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timekeeping: Add xtime_shift and ntp_error_shift to struct timekeeper 

The xtime_nsec value in the timekeeper structure is shifted by a few
bits to improve precision. This happens to be the same value as the
clock->shift. To improve readability add xtime_shift to the timekeeper
and use it instead of the clock->shift. Likewise add ntp_error_shift
and replace all (NTP_SCALE_SHIFT - clock->shift) expressions.

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: <20090814134809.871899606@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Martin Schwidefsky 2009-08-14 15:47:27 +02:00 committed by Thomas Gleixner
parent 155ec60226
commit 23ce72117c
1 changed files with 19 additions and 14 deletions
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33
kernel/time/timekeeping.c
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@ -23,6 +23,8 @@
struct timekeeper {
/* Current clocksource used for timekeeping. */
struct clocksource *clock;
/* The shift value of the current clocksource. */
int shift;
/* Number of clock cycles in one NTP interval. */
cycle_t cycle_interval;
@ -36,6 +38,9 @@ struct timekeeper {
/* Difference between accumulated time and NTP time in ntp
* shifted nano seconds. */
s64 ntp_error;
/* Shift conversion between clock shifted nano seconds and
* ntp shifted nano seconds. */
int ntp_error_shift;
};
struct timekeeper timekeeper;
@ -75,8 +80,10 @@ static void timekeeper_setup_internals(struct clocksource *clock)
((u64) interval * clock->mult_orig) >> clock->shift;
timekeeper.xtime_nsec = 0;
timekeeper.shift = clock->shift;
timekeeper.ntp_error = 0;
timekeeper.ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;
}
/*
@ -641,8 +648,7 @@ static __always_inline int timekeeping_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 - timekeeper.clock->shift + 1);
tick_error = tick_length >> (timekeeper.ntp_error_shift + 1);
tick_error -= timekeeper.xtime_interval >> 1;
error = ((error - tick_error) >> look_ahead) + tick_error;
@ -673,8 +679,7 @@ static void timekeeping_adjust(s64 offset)
s64 error, interval = timekeeper.cycle_interval;
int adj;
error = timekeeper.ntp_error >>
(NTP_SCALE_SHIFT - timekeeper.clock->shift - 1);
error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);
if (error > interval) {
error >>= 2;
if (likely(error <= interval))
@ -696,7 +701,7 @@ static void timekeeping_adjust(s64 offset)
timekeeper.xtime_interval += interval;
timekeeper.xtime_nsec -= offset;
timekeeper.ntp_error -= (interval - offset) <<
(NTP_SCALE_SHIFT - timekeeper.clock->shift);
timekeeper.ntp_error_shift;
}
/**
@ -708,7 +713,7 @@ void update_wall_time(void)
{
struct clocksource *clock;
cycle_t offset;
s64 nsecs;
u64 nsecs;
/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
@ -720,13 +725,13 @@ void update_wall_time(void)
#else
offset = timekeeper.cycle_interval;
#endif
timekeeper.xtime_nsec = (s64)xtime.tv_nsec << clock->shift;
timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;
/* normally this loop will run just once, however in the
* case of lost or late ticks, it will accumulate correctly.
*/
while (offset >= timekeeper.cycle_interval) {
u64 nsecps = (u64)NSEC_PER_SEC << clock->shift;
u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift;
/* accumulate one interval */
offset -= timekeeper.cycle_interval;
@ -748,7 +753,7 @@ void update_wall_time(void)
/* accumulate error between NTP and clock interval */
timekeeper.ntp_error += tick_length;
timekeeper.ntp_error -= timekeeper.xtime_interval <<
(NTP_SCALE_SHIFT - clock->shift);
timekeeper.ntp_error_shift;
}
/* correct the clock when NTP error is too big */
@ -773,16 +778,16 @@ void update_wall_time(void)
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);
timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
}
/* store full nanoseconds into xtime after rounding it up and
* add the remainder to the error difference.
*/
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);
xtime.tv_nsec = ((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.shift;
timekeeper.ntp_error += timekeeper.xtime_nsec <<
timekeeper.ntp_error_shift;
nsecs = clocksource_cyc2ns(offset, clock->mult, clock->shift);
update_xtime_cache(nsecs);