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Subject[tip:timers/core] timekeeping: Update clocksource with stop_machine
Commit-ID:  75c5158f70c065b9704b924503d96e8297838f79
Gitweb: http://git.kernel.org/tip/75c5158f70c065b9704b924503d96e8297838f79
Author: Martin Schwidefsky <schwidefsky@de.ibm.com>
AuthorDate: Fri, 14 Aug 2009 15:47:30 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 15 Aug 2009 10:55:46 +0200

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>


---
include/linux/clocksource.h | 2 +
kernel/time/clocksource.c | 112 +++++++++++++++++--------------------------
kernel/time/timekeeping.c | 41 ++++++++++------
3 files changed, 72 insertions(+), 83 deletions(-)
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index e34015e..9ea40ff 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -291,4 +291,6 @@ static inline void update_vsyscall_tz(void)
}
#endif

+extern void timekeeping_notify(struct clocksource *clock);
+
#endif /* _LINUX_CLOCKSOURCE_H */
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 @@ 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;
}

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 27ae01b..41579e7 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -18,6 +18,7 @@
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/tick.h>
+#include <linux/stop_machine.h>

/* Structure holding internal timekeeping values. */
struct timekeeper {
@@ -179,6 +180,7 @@ void timekeeping_leap_insert(int leapsecond)
}

#ifdef CONFIG_GENERIC_TIME
+
/**
* timekeeping_forward_now - update clock to the current time
*
@@ -351,31 +353,40 @@ EXPORT_SYMBOL(do_settimeofday);
*
* Accumulates current time interval and initializes new clocksource
*/
-static void change_clocksource(void)
+static int change_clocksource(void *data)
{
struct clocksource *new, *old;

- new = clocksource_get_next();
-
- if (!new || timekeeper.clock == new)
- return;
+ new = (struct clocksource *) data;

timekeeping_forward_now();
+ if (!new->enable || new->enable(new) == 0) {
+ old = timekeeper.clock;
+ timekeeper_setup_internals(new);
+ if (old->disable)
+ old->disable(old);
+ }
+ return 0;
+}

- if (new->enable && !new->enable(new))
+/**
+ * timekeeping_notify - Install a new clock source
+ * @clock: pointer to the clock source
+ *
+ * This function is called from clocksource.c after a new, better clock
+ * source has been registered. The caller holds the clocksource_mutex.
+ */
+void timekeeping_notify(struct clocksource *clock)
+{
+ if (timekeeper.clock == clock)
return;
-
- old = timekeeper.clock;
- timekeeper_setup_internals(new);
-
- if (old->disable)
- old->disable(old);
-
+ stop_machine(change_clocksource, clock, NULL);
tick_clock_notify();
}
+
#else /* GENERIC_TIME */
+
static inline void timekeeping_forward_now(void) { }
-static inline void change_clocksource(void) { }

/**
* ktime_get - get the monotonic time in ktime_t format
@@ -416,6 +427,7 @@ void ktime_get_ts(struct timespec *ts)
ts->tv_nsec + tomono.tv_nsec);
}
EXPORT_SYMBOL_GPL(ktime_get_ts);
+
#endif /* !GENERIC_TIME */

/**
@@ -773,7 +785,6 @@ void update_wall_time(void)
update_xtime_cache(nsecs);

/* check to see if there is a new clocksource to use */
- change_clocksource();
update_vsyscall(&xtime, timekeeper.clock);
}


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