3 files changed, 62 insertions, 67 deletions

diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index d4000649942a..6f6971da761c 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -323,8 +323,7 @@ static int tsc_update_callback(void)
 
         /* check to see if we should switch to the safe clocksource: */
         if (clocksource_tsc.rating != 0 && check_tsc_unstable()) {
-                clocksource_tsc.rating = 0;
-                clocksource_reselect();
+                clocksource_change_rating(&clocksource_tsc, 0);
                 change = 1;
         }
 
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 1622d23a8dc3..55d714052374 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -178,8 +178,8 @@ static inline void clocksource_calculate_interval(struct clocksource *c,
 
 
 /* used to install a new clocksource */
-int clocksource_register(struct clocksource*);
-void clocksource_reselect(void);
-struct clocksource* clocksource_get_next(void);
+extern int clocksource_register(struct clocksource*);
+extern struct clocksource* clocksource_get_next(void);
+extern void clocksource_change_rating(struct clocksource *cs, int rating);
 
 #endif /* _LINUX_CLOCKSOURCE_H */
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index d9ef176c4e09..2f6a3d6e43bc 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -48,6 +48,7 @@ extern struct clocksource clocksource_jiffies;
  */
 static struct clocksource *curr_clocksource = &clocksource_jiffies;
 static struct clocksource *next_clocksource;
+static struct clocksource *clocksource_override;
 static LIST_HEAD(clocksource_list);
 static DEFINE_SPINLOCK(clocksource_lock);
 static char override_name[32];
@@ -84,60 +85,46 @@ struct clocksource *clocksource_get_next(void)
 }
 
 /**
- * select_clocksource - Finds the best registered clocksource.
+ * select_clocksource - Selects the best registered clocksource.
  *
  * Private function. Must hold clocksource_lock when called.
  *
- * Looks through the list of registered clocksources, returning
- * the one with the highest rating value. If there is a clocksource
- * name that matches the override string, it returns that clocksource.
+ * Select the clocksource with the best rating, or the clocksource,
+ * which is selected by userspace override.
  */
 static struct clocksource *select_clocksource(void)
 {
-        struct clocksource *best = NULL;
-        struct list_head *tmp;
-
-        list_for_each(tmp, &clocksource_list) {
-                struct clocksource *src;
+        if (list_empty(&clocksource_list))
+                return NULL;
 
-                src = list_entry(tmp, struct clocksource, list);
-                if (!best)
-                        best = src;
-
-                /* check for override: */
-                if (strlen(src->name) == strlen(override_name) &&
-                    !strcmp(src->name, override_name)) {
-                        best = src;
-                        break;
-                }
-                /* pick the highest rating: */
-                if (src->rating > best->rating)
-                        best = src;
-        }
+        if (clocksource_override)
+                return clocksource_override;
 
-        return best;
+        return list_entry(clocksource_list.next, struct clocksource, list);
 }
 
-/**
- * is_registered_source - Checks if clocksource is registered
- * @c:          pointer to a clocksource
- *
- * Private helper function. Must hold clocksource_lock when called.
- *
- * Returns one if the clocksource is already registered, zero otherwise.
+/*
+ * Enqueue the clocksource sorted by rating
  */
-static int is_registered_source(struct clocksource *c)
+static int clocksource_enqueue(struct clocksource *c)
 {
-        int len = strlen(c->name);
-        struct list_head *tmp;
+        struct list_head *tmp, *entry = &clocksource_list;
 
         list_for_each(tmp, &clocksource_list) {
-                struct clocksource *src;
-
-                src = list_entry(tmp, struct clocksource, list);
-                if (strlen(src->name) == len && !strcmp(src->name, c->name))
-                        return 1;
+                struct clocksource *cs;
+
+                cs = list_entry(tmp, struct clocksource, list);
+                if (cs == c)
+                        return -EBUSY;
+                /* Keep track of the place, where to insert */
+                if (cs->rating >= c->rating)
+                        entry = tmp;
         }
+        list_add(&c->list, entry);
+
+        if (strlen(c->name) == strlen(override_name) &&
+            !strcmp(c->name, override_name))
+                clocksource_override = c;
 
         return 0;
 }
@@ -150,42 +137,32 @@ static int is_registered_source(struct clocksource *c)
  */
 int clocksource_register(struct clocksource *c)
 {
-        int ret = 0;
         unsigned long flags;
+        int ret = 0;
 
         spin_lock_irqsave(&clocksource_lock, flags);
-        /* check if clocksource is already registered */
-        if (is_registered_source(c)) {
-                printk("register_clocksource: Cannot register %s. "
-                       "Already registered!", c->name);
-                ret = -EBUSY;
-        } else {
-                /* register it */
-                list_add(&c->list, &clocksource_list);
-                /* scan the registered clocksources, and pick the best one */
+        ret = clocksource_enqueue(c);
+        if (!ret)
                 next_clocksource = select_clocksource();
-        }
         spin_unlock_irqrestore(&clocksource_lock, flags);
         return ret;
 }
 EXPORT_SYMBOL(clocksource_register);
 
 /**
- * clocksource_reselect - Rescan list for next clocksource
+ * clocksource_change_rating - Change the rating of a registered clocksource
  *
- * A quick helper function to be used if a clocksource changes its
- * rating. Forces the clocksource list to be re-scanned for the best
- * clocksource.
  */
-void clocksource_reselect(void)
+void clocksource_change_rating(struct clocksource *cs, int rating)
 {
         unsigned long flags;
 
         spin_lock_irqsave(&clocksource_lock, flags);
+        list_del(&cs->list);
+        clocksource_enqueue(cs);
         next_clocksource = select_clocksource();
         spin_unlock_irqrestore(&clocksource_lock, flags);
 }
-EXPORT_SYMBOL(clocksource_reselect);
 
 #ifdef CONFIG_SYSFS
 /**
@@ -221,7 +198,11 @@ sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
                                           const char *buf, size_t count)
 {
+        struct clocksource *ovr = NULL;
+        struct list_head *tmp;
         size_t ret = count;
+        int len;
+
         /* strings from sysfs write are not 0 terminated! */
         if (count >= sizeof(override_name))
                 return -EINVAL;
@@ -229,17 +210,32 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev,
         /* strip of \n: */
         if (buf[count-1] == '\n')
                 count--;
-        if (count < 1)
-                return -EINVAL;
 
         spin_lock_irq(&clocksource_lock);
 
-        /* copy the name given: */
-        memcpy(override_name, buf, count);
+        if (count > 0)
+                memcpy(override_name, buf, count);
         override_name[count] = 0;
 
-        /* try to select it: */
-        next_clocksource = select_clocksource();
+        len = strlen(override_name);
+        if (len) {
+                ovr = clocksource_override;
+                /* try to select it: */
+                list_for_each(tmp, &clocksource_list) {
+                        struct clocksource *cs;
+
+                        cs = list_entry(tmp, struct clocksource, list);
+                        if (strlen(cs->name) == len &&
+                            !strcmp(cs->name, override_name))
+                                ovr = cs;
+                }
+        }
+
+        /* Reselect, when the override name has changed */
+        if (ovr != clocksource_override) {
+                clocksource_override = ovr;
+                next_clocksource = select_clocksource();
+        }
 
         spin_unlock_irq(&clocksource_lock);