[PATCH] hrtimers: add high resolution timer support

Implement high resolution timers on top of the hrtimers infrastructure and the
clockevents / tick-management framework.  This provides accurate timers for
all hrtimer subsystem users.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

8 files changed, 650 insertions, 58 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 52bf1edd9df5..abd575cfc759 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -609,6 +609,10 @@ and is between 256 and 4096 characters. It is defined in the file
                         highmem otherwise. This also works to reduce highmem
                         size on bigger boxes.
 
+        highres=        [KNL] Enable/disable high resolution timer mode.
+                        Valid parameters: "on", "off"
+                        Default: "on"
+
         hisax=          [HW,ISDN]
                         See Documentation/isdn/README.HiSax.
 
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index e95c96c971c0..4ecd991431b4 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -41,16 +41,35 @@ enum hrtimer_restart {
 };
 
 /*
- * Bit values to track state of the timer
+ * hrtimer callback modes:
+ *
+ *      HRTIMER_CB_SOFTIRQ:             Callback must run in softirq context
+ *      HRTIMER_CB_IRQSAFE:             Callback may run in hardirq context
+ *      HRTIMER_CB_IRQSAFE_NO_RESTART:  Callback may run in hardirq context and
+ *                                      does not restart the timer
+ *      HRTIMER_CB_IRQSAFE_NO_SOFTIRQ:  Callback must run in softirq context
+ *                                      Special mode for tick emultation
+ */
+enum hrtimer_cb_mode {
+        HRTIMER_CB_SOFTIRQ,
+        HRTIMER_CB_IRQSAFE,
+        HRTIMER_CB_IRQSAFE_NO_RESTART,
+        HRTIMER_CB_IRQSAFE_NO_SOFTIRQ,
+};
+
+/*
+ * Values to track state of the timer
  *
  * Possible states:
  *
  * 0x00         inactive
  * 0x01         enqueued into rbtree
  * 0x02         callback function running
+ * 0x04         callback pending (high resolution mode)
+ *
+ * Special case:
  * 0x03         callback function running and enqueued
  *              (was requeued on another CPU)
- *
  * The "callback function running and enqueued" status is only possible on
  * SMP. It happens for example when a posix timer expired and the callback
  * queued a signal. Between dropping the lock which protects the posix timer
@@ -67,6 +86,7 @@ enum hrtimer_restart {
 #define HRTIMER_STATE_INACTIVE  0x00
 #define HRTIMER_STATE_ENQUEUED  0x01
 #define HRTIMER_STATE_CALLBACK  0x02
+#define HRTIMER_STATE_PENDING   0x04
 
 /**
  * struct hrtimer - the basic hrtimer structure
@@ -77,8 +97,17 @@ enum hrtimer_restart {
  * @function:   timer expiry callback function
  * @base:       pointer to the timer base (per cpu and per clock)
  * @state:      state information (See bit values above)
+ * @cb_mode:    high resolution timer feature to select the callback execution
+ *               mode
+ * @cb_entry:   list head to enqueue an expired timer into the callback list
+ * @start_site: timer statistics field to store the site where the timer
+ *              was started
+ * @start_comm: timer statistics field to store the name of the process which
+ *              started the timer
+ * @start_pid: timer statistics field to store the pid of the task which
+ *              started the timer
  *
- * The hrtimer structure must be initialized by init_hrtimer_#CLOCKTYPE()
+ * The hrtimer structure must be initialized by hrtimer_init()
  */
 struct hrtimer {
         struct rb_node                  node;
@@ -86,6 +115,10 @@ struct hrtimer {
         enum hrtimer_restart            (*function)(struct hrtimer *);
         struct hrtimer_clock_base       *base;
         unsigned long                   state;
+#ifdef CONFIG_HIGH_RES_TIMERS
+        enum hrtimer_cb_mode            cb_mode;
+        struct list_head                cb_entry;
+#endif
 };
 
 /**
@@ -110,6 +143,9 @@ struct hrtimer_sleeper {
  * @get_time:           function to retrieve the current time of the clock
  * @get_softirq_time:   function to retrieve the current time from the softirq
  * @softirq_time:       the time when running the hrtimer queue in the softirq
+ * @cb_pending:         list of timers where the callback is pending
+ * @offset:             offset of this clock to the monotonic base
+ * @reprogram:          function to reprogram the timer event
  */
 struct hrtimer_clock_base {
         struct hrtimer_cpu_base *cpu_base;
@@ -120,6 +156,12 @@ struct hrtimer_clock_base {
         ktime_t                 (*get_time)(void);
         ktime_t                 (*get_softirq_time)(void);
         ktime_t                 softirq_time;
+#ifdef CONFIG_HIGH_RES_TIMERS
+        ktime_t                 offset;
+        int                     (*reprogram)(struct hrtimer *t,
+                                             struct hrtimer_clock_base *b,
+                                             ktime_t n);
+#endif
 };
 
