8 files changed, 930 insertions, 3 deletions

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
new file mode 100644
index 00000000000..9ec54eb3667
--- /dev/null
+++ b/kernel/time/Kconfig
@@ -0,0 +1,15 @@
+#
+# Timer subsystem related configuration options
+#
+config TICK_ONESHOT
+        bool
+        default n
+
+config NO_HZ
+        bool "Tickless System (Dynamic Ticks)"
+        depends on GENERIC_TIME && GENERIC_CLOCKEVENTS
+        select TICK_ONESHOT
+        help
+          This option enables a tickless system: timer interrupts will
+          only trigger on an as-needed basis both when the system is
+          busy and when the system is idle.
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index a941743c3ff..f246bc836b9 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -3,3 +3,5 @@ obj-y += ntp.o clocksource.o jiffies.o
 obj-$(CONFIG_GENERIC_CLOCKEVENTS)               += clockevents.o
 obj-$(CONFIG_GENERIC_CLOCKEVENTS)               += tick-common.o
 obj-$(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST)     += tick-broadcast.o
+obj-$(CONFIG_TICK_ONESHOT)                      += tick-oneshot.o
+obj-$(CONFIG_TICK_ONESHOT)                      += tick-sched.o
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 3cb8ac97827..193a0793af9 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -29,6 +29,7 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
+#include <linux/tick.h>
 
 /* XXX - Would like a better way for initializing curr_clocksource */
 extern struct clocksource clocksource_jiffies;
@@ -109,6 +110,13 @@ static void clocksource_watchdog(unsigned long data)
                         if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
                             (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
                                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+                                /*
+                                 * We just marked the clocksource as
+                                 * highres-capable, notify the rest of the
+                                 * system as well so that we transition
+                                 * into high-res mode:
+                                 */
+                                tick_clock_notify();
                         }
                         cs->flags |= CLOCK_SOURCE_WATCHDOG;
                         cs->wd_last = csnow;
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 0ee4968ff79..8314ecb32d3 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -29,7 +29,7 @@
 
 struct tick_device tick_broadcast_device;
 static cpumask_t tick_broadcast_mask;
-DEFINE_SPINLOCK(tick_broadcast_lock);
+static DEFINE_SPINLOCK(tick_broadcast_lock);
 
 /*
  * Start the device in periodic mode
@@ -215,6 +215,8 @@ static void tick_do_broadcast_on_off(void *why)
         else {
                 if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
                         tick_broadcast_start_periodic(bc);
+                else
+                        tick_broadcast_setup_oneshot(bc);
         }
 out:
         spin_unlock_irqrestore(&tick_broadcast_lock, flags);
@@ -268,3 +270,190 @@ void tick_shutdown_broadcast(unsigned int *cpup)
 
