Re: [RFC][PATCH] new timeofday core subsystem (v.A0)

Ulrich Windl
2004-09-16T07:14:24Z

On 15 Sep 2004 at 11:48, john stultz wrote:

> NTP adjustments need to be applied smoothly and consistently as time
> progresses. Adjustment to the NTP parameters occur at do_adjtimex and at

Actually I think (constant) NTP adjustments need to be applied any time. That's
why I even tried to correct the TSC interpolation between ticks (If you visit the
PPSkit patch, that's the "nanoscale" thing). The "constant adjustment values" are
updated regularly also (per tick, per second, per NTP update).

The basic thought was: If the time between two ticks is not 1/HZ the TSC
interpolation (that is calibrated against the timer ticks) also will not
interpolate between 1/HZ ticks. I assumed the TSC interpolations is wrong by the
same percentage the timer interrupts are. Thus I tried to reversely apply the
frequency error learnt through NTP even to the TSC interpolation (in addition to
the time increments every tick). My code however has the problem that I ran out of
significant bits during several muliplies and divides, while supporting that
maximum imaginable frequency range for TSC. Even with the best oscillator, it
won't reach single nanosecond precision as I don't have enough bits for them.

Regards,
Ulrich