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DEFINITIONS
This source file includes following definitions.
- update_xtime_cache
- __get_nsec_offset
- getnstimeofday
- do_gettimeofday
- do_settimeofday
- change_clocksource
- change_clocksource
- __get_nsec_offset
- timekeeping_valid_for_hres
- read_persistent_clock
- timekeeping_init
- timekeeping_resume
- timekeeping_suspend
- timekeeping_init_device
- clocksource_bigadjust
- clocksource_adjust
- update_wall_time
- getboottime
- monotonic_to_bootbased
- get_seconds
- current_kernel_time
/*
* linux/kernel/time/timekeeping.c
*
* Kernel timekeeping code and accessor functions
*
* This code was moved from linux/kernel/timer.c.
* Please see that file for copyright and history logs.
*
*/
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/sysdev.h>
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/time.h>
#include <linux/tick.h>
/*
* This read-write spinlock protects us from races in SMP while
* playing with xtime and avenrun.
*/
__cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
/*
* The current time
* wall_to_monotonic is what we need to add to xtime (or xtime corrected
* for sub jiffie times) to get to monotonic time. Monotonic is pegged
* at zero at system boot time, so wall_to_monotonic will be negative,
* however, we will ALWAYS keep the tv_nsec part positive so we can use
* the usual normalization.
*
* wall_to_monotonic is moved after resume from suspend for the monotonic
* time not to jump. We need to add total_sleep_time to wall_to_monotonic
* to get the real boot based time offset.
*
* - wall_to_monotonic is no longer the boot time, getboottime must be
* used instead.
*/
struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
static unsigned long total_sleep_time; /* seconds */
static struct timespec xtime_cache __attribute__ ((aligned (16)));
void update_xtime_cache(u64 nsec)
{
xtime_cache = xtime;
timespec_add_ns(&xtime_cache, nsec);
}
struct clocksource *clock;
#ifdef CONFIG_GENERIC_TIME
/**
* __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
*
* private function, must hold xtime_lock lock when being
* called. Returns the number of nanoseconds since the
* last call to update_wall_time() (adjusted by NTP scaling)
*/
static inline s64 __get_nsec_offset(void)
{
cycle_t cycle_now, cycle_delta;
s64 ns_offset;
/* read clocksource: */
cycle_now = clocksource_read(clock);
/* calculate the delta since the last update_wall_time: */
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
/* convert to nanoseconds: */
ns_offset = cyc2ns(clock, cycle_delta);
return ns_offset;
}
/**
* getnstimeofday - Returns the time of day in a timespec
* @ts: pointer to the timespec to be set
*
* Returns the time of day in a timespec.
*/
void getnstimeofday(struct timespec *ts)
{
unsigned long seq;
s64 nsecs;
do {
seq = read_seqbegin(&xtime_lock);
*ts = xtime;
nsecs = __get_nsec_offset();
} while (read_seqretry(&xtime_lock, seq));
timespec_add_ns(ts, nsecs);
}
EXPORT_SYMBOL(getnstimeofday);
/**
* do_gettimeofday - Returns the time of day in a timeval
* @tv: pointer to the timeval to be set
*
* NOTE: Users should be converted to using getnstimeofday()
*/
void do_gettimeofday(struct timeval *tv)
{
struct timespec now;
getnstimeofday(&now);
tv->tv_sec = now.tv_sec;
tv->tv_usec = now.tv_nsec/1000;
}
EXPORT_SYMBOL(do_gettimeofday);
/**
* do_settimeofday - Sets the time of day
* @tv: pointer to the timespec variable containing the new time
*
* Sets the time of day to the new time and update NTP and notify hrtimers
*/
int do_settimeofday(struct timespec *tv)
{
unsigned long flags;
time_t wtm_sec, sec = tv->tv_sec;
long wtm_nsec, nsec = tv->tv_nsec;
if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
return -EINVAL;
write_seqlock_irqsave(&xtime_lock, flags);
nsec -= __get_nsec_offset();
wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
set_normalized_timespec(&xtime, sec, nsec);
set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
update_xtime_cache(0);
clock->error = 0;
ntp_clear();
update_vsyscall(&xtime, clock);
write_sequnlock_irqrestore(&xtime_lock, flags);
/* signal hrtimers about time change */
clock_was_set();
return 0;
}
EXPORT_SYMBOL(do_settimeofday);
/**
* change_clocksource - Swaps clocksources if a new one is available
*
* Accumulates current time interval and initializes new clocksource
*/
static void change_clocksource(void)
{
struct clocksource *new;
cycle_t now;
u64 nsec;
new = clocksource_get_next();
if (clock == new)
return;
new->cycle_last = 0;
now = clocksource_read(new);
nsec = __get_nsec_offset();
timespec_add_ns(&xtime, nsec);
clock = new;
clock->cycle_last = now;
clock->error = 0;
clock->xtime_nsec = 0;
clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
tick_clock_notify();
/*
* We're holding xtime lock and waking up klogd would deadlock
* us on enqueue. So no printing!
