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Subject[RFC][patch 2/5] cleanup clocksource selection
From: Martin Schwidefsky <schwidefsky@de.ibm.com>

Introduce clocksource_dequeue & clocksource_update and move spinlock
calls. clocksource_update does nothing for GENERIC_TIME=n since
change_clocksource does nothing as well.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
kernel/time/clocksource.c | 123 ++++++++++++++++++++++++++--------------------
1 file changed, 70 insertions(+), 53 deletions(-)
Index: linux-2.6/kernel/time/clocksource.c
===================================================================
--- linux-2.6.orig/kernel/time/clocksource.c
+++ linux-2.6/kernel/time/clocksource.c
@@ -341,46 +341,25 @@ struct clocksource *clocksource_get_next
return curr_clocksource;
}

-/**
- * select_clocksource - Selects the best registered clocksource.
- *
- * Private function. Must hold clocksource_lock when called.
- *
- * Select the clocksource with the best rating, or the clocksource,
- * which is selected by userspace override.
- */
-static struct clocksource *select_clocksource(void)
-{
- struct clocksource *next;
-
- if (list_empty(&clocksource_list))
- return NULL;
-
- if (clocksource_override)
- next = clocksource_override;
- else
- next = list_entry(clocksource_list.next, struct clocksource,
- list);
-
- if (next == curr_clocksource)
- return NULL;
-
- return next;
-}
-
/*
* Enqueue the clocksource sorted by rating
*/
static int clocksource_enqueue(struct clocksource *c)
{
struct list_head *tmp, *entry = &clocksource_list;
+ unsigned long flags;
+ int rc;

+ spin_lock_irqsave(&clocksource_lock, flags);
+ rc = 0;
list_for_each(tmp, &clocksource_list) {
struct clocksource *cs;

cs = list_entry(tmp, struct clocksource, list);
- if (cs == c)
- return -EBUSY;
+ if (cs == c) {
+ rc = -EBUSY;
+ goto out;
+ }
/* Keep track of the place, where to insert */
if (cs->rating >= c->rating)
entry = tmp;
@@ -390,8 +369,23 @@ static int clocksource_enqueue(struct cl
if (strlen(c->name) == strlen(override_name) &&
!strcmp(c->name, override_name))
clocksource_override = c;
+out:
+ spin_unlock_irqrestore(&clocksource_lock, flags);
+ return rc;
+}
+
+/*
+ * Dequeue a clocksource
+ */
+static void clocksource_dequeue(struct clocksource *cs)
+{
+ unsigned long flags;

- return 0;
+ spin_lock_irqsave(&clocksource_lock, flags);
+ list_del(&cs->list);
+ if (clocksource_override == cs)
+ clocksource_override = NULL;
+ spin_unlock_irqrestore(&clocksource_lock, flags);
}

/**
@@ -539,6 +533,25 @@ void clocksource_forward_now(void)
}

/**
+ * select_clocksource - Selects the best registered clocksource.
+ *
+ * Private function. Must hold clocksource_lock when called.
+ *
+ * Select the clocksource with the best rating, or the clocksource,
+ * which is selected by userspace override.
+ */
+static struct clocksource *select_clocksource(void)
+{
+ if (list_empty(&clocksource_list))
+ return NULL;
+
+ if (clocksource_override)
+ return clocksource_override;
+
+ return list_entry(clocksource_list.next, struct clocksource, list);
+}
+
+/**
* change_clocksource - Swaps clocksources if a new one is available
*
* Accumulates current time interval and initializes new clocksource
@@ -577,6 +590,23 @@ void change_clocksource(void)
clock->name);
*/
}
+
+/**
+ * clocksource_update - Check if a better clocksource is available
+ */
+static void clocksource_update(void)
+{
+ struct clocksource *new;
+ unsigned long flags;
+
+ spin_lock_irqsave(&clocksource_lock, flags);
+ new = select_clocksource();
+ if (new)
+ next_clocksource = new;
+ spin_unlock_irqrestore(&clocksource_lock, flags);
+}
+#else /* CONFIG_GENERIC_TIME */
+static inline void clocksource_update(void) { }
#endif

/**
@@ -587,16 +617,13 @@ void change_clocksource(void)
*/
int clocksource_register(struct clocksource *c)
{
- unsigned long flags;
int ret;

- spin_lock_irqsave(&clocksource_lock, flags);
ret = clocksource_enqueue(c);
- if (!ret)
- next_clocksource = select_clocksource();
- spin_unlock_irqrestore(&clocksource_lock, flags);
- if (!ret)
+ if (!ret) {
+ clocksource_update();
clocksource_check_watchdog(c);
+ }
return ret;
}
EXPORT_SYMBOL(clocksource_register);
@@ -607,14 +634,10 @@ EXPORT_SYMBOL(clocksource_register);
*/
void clocksource_change_rating(struct clocksource *cs, int rating)
{
- unsigned long flags;
-
- spin_lock_irqsave(&clocksource_lock, flags);
- list_del(&cs->list);
+ clocksource_dequeue(cs);
cs->rating = rating;
clocksource_enqueue(cs);
- next_clocksource = select_clocksource();
- spin_unlock_irqrestore(&clocksource_lock, flags);
+ clocksource_update();
}

/**
@@ -622,14 +645,8 @@ void clocksource_change_rating(struct cl
*/
void clocksource_unregister(struct clocksource *cs)
{
- unsigned long flags;
-
- spin_lock_irqsave(&clocksource_lock, flags);
- list_del(&cs->list);
- if (clocksource_override == cs)
- clocksource_override = NULL;
- next_clocksource = select_clocksource();
- spin_unlock_irqrestore(&clocksource_lock, flags);
+ clocksource_dequeue(cs);
+ clocksource_update();
}

/**
@@ -721,13 +738,13 @@ static ssize_t sysfs_override_clocksourc
}

/* Reselect, when the override name has changed */
- if (ovr != clocksource_override) {
+ if (ovr != clocksource_override)
clocksource_override = ovr;
- next_clocksource = select_clocksource();
- }

spin_unlock_irq(&clocksource_lock);

+ clocksource_update();
+
return ret;
}

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.



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