clocksource: Cleanup clocksource selection
If a non high-resolution clocksource is first set as override clock
and then registered it becomes active even if the system is in one-shot
mode. Move the override check from sysfs_override_clocksource to the
clocksource selection. That fixes the bug and simplifies the code. The
check in clocksource_register for double registration of the same
clocksource is removed without replacement.
To find the initial clocksource a new weak function in jiffies.c is
defined that returns the jiffies clocksource. The architecture code
can then override the weak function with a more suitable clocksource,
e.g. the TOD clock on s390.
[ tglx: Folded in a fix from John Stultz ]
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134808.388024160@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 7466cb8..e91662e 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -21,7 +21,6 @@
*
* TODO WishList:
* o Allow clocksource drivers to be unregistered
- * o get rid of clocksource_jiffies extern
*/
#include <linux/clocksource.h>
@@ -107,12 +106,9 @@
}
EXPORT_SYMBOL(timecounter_cyc2time);
-/* XXX - Would like a better way for initializing curr_clocksource */
-extern struct clocksource clocksource_jiffies;
-
/*[Clocksource internal variables]---------
* curr_clocksource:
- * currently selected clocksource. Initialized to clocksource_jiffies.
+ * currently selected clocksource.
* next_clocksource:
* pending next selected clocksource.
* clocksource_list:
@@ -123,9 +119,8 @@
* override_name:
* Name of the user-specified clocksource.
*/
-static struct clocksource *curr_clocksource = &clocksource_jiffies;
+static struct clocksource *curr_clocksource;
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];
@@ -320,6 +315,7 @@
clocksource_resume_watchdog();
}
+#ifdef CONFIG_GENERIC_TIME
/**
* clocksource_get_next - Returns the selected clocksource
*
@@ -339,56 +335,65 @@
}
/**
- * select_clocksource - Selects the best registered clocksource.
+ * clocksource_select - Select the best clocksource available
*
* 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)
+static void clocksource_select(void)
{
- struct clocksource *next;
+ struct clocksource *best, *cs;
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;
+ return;
+ /* First clocksource on the list has the best rating. */
+ best = list_first_entry(&clocksource_list, struct clocksource, list);
+ /* Check for the override clocksource. */
+ list_for_each_entry(cs, &clocksource_list, list) {
+ if (strcmp(cs->name, override_name) != 0)
+ continue;
+ /*
+ * Check to make sure we don't switch to a non-highres
+ * capable clocksource if the tick code is in oneshot
+ * mode (highres or nohz)
+ */
+ if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
+ tick_oneshot_mode_active()) {
+ /* Override clocksource cannot be used. */
+ printk(KERN_WARNING "Override clocksource %s is not "
+ "HRT compatible. Cannot switch while in "
+ "HRT/NOHZ mode\n", cs->name);
+ override_name[0] = 0;
+ } else
+ /* Override clocksource can be used. */
+ best = cs;
+ break;
+ }
+ if (curr_clocksource != best)
+ next_clocksource = best;
}
+#else /* CONFIG_GENERIC_TIME */
+
+static void clocksource_select(void) { }
+
+#endif
+
/*
* Enqueue the clocksource sorted by rating
*/
-static int clocksource_enqueue(struct clocksource *c)
+static void clocksource_enqueue(struct clocksource *cs)
{
- struct list_head *tmp, *entry = &clocksource_list;
+ struct list_head *entry = &clocksource_list;
+ struct clocksource *tmp;
- list_for_each(tmp, &clocksource_list) {
- struct clocksource *cs;
-
- cs = list_entry(tmp, struct clocksource, list);
- if (cs == c)
- return -EBUSY;
+ list_for_each_entry(tmp, &clocksource_list, list)
/* 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;
+ if (tmp->rating >= cs->rating)
+ entry = &tmp->list;
+ list_add(&cs->list, entry);
}
/**
@@ -397,19 +402,16 @@
*
* Returns -EBUSY if registration fails, zero otherwise.
*/
-int clocksource_register(struct clocksource *c)
+int clocksource_register(struct clocksource *cs)
{
unsigned long flags;
- int ret;
spin_lock_irqsave(&clocksource_lock, flags);
- ret = clocksource_enqueue(c);
- if (!ret)
- next_clocksource = select_clocksource();
+ clocksource_enqueue(cs);
+ clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
- if (!ret)
- clocksource_check_watchdog(c);
- return ret;
+ clocksource_check_watchdog(cs);
+ return 0;
}
EXPORT_SYMBOL(clocksource_register);
@@ -425,7 +427,7 @@
list_del(&cs->list);
cs->rating = rating;
clocksource_enqueue(cs);
- next_clocksource = select_clocksource();
+ clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
@@ -438,9 +440,7 @@
spin_lock_irqsave(&clocksource_lock, flags);
list_del(&cs->list);
- if (clocksource_override == cs)
- clocksource_override = NULL;
- next_clocksource = select_clocksource();
+ clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
@@ -478,9 +478,7 @@
struct sysdev_attribute *attr,
const char *buf, size_t count)
{
- struct clocksource *ovr = NULL;
size_t ret = count;
- int len;
/* strings from sysfs write are not 0 terminated! */
if (count >= sizeof(override_name))
@@ -495,37 +493,7 @@
if (count > 0)
memcpy(override_name, buf, count);
override_name[count] = 0;
-
- len = strlen(override_name);
- if (len) {
- struct clocksource *cs;
-
- ovr = clocksource_override;
- /* try to select it: */
- list_for_each_entry(cs, &clocksource_list, list) {
- if (strlen(cs->name) == len &&
- !strcmp(cs->name, override_name))
- ovr = cs;
- }
- }
-
- /*
- * Check to make sure we don't switch to a non-highres capable
- * clocksource if the tick code is in oneshot mode (highres or nohz)
- */
- if (tick_oneshot_mode_active() && ovr &&
- !(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) {
- printk(KERN_WARNING "%s clocksource is not HRT compatible. "
- "Cannot switch while in HRT/NOHZ mode\n", ovr->name);
- ovr = NULL;
- override_name[0] = 0;
- }
-
- /* Reselect, when the override name has changed */
- if (ovr != clocksource_override) {
- clocksource_override = ovr;
- next_clocksource = select_clocksource();
- }
+ clocksource_select();
spin_unlock_irq(&clocksource_lock);