timekeeping: Update clocksource with stop_machine
update_wall_time calls change_clocksource HZ times per second to check
if a new clock source is available. In close to 100% of all calls
there is no new clock. Replace the tick based check by an update done
with stop_machine.
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: <20090814134810.711836357@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f18c9a6..a1657b5 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -109,35 +109,17 @@
/*[Clocksource internal variables]---------
* curr_clocksource:
* currently selected clocksource.
- * next_clocksource:
- * pending next selected clocksource.
* clocksource_list:
* linked list with the registered clocksources
- * clocksource_lock:
- * protects manipulations to curr_clocksource and next_clocksource
- * and the clocksource_list
+ * clocksource_mutex:
+ * protects manipulations to curr_clocksource and the clocksource_list
* override_name:
* Name of the user-specified clocksource.
*/
static struct clocksource *curr_clocksource;
-static struct clocksource *next_clocksource;
static LIST_HEAD(clocksource_list);
-static DEFINE_SPINLOCK(clocksource_lock);
+static DEFINE_MUTEX(clocksource_mutex);
static char override_name[32];
-static int finished_booting;
-
-/* clocksource_done_booting - Called near the end of core bootup
- *
- * Hack to avoid lots of clocksource churn at boot time.
- * We use fs_initcall because we want this to start before
- * device_initcall but after subsys_initcall.
- */
-static int __init clocksource_done_booting(void)
-{
- finished_booting = 1;
- return 0;
-}
-fs_initcall(clocksource_done_booting);
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static LIST_HEAD(watchdog_list);
@@ -356,18 +338,16 @@
void clocksource_resume(void)
{
struct clocksource *cs;
- unsigned long flags;
- spin_lock_irqsave(&clocksource_lock, flags);
+ mutex_lock(&clocksource_mutex);
- list_for_each_entry(cs, &clocksource_list, list) {
+ list_for_each_entry(cs, &clocksource_list, list)
if (cs->resume)
cs->resume();
- }
clocksource_resume_watchdog();
- spin_unlock_irqrestore(&clocksource_lock, flags);
+ mutex_unlock(&clocksource_mutex);
}
/**
@@ -383,28 +363,13 @@
}
#ifdef CONFIG_GENERIC_TIME
-/**
- * clocksource_get_next - Returns the selected clocksource
- *
- */
-struct clocksource *clocksource_get_next(void)
-{
- unsigned long flags;
- spin_lock_irqsave(&clocksource_lock, flags);
- if (next_clocksource && finished_booting) {
- curr_clocksource = next_clocksource;
- next_clocksource = NULL;
- }
- spin_unlock_irqrestore(&clocksource_lock, flags);
-
- return curr_clocksource;
-}
+static int finished_booting;
/**
* clocksource_select - Select the best clocksource available
*
- * Private function. Must hold clocksource_lock when called.
+ * Private function. Must hold clocksource_mutex when called.
*
* Select the clocksource with the best rating, or the clocksource,
* which is selected by userspace override.
@@ -413,7 +378,7 @@
{
struct clocksource *best, *cs;
- if (list_empty(&clocksource_list))
+ if (!finished_booting || list_empty(&clocksource_list))
return;
/* First clocksource on the list has the best rating. */
best = list_first_entry(&clocksource_list, struct clocksource, list);
@@ -438,13 +403,31 @@
best = cs;
break;
}
- if (curr_clocksource != best)
- next_clocksource = best;
+ if (curr_clocksource != best) {
+ printk(KERN_INFO "Switching to clocksource %s\n", best->name);
+ curr_clocksource = best;
+ timekeeping_notify(curr_clocksource);
+ }
}
+/*
+ * clocksource_done_booting - Called near the end of core bootup
+ *
+ * Hack to avoid lots of clocksource churn at boot time.
+ * We use fs_initcall because we want this to start before
+ * device_initcall but after subsys_initcall.
+ */
+static int __init clocksource_done_booting(void)
+{
+ finished_booting = 1;
+ clocksource_select();
+ return 0;
+}
+fs_initcall(clocksource_done_booting);
+
#else /* CONFIG_GENERIC_TIME */
-static void clocksource_select(void) { }
+static inline void clocksource_select(void) { }
#endif
@@ -471,13 +454,11 @@
*/
int clocksource_register(struct clocksource *cs)
{
- unsigned long flags;
-
- spin_lock_irqsave(&clocksource_lock, flags);
+ mutex_lock(&clocksource_mutex);
clocksource_enqueue(cs);
clocksource_select();
- spin_unlock_irqrestore(&clocksource_lock, flags);
clocksource_enqueue_watchdog(cs);
+ mutex_unlock(&clocksource_mutex);
return 0;
}
EXPORT_SYMBOL(clocksource_register);
@@ -487,14 +468,12 @@
*/
void clocksource_change_rating(struct clocksource *cs, int rating)
{
- unsigned long flags;
-
- spin_lock_irqsave(&clocksource_lock, flags);
+ mutex_lock(&clocksource_mutex);
list_del(&cs->list);
cs->rating = rating;
clocksource_enqueue(cs);
clocksource_select();
- spin_unlock_irqrestore(&clocksource_lock, flags);
+ mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_change_rating);
@@ -503,13 +482,11 @@
*/
void clocksource_unregister(struct clocksource *cs)
{
- unsigned long flags;
-
+ mutex_lock(&clocksource_mutex);
clocksource_dequeue_watchdog(cs);
- spin_lock_irqsave(&clocksource_lock, flags);
list_del(&cs->list);
clocksource_select();
- spin_unlock_irqrestore(&clocksource_lock, flags);
+ mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_unregister);
@@ -527,9 +504,9 @@
{
ssize_t count = 0;
- spin_lock_irq(&clocksource_lock);
+ mutex_lock(&clocksource_mutex);
count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
- spin_unlock_irq(&clocksource_lock);
+ mutex_unlock(&clocksource_mutex);
return count;
}
@@ -557,14 +534,14 @@
if (buf[count-1] == '\n')
count--;
- spin_lock_irq(&clocksource_lock);
+ mutex_lock(&clocksource_mutex);
if (count > 0)
memcpy(override_name, buf, count);
override_name[count] = 0;
clocksource_select();
- spin_unlock_irq(&clocksource_lock);
+ mutex_unlock(&clocksource_mutex);
return ret;
}
@@ -584,7 +561,7 @@
struct clocksource *src;
ssize_t count = 0;
- spin_lock_irq(&clocksource_lock);
+ mutex_lock(&clocksource_mutex);
list_for_each_entry(src, &clocksource_list, list) {
/*
* Don't show non-HRES clocksource if the tick code is
@@ -596,7 +573,7 @@
max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
"%s ", src->name);
}
- spin_unlock_irq(&clocksource_lock);
+ mutex_unlock(&clocksource_mutex);
count += snprintf(buf + count,
max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
@@ -651,11 +628,10 @@
*/
static int __init boot_override_clocksource(char* str)
{
- unsigned long flags;
- spin_lock_irqsave(&clocksource_lock, flags);
+ mutex_lock(&clocksource_mutex);
if (str)
strlcpy(override_name, str, sizeof(override_name));
- spin_unlock_irqrestore(&clocksource_lock, flags);
+ mutex_unlock(&clocksource_mutex);
return 1;
}