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timekeeping: Introduce struct timekeeper 

Add struct timekeeper to keep the internal values timekeeping.c needs
in regard to the currently selected clock source. This moves the
timekeeping intervals, xtime_nsec and the ntp error value from struct
clocksource to struct timekeeper. The raw_time is removed from the
clocksource as well. It gets treated like xtime as a global variable.
Eventually xtime raw_time should be moved to struct timekeeper.

[ tglx: minor cleanup ]

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: <20090814134809.613209842@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Martin Schwidefsky 2009-08-14 15:47:26 +02:00 committed by Thomas Gleixner
parent c55c87c892
commit 155ec60226
4 changed files with 165 additions and 133 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/s390/kernel/time.c
View File

@ -280,7 +280,6 @@ void __init time_init(void)
now = get_clock();
tod_to_timeval(now - TOD_UNIX_EPOCH, &xtime);
clocksource_tod.cycle_last = now;
clocksource_tod.raw_time = xtime;
tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, &ts);
set_normalized_timespec(&wall_to_monotonic, -ts.tv_sec, -ts.tv_nsec);
write_sequnlock_irqrestore(&xtime_lock, flags);

54
include/linux/clocksource.h
View File

@ -155,8 +155,6 @@ extern u64 timecounter_cyc2time(struct timecounter *tc,
* @flags: flags describing special properties
* @vread: vsyscall based read
* @resume: resume function for the clocksource, if necessary
* @cycle_interval: Used internally by timekeeping core, please ignore.
* @xtime_interval: Used internally by timekeeping core, please ignore.
*/
struct clocksource {
/*
@ -182,19 +180,12 @@ struct clocksource {
#define CLKSRC_FSYS_MMIO_SET(mmio, addr) do { } while (0)
#endif
/* timekeeping specific data, ignore */
cycle_t cycle_interval;
u64 xtime_interval;
u32 raw_interval;
/*
* Second part is written at each timer interrupt
* Keep it in a different cache line to dirty no
* more than one cache line.
*/
cycle_t cycle_last ____cacheline_aligned_in_smp;
u64 xtime_nsec;
s64 error;
struct timespec raw_time;
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
/* Watchdog related data, used by the framework */
@ -203,8 +194,6 @@ struct clocksource {
#endif
};
extern struct clocksource *clock; /* current clocksource */
/*
* Clock source flags bits::
*/
@ -270,50 +259,15 @@ static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
}
/**
* cyc2ns - converts clocksource cycles to nanoseconds
* @cs: Pointer to clocksource
* @cycles: Cycles
* clocksource_cyc2ns - converts clocksource cycles to nanoseconds
*
* Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
* Converts cycles to nanoseconds, using the given mult and shift.
*
* XXX - This could use some mult_lxl_ll() asm optimization
*/
static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
static inline s64 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift)
{
u64 ret = (u64)cycles;
ret = (ret * cs->mult) >> cs->shift;
return ret;
}
/**
* clocksource_calculate_interval - Calculates a clocksource interval struct
*
* @c: Pointer to clocksource.
* @length_nsec: Desired interval length in nanoseconds.
*
* Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
* pair and interval request.
*
* Unless you're the timekeeping code, you should not be using this!
*/
static inline void clocksource_calculate_interval(struct clocksource *c,
unsigned long length_nsec)
{
u64 tmp;
/* Do the ns -> cycle conversion first, using original mult */
tmp = length_nsec;
tmp <<= c->shift;
tmp += c->mult_orig/2;
do_div(tmp, c->mult_orig);
c->cycle_interval = (cycle_t)tmp;
if (c->cycle_interval == 0)
c->cycle_interval = 1;
/* Go back from cycles -> shifted ns, this time use ntp adjused mult */
c->xtime_interval = (u64)c->cycle_interval * c->mult;
c->raw_interval = ((u64)c->cycle_interval * c->mult_orig) >> c->shift;
return ((u64) cycles * mult) >> shift;
}

