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Commit e13a2e61 authored by John Stultz's avatar John Stultz Committed by Thomas Gleixner
Browse files

ntp: correct inconsistent interval/tick_length usage 



clocksource initialization and error accumulation.  This corrects a 280ppm
drift seen on some systems using acpi_pm, and affects other clocksources as
well (likely to a lesser degree).

Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 25f66630

include/linux/timex.h

+8 −1
Original line number Diff line number Diff line
@@ -232,7 +232,14 @@ static inline int ntp_synced(void) 
#else

#define NTP_INTERVAL_FREQ  (HZ)

#endif

#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)



#define CLOCK_TICK_OVERFLOW	(LATCH * HZ - CLOCK_TICK_RATE)

#define CLOCK_TICK_ADJUST	(((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \

					(s64)CLOCK_TICK_RATE)



/* Because using NSEC_PER_SEC would be too easy */

#define NTP_INTERVAL_LENGTH ((((s64)TICK_USEC * NSEC_PER_USEC * USER_HZ) + \

			      CLOCK_TICK_ADJUST) / NTP_INTERVAL_FREQ)



/* Returns how long ticks are at present, in ns / 2^(SHIFT_SCALE-10). */

extern u64 current_tick_length(void);

kernel/time/ntp.c

+0 −4
Original line number Diff line number Diff line
@@ -43,10 +43,6 @@ long time_freq; /* frequency offset (scaled ppm)*/ 
static long time_reftime;		/* time at last adjustment (s)	*/

long time_adjust;



#define CLOCK_TICK_OVERFLOW	(LATCH * HZ - CLOCK_TICK_RATE)

#define CLOCK_TICK_ADJUST	(((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \

					(s64)CLOCK_TICK_RATE)



static void ntp_update_frequency(void)

{

	u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)