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authorMiroslav Lichvar <mlichvar@redhat.com>2018-03-09 21:42:48 +0300
committerIngo Molnar <mingo@kernel.org>2018-03-10 11:12:41 +0300
commit78b98e3c5a66d569a53b8f57b6a698f912794a43 (patch)
treed4306491e8e4ce50d1fd8decfac0e5c9e14fc8cd /include/linux/timekeeper_internal.h
parentc2cda2a5bda9f1369c9d1ab54a20571c13cf2743 (diff)
downloadlinux-78b98e3c5a66d569a53b8f57b6a698f912794a43.tar.xz
timekeeping/ntp: Determine the multiplier directly from NTP tick length
When the length of the NTP tick changes significantly, e.g. when an NTP/PTP application is correcting the initial offset of the clock, a large value may accumulate in the NTP error before the multiplier converges to the correct value. It may then take a very long time (hours or even days) before the error is corrected. This causes the clock to have an unstable frequency offset, which has a negative impact on the stability of synchronization with precise time sources (e.g. NTP/PTP using hardware timestamping or the PTP KVM clock). Use division to determine the correct multiplier directly from the NTP tick length and replace the iterative approach. This removes the last major source of the NTP error. The only remaining source is now limited resolution of the multiplier, which is corrected by adding 1 to the multiplier when the system clock is behind the NTP time. Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com> Signed-off-by: John Stultz <john.stultz@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Stephen Boyd <stephen.boyd@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1520620971-9567-3-git-send-email-john.stultz@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/timekeeper_internal.h')
-rw-r--r--include/linux/timekeeper_internal.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index d315c3d6725c..7acb953298a7 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -117,6 +117,8 @@ struct timekeeper {
s64 ntp_error;
u32 ntp_error_shift;
u32 ntp_err_mult;
+ /* Flag used to avoid updating NTP twice with same second */
+ u32 skip_second_overflow;
#ifdef CONFIG_DEBUG_TIMEKEEPING
long last_warning;
/*