[LEAPSECS] Bloomberg announced its smear

Martin Burnicki martin.burnicki at burnicki.net
Thu Sep 29 03:34:27 EDT 2016


Harlan Stenn wrote:
> Martin,
> Cosine smearing might need to be a choice.  It's harder to track the
> leap second if you get a sample during when both phase and frequency are
> changing.

Indeed it could be just a choice, but I think it's a very good one.

Leap smearing in general is just a hack to workaround the limitations in
POSIX time which can severely affect client applications, e.g. problems
with databases when the client kernel just steps the time back by 1 s
and thus duplicate time stamps occur.

I agree that it would be better to have a proper solution for this
problem, and I believe that Dave Mills' idea to stop the time during an
inserted leap second, and increment it only by 1 LSB whenever an
application queries the time would solve most of the problems we see.

However, quite some time ago one of the Linux kernel developers said
it's just much more complex (and thus more expensive, with regard to
execution time) to implement this in the kernel.

If all servers used by a client do the smearing in the same way then the
NTP clients will will happily move across the leap second.

We (Meinberg) have quite a number of customers who asked for a solution
for problems with leap seconds, and this works very well if their
corporate NTP servers (e.g. Meinberg LANTIME NTP servers) smear the leap
second. Of course this is only an option if the customers applications
can tolerate that the time is temporarily off UTC, but this is often the
least evil.


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