Re: net6501 - large clock drift under high load

On 10/24/2014 09:40 AM, Bryan K. Walton wrote:
> I've been troubleshooting a problem with large clock drift on my net6501
> for a while. It is running Debian 7, with kernel 3.2.58.
>
> Of course, I've got a NTP server running on it.  And I generally have no
> problems with time sync during normal system usage (low load)
>
> But what I've discovered is that during periods of high system load (like
> when I'm running rsnapshot on the box to do home backups, the clock starts
> drifting quickly.  The CPU load on the net6501 around that time is very
> high, around 2.5.  The clock drifts enough that ntp thinks that my time
> sources are failing sanity checks.
>
> So then, NTP quits synchronizing the time.  After a day or two of this,
> with other high load times, the system time gets so far from the time of
> the outside time servers, that NTP just quits running.
>
> Has anybody else noticed this?  Is there anything I can do to address the
> clock drift during high load times?  I never encountered this problem on
> my net4801.
>
My net6501 clock was really bad too, such that ntp continually had 
issues, but I don't think it was load related.

Here's the thread on the topic:

http://marc.info/?l=soekris-tech&m=137882317519994&w=2

My conclusion was that the system clock tick was not happening at quite 
the right rate.

Your problem could be more severe, clock ticks being dropped?  Do you 
have any "strange" kernel modules loaded, or any "strange" hardware in 
the box?

-- 
Thanks,
David Mansfield
Cobite, INC.