diff options
| author | Roman Zippel <zippel@linux-m68k.org> | 2008-09-22 23:42:44 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2008-09-24 17:33:13 +0200 |
| commit | d40e944c25fb4642adb2a4c580a48218a9f3f824 (patch) | |
| tree | 9be7107440704a84d17f9dde12991915931c5279 | |
| parent | timekeeping: fix rounding problem during clock update (diff) | |
| download | linux-d40e944c25fb4642adb2a4c580a48218a9f3f824.tar.xz linux-d40e944c25fb4642adb2a4c580a48218a9f3f824.zip | |
ntp: improve adjtimex frequency rounding
Change PPM_SCALE_INV_SHIFT so that it doesn't throw away any input bits
(19 is the amount of the factor 2 in PPM_SCALE), the output frequency
can then be calculated back to its input value, as the inverse divide
produce a slightly larger value, which is then correctly rounded by the
final shift.
Reported-by: Martin Ziegler <ziegler@uni-freiburg.de>
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Cc: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| -rw-r--r-- | include/linux/timex.h | 2 | ||||
| -rw-r--r-- | kernel/time/ntp.c | 5 |
2 files changed, 3 insertions, 4 deletions
diff --git a/include/linux/timex.h b/include/linux/timex.h index c00bcdd3ae42..9007313b5b71 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -82,7 +82,7 @@ */ #define SHIFT_USEC 16 /* frequency offset scale (shift) */ #define PPM_SCALE (NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC)) -#define PPM_SCALE_INV_SHIFT 20 +#define PPM_SCALE_INV_SHIFT 19 #define PPM_SCALE_INV ((1ll << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \ PPM_SCALE + 1) diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c index 450a45cb01c1..ddb0465a6baa 100644 --- a/kernel/time/ntp.c +++ b/kernel/time/ntp.c @@ -406,9 +406,8 @@ adj_done: if (time_status & (STA_UNSYNC|STA_CLOCKERR)) result = TIME_ERROR; - txc->freq = shift_right((s32)(time_freq >> PPM_SCALE_INV_SHIFT) * - (s64)PPM_SCALE_INV, - NTP_SCALE_SHIFT); + txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) * + (s64)PPM_SCALE_INV, NTP_SCALE_SHIFT); txc->maxerror = time_maxerror; txc->esterror = time_esterror; txc->status = time_status; |