Re: cvs commit: src/sys/kern

[Paul Herman <pherman@xxxxxxxxxxxxxxx>]

On Sun, 5 Dec 2004, Matthew Dillon wrote:

> :On an additional note -- and I suppose anything at this point is
> :nitpicking -- would it be worthwhile to preserve the original
> :drift?  Take an extreme example with the current code with a
> :machine booted at 12:00:00 when the clock adds a second every 30
> :seconds compared to a reference clock:
>
>    No, because the 'drift' isn't necessarily just a drift.  When you
>    boot a machine, for example, ntp will throw in a short-lived speed
>    up or slow down to get the clock synchronized, but that doesn't
>    necessarily mean that the clock is actually running slow or fast.

Agreed.  "drift" is probably the wrong word.

The example I gave was for the case of a fast running clock that 
does have drift.  However, even in the example where the clock just 
needs to be synchronized once and only once, the case is still the 
same:  the boottime isn't exactly what it says.  How much is it 
off?  The amount that was added/subtracted to basetime.  That is 
what basetime is for.

I'll just add that because uptime (the w(1) uptime, that is) must 
be monotonicaly increasing, the difference between boottime and 
basetime *must* be preserved.  Otherwise, w(1) uptime may jump back 
a bit if (basetime - boottime) > 0 before settimeofday() is called.

>    When the time is stepped, this sort of correct has to be reset as
>    well.  Also, ntpd expects it, and things would go haywire if it
>    weren't reset.

I'm not suggesting touching basetime, just boottime.

It may seem pedantic, but it is actually an case *for* the 
distiction between boottime & basetime; the reason for basetime's 
existence.  In essense, boottime (relative to basetime, of course) 
is the mechanism to correct gd_time_seconds (be it drift correction 
just one time corrected.)

-Paul.