 #define HRTIMER_MAX_CLOCK_BASES 2
@@ -131,19 +173,74 @@ struct hrtimer_clock_base {
  * @lock_key:           the lock_class_key for use with lockdep
  * @clock_base:         array of clock bases for this cpu
  * @curr_timer:         the timer which is executing a callback right now
+ * @expires_next:       absolute time of the next event which was scheduled
+ *                      via clock_set_next_event()
+ * @hres_active:        State of high resolution mode
+ * @check_clocks:       Indictator, when set evaluate time source and clock
+ *                      event devices whether high resolution mode can be
+ *                      activated.
+ * @cb_pending:         Expired timers are moved from the rbtree to this
+ *                      list in the timer interrupt. The list is processed
+ *                      in the softirq.
+ * @nr_events:          Total number of timer interrupt events
  */
 struct hrtimer_cpu_base {
         spinlock_t                      lock;
         struct lock_class_key           lock_key;
         struct hrtimer_clock_base       clock_base[HRTIMER_MAX_CLOCK_BASES];
+#ifdef CONFIG_HIGH_RES_TIMERS
+        ktime_t                         expires_next;
+        int                             hres_active;
+        struct list_head                cb_pending;
+        unsigned long                   nr_events;
+#endif
 };
 
+#ifdef CONFIG_HIGH_RES_TIMERS
+struct clock_event_device;
+
+extern void clock_was_set(void);
+extern void hrtimer_interrupt(struct clock_event_device *dev);
+
+/*
+ * In high resolution mode the time reference must be read accurate
+ */
+static inline ktime_t hrtimer_cb_get_time(struct hrtimer *timer)
+{
+        return timer->base->get_time();
+}
+
+/*
+ * The resolution of the clocks. The resolution value is returned in
+ * the clock_getres() system call to give application programmers an
+ * idea of the (in)accuracy of timers. Timer values are rounded up to
+ * this resolution values.
+ */
+# define KTIME_HIGH_RES         (ktime_t) { .tv64 = 1 }
+# define KTIME_MONOTONIC_RES    KTIME_HIGH_RES
+
+#else
+
+# define KTIME_MONOTONIC_RES    KTIME_LOW_RES
+
 /*
  * clock_was_set() is a NOP for non- high-resolution systems. The
  * time-sorted order guarantees that a timer does not expire early and
  * is expired in the next softirq when the clock was advanced.
  */
-#define clock_was_set()         do { } while (0)
+static inline void clock_was_set(void) { }
+
+/*
+ * In non high resolution mode the time reference is taken from
+ * the base softirq time variable.
+ */
+static inline ktime_t hrtimer_cb_get_time(struct hrtimer *timer)
+{
+        return timer->base->softirq_time;
+}
+
+#endif
+
 extern ktime_t ktime_get(void);
 extern ktime_t ktime_get_real(void);
 
@@ -168,9 +265,7 @@ static inline int hrtimer_restart(struct hrtimer *timer)
 extern ktime_t hrtimer_get_remaining(const struct hrtimer *timer);
 extern int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp);
 
-#ifdef CONFIG_NO_IDLE_HZ
 extern ktime_t hrtimer_get_next_event(void);
-#endif
 
 /*
  * A timer is active, when it is enqueued into the rbtree or the callback
@@ -181,6 +276,15 @@ static inline int hrtimer_active(const struct hrtimer *timer)
         return timer->state != HRTIMER_STATE_INACTIVE;
 }
 
+/*
+ * Helper function to check, whether the timer is on one of the queues
+ */
+static inline int hrtimer_is_queued(struct hrtimer *timer)
+{
+        return timer->state &
+                (HRTIMER_STATE_ENQUEUED | HRTIMER_STATE_PENDING);
+}
+
 /* Forward a hrtimer so it expires after now: */
 extern unsigned long
 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval);
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 690113d07698..e5ea1411050b 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -242,6 +242,9 @@ enum
         BLOCK_SOFTIRQ,
         TASKLET_SOFTIRQ,
         SCHED_SOFTIRQ,
+#ifdef CONFIG_HIGH_RES_TIMERS
+        HRTIMER_SOFTIRQ,
+#endif
 };
 
 /* softirq mask and active fields moved to irq_cpustat_t in
diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index 7444a6326231..c68c7ac6b232 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -261,8 +261,7 @@ static inline s64 ktime_to_ns(const ktime_t kt)
  * idea of the (in)accuracy of timers. Timer values are rounded up to
  * this resolution values.
  */
-#define KTIME_REALTIME_RES      (ktime_t){ .tv64 = TICK_NSEC }
-#define KTIME_MONOTONIC_RES     (ktime_t){ .tv64 = TICK_NSEC }
+#define KTIME_LOW_RES           (ktime_t){ .tv64 = TICK_NSEC }
 