printk(KERN_INFO "Time: %s clocksource has been installed.\n",
clock->name);
*/
}
#else
static inline void change_clocksource(void) { }
static inline s64 __get_nsec_offset(void) { return 0; }
#endif
/**
* timekeeping_valid_for_hres - Check if timekeeping is suitable for hres
*/
int timekeeping_valid_for_hres(void)
{
unsigned long seq;
int ret;
do {
seq = read_seqbegin(&xtime_lock);
ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
} while (read_seqretry(&xtime_lock, seq));
return ret;
}
/**
* read_persistent_clock - Return time in seconds from the persistent clock.
*
* Weak dummy function for arches that do not yet support it.
* Returns seconds from epoch using the battery backed persistent clock.
* Returns zero if unsupported.
*
* XXX - Do be sure to remove it once all arches implement it.
*/
unsigned long __attribute__((weak)) read_persistent_clock(void)
{
return 0;
}
/*
* timekeeping_init - Initializes the clocksource and common timekeeping values
*/
void __init timekeeping_init(void)
{
unsigned long flags;
unsigned long sec = read_persistent_clock();
write_seqlock_irqsave(&xtime_lock, flags);
ntp_init();
clock = clocksource_get_next();
clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
clock->cycle_last = clocksource_read(clock);
xtime.tv_sec = sec;
xtime.tv_nsec = 0;
set_normalized_timespec(&wall_to_monotonic,
-xtime.tv_sec, -xtime.tv_nsec);
update_xtime_cache(0);
total_sleep_time = 0;
write_sequnlock_irqrestore(&xtime_lock, flags);
}
/* flag for if timekeeping is suspended */
static int timekeeping_suspended;
/* time in seconds when suspend began */
static unsigned long timekeeping_suspend_time;
/* xtime offset when we went into suspend */
static s64 timekeeping_suspend_nsecs;
/**
* timekeeping_resume - Resumes the generic timekeeping subsystem.
* @dev: unused
*
* This is for the generic clocksource timekeeping.
* xtime/wall_to_monotonic/jiffies/etc are
* still managed by arch specific suspend/resume code.
*/
static int timekeeping_resume(struct sys_device *dev)
{
unsigned long flags;
unsigned long now = read_persistent_clock();
clocksource_resume();
write_seqlock_irqsave(&xtime_lock, flags);
if (now && (now > timekeeping_suspend_time)) {
unsigned long sleep_length = now - timekeeping_suspend_time;
xtime.tv_sec += sleep_length;
wall_to_monotonic.tv_sec -= sleep_length;
total_sleep_time += sleep_length;
}
/* Make sure that we have the correct xtime reference */
timespec_add_ns(&xtime, timekeeping_suspend_nsecs);
update_xtime_cache(0);
/* re-base the last cycle value */
clock->cycle_last = 0;
clock->cycle_last = clocksource_read(clock);
clock->error = 0;
timekeeping_suspended = 0;
write_sequnlock_irqrestore(&xtime_lock, flags);
touch_softlockup_watchdog();
clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
/* Resume hrtimers */
hres_timers_resume();
return 0;
}
static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
{
unsigned long flags;
timekeeping_suspend_time = read_persistent_clock();
write_seqlock_irqsave(&xtime_lock, flags);
/* Get the current xtime offset */
timekeeping_suspend_nsecs = __get_nsec_offset();
timekeeping_suspended = 1;
write_sequnlock_irqrestore(&xtime_lock, flags);
clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
return 0;
}
/* sysfs resume/suspend bits for timekeeping */
static struct sysdev_class timekeeping_sysclass = {
.name = "timekeeping",
.resume = timekeeping_resume,
.suspend = timekeeping_suspend,
};
static struct sys_device device_timer = {
.id = 0,
.cls = &timekeeping_sysclass,
};
static int __init timekeeping_init_device(void)
{
int error = sysdev_class_register(&timekeeping_sysclass);
if (!error)
error = sysdev_register(&device_timer);
return error;
}
device_initcall(timekeeping_init_device);
/*
* If the error is already larger, we look ahead even further
* to compensate for late or lost adjustments.
