[ntp:questions] Lep seconds

David L. Mills mills at udel.edu
Tue Jan 8 16:29:39 UTC 2008


I'm a little anxious about the non-kernel step. My original kernel code 
for the Alpha carefully crafted monotonicity. In particular, the clock 
would not be stepped back unless more than two seconds. This was done 
purposely so that a leap back of only one second would simply stop the 
clock or allow it to creep forward on nanosecond per call until the 
second was amortized. I doubt very much that this design is universal.

Martin Burnicki wrote:

> Dave,
> David L. Mills wrote:
>>In the current development code when the kernel does not implement a
>>leap function, the clock is stepped "near" the leap epoch. Here, "near
>>means within one second early or late and yes, this can be considered
>>pinball behavior. This should probably be an option.
> I've already seen that change, and I'm going to do some tests with the new
> function. 
> Shortly before the latest leap second I had added some code to handle the
> leap second correctly under Windows. This is in the Windows-only portion of
> the code and I'm afraid this interferes now with your latest changes.
> BTW, as already mentioned in one of my other posts: wouldn't it be a good
> idea to generate a log entry which tells from which upstream source a leap
> second announcement has been received? 
> We have seen several times in the past that ntpd thought it had to introduce
> a leap second because some bad guy had passed a faulty leap second
> announcement. Knowing the source of the announcement would help to identify
> the original source of the announcement.
> Martin

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