 /* Get the monotonic time in timespec format: */
 extern void ktime_get_ts(struct timespec *ts);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index e04ef38ea3be..62aad8e1a383 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -3,7 +3,7 @@
  *
  *  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 <tglx@timesys.com>
+ *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
  *
  *  High-resolution kernel timers
  *
@@ -32,13 +32,17 @@
  */
 
 #include <linux/cpu.h>
+#include <linux/irq.h>
 #include <linux/module.h>
 #include <linux/percpu.h>
 #include <linux/hrtimer.h>
 #include <linux/notifier.h>
 #include <linux/syscalls.h>
+#include <linux/kallsyms.h>
 #include <linux/interrupt.h>
 #include <linux/tick.h>
+#include <linux/seq_file.h>
+#include <linux/err.h>
 
 #include <asm/uaccess.h>
 
@@ -81,7 +85,7 @@ EXPORT_SYMBOL_GPL(ktime_get_real);
  * This ensures that we capture erroneous accesses to these clock ids
  * rather than moving them into the range of valid clock id's.
  */
-static DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
+DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
 {
 
         .clock_base =
@@ -89,12 +93,12 @@ static DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
                 {
                         .index = CLOCK_REALTIME,
                         .get_time = &ktime_get_real,
-                        .resolution = KTIME_REALTIME_RES,
+                        .resolution = KTIME_LOW_RES,
                 },
                 {
                         .index = CLOCK_MONOTONIC,
                         .get_time = &ktime_get,
-                        .resolution = KTIME_MONOTONIC_RES,
+                        .resolution = KTIME_LOW_RES,
                 },
         }
 };
@@ -151,14 +155,6 @@ static void hrtimer_get_softirq_time(struct hrtimer_cpu_base *base)
 }
 
 /*
- * Helper function to check, whether the timer is on one of the queues
- */
-static inline int hrtimer_is_queued(struct hrtimer *timer)
-{
-        return timer->state & HRTIMER_STATE_ENQUEUED;
-}
-
-/*
  * Helper function to check, whether the timer is running the callback
  * function
  */
@@ -226,7 +222,7 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base)
                  * completed. There is no conflict as we hold the lock until
                  * the timer is enqueued.
                  */
-                if (unlikely(timer->state & HRTIMER_STATE_CALLBACK))
+                if (unlikely(hrtimer_callback_running(timer)))
                         return base;
 
                 /* See the comment in lock_timer_base() */
@@ -250,7 +246,7 @@ lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
         return base;
 }
 
-#define switch_hrtimer_base(t, b)       (b)
+# define switch_hrtimer_base(t, b)      (b)
 
 #endif  /* !CONFIG_SMP */
 
@@ -281,9 +277,6 @@ ktime_t ktime_add_ns(const ktime_t kt, u64 nsec)
 
         return ktime_add(kt, tmp);
 }
-
-#else /* CONFIG_KTIME_SCALAR */
-
 # endif /* !CONFIG_KTIME_SCALAR */
 
 /*
@@ -308,6 +301,290 @@ unsigned long ktime_divns(const ktime_t kt, s64 div)
 }
 #endif /* BITS_PER_LONG >= 64 */
 
