[patch 12/19] high-res timers: core

[Thomas Gleixner]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Add the core bits of high-res timers support.

The design makes use of the existing hrtimers subsystem which manages a
per-CPU and per-clock tree of timers, and the clockevents framework, which
provides a standard API to request programmable clock events from.  The core
code does not have to know about the clock details - it makes use of
clockevents_set_next_event().

Once the preliminaries for high resolution mode (a continous time source for
time keeping and a reprogrammable clock event device) are available, the
hrtimer code is switched to high resolution mode.  The per-cpu clock event
devices are switched into one shot mode and on SMP systems an eventually
available global clock event device (e.g.  PIT on i386) is switched off.  The
periodic tick, which updates jiffies and calls update_process_times and
profiling, is provided by a per-cpu hrtimer.  The callback function is
executed in the timer interrupt context.  The hrtimer based implementation of
the periodic tick is designed to be extended with dynamic tick functionality.

The impact to non-high-res architectures is intended to be minimal.

More detailed information is available in Documentation/hrtimer/highres.txt

Build-fixes-from: Valdis.Kletnieks <Valdis.Kletnieks@xxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>

Index: linux-2.6.19-rc5-mm1/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.19-rc5-mm1.orig/Documentation/kernel-parameters.txt	2006-11-09 21:06:17.000000000 +0100
+++ linux-2.6.19-rc5-mm1/Documentation/kernel-parameters.txt	2006-11-09 21:06:24.000000000 +0100
@@ -594,6 +594,10 @@ and is between 256 and 4096 characters. 
 			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.
 
Index: linux-2.6.19-rc5-mm1/include/linux/hrtimer.h
===================================================================
--- linux-2.6.19-rc5-mm1.orig/include/linux/hrtimer.h	2006-11-09 21:06:13.000000000 +0100
+++ linux-2.6.19-rc5-mm1/include/linux/hrtimer.h	2006-11-09 21:06:24.000000000 +0100
@@ -17,6 +17,7 @@
 
 #include <linux/rbtree.h>
 #include <linux/ktime.h>
+#include <linux/timer.h>
 #include <linux/init.h>
 #include <linux/list.h>
 #include <linux/wait.h>
@@ -41,6 +42,23 @@ enum hrtimer_restart {
 };
 
 /*
+ * 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,
+};
+
+/*
  * Bit values to track state of the timer
  *
  * Possible states:
@@ -50,6 +68,7 @@ enum hrtimer_restart {
  * 0x02		callback function running
  * 0x03		callback function running and enqueued
  *		(was requeued on another CPU)
+ * 0x04		callback pending (high resolution mode)
  *
  * The "callback function running and enqueued" status is only possible on
  * SMP. It happens for example when a posix timer expired and the callback
@@ -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
@@ -77,6 +97,9 @@ 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
  *
  * The hrtimer structure must be initialized by init_hrtimer_#CLOCKTYPE()
  */
@@ -86,6 +109,10 @@ 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 +137,9 @@ 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 +150,12 @@ 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
@@ -131,20 +167,77 @@ 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.
+ * @sched_timer:	hrtimer to schedule the periodic tick in high
+ *			resolution mode
  */
 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;
+	unsigned long			check_clocks;
+	struct list_head		cb_pending;
+	struct hrtimer			sched_timer;
+#endif
 };
 
+#ifdef CONFIG_HIGH_RES_TIMERS
+
+extern void hrtimer_clock_notify(void);
+extern void clock_was_set(void);
+extern void hrtimer_interrupt(struct pt_regs *regs);
+
+/*
+ * 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)
-#define hrtimer_clock_notify()	do { } while (0)
+static inline void clock_was_set(void) { }
+static inline void hrtimer_clock_notify(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);
 
Index: linux-2.6.19-rc5-mm1/include/linux/interrupt.h
===================================================================
--- linux-2.6.19-rc5-mm1.orig/include/linux/interrupt.h	2006-11-09 20:55:32.000000000 +0100
+++ linux-2.6.19-rc5-mm1/include/linux/interrupt.h	2006-11-09 21:06:24.000000000 +0100
@@ -236,7 +236,10 @@ enum
 	NET_TX_SOFTIRQ,
 	NET_RX_SOFTIRQ,
 	BLOCK_SOFTIRQ,
-	TASKLET_SOFTIRQ
+	TASKLET_SOFTIRQ,
+#ifdef CONFIG_HIGH_RES_TIMERS
+	HRTIMER_SOFTIRQ,
+#endif
 };
 