         spin_unlock_irqrestore(&tick_broadcast_lock, flags);
 }
+
+#ifdef CONFIG_TICK_ONESHOT
+
+static cpumask_t tick_broadcast_oneshot_mask;
+
+static int tick_broadcast_set_event(ktime_t expires, int force)
+{
+        struct clock_event_device *bc = tick_broadcast_device.evtdev;
+        ktime_t now = ktime_get();
+        int res;
+
+        for(;;) {
+                res = clockevents_program_event(bc, expires, now);
+                if (!res || !force)
+                        return res;
+                now = ktime_get();
+                expires = ktime_add(now, ktime_set(0, bc->min_delta_ns));
+        }
+}
+
+/*
+ * Reprogram the broadcast device:
+ *
+ * Called with tick_broadcast_lock held and interrupts disabled.
+ */
+static int tick_broadcast_reprogram(void)
+{
+        ktime_t expires = { .tv64 = KTIME_MAX };
+        struct tick_device *td;
+        int cpu;
+
+        /*
+         * Find the event which expires next:
+         */
+        for (cpu = first_cpu(tick_broadcast_oneshot_mask); cpu != NR_CPUS;
+             cpu = next_cpu(cpu, tick_broadcast_oneshot_mask)) {
+                td = &per_cpu(tick_cpu_device, cpu);
+                if (td->evtdev->next_event.tv64 < expires.tv64)
+                        expires = td->evtdev->next_event;
+        }
+
+        if (expires.tv64 == KTIME_MAX)
+                return 0;
+
+        return tick_broadcast_set_event(expires, 0);
+}
+
+/*
+ * Handle oneshot mode broadcasting
+ */
+static void tick_handle_oneshot_broadcast(struct clock_event_device *dev)
+{
+        struct tick_device *td;
+        cpumask_t mask;
+        ktime_t now;
+        int cpu;
+
+        spin_lock(&tick_broadcast_lock);
+again:
+        dev->next_event.tv64 = KTIME_MAX;
+        mask = CPU_MASK_NONE;
+        now = ktime_get();
+        /* Find all expired events */
+        for (cpu = first_cpu(tick_broadcast_oneshot_mask); cpu != NR_CPUS;
+             cpu = next_cpu(cpu, tick_broadcast_oneshot_mask)) {
+                td = &per_cpu(tick_cpu_device, cpu);
+                if (td->evtdev->next_event.tv64 <= now.tv64)
+                        cpu_set(cpu, mask);
+        }
+
+        /*
+         * Wakeup the cpus which have an expired event. The broadcast
+         * device is reprogrammed in the return from idle code.
+         */
+        if (!tick_do_broadcast(mask)) {
+                /*
+                 * The global event did not expire any CPU local
+                 * events. This happens in dyntick mode, as the
+                 * maximum PIT delta is quite small.
+                 */
+                if (tick_broadcast_reprogram())
+                        goto again;
+        }
+        spin_unlock(&tick_broadcast_lock);
+}
+
+/*
+ * Powerstate information: The system enters/leaves a state, where
+ * affected devices might stop
+ */
+void tick_broadcast_oneshot_control(unsigned long reason)
+{
+        struct clock_event_device *bc, *dev;
+        struct tick_device *td;
+        unsigned long flags;
+        int cpu;
+
+        spin_lock_irqsave(&tick_broadcast_lock, flags);
+
+        /*
+         * Periodic mode does not care about the enter/exit of power
+         * states
+         */
+        if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
+                goto out;
+
+        bc = tick_broadcast_device.evtdev;
+        cpu = smp_processor_id();
+        td = &per_cpu(tick_cpu_device, cpu);
+        dev = td->evtdev;
+
+        if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
+                goto out;
+
+        if (reason == CLOCK_EVT_NOTIFY_BROADCAST_ENTER) {
+                if (!cpu_isset(cpu, tick_broadcast_oneshot_mask)) {
+                        cpu_set(cpu, tick_broadcast_oneshot_mask);
+                        clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
+                        if (dev->next_event.tv64 < bc->next_event.tv64)
+                                tick_broadcast_set_event(dev->next_event, 1);
+                }
+        } else {
+                if (cpu_isset(cpu, tick_broadcast_oneshot_mask)) {
+                        cpu_clear(cpu, tick_broadcast_oneshot_mask);
+                        clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
+                        if (dev->next_event.tv64 != KTIME_MAX)
+                                tick_program_event(dev->next_event, 1);
+                }
+        }
+
+out:
+        spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+}
+
+/**
+ * tick_broadcast_setup_highres - setup the broadcast device for highres
+ */
+void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
+{
+        if (bc->mode != CLOCK_EVT_MODE_ONESHOT) {
+                bc->event_handler = tick_handle_oneshot_broadcast;
+                clockevents_set_mode(bc, CLOCK_EVT_MODE_ONESHOT);
+                bc->next_event.tv64 = KTIME_MAX;
+        }
+}
+
+/*
+ * Select oneshot operating mode for the broadcast device
+ */
+void tick_broadcast_switch_to_oneshot(void)
+{
+        struct clock_event_device *bc;
+        unsigned long flags;
+
+        spin_lock_irqsave(&tick_broadcast_lock, flags);
+
+        tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT;
+        bc = tick_broadcast_device.evtdev;
+        if (bc)
+                tick_broadcast_setup_oneshot(bc);
+        spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+}
+
+
+/*
+ * Remove a dead CPU from broadcasting
+ */
+void tick_shutdown_broadcast_oneshot(unsigned int *cpup)
+{
+        struct clock_event_device *bc;
+        unsigned long flags;
+        unsigned int cpu = *cpup;
+
+        spin_lock_irqsave(&tick_broadcast_lock, flags);
+
+        bc = tick_broadcast_device.evtdev;
+        cpu_clear(cpu, tick_broadcast_oneshot_mask);
+
+        if (tick_broadcast_device.mode == TICKDEV_MODE_ONESHOT) {
+                if (bc && cpus_empty(tick_broadcast_oneshot_mask))
+                        clockevents_set_mode(bc, CLOCK_EVT_MODE_SHUTDOWN);
+        }
+
+        spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+}
+
+#endif
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 48167a6ae55..c35d449be03 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -34,6 +34,16 @@ ktime_t tick_period;
 static int tick_do_timer_cpu = -1;
 DEFINE_SPINLOCK(tick_device_lock);
 
