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/*

 *  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

 *

 *  For licencing details see kernel-base/COPYING

 */

#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/profile.h>

#include <linux/sched.h>

#include <linux/tick.h>

#include <asm/irq_regs.h>

#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;

        /* 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);

        }

        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.

 */

void tick_nohz_update_jiffies(void)

{

        int cpu = smp_processor_id();

        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

        unsigned long flags;

        ktime_t now;

        if (!ts->tick_stopped)

                return;

        touch_softlockup_watchdog();

        cpu_clear(cpu, nohz_cpu_mask);

        now = ktime_get();

        local_irq_save(flags);

        tick_do_update_jiffies64(now);

        local_irq_restore(flags);

}

/**

 * tick_nohz_stop_sched_tick - 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 either from the idle loop or from irq_exit() when an idle period was

 * just interrupted by an interrupt which did not cause a reschedule.

 */

void tick_nohz_stop_sched_tick(void)

{

        unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;

        struct tick_sched *ts;

        ktime_t last_update, expires, now, delta;

        struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;

        int cpu;

        local_irq_save(flags);

        cpu = smp_processor_id();

        ts = &per_cpu(tick_cpu_sched, cpu);

        /*

         * 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 = -1;

        }

        if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))

                goto end;

        if (need_resched())

                goto end;

        cpu = smp_processor_id();

        if (unlikely(local_softirq_pending())) {

                static int ratelimit;

                if (ratelimit < 10) {

                        printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",

                               local_softirq_pending());

                        ratelimit++;

                }

        }

        now = ktime_get();

        /*

         * When called from irq_exit we need to account the idle sleep time

         * correctly.

         */

        if (ts->tick_stopped) {

                delta = ktime_sub(now, ts->idle_entrytime);

                ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);

        }

        ts->idle_entrytime = now;

        ts->idle_calls++;

        /* Read jiffies and the time when jiffies were updated last */

        do {

                seq = read_seqbegin(&xtime_lock);

                last_update = last_jiffies_update;

                last_jiffies = jiffies;

        } while (read_seqretry(&xtime_lock, seq));

        /* Get the next timer wheel timer */

        next_jiffies = get_next_timer_interrupt(last_jiffies);

        delta_jiffies = next_jiffies - last_jiffies;

        if (rcu_needs_cpu(cpu))

                delta_jiffies = 1;

        /*

         * 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 (delta_jiffies > 1)

                        cpu_set(cpu, nohz_cpu_mask);

                /*

                 * 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) {

                        if (select_nohz_load_balancer(1)) {

                                /*

                                 * sched tick not stopped!

                                 */

                                cpu_clear(cpu, nohz_cpu_mask);

                                goto out;

                        }

                        ts->idle_tick = ts->sched_timer.expires;

                        ts->tick_stopped = 1;

                        ts->idle_jiffies = last_jiffies;

                }

                /*

                 * 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.

                 */

                if (cpu == tick_do_timer_cpu)

                        tick_do_timer_cpu = -1;

                ts->idle_sleeps++;

                /*

                 * delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that

                 * there is no timer pending or at least extremly far

                 * into the future (12 days for HZ=1000). In this case

                 * we simply stop the tick timer:

                 */

                if (unlikely(delta_jiffies >= NEXT_TIMER_MAX_DELTA)) {

                        ts->idle_expires.tv64 = KTIME_MAX;

                        if (ts->nohz_mode == NOHZ_MODE_HIGHRES)

                                hrtimer_cancel(&ts->sched_timer);

                        goto out;

                }

                /*

                 * calculate the expiry time for the next timer wheel

                 * timer

                 */

                expires = ktime_add_ns(last_update, tick_period.tv64 *

                                       delta_jiffies);

                ts->idle_expires = expires;

                if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {

                        hrtimer_start(&ts->sched_timer, expires,

                                      HRTIMER_MODE_ABS);

                        /* 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());

                cpu_clear(cpu, nohz_cpu_mask);

        }

        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);

end:

        local_irq_restore(flags);

}

/**

 * 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;