6
kernel/time/clocksource.c
View File

@ -177,7 +177,8 @@ static void clocksource_watchdog(unsigned long data)
goto out;
wdnow = watchdog->read(watchdog);
wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
wd_nsec = clocksource_cyc2ns((wdnow - watchdog_last) & watchdog->mask,
watchdog->mult, watchdog->shift);
watchdog_last = wdnow;
list_for_each_entry(cs, &watchdog_list, wd_list) {
@ -196,7 +197,8 @@ static void clocksource_watchdog(unsigned long data)
}
/* Check the deviation from the watchdog clocksource. */
cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
cs->mask, cs->mult, cs->shift);
cs->wd_last = csnow;
if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
clocksource_unstable(cs, cs_nsec - wd_nsec);

237
kernel/time/timekeeping.c
View File

@ -19,6 +19,65 @@
#include <linux/time.h>
#include <linux/tick.h>
/* Structure holding internal timekeeping values. */
struct timekeeper {
/* Current clocksource used for timekeeping. */
struct clocksource *clock;
/* Number of clock cycles in one NTP interval. */
cycle_t cycle_interval;
/* Number of clock shifted nano seconds in one NTP interval. */
u64 xtime_interval;
/* Raw nano seconds accumulated per NTP interval. */
u32 raw_interval;
/* Clock shifted nano seconds remainder not stored in xtime.tv_nsec. */
u64 xtime_nsec;
/* Difference between accumulated time and NTP time in ntp
* shifted nano seconds. */
s64 ntp_error;
};
struct timekeeper timekeeper;
/**
* timekeeper_setup_internals - Set up internals to use clocksource clock.
*
* @clock: Pointer to clocksource.
*
* Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
* pair and interval request.
*
* Unless you're the timekeeping code, you should not be using this!
*/
static void timekeeper_setup_internals(struct clocksource *clock)
{
cycle_t interval;
u64 tmp;
timekeeper.clock = clock;
clock->cycle_last = clock->read(clock);
/* Do the ns -> cycle conversion first, using original mult */
tmp = NTP_INTERVAL_LENGTH;
tmp <<= clock->shift;
tmp += clock->mult_orig/2;
do_div(tmp, clock->mult_orig);
if (tmp == 0)
tmp = 1;
interval = (cycle_t) tmp;
timekeeper.cycle_interval = interval;
/* Go back from cycles -> shifted ns */
timekeeper.xtime_interval = (u64) interval * clock->mult;
timekeeper.raw_interval =
((u64) interval * clock->mult_orig) >> clock->shift;
timekeeper.xtime_nsec = 0;
timekeeper.ntp_error = 0;
}
/*
* This read-write spinlock protects us from races in SMP while
@ -46,6 +105,11 @@ struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
static unsigned long total_sleep_time; /* seconds */
/*
* The raw monotonic time for the CLOCK_MONOTONIC_RAW posix clock.
*/
struct timespec raw_time;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
@ -56,42 +120,42 @@ void update_xtime_cache(u64 nsec)
timespec_add_ns(&xtime_cache, nsec);
}
struct clocksource *clock;
/* must hold xtime_lock */
void timekeeping_leap_insert(int leapsecond)
{
xtime.tv_sec += leapsecond;
wall_to_monotonic.tv_sec -= leapsecond;
update_vsyscall(&xtime, clock);
update_vsyscall(&xtime, timekeeper.clock);
}
#ifdef CONFIG_GENERIC_TIME
/**
* clocksource_forward_now - update clock to the current time
* timekeeping_forward_now - update clock to the current time
*
* Forward the current clock to update its state since the last call to
* update_wall_time(). This is useful before significant clock changes,
* as it avoids having to deal with this time offset explicitly.
*/
static void clocksource_forward_now(void)
static void timekeeping_forward_now(void)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
s64 nsec;
clock = timekeeper.clock;
cycle_now = clock->read(clock);
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
clock->cycle_last = cycle_now;
nsec = cyc2ns(clock, cycle_delta);
nsec = clocksource_cyc2ns(cycle_delta, clock->mult, clock->shift);
