Re: [Xen-users] Time/clock issues with Xen 3.0.3?

[marek cervenka <cervajs@xxxxxxxxxx>]

> On 27 Nov 2006 at 11:24, Harald Koenig wrote:
>
> > I see the same problem here (xen-3.0.2 from SUSE 10.1):
> > dom0 is synched via ntpd, and the domUs drift away from dom0 and ntp server.
> Harald,
>
> use independent clocks everywhere, and it will work: "rkdvmso1" is a Dom0, every
> other is a DomU somewhere:
i (and others too) do not want run ntpd in every domU. this is wasting of 
resources
> # ntpq -p
>     remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> LOCAL(0)        LOCAL(0)        10 l   12   64  377    0.000    0.000   0.001
> *rkdvmso1.dvm.kl 132.199.176.97   2 u  987 1024  377    0.207    0.035   0.742
> +rksapas01.dvm.k 192.168.0.61     3 u  997 1024  377    0.120    0.020   0.772
> +rksapas02.dvm.k 192.168.0.61     3 u  992 1024  377    0.101    0.049   0.769
> +rksapas03.dvm.k 192.168.0.62     3 u  995 1024  377    0.282    0.019   4.211
> +rksapas04.dvm.k 192.168.0.62     3 u  997 1024  377    0.274    0.001   0.775
> +rksapas05.dvm.k 192.168.0.63     3 u   78 1024  377    0.281   -0.093   0.800
> +rksapas06.dvm.k 192.168.0.63     3 u  999 1024  377    0.230   -0.213   0.825
> rksapas07.dvm.k .INIT.          16 u    - 1024    0    0.000    0.000 4000.00
> +rksapas08.dvm.k 192.168.0.41     4 u   78 1024  377    0.243   -0.168   0.796
>
> Ulrich
>
>
> > for an example how to reproduce this problem, see below...
> >
> >
> > right now I use a cron job on dom0 which re-sets the dom0 clock
> > via date -s `date` (ntpdate doesn't work here).
> >
> >
> > On Nov 25, Tim Post wrote:
> >
> > > What are the values of /proc/sys/xen/independent_wallclock
> > > and /proc/sys/xen/permitted_clock_jitter respectively?
> >         os2 koenig > cat /proc/sys/xen/independent_wallclock
> >         0
> >
> >         os2 koenig > cat /proc/sys/xen/permitted_clock_jitter
> >         10000000
> >
> > maybe I should just set /proc/sys/xen/independent_wallclock to 1
> > and run ntpd on all domUs ?
> >
> >
> > now, how I was able to reproduce the domU clock due to ntp clock drift in dom0
> > using SUSE 10.1 xen stuff.  in this examle both xen, dom0 and domU are SUSE 10.1
> > and use the SUSE xen-kernel, but on my real XEN server I run may different
> > distributions and kernels -- all alike...
> >
> >
> > step 1: perfect clock sync with drift==0 :
> >
> > run ntpd on dom0 with the following config file /etc/ntp.conf which uses
> > only the dom0 system clock as "source", so it doesn't adjust the clock
> > ever.
> >
> > ----------------------------- /etc/ntp.conf -----------------------------------
> > restrict default noquery notrust nomodify
> > restrict 127.0.0.1
> > restrict 192.168.8.0 mask 255.255.255.0
> > server 127.127.1.1
> > driftfile /var/lib/ntp/drift/ntp.drift
> > logfile /var/log/ntp
> > -------------------------------------------------------------------------------
> >
> > before starting ntpd, make sure the clock drift is set to zero with
> >
> >         echo 0 > /var/lib/ntp/drift/ntp.drift
> >
> > now start ntpd, start domU (don't run ntpd in domU) and check the domU
> > clock drift with
> >
> >         ntpdate -d dom0
> >
> > that's how it should always work (in theory;).  but in real world
> > the real clock drift of a PC clock is not zero. prrtty often the clock
> > shows a frequency error of 100 ppm and more (which is 8.64 secs per day!).
> >
> >
> > now, let's add some drift to dom0:
> >
> >         /etc/init.d/ntpd stop
> >         echo 100 > /var/lib/ntp/drift/ntp.drift
> >         /etc/init.d/ntpd start
> >
> >
> > now you check the domU clock by running ntpdate on domU:
> >
> >         ntpdate -d dom0 ; sleep 60 ; ntpdate -d dom0
> >
> > and there will be a domU clock drift relative to dom0 or any other ntpd server
> > of ~6 msec per minute == 100 ppm.  qed.
> >
> >
> > hope this helps to track and fix this clock problem!
> >
> > Harald Koenig
> > --
> > "I hope to die                                      ___       _____
> > before I *have* to use Microsoft Word.",           0--,|    /OOOOOOO\
> > Donald E. Knuth, 02-Oct-2001 in Tuebingen.        <_/  /  /OOOOOOOOOOO\
> >                                                     \  \/OOOOOOOOOOOOOOO\
> >                                                       \ OOOOOOOOOOOOOOOOO|//
> > Harald Koenig                                          \/\/\/\/\/\/\/\/\/
> > science+computing ag                                    //  /     \\  \
> > koenig@xxxxxxxxxxxxxxxxxxxx                            ^^^^^       ^^^^^
> >
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>
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---------------------------------------
Marek Cervenka
=======================================


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