Re: [chrony-dev] PPSAPI: kernel consumer

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Tue, Feb 09, 2010 at 02:04:39AM +0300, Alexander Gordeev wrote:
> I still don't get the philosophy/complexity problems. BTW I don't have
> any code to add to chrony.
> 
> I hope other chrony developers will still consider adding kernel
> consumer support a valuable feature or maybe just add it to allow the
> user to choose the possibilities.

I wouldn't mind adding support for it if it was just setting a flag,
like in ntpd which in normal operation doesn't read anything from
kernel back. In chrony the frequency and phase adjustments would need
to go through several layers in opposite direction, it doesn't seem to
be easy to implement.

I'm still not sure what would be the benefit.

> > Running at a shorter poll interval may make chrony
> > more responsive and not decrease the accuracy. Try it.

I wouldn't recommend using poll below 2. It's likely to be unstable
due to the kernel interface deficiencies. The most extreme setting
you might want to try is "poll 1 filter 1 dpoll -1".

BTW, I was thinking about the adjtimex problem with detecting when
were the values actually updated and it might be possible to find the
edge by setting adjtime to slew 1 us and then run readonly adjtime in
a loop every millisecond or so until it reports that there is no
offset left.

This could make the measurements done while slewing much more
accurate. Not sure how reliable it would be, I'll run some tests.

-- 
Miroslav Lichvar

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