+/* High resolution timer related functions */
+#ifdef CONFIG_HIGH_RES_TIMERS
+
+/*
+ * High resolution timer enabled ?
+ */
+static int hrtimer_hres_enabled __read_mostly  = 1;
+
+/*
+ * Enable / Disable high resolution mode
+ */
+static int __init setup_hrtimer_hres(char *str)
+{
+        if (!strcmp(str, "off"))
+                hrtimer_hres_enabled = 0;
+        else if (!strcmp(str, "on"))
+                hrtimer_hres_enabled = 1;
+        else
+                return 0;
+        return 1;
+}
+
+__setup("highres=", setup_hrtimer_hres);
+
+/*
+ * hrtimer_high_res_enabled - query, if the highres mode is enabled
+ */
+static inline int hrtimer_is_hres_enabled(void)
+{
+        return hrtimer_hres_enabled;
+}
+
+/*
+ * Is the high resolution mode active ?
+ */
+static inline int hrtimer_hres_active(void)
+{
+        return __get_cpu_var(hrtimer_bases).hres_active;
+}
+
+/*
+ * Reprogram the event source with checking both queues for the
+ * next event
+ * Called with interrupts disabled and base->lock held
+ */
+static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base)
+{
+        int i;
+        struct hrtimer_clock_base *base = cpu_base->clock_base;
+        ktime_t expires;
+
+        cpu_base->expires_next.tv64 = KTIME_MAX;
+
+        for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
+                struct hrtimer *timer;
+
+                if (!base->first)
+                        continue;
+                timer = rb_entry(base->first, struct hrtimer, node);
+                expires = ktime_sub(timer->expires, base->offset);
+                if (expires.tv64 < cpu_base->expires_next.tv64)
+                        cpu_base->expires_next = expires;
+        }
+
+        if (cpu_base->expires_next.tv64 != KTIME_MAX)
+                tick_program_event(cpu_base->expires_next, 1);
+}
+
+/*
+ * Shared reprogramming for clock_realtime and clock_monotonic
+ *
+ * When a timer is enqueued and expires earlier than the already enqueued
+ * timers, we have to check, whether it expires earlier than the timer for
+ * which the clock event device was armed.
+ *
+ * Called with interrupts disabled and base->cpu_base.lock held
+ */
+static int hrtimer_reprogram(struct hrtimer *timer,
+                             struct hrtimer_clock_base *base)
+{
+        ktime_t *expires_next = &__get_cpu_var(hrtimer_bases).expires_next;
+        ktime_t expires = ktime_sub(timer->expires, base->offset);
+        int res;
+
+        /*
+         * When the callback is running, we do not reprogram the clock event
+         * device. The timer callback is either running on a different CPU or
+         * the callback is executed in the hrtimer_interupt context. The
+         * reprogramming is handled either by the softirq, which called the
+         * callback or at the end of the hrtimer_interrupt.
+         */
+        if (hrtimer_callback_running(timer))
+                return 0;
+
+        if (expires.tv64 >= expires_next->tv64)
+                return 0;
+
+        /*
+         * Clockevents returns -ETIME, when the event was in the past.
+         */
+        res = tick_program_event(expires, 0);
+        if (!IS_ERR_VALUE(res))
+                *expires_next = expires;
+        return res;
+}
+
+
+/*
+ * Retrigger next event is called after clock was set
+ *
+ * Called with interrupts disabled via on_each_cpu()
+ */
+static void retrigger_next_event(void *arg)
+{
+        struct hrtimer_cpu_base *base;
+        struct timespec realtime_offset;
+        unsigned long seq;
+
+        if (!hrtimer_hres_active())
+                return;
+
+        do {
+                seq = read_seqbegin(&xtime_lock);
+                set_normalized_timespec(&realtime_offset,
+                                        -wall_to_monotonic.tv_sec,
+                                        -wall_to_monotonic.tv_nsec);
+        } while (read_seqretry(&xtime_lock, seq));
+
+        base = &__get_cpu_var(hrtimer_bases);
+
+        /* Adjust CLOCK_REALTIME offset */
+        spin_lock(&base->lock);
+        base->clock_base[CLOCK_REALTIME].offset =
+                timespec_to_ktime(realtime_offset);
+
+        hrtimer_force_reprogram(base);
+        spin_unlock(&base->lock);
+}
+
+/*
+ * Clock realtime was set
+ *
+ * Change the offset of the realtime clock vs. the monotonic
+ * clock.
+ *
+ * We might have to reprogram the high resolution timer interrupt. On
+ * SMP we call the architecture specific code to retrigger _all_ high
+ * resolution timer interrupts. On UP we just disable interrupts and
+ * call the high resolution interrupt code.
+ */
+void clock_was_set(void)
+{
+        /* Retrigger the CPU local events everywhere */
+        on_each_cpu(retrigger_next_event, NULL, 0, 1);
+}
+
+/*
+ * Check, whether the timer is on the callback pending list
+ */
+static inline int hrtimer_cb_pending(const struct hrtimer *timer)
+{
+        return timer->state & HRTIMER_STATE_PENDING;
+}
+
+/*
+ * Remove a timer from the callback pending list
+ */
+static inline void hrtimer_remove_cb_pending(struct hrtimer *timer)
+{
+        list_del_init(&timer->cb_entry);
+}
+
+/*
+ * Initialize the high resolution related parts of cpu_base
+ */
+static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base)
+{
+        base->expires_next.tv64 = KTIME_MAX;
+        base->hres_active = 0;
+        INIT_LIST_HEAD(&base->cb_pending);
+}
+
+/*
+ * Initialize the high resolution related parts of a hrtimer
+ */
+static inline void hrtimer_init_timer_hres(struct hrtimer *timer)
+{
+        INIT_LIST_HEAD(&timer->cb_entry);
+}
+
+/*
+ * When High resolution timers are active, try to reprogram. Note, that in case
+ * the state has HRTIMER_STATE_CALLBACK set, no reprogramming and no expiry
+ * check happens. The timer gets enqueued into the rbtree. The reprogramming
+ * and expiry check is done in the hrtimer_interrupt or in the softirq.
+ */
+static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
+                                            struct hrtimer_clock_base *base)
+{
+        if (base->cpu_base->hres_active && hrtimer_reprogram(timer, base)) {
+
+                /* Timer is expired, act upon the callback mode */
+                switch(timer->cb_mode) {
+                case HRTIMER_CB_IRQSAFE_NO_RESTART:
+                        /*
+                         * We can call the callback from here. No restart
+                         * happens, so no danger of recursion
+                         */
+                        BUG_ON(timer->function(timer) != HRTIMER_NORESTART);
+                        return 1;
+                case HRTIMER_CB_IRQSAFE_NO_SOFTIRQ:
+                        /*
+                         * This is solely for the sched tick emulation with
+                         * dynamic tick support to ensure that we do not
+                         * restart the tick right on the edge and end up with
+                         * the tick timer in the softirq ! The calling site
+                         * takes care of this.
+                         */
+                        return 1;
+                case HRTIMER_CB_IRQSAFE:
+                case HRTIMER_CB_SOFTIRQ:
+                        /*
+                         * Move everything else into the softirq pending list !
+                         */
+                        list_add_tail(&timer->cb_entry,
+                                      &base->cpu_base->cb_pending);
+                        timer->state = HRTIMER_STATE_PENDING;
+                        raise_softirq(HRTIMER_SOFTIRQ);
+                        return 1;
+                default:
+                        BUG();
+                }
+        }
+        return 0;
+}
+
+/*
+ * Switch to high resolution mode
+ */
+static void hrtimer_switch_to_hres(void)
+{
+        struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);
+        unsigned long flags;
+
+        if (base->hres_active)
+                return;
+
+        local_irq_save(flags);
+
+        if (tick_init_highres()) {
+                local_irq_restore(flags);
+                return;
+        }
+        base->hres_active = 1;
+        base->clock_base[CLOCK_REALTIME].resolution = KTIME_HIGH_RES;
+        base->clock_base[CLOCK_MONOTONIC].resolution = KTIME_HIGH_RES;
+
+        tick_setup_sched_timer();
+
+        /* "Retrigger" the interrupt to get things going */
+        retrigger_next_event(NULL);
+        local_irq_restore(flags);
+        printk(KERN_INFO "Switched to high resolution mode on CPU %d\n",
+               smp_processor_id());
+}
+
+#else
+
+static inline int hrtimer_hres_active(void) { return 0; }
+static inline int hrtimer_is_hres_enabled(void) { return 0; }
+static inline void hrtimer_switch_to_hres(void) { }
+static inline void hrtimer_force_reprogram(struct hrtimer_cpu_base *base) { }
+static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
+                                            struct hrtimer_clock_base *base)
+{
+        return 0;
+}
+static inline int hrtimer_cb_pending(struct hrtimer *timer) { return 0; }
+static inline void hrtimer_remove_cb_pending(struct hrtimer *timer) { }
+static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }
+static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { }
+
+#endif /* CONFIG_HIGH_RES_TIMERS */
+
 /*
  * Counterpart to lock_timer_base above:
  */
@@ -365,7 +642,7 @@ hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
  * red black tree is O(log(n)). Must hold the base lock.
  */
 static void enqueue_hrtimer(struct hrtimer *timer,
-                            struct hrtimer_clock_base *base)
+                            struct hrtimer_clock_base *base, int reprogram)
 {
         struct rb_node **link = &base->active.rb_node;
         struct rb_node *parent = NULL;
@@ -391,6 +668,22 @@ static void enqueue_hrtimer(struct hrtimer *timer,
          * Insert the timer to the rbtree and check whether it
          * replaces the first pending timer
          */
+        if (!base->first || timer->expires.tv64 <
+            rb_entry(base->first, struct hrtimer, node)->expires.tv64) {
+                /*
+                 * Reprogram the clock event device. When the timer is already
+                 * expired hrtimer_enqueue_reprogram has either called the
+                 * callback or added it to the pending list and raised the
+                 * softirq.
+                 *
+                 * This is a NOP for !HIGHRES
+                 */
+                if (reprogram && hrtimer_enqueue_reprogram(timer, base))
+                        return;
+
+                base->first = &timer->node;
+        }
+
         rb_link_node(&timer->node, parent, link);
         rb_insert_color(&timer->node, &base->active);
         /*
@@ -398,28 +691,38 @@ static void enqueue_hrtimer(struct hrtimer *timer,
          * state of a possibly running callback.
          */
         timer->state |= HRTIMER_STATE_ENQUEUED;
-
-        if (!base->first || timer->expires.tv64 <
-            rb_entry(base->first, struct hrtimer, node)->expires.tv64)
-                base->first = &timer->node;
 }
 
