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timekeeping: Update clocksource with stop_machine

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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>
This commit is contained in:
Martin Schwidefsky
2009-08-14 15:47:30 +02:00
committed by Thomas Gleixner
parent 2ba2a3054f
commit 75c5158f70
3 changed files with 72 additions and 83 deletions
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41
kernel/time/timekeeping.c
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@@ -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);
}