 /* softirq mask and active fields moved to irq_cpustat_t in
Index: linux-2.6.19-rc5-mm1/include/linux/ktime.h
===================================================================
--- linux-2.6.19-rc5-mm1.orig/include/linux/ktime.h	2006-11-09 20:55:32.000000000 +0100
+++ linux-2.6.19-rc5-mm1/include/linux/ktime.h	2006-11-09 21:06:24.000000000 +0100
@@ -261,8 +261,7 @@ static inline u64 ktime_to_ns(const ktim
  * 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);
Index: linux-2.6.19-rc5-mm1/kernel/hrtimer.c
===================================================================
--- linux-2.6.19-rc5-mm1.orig/kernel/hrtimer.c	2006-11-09 21:06:13.000000000 +0100
+++ linux-2.6.19-rc5-mm1/kernel/hrtimer.c	2006-11-09 21:06:24.000000000 +0100
@@ -38,7 +38,12 @@
 #include <linux/hrtimer.h>
 #include <linux/notifier.h>
 #include <linux/syscalls.h>
+#include <linux/kallsyms.h>
 #include <linux/interrupt.h>
+#include <linux/clockchips.h>
+#include <linux/profile.h>
+#include <linux/seq_file.h>
+#include <linux/err.h>
 
 #include <asm/uaccess.h>
 
@@ -81,7 +86,7 @@ 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 +94,12 @@ static DEFINE_PER_CPU(struct hrtimer_cpu
 		{
 			.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,
 		},
 	}
 };
@@ -228,7 +233,7 @@ lock_hrtimer_base(const struct hrtimer *
 	return base;
 }
 
-#define switch_hrtimer_base(t, b)	(b)
+# define switch_hrtimer_base(t, b)	(b)
 
 #endif	/* !CONFIG_SMP */
 
@@ -265,9 +270,6 @@ ktime_t ktime_add_ns(const ktime_t kt, u
 
 	return ktime_add(kt, tmp);
 }
-
-#else /* CONFIG_KTIME_SCALAR */
-
 # endif /* !CONFIG_KTIME_SCALAR */
 