+/**
+ * tick_is_oneshot_available - check for a oneshot capable event device
+ */
+int tick_is_oneshot_available(void)
+{
+        struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
+
+        return dev && (dev->features & CLOCK_EVT_FEAT_ONESHOT);
+}
+
 /*
  * Periodic tick
  */
@@ -162,6 +172,8 @@ static void tick_setup_device(struct tick_device *td,
 
         if (td->mode == TICKDEV_MODE_PERIODIC)
                 tick_setup_periodic(newdev, 0);
+        else
+                tick_setup_oneshot(newdev, handler, next_event);
 }
 
 /*
@@ -209,6 +221,12 @@ static int tick_check_new_device(struct clock_event_device *newdev)
          */
         if (curdev) {
                 /*
+                 * Prefer one shot capable devices !
+                 */
+                if ((curdev->features & CLOCK_EVT_FEAT_ONESHOT) &&
+                    !(newdev->features & CLOCK_EVT_FEAT_ONESHOT))
+                        goto out_bc;
+                /*
                  * Check the rating
                  */
                 if (curdev->rating >= newdev->rating)
@@ -226,6 +244,8 @@ static int tick_check_new_device(struct clock_event_device *newdev)
         }
         clockevents_exchange_device(curdev, newdev);
         tick_setup_device(td, newdev, cpu, cpumask);
+        if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
+                tick_oneshot_notify();
 
         spin_unlock_irqrestore(&tick_device_lock, flags);
         return NOTIFY_STOP;
@@ -285,7 +305,13 @@ static int tick_notify(struct notifier_block *nb, unsigned long reason,
                 tick_broadcast_on_off(reason, dev);
                 break;
 
+        case CLOCK_EVT_NOTIFY_BROADCAST_ENTER:
+        case CLOCK_EVT_NOTIFY_BROADCAST_EXIT:
+                tick_broadcast_oneshot_control(reason);
+                break;
+
         case CLOCK_EVT_NOTIFY_CPU_DEAD:
+                tick_shutdown_broadcast_oneshot(dev);
                 tick_shutdown_broadcast(dev);
                 tick_shutdown(dev);
                 break;
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 9272f446b21..54861a0f29f 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -10,12 +10,57 @@ extern void tick_setup_periodic(struct clock_event_device *dev, int broadcast);
 extern void tick_handle_periodic(struct clock_event_device *dev);
 
 /*
+ * NO_HZ / high resolution timer shared code
+ */
+#ifdef CONFIG_TICK_ONESHOT
+extern void tick_setup_oneshot(struct clock_event_device *newdev,
+                               void (*handler)(struct clock_event_device *),
+                               ktime_t nextevt);
+extern int tick_program_event(ktime_t expires, int force);
+extern void tick_oneshot_notify(void);
+extern int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *));
+
+# ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
+extern void tick_broadcast_setup_oneshot(struct clock_event_device *bc);
+extern void tick_broadcast_oneshot_control(unsigned long reason);
+extern void tick_broadcast_switch_to_oneshot(void);
+extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
+# else /* BROADCAST */
+static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
+{
+        BUG();
+}
+static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
+static inline void tick_broadcast_switch_to_oneshot(void) { }
+static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
+# endif /* !BROADCAST */
+
+#else /* !ONESHOT */
+static inline
+void tick_setup_oneshot(struct clock_event_device *newdev,
+                        void (*handler)(struct clock_event_device *),
+                        ktime_t nextevt)
+{
+        BUG();
+}
+static inline int tick_program_event(ktime_t expires, int force)
+{
+        return 0;
+}
+static inline void tick_oneshot_notify(void) { }
+static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
+{
+        BUG();
+}
+static inline void tick_broadcast_oneshot_control(unsigned long reason) { }
+static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
+#endif /* !TICK_ONESHOT */
+
+/*
  * Broadcasting support
  */
 #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
 extern int tick_do_broadcast(cpumask_t mask);
-extern struct tick_device tick_broadcast_device;
-extern spinlock_t tick_broadcast_lock;
 