/* If arch requires, add in gettimeoffset() */
nsec += arch_gettimeoffset();
timespec_add_ns(&xtime, nsec);
nsec = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
clock->raw_time.tv_nsec += nsec;
nsec = clocksource_cyc2ns(cycle_delta, clock->mult_orig, clock->shift);
timespec_add_ns(&raw_time, nsec);
}
/**
@ -103,6 +167,7 @@ static void clocksource_forward_now(void)
void getnstimeofday(struct timespec *ts)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
unsigned long seq;
s64 nsecs;
@ -114,13 +179,15 @@ void getnstimeofday(struct timespec *ts)
*ts = xtime;
/* read clocksource: */
clock = timekeeper.clock;
cycle_now = clock->read(clock);
/* calculate the delta since the last update_wall_time: */
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
/* convert to nanoseconds: */
nsecs = cyc2ns(clock, cycle_delta);
nsecs = clocksource_cyc2ns(cycle_delta, clock->mult,
clock->shift);
/* If arch requires, add in gettimeoffset() */
nsecs += arch_gettimeoffset();
@ -135,6 +202,7 @@ EXPORT_SYMBOL(getnstimeofday);
ktime_t ktime_get(void)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
unsigned int seq;
s64 secs, nsecs;
@ -146,13 +214,15 @@ ktime_t ktime_get(void)
nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
/* read clocksource: */
clock = timekeeper.clock;
cycle_now = clock->read(clock);
/* calculate the delta since the last update_wall_time: */
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
/* convert to nanoseconds: */
nsecs += cyc2ns(clock, cycle_delta);
nsecs += clocksource_cyc2ns(cycle_delta, clock->mult,
clock->shift);
} while (read_seqretry(&xtime_lock, seq));
/*
@ -174,6 +244,7 @@ EXPORT_SYMBOL_GPL(ktime_get);
void ktime_get_ts(struct timespec *ts)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
struct timespec tomono;
unsigned int seq;
s64 nsecs;
@ -186,13 +257,15 @@ void ktime_get_ts(struct timespec *ts)
tomono = wall_to_monotonic;
/* read clocksource: */
clock = timekeeper.clock;
cycle_now = clock->read(clock);
/* calculate the delta since the last update_wall_time: */
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
/* convert to nanoseconds: */
nsecs = cyc2ns(clock, cycle_delta);
nsecs = clocksource_cyc2ns(cycle_delta, clock->mult,
clock->shift);
} while (read_seqretry(&xtime_lock, seq));
@ -233,7 +306,7 @@ int do_settimeofday(struct timespec *tv)
write_seqlock_irqsave(&xtime_lock, flags);
clocksource_forward_now();
timekeeping_forward_now();
ts_delta.tv_sec = tv->tv_sec - xtime.tv_sec;
ts_delta.tv_nsec = tv->tv_nsec - xtime.tv_nsec;
@ -243,10 +316,10 @@ int do_settimeofday(struct timespec *tv)
update_xtime_cache(0);
clock->error = 0;
timekeeper.ntp_error = 0;
ntp_clear();
update_vsyscall(&xtime, clock);
update_vsyscall(&xtime, timekeeper.clock);
write_sequnlock_irqrestore(&xtime_lock, flags);
@ -269,10 +342,10 @@ static void change_clocksource(void)
new = clocksource_get_next();
if (!new || clock == new)
if (!new || timekeeper.clock == new)
return;
clocksource_forward_now();
timekeeping_forward_now();
if (new->enable && !new->enable(new))
return;
@ -284,9 +357,9 @@ static void change_clocksource(void)
*/
new->mult_orig = new->mult;
new->raw_time = clock->raw_time;
old = clock;
clock = new;
old = timekeeper.clock;
timekeeper_setup_internals(new);
/*
* Save mult_orig in mult so that the value can be restored
* regardless if ->enable() updates the value of mult or not.
@ -295,22 +368,10 @@ static void change_clocksource(void)
if (old->disable)
old->disable(old);
clock->cycle_last = clock->read(clock);
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 /* GENERIC_TIME */
static inline void clocksource_forward_now(void) { }
static inline void timekeeping_forward_now(void) { }
static inline void change_clocksource(void) { }
/**
@ -380,20 +441,23 @@ void getrawmonotonic(struct timespec *ts)
