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Commit 75c5158f authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Thomas Gleixner
Browse files

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: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134810.711836357@de.ibm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 2ba2a305

include/linux/clocksource.h

+2 −0
Original line number Diff line number Diff line
@@ -291,4 +291,6 @@ static inline void update_vsyscall_tz(void) 
}

#endif



extern void timekeeping_notify(struct clocksource *clock);



#endif /* _LINUX_CLOCKSOURCE_H */

kernel/time/clocksource.c

+44 −68
Original line number Diff line number Diff line
@@ -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;

}

kernel/time/timekeeping.c

+26 −15
Original line number Diff line number Diff line
@@ -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))

		return;



	if (!new->enable || new->enable(new) == 0) {

		old = timekeeper.clock;

		timekeeper_setup_internals(new);



		if (old->disable)

			old->disable(old);

	}

	return 0;

}



/**

 * 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;

	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);

}