linux/kernel/time/timekeeping.c
Thomas Gleixner 6a669ee8a7 timekeeping: Prevent time going backwards on resume
Timekeeping resume adjusts xtime by adding the slept time in seconds and
resets the reference value of the clock source (clock->cycle_last).
clock->cycle last is used to calculate the delta between the last xtime
update and the readout of the clock source in __get_nsec_offset(). xtime
plus the offset is the current time. The resume code ignores the delta
which had already elapsed between the last xtime update and the actual
time of suspend. If the suspend time is short, then we can see time
going backwards on resume.

Suspend:
offs_s = clock->read() - clock->cycle_last;
now = xtime + offs_s;
timekeeping_suspend_time = read_rtc();

Resume:
sleep_time = read_rtc() - timekeeping_suspend_time;
xtime.tv_sec += sleep_time;
clock->cycle_last = clock->read();
offs_r = clock->read() - clock->cycle_last;
now = xtime + offs_r;

if sleep_time_seconds == 0 and offs_r < offs_s, then time goes
backwards.

Fix this by storing the offset from the last xtime update and add it to
xtime during resume, when we reset clock->cycle_last:

sleep_time = read_rtc() - timekeeping_suspend_time;
xtime.tv_sec += sleep_time;
xtime += offs_s;	/* Fixup xtime offset at suspend time */
clock->cycle_last = clock->read();
offs_r = clock->read() - clock->cycle_last;
now = xtime + offs_r;

Thanks to Marcelo for tracking this down on the OLPC and providing the
necessary details to analyze the root cause.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Tosatti <marcelo@kvack.org>
2007-09-16 15:36:43 +02:00

556 lines
14 KiB
C

/*
* 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.
*/
__attribute__((weak)) __cacheline_aligned_in_smp DEFINE_SEQLOCK(xtime_lock);
EXPORT_SYMBOL(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 */
EXPORT_SYMBOL(xtime);
#ifdef CONFIG_NO_HZ
static struct timespec xtime_cache __attribute__ ((aligned (16)));
static inline void update_xtime_cache(u64 nsec)
{
xtime_cache = xtime;
timespec_add_ns(&xtime_cache, nsec);
}
#else
#define xtime_cache xtime
/* We do *not* want to evaluate the argument for this case */
#define update_xtime_cache(n) do { } while (0)
#endif
static struct clocksource *clock; /* pointer to current clocksource */
#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;
}
/**
* __get_realtime_clock_ts - Returns the time of day in a timespec
* @ts: pointer to the timespec to be set
*
* Returns the time of day in a timespec. Used by
* do_gettimeofday() and get_realtime_clock_ts().
*/
static inline void __get_realtime_clock_ts(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);
}
/**
* 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)
{
__get_realtime_clock_ts(ts);
}
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 get_realtime_clock_ts()
*/
void do_gettimeofday(struct timeval *tv)
{
struct timespec now;
__get_realtime_clock_ts(&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);
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;
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();
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_is_continuous - check to see if timekeeping is free running
*/
int timekeeping_is_continuous(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_clear();
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);
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);
/* re-base the last cycle value */
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 = {
.resume = timekeeping_resume,
.suspend = timekeeping_suspend,
set_kset_name("timekeeping"),
};
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 adusted
* within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
*/
error2 = clock->error >> (TICK_LENGTH_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 = current_tick_length() >>
(TICK_LENGTH_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 >> (TICK_LENGTH_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) <<
(TICK_LENGTH_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 += current_tick_length();
clock->error -= clock->xtime_interval << (TICK_LENGTH_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);