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Subject[tip:timers/core] clocksource: Refactor clocksource watchdog
Commit-ID:  fb63a0ebe615fba9de8c75ea44ded999d1e24c65
Gitweb: http://git.kernel.org/tip/fb63a0ebe615fba9de8c75ea44ded999d1e24c65
Author: Martin Schwidefsky <schwidefsky@de.ibm.com>
AuthorDate: Fri, 14 Aug 2009 15:47:24 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 15 Aug 2009 10:55:46 +0200

clocksource: Refactor clocksource watchdog

Refactor clocksource watchdog code to make it more readable. Add
clocksource_dequeue_watchdog to remove a clocksource from the watchdog
list when it is unregistered.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134809.110881699@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>


---
kernel/time/clocksource.c | 97 ++++++++++++++++++++++++++++++++-------------
1 files changed, 69 insertions(+), 28 deletions(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 89a7b91..56aaa74 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -145,6 +145,7 @@ static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last;
+static int watchdog_running;

/*
* Interval: 0.5sec Threshold: 0.0625s
@@ -168,6 +169,8 @@ static void clocksource_watchdog(unsigned long data)
int64_t wd_nsec, cs_nsec;

spin_lock(&watchdog_lock);
+ if (!watchdog_running)
+ goto out;

wdnow = watchdog->read(watchdog);
wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
@@ -217,9 +220,30 @@ static void clocksource_watchdog(unsigned long data)
watchdog_timer.expires += WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer, next_cpu);
}
+out:
spin_unlock(&watchdog_lock);
}

+static inline void clocksource_start_watchdog(void)
+{
+ if (watchdog_running || !watchdog || list_empty(&watchdog_list))
+ return;
+ init_timer(&watchdog_timer);
+ watchdog_timer.function = clocksource_watchdog;
+ watchdog_last = watchdog->read(watchdog);
+ watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
+ add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
+ watchdog_running = 1;
+}
+
+static inline void clocksource_stop_watchdog(void)
+{
+ if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
+ return;
+ del_timer(&watchdog_timer);
+ watchdog_running = 0;
+}
+
static inline void clocksource_reset_watchdog(void)
{
struct clocksource *cs;
@@ -237,55 +261,70 @@ static void clocksource_resume_watchdog(void)
spin_unlock_irqrestore(&watchdog_lock, flags);
}

-static void clocksource_check_watchdog(struct clocksource *cs)
+static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
unsigned long flags;

spin_lock_irqsave(&watchdog_lock, flags);
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
- int started = !list_empty(&watchdog_list);
-
+ /* cs is a clocksource to be watched. */
list_add(&cs->wd_list, &watchdog_list);
- if (!started && watchdog) {
- watchdog_last = watchdog->read(watchdog);
- watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
- add_timer_on(&watchdog_timer,
- cpumask_first(cpu_online_mask));
- }
+ cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
} else {
+ /* cs is a watchdog. */
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
-
+ /* Pick the best watchdog. */
if (!watchdog || cs->rating > watchdog->rating) {
- if (watchdog)
- del_timer(&watchdog_timer);
watchdog = cs;
- init_timer(&watchdog_timer);
- watchdog_timer.function = clocksource_watchdog;
-
/* Reset watchdog cycles */
clocksource_reset_watchdog();
- /* Start if list is not empty */
- if (!list_empty(&watchdog_list)) {
- watchdog_last = watchdog->read(watchdog);
- watchdog_timer.expires =
- jiffies + WATCHDOG_INTERVAL;
- add_timer_on(&watchdog_timer,
- cpumask_first(cpu_online_mask));
- }
}
}
+ /* Check if the watchdog timer needs to be started. */
+ clocksource_start_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
-#else
-static void clocksource_check_watchdog(struct clocksource *cs)
+
+static void clocksource_dequeue_watchdog(struct clocksource *cs)
+{
+ struct clocksource *tmp;
+ unsigned long flags;
+
+ spin_lock_irqsave(&watchdog_lock, flags);
+ if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
+ /* cs is a watched clocksource. */
+ list_del_init(&cs->wd_list);
+ } else if (cs == watchdog) {
+ /* Reset watchdog cycles */
+ clocksource_reset_watchdog();
+ /* Current watchdog is removed. Find an alternative. */
+ watchdog = NULL;
+ list_for_each_entry(tmp, &clocksource_list, list) {
+ if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
+ continue;
+ if (!watchdog || tmp->rating > watchdog->rating)
+ watchdog = tmp;
+ }
+ }
+ cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
+ /* Check if the watchdog timer needs to be stopped. */
+ clocksource_stop_watchdog();
+ spin_unlock_irqrestore(&watchdog_lock, flags);
+}
+
+#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
+
+static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}

+static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
-#endif
+
+#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */

/**
* clocksource_resume - resume the clocksource(s)
@@ -414,14 +453,13 @@ int clocksource_register(struct clocksource *cs)
clocksource_enqueue(cs);
clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
- clocksource_check_watchdog(cs);
+ clocksource_enqueue_watchdog(cs);
return 0;
}
EXPORT_SYMBOL(clocksource_register);

/**
* clocksource_change_rating - Change the rating of a registered clocksource
- *
*/
void clocksource_change_rating(struct clocksource *cs, int rating)
{
@@ -434,6 +472,7 @@ void clocksource_change_rating(struct clocksource *cs, int rating)
clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
+EXPORT_SYMBOL(clocksource_change_rating);

/**
* clocksource_unregister - remove a registered clocksource
@@ -442,11 +481,13 @@ void clocksource_unregister(struct clocksource *cs)
{
unsigned long flags;

+ clocksource_dequeue_watchdog(cs);
spin_lock_irqsave(&clocksource_lock, flags);
list_del(&cs->list);
clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
+EXPORT_SYMBOL(clocksource_unregister);

#ifdef CONFIG_SYSFS
/**

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