[no subject]

[Ashwin Chaugule]

	hrtimer: Eliminate needless reprogramming of clock events
 	device.

	On NOHZ systems the following timers,

	-  tick_nohz_restart_sched_tick (tick_sched_timer)
	-  hrtimer_start (tick_sched_timer)

	were reprogramming the clock events device far more often than needed.
	No specific test case was required to observe this effect. This
	occurred because, there was no check to see if the currently removed
	or restarted hrtimer was:

	1) the one which previously armed the clock events device.
	2) going to be replaced by another timer which has the same expiry time.

	This patch avoids the extra programming and results in faster application
 	startup time by ~4% amongst other benefits.

	modified:   kernel/hrtimer.c

	[tglx: simplified code]

	Signed-off-by: Ashwin Chaugule <ashwinc@xxxxxxxxxxx>
---
 kernel/hrtimer.c |   53 +++++++++++++++++++++++++++++++++++------------------
 1 files changed, 35 insertions(+), 18 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 49da79a..24c8cc3 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -4,6 +4,7 @@
  *  Copyright(C) 2005-2006, Thomas Gleixner <tglx@xxxxxxxxxxxxx>
  *  Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
  *  Copyright(C) 2006-2007  Timesys Corp., Thomas Gleixner
+ *  Copyright(C) 2009 Code Aurora Forum., Ashwin Chaugule
  *
  *  High-resolution kernel timers
  *
@@ -542,13 +543,14 @@ static inline int hrtimer_hres_active(void)
  * next event
  * Called with interrupts disabled and base->lock held
  */
-static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base)
+static void
+hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
 {
 	int i;
 	struct hrtimer_clock_base *base = cpu_base->clock_base;
-	ktime_t expires;
+	ktime_t expires, expires_next;
 
-	cpu_base->expires_next.tv64 = KTIME_MAX;
+	expires_next.tv64 = KTIME_MAX;
 
 	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
 		struct hrtimer *timer;
@@ -564,10 +566,15 @@ static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base)
 		 */
 		if (expires.tv64 < 0)
 			expires.tv64 = 0;
-		if (expires.tv64 < cpu_base->expires_next.tv64)
-			cpu_base->expires_next = expires;
+		if (expires.tv64 < expires_next.tv64)
+			expires_next = expires;
 	}
 
+	if (skip_equal && expires_next.tv64 == cpu_base->expires_next.tv64)
+		return;
+
+	cpu_base->expires_next.tv64 = expires_next.tv64;
+
 	if (cpu_base->expires_next.tv64 != KTIME_MAX)
 		tick_program_event(cpu_base->expires_next, 1);
 }
@@ -650,7 +657,7 @@ static void retrigger_next_event(void *arg)
 	base->clock_base[CLOCK_REALTIME].offset =
 		timespec_to_ktime(realtime_offset);
 
-	hrtimer_force_reprogram(base);
+	hrtimer_force_reprogram(base, 0);
 	spin_unlock(&base->lock);
 }
 
@@ -763,7 +770,8 @@ static int hrtimer_switch_to_hres(void)
 static inline int hrtimer_hres_active(void) { return 0; }
 static inline int hrtimer_is_hres_enabled(void) { return 0; }
 static inline int hrtimer_switch_to_hres(void) { return 0; }
-static inline void hrtimer_force_reprogram(struct hrtimer_cpu_base *base) { }
+static inline void
+hrtimer_force_reprogram(struct hrtimer_cpu_base *base, int skip_equal) { }
 static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
 					    struct hrtimer_clock_base *base,
 					    int wakeup)
@@ -906,19 +914,28 @@ static void __remove_hrtimer(struct hrtimer *timer,
 			     struct hrtimer_clock_base *base,
 			     unsigned long newstate, int reprogram)
 {
-	if (timer->state & HRTIMER_STATE_ENQUEUED) {
-		/*
-		 * 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);
+	ktime_t expires;
+
+	if (!(timer->state & HRTIMER_STATE_ENQUEUED))
+		goto out;
+
+	/*
+	 * 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()) {
+			expires = ktime_sub(hrtimer_get_expires(timer),
+					    base->offset);
+			if (base->cpu_base->expires_next.tv64 == expires.tv64)
+				hrtimer_force_reprogram(base->cpu_base, 1);
 		}
-		rb_erase(&timer->node, &base->active);
 	}
+
+	rb_erase(&timer->node, &base->active);
+out:
 	timer->state = newstate;
 }
 
-- 
1.5.6.3


Cheers,
Ashwin

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