[ntp:questions] May 2013 Windows Update causing rapid 'ntpd' drift

Jeroen Mostert jmostert at xs4all.nl
Sat May 18 18:24:37 UTC 2013


On 2013-05-18 15:50, starlight.2013q2 at binnacle.cx wrote:
> Just installed this month's Windows Update patches on an old/slow Windows XP
> laptop (1.5GHz Pentium-M) and it appears to have damaged Windows 'ntpd'
> time-keeping.
>
> Has anyone else observed this?
>
FWIW, I'm running 4.2.7p362 on 91 Windows servers. This issue does not occur on 
any of them. I have no Windows XP or Windows Server 2003 32-bit machines, 
however. I checked two fully patched Windows Server 2003 64-bit machines (which 
is almost but not quite the same as Windows XP). The offset stays under 250 
microseconds, and the server is not local LAN but on a VPN. Polling interval 
maximum of clients is capped at 16 seconds; the server syncs with the NTP pool 
using regular settings.

> Restarted 'ntpd' with the -M option added and it looks like it's doing ok now
> at around -55 PPM, but -M has its down-sides so I prefer to avoid using it if
> possible.
>
Unfortunately (for you) both my servers are using -M so my comparison might be 
entirely useless if it wasn't already. I can see why you wouldn't want to use it 
on a laptop, of course. Also, obviously, the servers are not using 
variable-frequency CPU settings.

> Running a somewhat older version 4.2.4p4 against two local CDMA time servers.
> Generally get offsets under 100 microseconds. The version running here is
> patched to allow a one-second polling interval, which I've found necessary to
> obtain decent time-keeping with Windows.
>
You should definitely try a more recent ntpd version, since there's been 
considerable improvements in timekeeping on Windows (though most improvements 
focused on Vista and beyond). In particular, very frequent polling doesn't seem 
to be required in any case.

It's a bit of a crapshoot, but you can also try using the /USEPMTIMER option in 
boot.ini if you're using the ACPI HAL. Timer frequency is quite a mess on 
Windows, but /USEPMTIMER typically does *something*. Whether it has any effect 
on ntpd is another matter. BIOS and driver updates can also make a difference.

-- 
J.



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