time jumps forward/backwards

[Benjamin Gamsa]

Benjamin Gamsa wrote:
> Benjamin Gamsa wrote:
>> Paul Mackerras wrote:
>>> Ben Gamsa writes:
>>>
>>>> It appears to be the case that when the time on the system is around 
>>>> the epoch (1970), that time will occasionally jump forward and then 
>>>> backward by about 17592 seconds.  When it jumps forward, it always 
>>>> jumps back a few milliseconds later.  However, it's not always easy 
>>>> to catch these occurrences.  The delta is more specifically about 
>>>> 17592186059 usec, give or take a few 10s of microseconds (most of 
>>>> the time), despite the fact that the user-level program I have that 
>>>> is testing it only checks every 10 milliseconds.
>>>
>>> I don't think the time code in the kernel is designed to handle
>>> negative values, i.e., times before the epoch.  If you want it to do
>>> that you'll have to check places like arch/powerpc/kernel/time.c,
>>> kernel/time/timekeeping.c, arch/powerpc/include/asm/time.h, etc., and
>>> make sure that it uses signed types where necessary and that the
>>> arithmetic is correct.
>>>
>>
>> The time never goes negative.  It starts off at the epoch and moves 
>> forward, but sometimes it jumps forward by 17952 seconds, and then 
>> immediately jumps back.  But it never goes negative (or prior to 1970).
>>
> 
> One important thing I forgot to add is that ntpd is running on this 
> system, but the ntp servers are not available.  I suspect the problem 
> may be related to ntpd, even though I've seen the time jump even when I 
> had ntpd stopped within gdb.  I've not yet been able to confirm if the 
> problem still occurs when ntpd is never even started, although I will be 
> testing that soon (the tests often require many hours to establish if 
> there are no jumps).

For what it's worth, the problem occurs even when ntp is not even started.

	ben