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>

1 files changed, 44 insertions, 68 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index f18c9a6bdcf4..a1657b5fdeb9 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -109,35 +109,17 @@ EXPORT_SYMBOL(timecounter_cyc2time);
 /*[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 @@ static inline void clocksource_resume_watchdog(void) { }
 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 @@ void clocksource_touch_watchdog(void)
 }
 
 #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 @@ static void clocksource_select(void)
 {
         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 @@ static void clocksource_select(void)
                         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 @@ static void clocksource_enqueue(struct clocksource *cs)
  */
 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 @@ EXPORT_SYMBOL(clocksource_register);
  */
 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 @@ EXPORT_SYMBOL(clocksource_change_rating);
  */
 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 @@ sysfs_show_current_clocksources(struct sys_device *dev,
 {
         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 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev,
         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 @@ sysfs_show_available_clocksources(struct sys_device *dev,
         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 @@ sysfs_show_available_clocksources(struct sys_device *dev,
                                   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 @@ device_initcall(init_clocksource_sysfs);
  */
 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;
 }