Groups > linux.debian.user > #196553

Re: Slow clock on Xen 4.8 after upgrade

From	Mike <debian@norgie.net>
Newsgroups	linux.debian.user
Subject	Re: Slow clock on Xen 4.8 after upgrade
Date	2018-06-11 11:10 +0200
Message-ID	<vZqZP-1i2-11@gated-at.bofh.it> (permalink)
References	<vY8Vk-3a0-7@gated-at.bofh.it> <vY9ol-3Bd-3@gated-at.bofh.it>
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On Thu, Jun 07, 2018 at 11:06:12PM +0300, Abdullah Ramazanoğlu wrote:
> On Thu, 7 Jun 2018 19:32:35 +0100 Mike said:
> 
> [--8<--]
> 
> > In the end I used adjtimex -t 10065 -f 3058784 to speed the clock up a
> > bit and that has allowed NTP to be able to keep it under control.
> > 
> > So the issue with the slow clock appears to have been compenstated for
> > but I'd be intersted to know what actually caused it.  I've drawn a bit
> > of a blank on that one and would be grateful if anyone could offer any
> > thoughts?
> 
> Could there be a race condition between hwclock(8) and adjtimex?
> 
> IOW, there is a possibility that perhaps there was a drift rate set by hwclock
> and this was the cause of excessive drift. Now that adjtimex counter balances
> hwclock by an opposite drift rate, it can result in hwclock and adjtimex
> fighting against each other. Just a possibility.
> 
> I would have checked /etc/adjtime to ensure that no drift ratio set by hwclock.
> More info about hwclock drift setting and /etc/adjtime format in hwclock man
> page.
>

Thanks for the reply.

I did do some fiddling in /etc/adjtime (setting the drift ratio to 0 to
see if that resolved the issue, although it was unclear to me from the
docs I read how and when this file gets read (I believe it's hwclock
that reads it but when, other than on boot?)  I did keep  a copy of the
original before I fiddled with it:

3.619663 1452036888 0.000000
1452036888
UTC

I believe this means that it hasn't been updated since the begining of
time and that there's a drift of 3s a day between the hardware and
system clocks?  I assume this should not account for the ~15 mins a day
drift I was seeing?

Regards,
Mike.

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Thread

Slow clock on Xen 4.8 after upgrade Mike <debian@norgie.net> - 2018-06-07 21:40 +0200
  Re: Slow clock on Xen 4.8 after upgrade Abdullah Ramazanoğlu <ar018@yahoo.com> - 2018-06-07 22:10 +0200
    Re: Slow clock on Xen 4.8 after upgrade Mike <debian@norgie.net> - 2018-06-11 11:10 +0200

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