[ntp:questions] no ntp synchronisation: 2s to 6s time shift !

Thierry MARTIN thierry-martin at ifrance.com
Tue Feb 19 15:43:10 UTC 2008

Hi All,

Sorry for beeing too enthousiastic about my initial test...

I launched another test with clocksource=acpi_pm, on the same machine.
The results are bad now (> 500ms in a few hours).

FYI, the command I launched:
# rm /etc/adjtime;
# ntpdate ntp.cines.fr;
# hwclock --systohc;
# adjtimex -a

Then I watch:
# ntpdate -q ntp.cines.fr

Keeping a linux system with the correct time without any external 
synchronisation really seems hard...

Best regards

Thierry MARTIN a écrit :
> Oups?
> If I understand your post, tsc is the same as acpi_pm ?
> Was I just a lucky guy with this config?
> (:- You've just killed my enthousiasm ... :-)
> David Woolley a écrit :
>> Thierry MARTIN wrote:
>>> I have been trying acpi_pm clocksource for a few days now and the 
>>> results are quite good :-).
>>> The time drift is less than 1s per day (I would even say less that 
>>> 500ms but this has to be confirmed) which is much better than the 
>>> default config with tsc (>2s /day).
>> It's almost certain that the same hardware time source is used for 
>> both, so discrepancies are likely to be attributable to software 
>> issues (although those may include problems in calibrating the 
>> frequency of various sources empirically, rather than by knowing how 
>> they derive from the common source).

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