}

/**

 * tick_nohz_restart_sched_tick - restart the idle tick from the idle task

 *

 * Restart the idle tick when the CPU is woken up from idle

 */

void tick_nohz_restart_sched_tick(void)

{

        int cpu = smp_processor_id();

        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

        unsigned long ticks;

        ktime_t now, delta;

        if (!ts->tick_stopped)

                return;

        /* Update jiffies first */

        now = ktime_get();

        local_irq_disable();

        select_nohz_load_balancer(0);

        tick_do_update_jiffies64(now);

        cpu_clear(cpu, nohz_cpu_mask);

        /* Account the idle time */

        delta = ktime_sub(now, ts->idle_entrytime);

        ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);

        /*

         * 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) {

                add_preempt_count(HARDIRQ_OFFSET);

                account_system_time(current, HARDIRQ_OFFSET,

                                    jiffies_to_cputime(ticks));

                sub_preempt_count(HARDIRQ_OFFSET);

        }

        /*

         * Cancel the scheduled timer and restore the tick

         */

        ts->tick_stopped  = 0;

        hrtimer_cancel(&ts->sched_timer);

        ts->sched_timer.expires = ts->idle_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(&ts->sched_timer,

                                      ts->sched_timer.expires,

                                      HRTIMER_MODE_ABS);

                        /* Check, if the timer was already in the past */

                        if (hrtimer_active(&ts->sched_timer))

                                break;

                } else {

                        if (!tick_program_event(ts->sched_timer.expires, 0))

                                break;

                }

                /* Update jiffies and reread time */

                tick_do_update_jiffies64(now);

                now = ktime_get();

        }

        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(ts->sched_timer.expires, 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 == -1))

                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);

        /* Do not restart, when we are in the idle loop */

        if (ts->tick_stopped)

                return;

        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 (;;) {

                ts->sched_timer.expires = next;

                if (!tick_program_event(next, 0))

                        break;

                next = ktime_add(next, tick_period);

        }

        local_irq_enable();

        printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",

               smp_processor_id());

}

#else

static inline void tick_nohz_switch_to_nohz(void) { }

#endif /* NO_HZ */

/*

 * 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 hrtimer_cpu_base *base = timer->base->cpu_base;

        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 == -1))

                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();

                        ts->idle_jiffies++;

                }

                /*

                 * update_process_times() might take tasklist_lock, hence

                 * drop the base lock. sched-tick hrtimers are per-CPU and

                 * never accessible by userspace APIs, so this is safe to do.

                 */

                spin_unlock(&base->lock);

                update_process_times(user_mode(regs));

                profile_tick(CPU_PROFILING);

                spin_lock(&base->lock);

        }

        /* Do not restart, when we are in the idle loop */

        if (ts->tick_stopped)

                return HRTIMER_NORESTART;

        hrtimer_forward(timer, now, tick_period);

        return HRTIMER_RESTART;

}

/**

 * 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();

        u64 offset;

        /*

         * Emulate tick processing via per-CPU hrtimers:

         */

        hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);

        ts->sched_timer.function = tick_sched_timer;

        ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;

        /* Get the next period (per cpu) */

        ts->sched_timer.expires = tick_init_jiffy_update();

        offset = ktime_to_ns(tick_period) >> 1;

        do_div(offset, num_possible_cpus());

        offset *= smp_processor_id();

        ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);

        for (;;) {

                hrtimer_forward(&ts->sched_timer, now, tick_period);

                hrtimer_start(&ts->sched_timer, ts->sched_timer.expires,

                              HRTIMER_MODE_ABS);

                /* 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

}

void tick_cancel_sched_timer(int cpu)

{

        struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);

        if (ts->sched_timer.base)

                hrtimer_cancel(&ts->sched_timer);

        ts->tick_stopped = 0;

        ts->nohz_mode = NOHZ_MODE_INACTIVE;

}

#endif /* HIGH_RES_TIMERS */

/**

 * 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_is_continuous() || !tick_is_oneshot_available())

                return 0;

        if (!allow_nohz)

                return 1;

        tick_nohz_switch_to_nohz();

        return 0;

}