Commit f1b82746 authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Thomas Gleixner
Browse files

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: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134808.388024160@de.ibm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 1be39679

arch/s390/kernel/time.c

+4 −0
Original line number Diff line number Diff line
@@ -205,6 +205,10 @@ static struct clocksource clocksource_tod = { 
	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,

};



struct clocksource * __init clocksource_default_clock(void)

{

	return &clocksource_tod;

}



void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)

{

include/linux/clocksource.h

+2 −0
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#include <linux/list.h>

#include <linux/cache.h>

#include <linux/timer.h>

#include <linux/init.h>

#include <asm/div64.h>

#include <asm/io.h>
@@ -322,6 +323,7 @@ extern void clocksource_touch_watchdog(void); 
extern struct clocksource* clocksource_get_next(void);

extern void clocksource_change_rating(struct clocksource *cs, int rating);

extern void clocksource_resume(void);

extern struct clocksource * __init __weak clocksource_default_clock(void);



#ifdef CONFIG_GENERIC_TIME_VSYSCALL

extern void update_vsyscall(struct timespec *ts, struct clocksource *c);

kernel/time/clocksource.c

+51 −83
Original line number Diff line number Diff line
@@ -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 @@ u64 timecounter_cyc2time(struct timecounter *tc, 
}

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 @@ extern struct clocksource clocksource_jiffies; 
 * 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 @@ void clocksource_touch_watchdog(void) 
	clocksource_resume_watchdog();

}



#ifdef CONFIG_GENERIC_TIME

/**

 * clocksource_get_next - Returns the selected clocksource

 *
@@ -339,56 +335,65 @@ struct clocksource *clocksource_get_next(void) 
}



/**

 * 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;

		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;

}



	if (clocksource_override)

		next = clocksource_override;

	else

		next = list_entry(clocksource_list.next, struct clocksource,

				  list);

#else /* CONFIG_GENERIC_TIME */



	if (next == curr_clocksource)

		return NULL;

static void clocksource_select(void) { }



	return next;

}

#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;



	list_for_each(tmp, &clocksource_list) {

		struct clocksource *cs;

	struct list_head *entry = &clocksource_list;

	struct clocksource *tmp;



		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 @@ static int clocksource_enqueue(struct clocksource *c) 
 *

 * 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 @@ void clocksource_change_rating(struct clocksource *cs, int rating) 
	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 @@ void clocksource_unregister(struct clocksource *cs) 


	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 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev, 
					  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 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev, 
	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);

kernel/time/jiffies.c

+5 −1
Original line number Diff line number Diff line
@@ -61,7 +61,6 @@ struct clocksource clocksource_jiffies = { 
	.read		= jiffies_read,

	.mask		= 0xffffffff, /*32bits*/

	.mult		= NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */

	.mult_orig	= NSEC_PER_JIFFY << JIFFIES_SHIFT,

	.shift		= JIFFIES_SHIFT,

};
@@ -71,3 +70,8 @@ static int __init init_jiffies_clocksource(void) 
}



core_initcall(init_jiffies_clocksource);



struct clocksource * __init __weak clocksource_default_clock(void)

{

	return &clocksource_jiffies;

}

kernel/time/timekeeping.c

+2 −2
Original line number Diff line number Diff line
@@ -269,7 +269,7 @@ static void change_clocksource(void) 


	new = clocksource_get_next();



	if (clock == new)

	if (!new || clock == new)

		return;



	clocksource_forward_now();
@@ -446,7 +446,7 @@ void __init timekeeping_init(void) 


	ntp_init();



	clock = clocksource_get_next();

	clock = clocksource_default_clock();

	if (clock->enable)

		clock->enable(clock);

	/* set mult_orig on enable */

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