 /*
  * __remove_hrtimer - internal function to remove a timer
  *
  * Caller must hold the base lock.
+ *
+ * High resolution timer mode reprograms the clock event device when the
+ * timer is the one which expires next. The caller can disable this by setting
+ * reprogram to zero. This is useful, when the context does a reprogramming
+ * anyway (e.g. timer interrupt)
  */
 static void __remove_hrtimer(struct hrtimer *timer,
                              struct hrtimer_clock_base *base,
-                             unsigned long newstate)
+                             unsigned long newstate, int reprogram)
 {
-        /*
-         * Remove the timer from the rbtree and replace the
-         * first entry pointer if necessary.
-         */
-        if (base->first == &timer->node)
-                base->first = rb_next(&timer->node);
-        rb_erase(&timer->node, &base->active);
+        /* High res. callback list. NOP for !HIGHRES */
+        if (hrtimer_cb_pending(timer))
+                hrtimer_remove_cb_pending(timer);
+        else {
+                /*
+                 * Remove the timer from the rbtree and replace the
+                 * first entry pointer if necessary.
+                 */
+                if (base->first == &timer->node) {
+                        base->first = rb_next(&timer->node);
+                        /* Reprogram the clock event device. if enabled */
+                        if (reprogram && hrtimer_hres_active())
+                                hrtimer_force_reprogram(base->cpu_base);
+                }
+                rb_erase(&timer->node, &base->active);
+        }
         timer->state = newstate;
 }
 
