From e13a2e61dd5152f5499d2003470acf9c838eab84 Mon Sep 17 00:00:00 2001
From: john stultz <johnstul@us.ibm.com>
Date: Sun, 10 Feb 2008 10:48:03 +0100
Subject: [PATCH] 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 <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/timex.h | 9 ++++++++-
kernel/time/ntp.c | 4 ----
2 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/include/linux/timex.h b/include/linux/timex.h
index 8ea3e71ba7fa..c3f374786a43 100644
--- 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
index e64efaf957e8..c88b5910e7ab 100644
--- 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)
--
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