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Subject[RFC] [PATCH 1/1] hrtimers: Cache next hrtimer
From 6558900969ef1f4492aad4d9a2a87cd8900dee92 Mon Sep 17 00:00:00 2001
From: Ashwin Chaugule <ashwinc@quicinc.com>
Date: Thu, 27 Aug 2009 10:42:48 -0400
Subject: [PATCH][hrtimers] Cache next hrtimer

Cached the hrtimer which causes the expire_next
value to change. This is to avoid unnecessary re-programming
of the clock events device.

modified: include/linux/hrtimer.h
modified: kernel/hrtimer.c

Signed-off-by: Ashwin Chaugule <ashwinc@quicinc.com>
---
include/linux/hrtimer.h | 5 ++-
kernel/hrtimer.c | 81 +++++++++++++++++++++++++++++++---------------
2 files changed, 58 insertions(+), 28 deletions(-)
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index bd37078..dd8fa9b 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -4,7 +4,8 @@
* hrtimers - High-resolution kernel timers
*
* Copyright(C) 2005, Thomas Gleixner <tglx@linutronix.de>
- * Copyright(C) 2005, Red Hat, Inc., Ingo Molnar
+ * Copyright(C) 2005, Red Hat, Inc., Ingo Molnar
+ * Copyright(C) 2009, Code Aurora Forum. All rights reserved.
*
* data type definitions, declarations, prototypes
*
@@ -157,6 +158,7 @@ struct hrtimer_clock_base {
* and timers
* @clock_base: array of clock bases for this cpu
* @curr_timer: the timer which is executing a callback right now
+ * @next_hrtimer: the hrtimer that caused expires_next to change
* @expires_next: absolute time of the next event which was scheduled
* via clock_set_next_event()
* @hres_active: State of high resolution mode
@@ -169,6 +171,7 @@ struct hrtimer_cpu_base {
spinlock_t lock;
struct hrtimer_clock_base clock_base[HRTIMER_MAX_CLOCK_BASES];
#ifdef CONFIG_HIGH_RES_TIMERS
+ struct hrtimer *next_hrtimer;
ktime_t expires_next;
int hres_active;
unsigned long nr_events;
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index f394d2a..d823987 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -4,6 +4,8 @@
* 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
+ * Copyright(C) 2009, Code Aurora Forum. All rights reserved.
+ *
*
* High-resolution kernel timers
*
@@ -508,8 +510,10 @@ 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)
+ if (expires.tv64 < cpu_base->expires_next.tv64) {
cpu_base->expires_next = expires;
+ cpu_base->next_hrtimer = timer;
+ }
}

if (cpu_base->expires_next.tv64 != KTIME_MAX)
@@ -529,6 +533,7 @@ static int hrtimer_reprogram(struct hrtimer *timer,
struct hrtimer_clock_base *base)
{
ktime_t *expires_next = &__get_cpu_var(hrtimer_bases).expires_next;
+ struct hrtimer *next_hrtimer = __get_cpu_var(hrtimer_bases).next_hrtimer;
ktime_t expires = ktime_sub(hrtimer_get_expires(timer), base->offset);
int res;

@@ -560,8 +565,10 @@ static int hrtimer_reprogram(struct hrtimer *timer,
* Clockevents returns -ETIME, when the event was in the past.
*/
res = tick_program_event(expires, 0);
- if (!IS_ERR_VALUE(res))
+ if (!IS_ERR_VALUE(res)) {
*expires_next = expires;
+ next_hrtimer = timer;
+ }
return res;
}

@@ -634,6 +641,7 @@ static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base)
{
base->expires_next.tv64 = KTIME_MAX;
base->hres_active = 0;
+ base->next_hrtimer = NULL;
}

/*
@@ -843,16 +851,20 @@ static void __remove_hrtimer(struct hrtimer *timer,
struct hrtimer_clock_base *base,
unsigned long newstate, int reprogram)
{
- if (timer->state & HRTIMER_STATE_ENQUEUED) {
+ struct hrtimer *next_hrtimer = __get_cpu_var(hrtimer_bases).next_hrtimer;
+
+ if (hrtimer_is_queued(timer)) {
/*
* 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);
+ if (next_hrtimer == timer) {
+ /* Reprogram the clock event device. if enabled */
+ if (reprogram && hrtimer_hres_active())
+ hrtimer_force_reprogram(base->cpu_base);
+ }
}
rb_erase(&timer->node, &base->active);
}
@@ -865,25 +877,22 @@ static void __remove_hrtimer(struct hrtimer *timer,
static inline int
remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base)
{
- if (hrtimer_is_queued(timer)) {
- int reprogram;
+ 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.
- */
- debug_hrtimer_deactivate(timer);
- timer_stats_hrtimer_clear_start_info(timer);
- reprogram = base->cpu_base == &__get_cpu_var(hrtimer_bases);
- __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE,
- reprogram);
- return 1;
- }
- return 0;
+ /*
+ * 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.
+ */
+ debug_hrtimer_deactivate(timer);
+ timer_stats_hrtimer_clear_start_info(timer);
+ reprogram = base->cpu_base == &__get_cpu_var(hrtimer_bases);
+ __remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE,
+ reprogram);
+ return 1;
}

/**
@@ -903,12 +912,26 @@ hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, unsigned long delta_n
{
struct hrtimer_clock_base *base, *new_base;
unsigned long flags;
- int ret, leftmost;
+ int ret = 0;
+ int leftmost;

base = lock_hrtimer_base(timer, &flags);

/* Remove an active timer from the queue: */
- ret = remove_hrtimer(timer, base);
+ if (hrtimer_is_queued(timer)) {
+ if (timer == __get_cpu_var(hrtimer_bases).next_hrtimer)
+ ret = remove_hrtimer(timer, base);
+ else {
+ debug_hrtimer_deactivate(timer);
+ timer_stats_hrtimer_clear_start_info(timer);
+ if (base->first == &timer->node) {
+ base->first = rb_next(&timer->node);
+ }
+ rb_erase(&timer->node, &base->active);
+ timer->state = HRTIMER_STATE_INACTIVE;
+ ret = 1;
+ }
+ }

/* Switch the timer base, if necessary: */
new_base = switch_hrtimer_base(timer, base);
@@ -1196,6 +1219,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
{
struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
struct hrtimer_clock_base *base;
+ struct hrtimer *next_hrtimer = NULL;
ktime_t expires_next, now;
int nr_retries = 0;
int i;
@@ -1246,8 +1270,10 @@ void hrtimer_interrupt(struct clock_event_device *dev)

expires = ktime_sub(hrtimer_get_expires(timer),
base->offset);
- if (expires.tv64 < expires_next.tv64)
+ if (expires.tv64 < expires_next.tv64) {
expires_next = expires;
+ next_hrtimer = timer;
+ }
break;
}

@@ -1258,6 +1284,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
}

cpu_base->expires_next = expires_next;
+ cpu_base->next_hrtimer = next_hrtimer;

/* Reprogramming necessary ? */
if (expires_next.tv64 != KTIME_MAX) {
--
1.5.6.3
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