[ntp:questions] What level of timesynch error is typical onWinXP?

David L. Mills mills at udel.edu
Wed Nov 3 17:49:26 UTC 2010


Dave,

I don't think that is right. The adjtime() call can be in principle 
anything, accoridng to the Solaris and FreeBSD man pages, but the rate 
of adjustment is fixed at 500 PPM in the Unix implementation. If the 
Linux argument is limited to 500 microseconds, Linux is essentially 
unusable with NTP. I would be surprised if this were the case.

Dave

Dave Hart wrote:

>On Wed, Nov 3, 2010 at 09:24 UTC, Miroslav Lichvar <mlichvar at redhat.com> wrote:
>  
>
>>On Tue, Nov 02, 2010 at 10:03:30PM +0000, David L. Mills wrote:
>>    
>>
>>>I ran the same test here on four different machines with the
>>>expected results. These included Solaris on both SPARC and Intel
>>>machines, as well as two FreeBSD machines.
>>>      
>>>
>[...]
>  
>
>>Ok, I think I have found the problem. The adj_systime() routine is
>>called from adj_host_clock() with adjustments over 500 microseconds,
>>which means ntpd is trying to adjust the clock at a rate higher than
>>what uses the Linux adjtime(). It can't keep up and the lost offset
>>correction is what makes the ~170ppm frequency error.
>>    
>>
>
>Congratulations on isolating the problem.  If adjtime() is returning
>failure, ntpd will log that mentioning adj_systime.  Do you see any of
>those?
>
>Is it a feature or a bug that FreeBSD and Solaris can apparently slew
>faster than 500 PPM using adjtime()?
>
>If it's a feature, is there a way we can detect at configure time what
>the adjtime() slew limit is without actually trying it?  We don't want
>to require root for configure.
>
>Thanks for all the attention you've been putting towards the reference
>implementation recently, Miroslav.  You have found a bunch of issues
>and reported them, usually shortly after the inducing changes.  You've
>helped keep the quality up despite a lot of development churn.
>
>Cheers,
>Dave Hart
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>  
>




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