*/
static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
s64 *offset)
{
s64 tick_error, i;
u32 look_ahead, adj;
s32 error2, mult;
/*
* Use the current error value to determine how much to look ahead.
* The larger the error the slower we adjust for it to avoid problems
* with losing too many ticks, otherwise we would overadjust and
* produce an even larger error. The smaller the adjustment the
* faster we try to adjust for it, as lost ticks can do less harm
* here. This is tuned so that an error of about 1 msec is adjusted
* within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
*/
error2 = clock->error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
error2 = abs(error2);
for (look_ahead = 0; error2 > 0; look_ahead++)
error2 >>= 2;
/*
* Now calculate the error in (1 << look_ahead) ticks, but first
* remove the single look ahead already included in the error.
*/
tick_error = tick_length >> (NTP_SCALE_SHIFT - clock->shift + 1);
tick_error -= clock->xtime_interval >> 1;
error = ((error - tick_error) >> look_ahead) + tick_error;
/* Finally calculate the adjustment shift value. */
i = *interval;
mult = 1;
if (error < 0) {
error = -error;
*interval = -*interval;
*offset = -*offset;
mult = -1;
}
for (adj = 0; error > i; adj++)
error >>= 1;
*interval <<= adj;
*offset <<= adj;
return mult << adj;
}
/*
* Adjust the multiplier to reduce the error value,
* this is optimized for the most common adjustments of -1,0,1,
* for other values we can do a bit more work.
*/
static void clocksource_adjust(s64 offset)
{
s64 error, interval = clock->cycle_interval;
int adj;
error = clock->error >> (NTP_SCALE_SHIFT - clock->shift - 1);
if (error > interval) {
error >>= 2;
if (likely(error <= interval))
adj = 1;
else
adj = clocksource_bigadjust(error, &interval, &offset);
} else if (error < -interval) {
error >>= 2;
if (likely(error >= -interval)) {
adj = -1;
interval = -interval;
offset = -offset;
} else
adj = clocksource_bigadjust(error, &interval, &offset);
} else
return;
clock->mult += adj;
clock->xtime_interval += interval;
clock->xtime_nsec -= offset;
clock->error -= (interval - offset) <<
(NTP_SCALE_SHIFT - clock->shift);
}
/**
* update_wall_time - Uses the current clocksource to increment the wall time
*
* Called from the timer interrupt, must hold a write on xtime_lock.
*/
void update_wall_time(void)
{
cycle_t offset;
/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
return;
#ifdef CONFIG_GENERIC_TIME
offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
#else
offset = clock->cycle_interval;
#endif
clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;
/* normally this loop will run just once, however in the
* case of lost or late ticks, it will accumulate correctly.
*/
while (offset >= clock->cycle_interval) {
/* accumulate one interval */
clock->xtime_nsec += clock->xtime_interval;
clock->cycle_last += clock->cycle_interval;
offset -= clock->cycle_interval;
if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
xtime.tv_sec++;
second_overflow();
}
/* accumulate error between NTP and clock interval */
clock->error += tick_length;
clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
}
/* correct the clock when NTP error is too big */
clocksource_adjust(offset);
/* store full nanoseconds into xtime */
xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
update_xtime_cache(cyc2ns(clock, offset));
/* check to see if there is a new clocksource to use */
change_clocksource();
update_vsyscall(&xtime, clock);
}
/**
* getboottime - Return the real time of system boot.
* @ts: pointer to the timespec to be set
*
* Returns the time of day in a timespec.
*
* This is based on the wall_to_monotonic offset and the total suspend
* time. Calls to settimeofday will affect the value returned (which
* basically means that however wrong your real time clock is at boot time,
* you get the right time here).
*/
void getboottime(struct timespec *ts)
{
set_normalized_timespec(ts,
- (wall_to_monotonic.tv_sec + total_sleep_time),
- wall_to_monotonic.tv_nsec);
}
/**
* monotonic_to_bootbased - Convert the monotonic time to boot based.
* @ts: pointer to the timespec to be converted
*/
void monotonic_to_bootbased(struct timespec *ts)
{
ts->tv_sec += total_sleep_time;
}
unsigned long get_seconds(void)
{
return xtime_cache.tv_sec;
}
EXPORT_SYMBOL(get_seconds);
struct timespec current_kernel_time(void)
{
struct timespec now;
unsigned long seq;
do {
seq = read_seqbegin(&xtime_lock);
now = xtime_cache;
} while (read_seqretry(&xtime_lock, seq));
return now;
}
EXPORT_SYMBOL(current_kernel_time);