unsigned long seq;
s64 nsecs;
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
do {
seq = read_seqbegin(&xtime_lock);
/* read clocksource: */
clock = timekeeper.clock;
cycle_now = clock->read(clock);
/* calculate the delta since the last update_wall_time: */
cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
/* convert to nanoseconds: */
nsecs = ((s64)cycle_delta * clock->mult_orig) >> clock->shift;
nsecs = clocksource_cyc2ns(cycle_delta, clock->mult_orig,
clock->shift);
*ts = clock->raw_time;
*ts = raw_time;
} while (read_seqretry(&xtime_lock, seq));
@ -413,7 +477,7 @@ int timekeeping_valid_for_hres(void)
do {
seq = read_seqbegin(&xtime_lock);
ret = clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
ret = timekeeper.clock->flags & CLOCK_SOURCE_VALID_FOR_HRES;
} while (read_seqretry(&xtime_lock, seq));
@ -439,6 +503,7 @@ unsigned long __attribute__((weak)) read_persistent_clock(void)
*/
void __init timekeeping_init(void)
{
struct clocksource *clock;
unsigned long flags;
unsigned long sec = read_persistent_clock();
@ -451,11 +516,13 @@ void __init timekeeping_init(void)
clock->enable(clock);
/* set mult_orig on enable */
clock->mult_orig = clock->mult;
clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
clock->cycle_last = clock->read(clock);
timekeeper_setup_internals(clock);
xtime.tv_sec = sec;
xtime.tv_nsec = 0;
raw_time.tv_sec = 0;
raw_time.tv_nsec = 0;
set_normalized_timespec(&wall_to_monotonic,
-xtime.tv_sec, -xtime.tv_nsec);
update_xtime_cache(0);
@ -492,8 +559,8 @@ static int timekeeping_resume(struct sys_device *dev)
}
update_xtime_cache(0);
/* re-base the last cycle value */
clock->cycle_last = clock->read(clock);
clock->error = 0;
timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);
timekeeper.ntp_error = 0;
timekeeping_suspended = 0;
write_sequnlock_irqrestore(&xtime_lock, flags);
@ -514,7 +581,7 @@ static int timekeeping_suspend(struct sys_device *dev, pm_message_t state)
timekeeping_suspend_time = read_persistent_clock();
write_seqlock_irqsave(&xtime_lock, flags);
clocksource_forward_now();
timekeeping_forward_now();
timekeeping_suspended = 1;
write_sequnlock_irqrestore(&xtime_lock, flags);
@ -549,7 +616,7 @@ 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,
static __always_inline int timekeeping_bigadjust(s64 error, s64 *interval,
s64 *offset)
{
s64 tick_error, i;
@ -565,7 +632,7 @@ static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
* 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 = timekeeper.ntp_error >> (NTP_SCALE_SHIFT + 22 - 2 * SHIFT_HZ);
error2 = abs(error2);
for (look_ahead = 0; error2 > 0; look_ahead++)
error2 >>= 2;
@ -574,8 +641,9 @@ static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
* 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;
tick_error = tick_length >>
(NTP_SCALE_SHIFT - timekeeper.clock->shift + 1);
tick_error -= timekeeper.xtime_interval >> 1;
error = ((error - tick_error) >> look_ahead) + tick_error;
/* Finally calculate the adjustment shift value. */
@ -600,18 +668,19 @@ static __always_inline int clocksource_bigadjust(s64 error, s64 *interval,
* 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)
static void timekeeping_adjust(s64 offset)
{
s64 error, interval = clock->cycle_interval;
s64 error, interval = timekeeper.cycle_interval;
int adj;
error = clock->error >> (NTP_SCALE_SHIFT - clock->shift - 1);
error = timekeeper.ntp_error >>
(NTP_SCALE_SHIFT - timekeeper.clock->shift - 1);
if (error > interval) {
error >>= 2;
if (likely(error <= interval))
adj = 1;
else
adj = clocksource_bigadjust(error, &interval, &offset);
adj = timekeeping_bigadjust(error, &interval, &offset);
} else if (error < -interval) {
error >>= 2;
if (likely(error >= -interval)) {
@ -619,15 +688,15 @@ static void clocksource_adjust(s64 offset)