 extern int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu);
 extern int tick_check_broadcast_device(struct clock_event_device *dev);
diff --git a/kernel/time/tick-oneshot.c b/kernel/time/tick-oneshot.c
new file mode 100644
index 00000000000..2e8b7ff863c
--- /dev/null
+++ b/kernel/time/tick-oneshot.c
@@ -0,0 +1,84 @@
+/*
+ * linux/kernel/time/tick-oneshot.c
+ *
+ * This file contains functions which manage high resolution tick
+ * related events.
+ *
+ * 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
+ *
+ * This code is licenced under the GPL version 2. For details see
+ * kernel-base/COPYING.
+ */
+#include <linux/cpu.h>
+#include <linux/err.h>
+#include <linux/hrtimer.h>
+#include <linux/irq.h>
+#include <linux/percpu.h>
+#include <linux/profile.h>
+#include <linux/sched.h>
+#include <linux/tick.h>
+
+#include "tick-internal.h"
+
+/**
+ * tick_program_event
+ */
+int tick_program_event(ktime_t expires, int force)
+{
+        struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
+        ktime_t now = ktime_get();
+
+        while (1) {
+                int ret = clockevents_program_event(dev, expires, now);
+
+                if (!ret || !force)
+                        return ret;
+                now = ktime_get();
+                expires = ktime_add(now, ktime_set(0, dev->min_delta_ns));
+        }
+}
+
+/**
+ * tick_setup_oneshot - setup the event device for oneshot mode (hres or nohz)
+ */
+void tick_setup_oneshot(struct clock_event_device *newdev,
+                        void (*handler)(struct clock_event_device *),
+                        ktime_t next_event)
+{
+        newdev->event_handler = handler;
+        clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
+        clockevents_program_event(newdev, next_event, ktime_get());
+}
+
+/**
+ * tick_switch_to_oneshot - switch to oneshot mode
+ */
+int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *))
+{
+        struct tick_device *td = &__get_cpu_var(tick_cpu_device);
+        struct clock_event_device *dev = td->evtdev;
+
+        if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT) ||
+            !tick_device_is_functional(dev))
+                return -EINVAL;
+
+        td->mode = TICKDEV_MODE_ONESHOT;
+        dev->event_handler = handler;
+        clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
+        tick_broadcast_switch_to_oneshot();
+        return 0;
+}
+
+#ifdef CONFIG_HIGH_RES_TIMERS
+/**
+ * tick_init_highres - switch to high resolution mode
+ *
+ * Called with interrupts disabled.
+ */
+int tick_init_highres(void)
+{
+        return tick_switch_to_oneshot(hrtimer_interrupt);
+}
+#endif
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
new file mode 100644
index 00000000000..99d35e2af18
--- /dev/null
+++ b/kernel/time/tick-sched.c
@@ -0,0 +1,558 @@
+/*
+ *  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 "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;
+
+/*
+ * 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;
+
+        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;
+        int cpu;
+
+        local_irq_save(flags);
+
+        cpu = smp_processor_id();
+        ts = &per_cpu(tick_cpu_sched, cpu);
+
+        if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
+                goto end;
+
+        if (need_resched())
+                goto end;
+
+        cpu = smp_processor_id();
+        BUG_ON(local_softirq_pending());
+
+        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;
+
+        /*
+         * 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 || rcu_needs_cpu(cpu)))
+                goto out;
+
+        /* Schedule the tick, if we are at least one jiffie off */
+        if ((long)delta_jiffies >= 1) {
+
+                if (rcu_needs_cpu(cpu))
+                        delta_jiffies = 1;
+                else
+                        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) {
+                        ts->idle_tick = ts->sched_timer.expires;
+                        ts->tick_stopped = 1;
+                        ts->idle_jiffies = last_jiffies;
+                }
+                /*
+                 * 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;
+                ts->idle_sleeps++;
+
+                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;
+end:
+        local_irq_restore(flags);
+}
+
+/**
+ * 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();
+        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();
+        ktime_t now = ktime_get();
+
+        dev->next_event.tv64 = KTIME_MAX;
+
+        /* Check, if the jiffies need an update */
+        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();
+
+        /* Check, if the jiffies need an update */
+        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();
+
+        /*
+         * 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 */
+        ts->sched_timer.expires = tick_init_jiffy_update();
+
+        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;
+}