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/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 @@
}
#ifdef CONFIG_GENERIC_TIME
+
/**
* timekeeping_forward_now - update clock to the current time
*
@@ -351,31 +353,40 @@
*
* 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 @@
ts->tv_nsec + tomono.tv_nsec);
}
EXPORT_SYMBOL_GPL(ktime_get_ts);
+
#endif /* !GENERIC_TIME */
/**
@@ -773,7 +785,6 @@
update_xtime_cache(nsecs);
/* check to see if there is a new clocksource to use */
- change_clocksource();
update_vsyscall(&xtime, timekeeper.clock);
}
