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: John Stultz <[email protected]> Cc: Roman Zippel <[email protected]> Cc: Steven Rostedt <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]>
iegor · Feb 10, 2008 · e13a2e6 · e13a2e6
1 parent 25f6663
commit e13a2e6
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Showing 2 changed files with 8 additions and 5 deletions.
diff --git a/include/linux/timex.h b/include/linux/timex.h
@@ -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);

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
@@ -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)