[ntp:questions] Re: Clock skew too great

Richard B. Gilbert rgilbert88 at comcast.net
Tue Nov 15 12:56:47 UTC 2005


Sabrina Lautier wrote:

>First of all thanks a lot for your help.
>Sorry for the late delay but I was off yesterday.
>
>  
>
>>How large is the clock skew?
>>    
>>
>Huge... to give you an idea last Thursday around 5pm I synchronized the
>date and time and today at 11:30am the time on the machine is 14:23.
>
>  
>
>>What is your kernel parameter "HZ" set to ?
>>    
>>
>To nothing, the variable is not set.
>
>Would there be a link with the processor clock frequency ?
>
>$ dmesg | grep -i hz
>time.c: Using 1.193182 MHz PIT timer.
>time.c: Detected 2405.495 MHz processor.
>Detected 12.528 MHz APIC timer.
>ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
>powernow-k8:    0 : fid 0x10 (2400 MHz), vid 0x6 (1400 mV)
>powernow-k8:    1 : fid 0xe (2200 MHz), vid 0x8 (1350 mV)
>powernow-k8:    2 : fid 0xc (2000 MHz), vid 0xa (1300 mV)
>powernow-k8:    3 : fid 0xa (1800 MHz), vid 0xc (1250 mV)
>powernow-k8:    0 : fid 0x10 (2400 MHz), vid 0x6 (1400 mV)
>powernow-k8:    1 : fid 0xe (2200 MHz), vid 0x8 (1350 mV)
>powernow-k8:    2 : fid 0xc (2000 MHz), vid 0xa (1300 mV)
>powernow-k8:    3 : fid 0xa (1800 MHz), vid 0xc (1250 mV)
>
>  
>
>>If it's set to 1000, try changing it to 100.
>>    
>>
>Should I set it to 100 ?
>In which file to you set it ?
>
>What surprises me is that ntp does not report any error (file /var/log/ntp
>is empty).
>
>Rgds,
>Sabrina
>
>
>  
>
HZ is clearly not your problem even if your version of Linux implements 
it!   HZ governs the rate at which clock interrupts are generated.   The 
higher rate increases the probability that clock interrupts will be lost 
on systems that exhibit that behavior.   Your clock is fast, not slow.

Multiple processors with different speeds could be part of the problem.  
Can you force ntpd to run on only one of those processors?

It would be interesting to see the output of ntpq -p. It would also be 
interesting to know the value in the drift file at several different 
times; I believe that a new value is recorded once per hour.




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