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Commit 23ce7211 authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Thomas Gleixner
Browse files

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: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134809.871899606@de.ibm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 155ec602

kernel/time/timekeeping.c

+19 −14
Original line number Original line Diff line number Diff line
@@ -23,6 +23,8 @@ 
struct timekeeper {

struct timekeeper {

	/* Current clocksource used for timekeeping. */

	/* Current clocksource used for timekeeping. */

	struct clocksource *clock;

	struct clocksource *clock;

	/* The shift value of the current clocksource. */

	int	shift;





	/* Number of clock cycles in one NTP interval. */

	/* Number of clock cycles in one NTP interval. */

	cycle_t cycle_interval;

	cycle_t cycle_interval;
@@ -36,6 +38,9 @@ struct timekeeper { 
	/* Difference between accumulated time and NTP time in ntp

	/* Difference between accumulated time and NTP time in ntp

	 * shifted nano seconds. */

	 * shifted nano seconds. */

	s64	ntp_error;

	s64	ntp_error;

	/* Shift conversion between clock shifted nano seconds and

	 * ntp shifted nano seconds. */

	int	ntp_error_shift;

};

};





struct timekeeper timekeeper;

struct timekeeper timekeeper;
@@ -75,8 +80,10 @@ static void timekeeper_setup_internals(struct clocksource *clock) 
		((u64) interval * clock->mult_orig) >> clock->shift;

		((u64) interval * clock->mult_orig) >> clock->shift;





	timekeeper.xtime_nsec = 0;

	timekeeper.xtime_nsec = 0;

	timekeeper.shift = clock->shift;





	timekeeper.ntp_error = 0;

	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

	 * Now calculate the error in (1 << look_ahead) ticks, but first

	 * remove the single look ahead already included in the error.

	 * remove the single look ahead already included in the error.

	 */

	 */

	tick_error = tick_length >>

	tick_error = tick_length >> (timekeeper.ntp_error_shift + 1);

			(NTP_SCALE_SHIFT - timekeeper.clock->shift + 1);

	tick_error -= timekeeper.xtime_interval >> 1;

	tick_error -= timekeeper.xtime_interval >> 1;

	error = ((error - tick_error) >> look_ahead) + tick_error;

	error = ((error - tick_error) >> look_ahead) + tick_error;
@@ -673,8 +679,7 @@ static void timekeeping_adjust(s64 offset) 
	s64 error, interval = timekeeper.cycle_interval;

	s64 error, interval = timekeeper.cycle_interval;

	int adj;

	int adj;





	error = timekeeper.ntp_error >>

	error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);

		(NTP_SCALE_SHIFT - timekeeper.clock->shift - 1);

	if (error > interval) {

	if (error > interval) {

		error >>= 2;

		error >>= 2;

		if (likely(error <= interval))

		if (likely(error <= interval))
@@ -696,7 +701,7 @@ static void timekeeping_adjust(s64 offset) 
	timekeeper.xtime_interval += interval;

	timekeeper.xtime_interval += interval;

	timekeeper.xtime_nsec -= offset;

	timekeeper.xtime_nsec -= offset;

	timekeeper.ntp_error -= (interval - 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;

	struct clocksource *clock;

	cycle_t offset;

	cycle_t offset;

	s64 nsecs;

	u64 nsecs;





	/* Make sure we're fully resumed: */

	/* Make sure we're fully resumed: */

	if (unlikely(timekeeping_suspended))

	if (unlikely(timekeeping_suspended))
@@ -720,13 +725,13 @@ void update_wall_time(void) 
#else

#else

	offset = timekeeper.cycle_interval;

	offset = timekeeper.cycle_interval;

#endif

#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

	/* normally this loop will run just once, however in the

	 * case of lost or late ticks, it will accumulate correctly.

	 * case of lost or late ticks, it will accumulate correctly.

	 */

	 */

	while (offset >= timekeeper.cycle_interval) {

	while (offset >= timekeeper.cycle_interval) {

		u64 nsecps = (u64)NSEC_PER_SEC << clock->shift;

		u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift;





		/* accumulate one interval */

		/* accumulate one interval */

		offset -= timekeeper.cycle_interval;

		offset -= timekeeper.cycle_interval;
@@ -748,7 +753,7 @@ void update_wall_time(void) 
		/* accumulate error between NTP and clock interval */

		/* accumulate error between NTP and clock interval */

		timekeeper.ntp_error += tick_length;

		timekeeper.ntp_error += tick_length;

		timekeeper.ntp_error -= timekeeper.xtime_interval <<

		timekeeper.ntp_error -= timekeeper.xtime_interval <<

					(NTP_SCALE_SHIFT - clock->shift);

					timekeeper.ntp_error_shift;

	}

	}





	/* correct the clock when NTP error is too big */

	/* 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)) {

	if (unlikely((s64)timekeeper.xtime_nsec < 0)) {

		s64 neg = -(s64)timekeeper.xtime_nsec;

		s64 neg = -(s64)timekeeper.xtime_nsec;

		timekeeper.xtime_nsec = 0;

		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

	/* store full nanoseconds into xtime after rounding it up and

	 * add the remainder to the error difference.

	 * add the remainder to the error difference.

	 */

	 */

	xtime.tv_nsec = ((s64)timekeeper.xtime_nsec >> clock->shift) + 1;

	xtime.tv_nsec =	((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;

	timekeeper.xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;

	timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.shift;

	timekeeper.ntp_error +=	timekeeper.xtime_nsec <<

	timekeeper.ntp_error +=	timekeeper.xtime_nsec <<

				(NTP_SCALE_SHIFT - clock->shift);

				timekeeper.ntp_error_shift;





	nsecs = clocksource_cyc2ns(offset, clock->mult, clock->shift);

	nsecs = clocksource_cyc2ns(offset, clock->mult, clock->shift);

	update_xtime_cache(nsecs);

	update_xtime_cache(nsecs);