 /*
@@ -295,11 +297,437 @@ static unsigned long ktime_divns(const k
 # define ktime_divns(kt, div)		(unsigned long)((kt).tv64 / (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);
+
+/*
+ * Is the high resolution mode active ?
+ */
+static inline int hrtimer_hres_active(void)
+{
+	return __get_cpu_var(hrtimer_bases).hres_active;
+}
+
+/*
+ * The time, when the last jiffy update happened. Protected by xtime_lock.
+ */
+static ktime_t last_jiffies_update;
+
+/*
+ * 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)
+		clockevents_set_next_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 (timer->state & HRTIMER_STATE_CALLBACK)
+		return 0;
+
+	if (expires.tv64 >= expires_next->tv64)
+		return 0;
+
+	/*
+	 * Clockevents returns -ETIME, when the event was in the past.
+	 */
+	res = clockevents_set_next_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);
+}
+
+/**
+ * hrtimer_clock_notify - A clock source or a clock event has been installed
+ *
+ * Notify the per cpu softirqs to recheck the clock sources and events
+ */
+void hrtimer_clock_notify(void)
+{
+	int i;
+
+	if (hrtimer_hres_enabled) {
+		for_each_possible_cpu(i)
+			set_bit(0, &per_cpu(hrtimer_bases, i).check_clocks);
+	}
+}
+
+static const ktime_t nsec_per_hz = { .tv64 = NSEC_PER_SEC / HZ };
+
+/*
+ * We switched off the global tick source when switching to high resolution
+ * mode. Update jiffies64.
+ *
+ * Must be called with interrupts disabled !
+ *
+ * FIXME: We need a mechanism to assign the update to a CPU. In principle this
+ * is not hard, but when dynamic ticks come into play it starts to be. We don't
+ * want to wake up a complete idle cpu just to update jiffies, so we need
+ * something more intellegent than a mere "do this only on CPUx".
+ */
+static void update_jiffies64(ktime_t now)
+{
+	unsigned long seq;
+	ktime_t delta;
+
+	/* Preevaluate to avoid lock contention */
+	do {
+		seq = read_seqbegin(&xtime_lock);
+		delta = ktime_sub(now, last_jiffies_update);
+	} while (read_seqretry(&xtime_lock, seq));
+
+	if (delta.tv64 < nsec_per_hz.tv64)
+		return;
+
+	/* Reevalute with xtime_lock held */
+	write_seqlock(&xtime_lock);
+
+	delta = ktime_sub(now, last_jiffies_update);
+	if (delta.tv64 >= nsec_per_hz.tv64) {
+		unsigned long ticks = 1;
+
+		delta = ktime_sub(delta, nsec_per_hz);
+		last_jiffies_update = ktime_add(last_jiffies_update,
+						nsec_per_hz);
+
+		/* Slow path for long timeouts */
+		if (unlikely(delta.tv64 >= nsec_per_hz.tv64)) {
+			s64 incr = ktime_to_ns(nsec_per_hz);
+
+			ticks = ktime_divns(delta, incr);
+
+			last_jiffies_update = ktime_add_ns(last_jiffies_update,
+							   incr * ticks);
+			ticks++;
+		}
+		do_timer(ticks);
+	}
+	write_sequnlock(&xtime_lock);
+}
+
+/*
+ * We rearm the timer until we get disabled by the idle code
+ * Called with interrupts disabled.
+ */
+static enum hrtimer_restart hrtimer_sched_tick(struct hrtimer *timer)
+{
+	struct hrtimer_cpu_base *cpu_base =
+		container_of(timer, struct hrtimer_cpu_base, sched_timer);
+ 	struct pt_regs *regs = get_irq_regs();
+
+	/*
+	 * Do not call, when we are not in irq context and have
+	 * no valid regs pointer
+	 */
+	if (regs) {
+		/*
+		 * 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(&cpu_base->lock);
+		update_process_times(user_mode(regs));
+		profile_tick(CPU_PROFILING);
+		spin_lock(&cpu_base->lock);
+	}
+
+	hrtimer_forward(timer, hrtimer_cb_get_time(timer), nsec_per_hz);
+
+	return HRTIMER_RESTART;
+}
+
+/*
+ * A change in the clock source or clock events was detected.
+ * Check the clock source and the events, whether we can switch to
+ * high resolution mode or not.
+ *
+ * TODO: Handle the removal of clock sources / events
+ */
+static void hrtimer_check_clocks(void)
+{
+	struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);
+	unsigned long flags;
+	ktime_t now;
+
+	if (!test_and_clear_bit(0, &base->check_clocks))
+		return;
+
+	if (!timekeeping_is_continuous())
+		return;
+
+	if (!clockevents_next_event_available())
+		return;
+
+	local_irq_save(flags);
+
+	if (base->hres_active) {
+		local_irq_restore(flags);
+		return;
+	}
+
+	now = ktime_get();
+	if (clockevents_init_next_event()) {
+		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;
+
+	/* Did we start the jiffies update yet ? */
+	if (last_jiffies_update.tv64 == 0) {
+		write_seqlock(&xtime_lock);
+		last_jiffies_update = now;
+		write_sequnlock(&xtime_lock);
+	}
+
+	/*
+	 * Emulate tick processing via per-CPU hrtimers:
+	 */
+	hrtimer_init(&base->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	base->sched_timer.function = hrtimer_sched_tick;
+	base->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
+	hrtimer_start(&base->sched_timer, nsec_per_hz, HRTIMER_MODE_REL);
+
+	/* "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());
+}
+
+/*
+ * 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;
+	set_bit(0, &base->check_clocks);
+	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;
+}
+
+/*
+ * Called after timekeeping resumed and updated jiffies64. Set the jiffies
+ * update time to now.
+ */
+static inline void hrtimer_resume_jiffy_update(void)
+{
+	unsigned long flags;
+	ktime_t now = ktime_get();
+
+	write_seqlock_irqsave(&xtime_lock, flags);
+	last_jiffies_update = now;
+	write_sequnlock_irqrestore(&xtime_lock, flags);
+}
+
+#else
+
+static inline int hrtimer_hres_active(void) { return 0; }
+static inline void hrtimer_check_clocks(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) { }
+static inline void hrtimer_resume_jiffy_update(void) { }
+
+#endif /* CONFIG_HIGH_RES_TIMERS */
+
 /*
  * Timekeeping resumed notification
  */
 void hrtimer_notify_resume(void)
 {
+	hrtimer_resume_jiffy_update();
 	clockevents_resume_events();
 	clock_was_set();
 }
@@ -361,7 +789,7 @@ hrtimer_forward(struct hrtimer *timer, k
  * 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;
@@ -387,6 +815,22 @@ static void enqueue_hrtimer(struct hrtim
 	 * 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);
 	/*
@@ -394,28 +838,38 @@ static void enqueue_hrtimer(struct hrtim
 	 * 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;
 }
 