@@ -430,7 +733,19 @@ static inline int
 remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base)
 {
         if (hrtimer_is_queued(timer)) {
-                __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE);
+                int reprogram;
+
+                /*
+                 * Remove the timer and force reprogramming when high
+                 * resolution mode is active and the timer is on the current
+                 * CPU. If we remove a timer on another CPU, reprogramming is
+                 * skipped. The interrupt event on this CPU is fired and
+                 * reprogramming happens in the interrupt handler. This is a
+                 * rare case and less expensive than a smp call.
+                 */
+                reprogram = base->cpu_base == &__get_cpu_var(hrtimer_bases);
+                __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE,
+                                 reprogram);
                 return 1;
         }
         return 0;
@@ -476,7 +791,7 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
         }
         timer->expires = tim;
 
-        enqueue_hrtimer(timer, new_base);
+        enqueue_hrtimer(timer, new_base, base == new_base);
 
         unlock_hrtimer_base(timer, &flags);
 
@@ -567,17 +882,19 @@ ktime_t hrtimer_get_next_event(void)
 
         spin_lock_irqsave(&cpu_base->lock, flags);
 
-        for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
-                struct hrtimer *timer;
+        if (!hrtimer_hres_active()) {
+                for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
+                        struct hrtimer *timer;
 
-                if (!base->first)
-                        continue;
+                        if (!base->first)
+                                continue;
 
-                timer = rb_entry(base->first, struct hrtimer, node);
-                delta.tv64 = timer->expires.tv64;
-                delta = ktime_sub(delta, base->get_time());
-                if (delta.tv64 < mindelta.tv64)
-                        mindelta.tv64 = delta.tv64;
+                        timer = rb_entry(base->first, struct hrtimer, node);
+                        delta.tv64 = timer->expires.tv64;
+                        delta = ktime_sub(delta, base->get_time());
+                        if (delta.tv64 < mindelta.tv64)
+                                mindelta.tv64 = delta.tv64;
+                }
         }
 
         spin_unlock_irqrestore(&cpu_base->lock, flags);
@@ -607,6 +924,7 @@ void hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
                 clock_id = CLOCK_MONOTONIC;
 
         timer->base = &cpu_base->clock_base[clock_id];
+        hrtimer_init_timer_hres(timer);
 }
 EXPORT_SYMBOL_GPL(hrtimer_init);
 
@@ -629,6 +947,139 @@ int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
 }
 EXPORT_SYMBOL_GPL(hrtimer_get_res);
 
