Re: [PATCH] time, Fix setting of hardware clock in NTP code

From: John Stultz
Date: Fri Feb 08 2013 - 18:12:15 EST

On 02/08/2013 02:59 PM, Prarit Bhargava wrote:
At init time, if the system time is "warped" forward in warp_clock()
it will differ from the hardware clock by sys_tz.tz_minuteswest. This time
difference is not taken into account when ntp updates the hardware clock,
and this causes the system time to jump forward by this offset every reboot.

The kernel must take this offset into account when writing the system time
to the hardware clock in the ntp code. This patch adds
persistent_clock_is_local which indicates that an offset has been applied
in warp_clock() and accounts for the "warp" before writing the hardware

x86 does not have this problem as rtc writes are software limited to a
+/-15 minute window relative to the current rtc time. Other arches, such
as powerpc, however do a full synchronization of the system time to the
rtc and will see this problem.

Ok, I've got this queued in my tree. What sort of testing did you do with it?

I want to make sure we don't run into any bad interactions with the existing 15min cap on x86.


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