@@ -426,7 +880,19 @@ 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;
@@ -472,7 +938,7 @@ hrtimer_start(struct hrtimer *timer, kti
 	}
 	timer->expires = tim;
 
-	enqueue_hrtimer(timer, new_base);
+	enqueue_hrtimer(timer, new_base, base == new_base);
 
 	unlock_hrtimer_base(timer, &flags);
 
@@ -603,6 +1069,7 @@ void hrtimer_init(struct hrtimer *timer,
 		clock_id = CLOCK_MONOTONIC;
 
 	timer->base = &cpu_base->clock_base[clock_id];
+	hrtimer_init_timer_hres(timer);
 }
 EXPORT_SYMBOL_GPL(hrtimer_init);
 
@@ -625,6 +1092,138 @@ int hrtimer_get_res(const clockid_t whic
 }
 EXPORT_SYMBOL_GPL(hrtimer_get_res);
 
+#ifdef CONFIG_HIGH_RES_TIMERS
+
+/*
+ * High resolution timer interrupt
+ * Called with interrupts disabled
+ */
+void hrtimer_interrupt(struct pt_regs *regs)
+{
+	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);
+
+ retry:
+	now = ktime_get();
+
+	/* Check, if the jiffies need an update */
+	update_jiffies64(now);
+
+	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);
+
+			if (timer->function(timer) != HRTIMER_NORESTART) {
+				BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
+				/*
+				 * Do not reprogram. We do this when we break
+				 * out of the loop !
+				 */
+				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 (clockevents_set_next_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:
  */
@@ -652,7 +1251,7 @@ static inline void run_hrtimer_queue(str
 			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);
@@ -662,7 +1261,7 @@ static inline void run_hrtimer_queue(str
 		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);
@@ -670,12 +1269,21 @@ static inline void run_hrtimer_queue(str
 
 /*
  * 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;
 
+	hrtimer_check_clocks();
+
+	if (hrtimer_hres_active())
+		return;
+
 	hrtimer_get_softirq_time(cpu_base);
 
 	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
@@ -702,6 +1310,9 @@ void hrtimer_init_sleeper(struct hrtimer
 {
 	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)
@@ -712,7 +1323,8 @@ static int __sched do_nanosleep(struct h
 		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;
@@ -817,6 +1429,7 @@ static void __devinit init_hrtimers_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
@@ -830,9 +1443,12 @@ static void migrate_hrtimer_list(struct 
 	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);
+		__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);
 	}
 }
 
@@ -895,5 +1511,8 @@ 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
 }
 
Index: linux-2.6.19-rc5-mm1/kernel/itimer.c
===================================================================
--- linux-2.6.19-rc5-mm1.orig/kernel/itimer.c	2006-11-09 21:06:03.000000000 +0100
+++ linux-2.6.19-rc5-mm1/kernel/itimer.c	2006-11-09 21:06:24.000000000 +0100
@@ -136,7 +136,7 @@ enum hrtimer_restart it_real_fn(struct h
 	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;
 	}
Index: linux-2.6.19-rc5-mm1/kernel/posix-timers.c
===================================================================
--- linux-2.6.19-rc5-mm1.orig/kernel/posix-timers.c	2006-11-09 21:06:03.000000000 +0100
+++ linux-2.6.19-rc5-mm1/kernel/posix-timers.c	2006-11-09 21:06:24.000000000 +0100
@@ -356,7 +356,7 @@ static enum hrtimer_restart posix_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;
Index: linux-2.6.19-rc5-mm1/kernel/time/Kconfig
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.19-rc5-mm1/kernel/time/Kconfig	2006-11-09 21:06:24.000000000 +0100
@@ -0,0 +1,11 @@
+#
+# Timer subsystem related configuration options
+#
+config HIGH_RES_TIMERS
+	bool "High Resolution Timer Support"
+	depends on GENERIC_TIME && GENERIC_CLOCKEVENTS
+	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.
+
Index: linux-2.6.19-rc5-mm1/kernel/timer.c
===================================================================
--- linux-2.6.19-rc5-mm1.orig/kernel/timer.c	2006-11-09 21:06:02.000000000 +0100
+++ linux-2.6.19-rc5-mm1/kernel/timer.c	2006-11-09 21:06:24.000000000 +0100
@@ -1048,6 +1048,7 @@ static void update_wall_time(void)
 	if (change_clocksource()) {
 		clock->error = 0;
 		clock->xtime_nsec = 0;
+		hrtimer_clock_notify();
 		clocksource_calculate_interval(clock, tick_nsec);
 	}
 }

--

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