+#ifdef CONFIG_HIGH_RES_TIMERS
+
+/*
+ * High resolution timer interrupt
+ * Called with interrupts disabled
+ */
+void hrtimer_interrupt(struct clock_event_device *dev)
+{
+        struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
+        struct hrtimer_clock_base *base;
+        ktime_t expires_next, now;
+        int i, raise = 0;
+
+        BUG_ON(!cpu_base->hres_active);
+        cpu_base->nr_events++;
+        dev->next_event.tv64 = KTIME_MAX;
+
+ retry:
+        now = ktime_get();
+
+        expires_next.tv64 = KTIME_MAX;
+
+        base = cpu_base->clock_base;
+
+        for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
+                ktime_t basenow;
+                struct rb_node *node;
+
+                spin_lock(&cpu_base->lock);
+
+                basenow = ktime_add(now, base->offset);
+
+                while ((node = base->first)) {
+                        struct hrtimer *timer;
+
+                        timer = rb_entry(node, struct hrtimer, node);
+
+                        if (basenow.tv64 < timer->expires.tv64) {
+                                ktime_t expires;
+
+                                expires = ktime_sub(timer->expires,
+                                                    base->offset);
+                                if (expires.tv64 < expires_next.tv64)
+                                        expires_next = expires;
+                                break;
+                        }
+
+                        /* Move softirq callbacks to the pending list */
+                        if (timer->cb_mode == HRTIMER_CB_SOFTIRQ) {
+                                __remove_hrtimer(timer, base,
+                                                 HRTIMER_STATE_PENDING, 0);
+                                list_add_tail(&timer->cb_entry,
+                                              &base->cpu_base->cb_pending);
+                                raise = 1;
+                                continue;
+                        }
+
+                        __remove_hrtimer(timer, base,
+                                         HRTIMER_STATE_CALLBACK, 0);
+
+                        /*
+                         * Note: We clear the CALLBACK bit after
+                         * enqueue_hrtimer to avoid reprogramming of
+                         * the event hardware. This happens at the end
+                         * of this function anyway.
+                         */
+                        if (timer->function(timer) != HRTIMER_NORESTART) {
+                                BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
+                                enqueue_hrtimer(timer, base, 0);
+                        }
+                        timer->state &= ~HRTIMER_STATE_CALLBACK;
+                }
+                spin_unlock(&cpu_base->lock);
+                base++;
+        }
+
+        cpu_base->expires_next = expires_next;
+
+        /* Reprogramming necessary ? */
+        if (expires_next.tv64 != KTIME_MAX) {
+                if (tick_program_event(expires_next, 0))
+                        goto retry;
+        }
+
+        /* Raise softirq ? */
+        if (raise)
+                raise_softirq(HRTIMER_SOFTIRQ);
+}
+
+static void run_hrtimer_softirq(struct softirq_action *h)
+{
+        struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
+
+        spin_lock_irq(&cpu_base->lock);
+
+        while (!list_empty(&cpu_base->cb_pending)) {
+                enum hrtimer_restart (*fn)(struct hrtimer *);
+                struct hrtimer *timer;
+                int restart;
+
+                timer = list_entry(cpu_base->cb_pending.next,
+                                   struct hrtimer, cb_entry);
+
+                fn = timer->function;
+                __remove_hrtimer(timer, timer->base, HRTIMER_STATE_CALLBACK, 0);
+                spin_unlock_irq(&cpu_base->lock);
+
+                restart = fn(timer);
+
+                spin_lock_irq(&cpu_base->lock);
+
+                timer->state &= ~HRTIMER_STATE_CALLBACK;
+                if (restart == HRTIMER_RESTART) {
+                        BUG_ON(hrtimer_active(timer));
+                        /*
+                         * Enqueue the timer, allow reprogramming of the event
+                         * device
+                         */
+                        enqueue_hrtimer(timer, timer->base, 1);
+                } else if (hrtimer_active(timer)) {
+                        /*
+                         * If the timer was rearmed on another CPU, reprogram
+                         * the event device.
+                         */
+                        if (timer->base->first == &timer->node)
+                                hrtimer_reprogram(timer, timer->base);
+                }
+        }
+        spin_unlock_irq(&cpu_base->lock);
+}
+
+#endif  /* CONFIG_HIGH_RES_TIMERS */
+
 /*
  * Expire the per base hrtimer-queue:
  */
@@ -656,7 +1107,7 @@ static inline void run_hrtimer_queue(struct hrtimer_cpu_base *cpu_base,
                         break;
 
                 fn = timer->function;
-                __remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK);
+                __remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK, 0);
                 spin_unlock_irq(&cpu_base->lock);
 
                 restart = fn(timer);
@@ -666,7 +1117,7 @@ static inline void run_hrtimer_queue(struct hrtimer_cpu_base *cpu_base,
                 timer->state &= ~HRTIMER_STATE_CALLBACK;
                 if (restart != HRTIMER_NORESTART) {
                         BUG_ON(hrtimer_active(timer));
-                        enqueue_hrtimer(timer, base);
+                        enqueue_hrtimer(timer, base, 0);
                 }
         }
         spin_unlock_irq(&cpu_base->lock);
@@ -674,12 +1125,19 @@ static inline void run_hrtimer_queue(struct hrtimer_cpu_base *cpu_base,
 
 /*
  * Called from timer softirq every jiffy, expire hrtimers:
+ *
+ * For HRT its the fall back code to run the softirq in the timer
+ * softirq context in case the hrtimer initialization failed or has
+ * not been done yet.
  */
 void hrtimer_run_queues(void)
 {
         struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
         int i;
 
