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

David Woolley david at ex.djwhome.demon.co.uk.invalid
Fri Feb 15 22:35:56 UTC 2008

Thierry MARTIN wrote:
> Oups?
> If I understand your post, tsc is the same as acpi_pm ?

No.  TSC, acpi_pm, the CTC based software clock that PCs have always 
had, etc., are all fed from the same crystal, but run at different 
multiples of that crystal's frequency.  Only the battery backed clock 
normally runs from a different crystal.

Software can get the readings wrong by missing ticks, or in the case of 
the TSC counter, at least, by trying to work out the processor clock 
speed, rather than being told it; typically they time the TSC clock 
against the CTC one, during startup, and use that to calculate effective 
CPU clock frequency.

The CPU clock frequency is slowed down by power management, so the TSC 
rate can vary.

More information about the questions mailing list