    		 * deadline if it comes back online later.
    		 */
    		ts->next_tick = 0;
    		return false;
    	}
    
    	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
    		ts->sleep_length = NSEC_PER_SEC / HZ;
    		return false;
    	}
    
    	if (need_resched())
    		return false;
    
    	if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
    		static int ratelimit;
    
    		if (ratelimit < 10 &&
    		    (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
    			pr_warn("NOHZ: local_softirq_pending %02x\n",
    				(unsigned int) local_softirq_pending());
    			ratelimit++;
    		}
    		return false;
    	}
    
    	if (tick_nohz_full_enabled()) {
    		/*
    		 * Keep the tick alive to guarantee timekeeping progression
    		 * if there are full dynticks CPUs around
    		 */
    		if (tick_do_timer_cpu == cpu)
    			return false;
    		/*
    		 * Boot safety: make sure the timekeeping duty has been
    		 * assigned before entering dyntick-idle mode,
    		 */
    		if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
    			return false;
    	}
    
    	return true;
    }
    
    static void __tick_nohz_idle_enter(struct tick_sched *ts)
    {
    	ktime_t now, expires;
    	int cpu = smp_processor_id();
    
    	now = tick_nohz_start_idle(ts);
    
    	if (can_stop_idle_tick(cpu, ts)) {
    		int was_stopped = ts->tick_stopped;
    
    		ts->idle_calls++;
    
    		expires = tick_nohz_stop_sched_tick(ts, now, cpu);
    		if (expires > 0LL) {
    			ts->idle_sleeps++;
    			ts->idle_expires = expires;
    		}
    
    		if (!was_stopped && ts->tick_stopped) {
    			ts->idle_jiffies = ts->last_jiffies;
    			nohz_balance_enter_idle(cpu);
    		}
    	}
    }
    
    /**
     * 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;
    
    	lockdep_assert_irqs_enabled();
    	/*
    	 * 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 = this_cpu_ptr(&tick_cpu_sched);
    	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 = this_cpu_ptr(&tick_cpu_sched);
    
    	if (ts->inidle)
    		__tick_nohz_idle_enter(ts);
    	else
    		tick_nohz_full_update_tick(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 = this_cpu_ptr(&tick_cpu_sched);
    
    	return ts->sleep_length;
    }
    
    /**
     * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value
     * for a particular CPU.
     *
     * Called from the schedutil frequency scaling governor in scheduler context.
     */
    unsigned long tick_nohz_get_idle_calls_cpu(int cpu)
    {
    	struct tick_sched *ts = tick_get_tick_sched(cpu);
    
    	return ts->idle_calls;
    }
    
    /**
     * tick_nohz_get_idle_calls - return the current idle calls counter value
     *
     * Called from the schedutil frequency scaling governor in scheduler context.
     */
    unsigned long tick_nohz_get_idle_calls(void)
    {
    	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
    
    	return ts->idle_calls;
    }
    
    static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
    {
    #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
    	unsigned long ticks;
    
    	if (vtime_accounting_cpu_enabled())
    		return;
    	/*
    	 * 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)
    {
    	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
    	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(ts, now);
    
    	if (ts->tick_stopped) {
    		tick_nohz_restart_sched_tick(ts, now);
    		tick_nohz_account_idle_ticks(ts);
    	}
    
    	local_irq_enable();
    }
    
    /*
     * The nohz low res interrupt handler
     */
    static void tick_nohz_handler(struct clock_event_device *dev)
    {
    	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
    	struct pt_regs *regs = get_irq_regs();
    	ktime_t now = ktime_get();
    
    	dev->next_event = KTIME_MAX;
    
    	tick_sched_do_timer(now);
    	tick_sched_handle(ts, regs);
    
    	/* No need to reprogram if we are running tickless  */
    	if (unlikely(ts->tick_stopped))
    		return;
    
    	hrtimer_forward(&ts->sched_timer, now, tick_period);
    	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
    }
    
    static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
    {
    	if (!tick_nohz_enabled)
    		return;
    	ts->nohz_mode = mode;
    	/* One update is enough */
    	if (!test_and_set_bit(0, &tick_nohz_active))
    		timers_update_migration(true);
    }
    
    /**
     * tick_nohz_switch_to_nohz - switch to nohz mode
     */
    static void tick_nohz_switch_to_nohz(void)
    {
    	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
    	ktime_t next;
    
    	if (!tick_nohz_enabled)
    		return;
    
    	if (tick_switch_to_oneshot(tick_nohz_handler))
    		return;
    
    	/*
    	 * 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();
    
    	hrtimer_set_expires(&ts->sched_timer, next);
    	hrtimer_forward_now(&ts->sched_timer, tick_period);
    	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
    	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
    }
    
    static inline void tick_nohz_irq_enter(void)
    {
    	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
    	ktime_t now;
    
    	if (!ts->idle_active && !ts->tick_stopped)
    		return;
    	now = ktime_get();
    	if (ts->idle_active)
    		tick_nohz_stop_idle(ts, now);
    	if (ts->tick_stopped)
    		tick_nohz_update_jiffies(now);
    }
    
    #else
    
    static inline void tick_nohz_switch_to_nohz(void) { }
    static inline void tick_nohz_irq_enter(void) { }
    static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
    
    #endif /* CONFIG_NO_HZ_COMMON */
    
    /*
     * Called from irq_enter to notify about the possible interruption of idle()
     */
    void tick_irq_enter(void)
    {
    	tick_check_oneshot_broadcast_this_cpu();
    	tick_nohz_irq_enter();
    }
    
    /*
     * 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.
     */
    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();
    
    	tick_sched_do_timer(now);
    
    	/*
    	 * Do not call, when we are not in irq context and have
    	 * no valid regs pointer
    	 */
    	if (regs)
    		tick_sched_handle(ts, regs);
    	else
    		ts->next_tick = 0;
    
    	/* No need to reprogram if we are in idle or full dynticks mode */
    	if (unlikely(ts->tick_stopped))
    		return HRTIMER_NORESTART;
    
    	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 = this_cpu_ptr(&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 jiffies_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);
    	}
    
    	hrtimer_forward(&ts->sched_timer, now, tick_period);
    	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
    	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
    }
    #endif /* HIGH_RES_TIMERS */
    
    #if defined CONFIG_NO_HZ_COMMON || 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
    
    	memset(ts, 0, sizeof(*ts));
    }
    #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 = this_cpu_ptr(&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). Called with interrupts disabled.
     */
    int tick_check_oneshot_change(int allow_nohz)
    {
    	struct tick_sched *ts = this_cpu_ptr(&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;
    }