[LEAPSECS] A standard for leap second smearing

[Tony Finch]

Steve Summit <scs+ls at eskimo.com> wrote:
>
> I think there are aspects of the implementation of any smearing
> that are maybe being glossed over.  I think it's important to
> distinguish pretty carefully between three distinct "clocks",
> or views of time:
> 1. The time exchanged between machines by a protocol such as NTP.
> 2. The time kept by an OS kernel (which is typically based on
>    oscillators that are disciplined by (1).)
> 3. The time returned to user-mode programs by system calls such
>    as gettimeofday.
>
> There seems to be a presumption in several comments in this
> thread that (3) is necessarily identical to (2), but I think
> that's a bad idea.

You are completely right up to here, but it's probably unwise to dictate
how (which part(s) of the system) leap second smear is implemented.

The advantage of a standard is that you could just tell someone your time
with a flag indicating whether it is smeared or not, and they can fairly
straightforwardly translate (provided they also know when the leap seconds
are). If there isn't a standard smear you need quite a lot more parameters
to describe its shape.

Of course if you take this approach then you have the problem of how to
extend protocols and APIs to communicate the smear bit.

Tony.
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