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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>
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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2
include/linux/clocksource.h
View File

@ -291,4 +291,6 @@ static inline void update_vsyscall_tz(void)
}
#endif
extern void timekeeping_notify(struct clocksource *clock);
#endif /* _LINUX_CLOCKSOURCE_H */

112
kernel/time/clocksource.c
View File

@ -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;
}

35
kernel/time/timekeeping.c
View File

@ -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);
}