[LinuxPPS] ntpd synchronization issues

[Hal V. Engel]

On Sunday 08 August 2010 09:55:08 am Felix Joussein wrote:
>   Hi Udo,
> What kernel version?
> 
> Current Stable (2.6.34)
> 
> What ntpd version?
> 
> The source, which is shipped with Ubuntu 10.04 which is 4.2.4p6.
> I build the source using: --enable-all-clocks --enable-ATOM
> --enable-parse-clocks --enable-accurate-adjtime --with-crypto
> 
> What refclock?
> 
> here's my ntp.conf:
> 
> # refclocks
> server 217.19.37.20 iburst minpoll 4 maxpoll 4 prefer
> server 217.19.37.26 iburst minpoll 4 maxpoll 4 prefer
> server 217.19.37.27 iburst minpoll 4 maxpoll 4 prefer
> 
> # PPS0
> server 127.127.22.0 iburst minpoll 4 maxpoll 4 prefer
> fudge  127.127.22.0 stratum 0 refid ATOM flag3 1
> 
> # PPS1
> server 127.127.22.1 iburst minpoll 4 maxpoll 4 prefer
> fudge  127.127.22.1 stratum 0 refid ATOM flag3 1
> 
> driftfile /var/lib/ntp/ntp.drift
> keysdir /etc/ntp
> crypto randfile /var/lib/ntp/.rnd
> crypto pw leapsecreet
> 
> 
> Any patches for kernel or ntpd?
> 
> Kernel: No
> ntpd: probably the Ubuntu patches
> 
> 
> But: I have had the same problem over the last year with kernel versions
> prior to 2.6.34 and ntpd source from ntpd.org
> So far I used this hardware:  Intel Atom N330, N270, N510, IC2, AMD X2,
> AMD Geode, VIA Eden
> 
> regards,
> 
> Felix

I am running AMD X2 hardware with an ASUS motherboard.  My system would sync 
the time fairly quickly with kernels before 2.6.28 then it started syncing 
very slowly.  Some patches to the kernel where posted here that fixed this 
problem and these became part of the main line kernel starting with 2.6.30 (I 
think).  I am now running un-patched gentoo-sources 2.6.34 which I upgrade 
from 2.6.28 and it syncs quickly and is down below 5 us offsets in perhaps 15 
minutes give or take.

The 2.6.34 kernel did introduce another timekeeping related issue for me 
however.  Starting with 2.6.32 the kernel was changed so that it requires a 
new kernel module to do hardware monitoring on some motherboards including 
mine.  Because of this I should now be using the ATK0110 module to get 
hardware readings using the ACPI interface (rather than lm_sensors directly 
poking the sensor hardware).  Without this module lm_sensors no longer works 
fully (no motherboard temperatures, voltages or fan speeds).  But with the 
ATK0110 module loaded ntp does not sync and time keeping is horrific.  I have 
opened a bug report on kernel.org about this but so far nothing has happened.  
Currently I do not have lm_sensors working fully on my machine.  My point is 
that how the kernel is configured and what modules you load can have a huge 
impact on time keeping and the ATK0110 module on MY HARDWARE is an example of 
this.  But it is also one I discovered by dumb luck and if I hadn't first had 
time keeping working nicely with 2.6.34 initially and then tried to fix the new 
lm_sensors problem I would not have known the cause of the timekeeping 
problem.  But it is clear that at least on some hardware the kernel ACPI 
modules can cause timekeeping issues and there may be other modules that 
impact timekeeping as well.

> 
> >> So my question is rather simple: Do you also have this problem?
> >
> > No... I did not measure time to get down to 0.00xxx but it is quick
> > enough.
> >
> >> Which distribution did you use?
> >
> > Fedora. But I compile ntpd and kernel.org myself.
> >
> >> Which hardware is the best?
> >
> > What demands do you have for the precision?
> >
> > Udo
> >
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