[ntp:questions] 500ppm - is it too small?

Danny Mayer mayer at ntp.org
Mon Aug 17 02:23:02 UTC 2009


Ulrich Windl wrote:
> "David J Taylor"
> <david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid> writes:
> 
>> I've recent been suggesting the Windows port of NTP as a program suitable for
>> an application where the timekeeping needed to be within a second or two.
>> Yes, NTP is overkill, but it has the advantages of multiple servers, best
>> server selection, adaptive poll rate, and memory of the clock drift etc.
>> However, on quite a few installations - at a guess between 1% and 5% - NTP has
>> failed because the click frequency error appears to be too great for NTP to
>> correct.
> 
> I still say NTP is no technology to fix bad hardware or clocks. Those
> Windows people all seem not to care much about time, while the NTFS
> filesystem stores timestamps in nanoseconds AFAIK.
> 
>> Is there any feeling for changing the 500ppm limit, perhaps to 1000ppm or even
>> as much as 5000ppm (to pull a figure out of the hat)?  Or is 500ppm generally
>> believed to be the worst error which should be compensated?
> 
> When increasing the PPM range, you must also decrease the polling
> interval. Do we really want that? I'd say no.
> (Interestingly Windows "genuine" NTP client adjusts the clock once per
> week by default. Why not use that service?)
> 
>> One possibility is that some of the problem PCs are portables, with some sort
>> of power-saving or even hibernation scheme.  I don't have direct visibility of
>> the type of PC.
> 
> Well if someone runs ntpd on a machine and does a suspend to disk (or to
> RAM), and then after a few hours resumes execution, ntpd will be really
> confused about the time it missed. I think those machines should not run
> NTP. Maybe the solution Microsoft provides fits the needs of those.
> 
> Regards,
> Ulrich

I do. My laptop performs that way and I regularly hibernate rather than
shutting down. I also use standby and switch between regular power and
battery. That's plenty of punishment for ntpd.

Danny

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.




More information about the questions mailing list