+        if (hrtimer_hres_active())
+                return;
+
         /*
          * This _is_ ugly: We have to check in the softirq context,
          * whether we can switch to highres and / or nohz mode. The
@@ -688,7 +1146,8 @@ void hrtimer_run_queues(void)
          * check bit in the tick_oneshot code, otherwise we might
          * deadlock vs. xtime_lock.
          */
-        tick_check_oneshot_change(1);
+        if (tick_check_oneshot_change(!hrtimer_is_hres_enabled()))
+                hrtimer_switch_to_hres();
 
         hrtimer_get_softirq_time(cpu_base);
 
@@ -716,6 +1175,9 @@ void hrtimer_init_sleeper(struct hrtimer_sleeper *sl, struct task_struct *task)
 {
         sl->timer.function = hrtimer_wakeup;
         sl->task = task;
+#ifdef CONFIG_HIGH_RES_TIMERS
+        sl->timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_RESTART;
+#endif
 }
 
 static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mode)
@@ -726,7 +1188,8 @@ static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mod
                 set_current_state(TASK_INTERRUPTIBLE);
                 hrtimer_start(&t->timer, t->timer.expires, mode);
 
-                schedule();
+                if (likely(t->task))
+                        schedule();
 
                 hrtimer_cancel(&t->timer);
                 mode = HRTIMER_MODE_ABS;
@@ -831,6 +1294,7 @@ static void __devinit init_hrtimers_cpu(int cpu)
         for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
                 cpu_base->clock_base[i].cpu_base = cpu_base;
 
+        hrtimer_init_hres(cpu_base);
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -843,10 +1307,13 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 
         while ((node = rb_first(&old_base->active))) {
                 timer = rb_entry(node, struct hrtimer, node);
-                BUG_ON(timer->state & HRTIMER_STATE_CALLBACK);
-                __remove_hrtimer(timer, old_base, HRTIMER_STATE_INACTIVE);
+                BUG_ON(hrtimer_callback_running(timer));
+                __remove_hrtimer(timer, old_base, HRTIMER_STATE_INACTIVE, 0);
                 timer->base = new_base;
-                enqueue_hrtimer(timer, new_base);
+                /*
+                 * Enqueue the timer. Allow reprogramming of the event device
+                 */
+                enqueue_hrtimer(timer, new_base, 1);
         }
 }
 
@@ -859,6 +1326,8 @@ static void migrate_hrtimers(int cpu)
         old_base = &per_cpu(hrtimer_bases, cpu);
         new_base = &get_cpu_var(hrtimer_bases);
 
+        tick_cancel_sched_timer(cpu);
+
         local_irq_disable();
 
         spin_lock(&new_base->lock);
@@ -910,5 +1379,8 @@ void __init hrtimers_init(void)
         hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE,
                           (void *)(long)smp_processor_id());
         register_cpu_notifier(&hrtimers_nb);
+#ifdef CONFIG_HIGH_RES_TIMERS
+        open_softirq(HRTIMER_SOFTIRQ, run_hrtimer_softirq, NULL);
+#endif
 }
 
diff --git a/kernel/itimer.c b/kernel/itimer.c
index 9cefe1d1eb13..4fc6c0caf5d4 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -136,7 +136,7 @@ enum hrtimer_restart it_real_fn(struct hrtimer *timer)
         send_group_sig_info(SIGALRM, SEND_SIG_PRIV, sig->tsk);
 
         if (sig->it_real_incr.tv64 != 0) {
-                hrtimer_forward(timer, timer->base->softirq_time,
+                hrtimer_forward(timer, hrtimer_cb_get_time(timer),
                                 sig->it_real_incr);
                 return HRTIMER_RESTART;
         }
diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
index 210f462c650e..44318ca71978 100644
--- a/kernel/posix-timers.c
+++ b/kernel/posix-timers.c
@@ -356,7 +356,7 @@ static enum hrtimer_restart posix_timer_fn(struct hrtimer *timer)
                 if (timr->it.real.interval.tv64 != 0) {
                         timr->it_overrun +=
                                 hrtimer_forward(timer,
-                                                timer->base->softirq_time,
+                                                hrtimer_cb_get_time(timer),
                                                 timr->it.real.interval);
                         ret = HRTIMER_RESTART;
                         ++timr->it_requeue_pending;
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 9ec54eb3667f..f66351126544 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -13,3 +13,13 @@ config NO_HZ
           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.
+
+config HIGH_RES_TIMERS
+        bool "High Resolution Timer Support"
+        depends on GENERIC_TIME && GENERIC_CLOCKEVENTS
+        select TICK_ONESHOT
+        help
+          This option enables high resolution timer support. If your
+          hardware is not capable then this option only increases
+          the size of the kernel image.
+