Re: [RFC][PATCH 2/2] Reduced NTP rework (part 2)
From: Ulrich Windl
Date: Tue Oct 04 2005 - 03:01:37 EST
On 27 Sep 2005 at 18:37, Roman Zippel wrote:
> On Thu, 22 Sep 2005, john stultz wrote:
> > +
> > + /* calculate the total continuous ppm adjustment */
> > + total_sppm = time_freq; /* already shifted by SHIFT_USEC */
> > + total_sppm += offset_adj_ppm << SHIFT_USEC;
> > + total_sppm += tick_adj_ppm << SHIFT_USEC;
> > + total_sppm += singleshot_adj_ppm << SHIFT_USEC;
> > }
> I'm not sure, why you still need this.
> As I already said, I don't think you need to change the kernel NTP model.
> This means in particular that the NTP time is still incremented in fixed
> intervals (although it's not necessary to do it at HZ frequency).
> I showed you how to do most of the calculation, so I'm a little confused,
> why the above is still used.
As playing with "tick" is considered obsolete by the NTP people, frequency errors
up to 500 PPM are corrected by the NTP kernel code. Thus, to provide continuous
time, you might be interested in adjusting tick interpolation (i.e. _use_ the
adjusted value whenever the clock is read).
> In general I would prefer to see the introduction of the timesource
> abstraction, which will first replace the arch callbacks do_gettimeofday/
> bye, Roman
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