interval = -interval;
offset = -offset;
} else
adj = clocksource_bigadjust(error, &interval, &offset);
adj = timekeeping_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);
timekeeper.clock->mult += adj;
timekeeper.xtime_interval += interval;
timekeeper.xtime_nsec -= offset;
timekeeper.ntp_error -= (interval - offset) <<
(NTP_SCALE_SHIFT - timekeeper.clock->shift);
}
/**
@ -637,53 +706,59 @@ static void clocksource_adjust(s64 offset)
*/
void update_wall_time(void)
{
struct clocksource *clock;
cycle_t offset;
s64 nsecs;
/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
return;
clock = timekeeper.clock;
#ifdef CONFIG_GENERIC_TIME
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#else
offset = clock->cycle_interval;
offset = timekeeper.cycle_interval;
#endif
clock->xtime_nsec = (s64)xtime.tv_nsec << clock->shift;
timekeeper.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 */
offset -= clock->cycle_interval;
clock->cycle_last += clock->cycle_interval;
while (offset >= timekeeper.cycle_interval) {
u64 nsecps = (u64)NSEC_PER_SEC << clock->shift;
clock->xtime_nsec += clock->xtime_interval;
if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
/* accumulate one interval */
offset -= timekeeper.cycle_interval;
clock->cycle_last += timekeeper.cycle_interval;
timekeeper.xtime_nsec += timekeeper.xtime_interval;
if (timekeeper.xtime_nsec >= nsecps) {
timekeeper.xtime_nsec -= nsecps;
xtime.tv_sec++;
second_overflow();
}
clock->raw_time.tv_nsec += clock->raw_interval;
if (clock->raw_time.tv_nsec >= NSEC_PER_SEC) {
clock->raw_time.tv_nsec -= NSEC_PER_SEC;
clock->raw_time.tv_sec++;
raw_time.tv_nsec += timekeeper.raw_interval;
if (raw_time.tv_nsec >= NSEC_PER_SEC) {
raw_time.tv_nsec -= NSEC_PER_SEC;
raw_time.tv_sec++;
}
/* accumulate error between NTP and clock interval */
clock->error += tick_length;
clock->error -= clock->xtime_interval << (NTP_SCALE_SHIFT - clock->shift);
timekeeper.ntp_error += tick_length;
timekeeper.ntp_error -= timekeeper.xtime_interval <<
(NTP_SCALE_SHIFT - clock->shift);
}
/* correct the clock when NTP error is too big */
clocksource_adjust(offset);
timekeeping_adjust(offset);
/*
* Since in the loop above, we accumulate any amount of time
* in xtime_nsec over a second into xtime.tv_sec, its possible for
* xtime_nsec to be fairly small after the loop. Further, if we're
* slightly speeding the clocksource up in clocksource_adjust(),
* slightly speeding the clocksource up in timekeeping_adjust(),
* its possible the required corrective factor to xtime_nsec could
* cause it to underflow.
*
@ -695,24 +770,26 @@ void update_wall_time(void)
* We'll correct this error next time through this function, when
* xtime_nsec is not as small.
*/
if (unlikely((s64)clock->xtime_nsec < 0)) {
s64 neg = -(s64)clock->xtime_nsec;
clock->xtime_nsec = 0;
clock->error += neg << (NTP_SCALE_SHIFT - clock->shift);
if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
s64 neg = -(s64)timekeeper.xtime_nsec;
timekeeper.xtime_nsec = 0;
timekeeper.ntp_error += neg << (NTP_SCALE_SHIFT - clock->shift);
}
/* store full nanoseconds into xtime after rounding it up and
* add the remainder to the error difference.
*/
xtime.tv_nsec = ((s64)clock->xtime_nsec >> clock->shift) + 1;
clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift);
xtime.tv_nsec = ((s64)timekeeper.xtime_nsec >> clock->shift) + 1;
timekeeper.xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
timekeeper.ntp_error += timekeeper.xtime_nsec <<
(NTP_SCALE_SHIFT - clock->shift);
update_xtime_cache(cyc2ns(clock, offset));
nsecs = clocksource_cyc2ns(offset, clock->mult, clock->shift);
update_xtime_cache(nsecs);
/* check to see if there is a new clocksource to use */
change_clocksource();
update_vsyscall(&xtime, clock);
update_vsyscall(&xtime, timekeeper.clock);
}
/**