[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>

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.
 

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);

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

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_LOW_RES		(ktime_t){ .tv64 = TICK_NSEC }
-#define KTIME_MONOTONIC_RES	(ktime_t){ .tv64 = TICK_NSEC }
 
 /* Get the monotonic time in timespec format: */
 extern void ktime_get_ts(struct timespec *ts);

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;
 	}

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;

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.
+