Linode Forum

[jed]

rsk wrote: Urm, if I can ask for clarification... is NTP necessary only when using paravirt kernels, or with the "oldstyle Xen" 2.6.18.8 too?
ISTR that one doesn't let me mess with the clock at all...
Until you decouple from the host clock by twiddling this knob in /proc:
Code: 10:36 jsmith@staff% uname -a
Linux staff.linode.com 2.6.18.8-linode22 #1 SMP Tue Nov 10 16:12:12 UTC 2009 i686 GNU/Linux
10:36 jsmith@staff% cat /proc/sys/xen/independent_wallclock
0

When set to 1, you can set your clock independently of the host.

Native Xen kernels (i.e., 2.6.18 and pals) have this configuration knob, and paravirtualized kernels do not -- their clock is automatically decoupled.

[rsk]

Danke. :)

[bryantrv]

jed wrote: rsk wrote: Urm, if I can ask for clarification... is NTP necessary only when using paravirt kernels, or with the "oldstyle Xen" 2.6.18.8 too?
ISTR that one doesn't let me mess with the clock at all...
Until you decouple from the host clock by twiddling this knob in /proc:
Code: 10:36 jsmith@staff% uname -a
Linux staff.linode.com 2.6.18.8-linode22 #1 SMP Tue Nov 10 16:12:12 UTC 2009 i686 GNU/Linux
10:36 jsmith@staff% cat /proc/sys/xen/independent_wallclock
0

When set to 1, you can set your clock independently of the host.

Native Xen kernels (i.e., 2.6.18 and pals) have this configuration knob, and paravirtualized kernels do not -- their clock is automatically decoupled.

Dumb question- do you simply edit the file (cat /proc/sys/xen/independent_wallclock ) and reboot?

[Alucard]

bryantrv wrote: Dumb question- do you simply edit the file (cat /proc/sys/xen/independent_wallclock ) and reboot?
No, since /proc will be recreated at boot. Set
xen.independent_wallclock = 1
in /etc/sysctl.conf then run "sysctl -p". You do not have to reboot; it will be set on subsequent boots.

[bryantrv]

Thanks- I should have known that :).

[mnordhoff]

kbrantley wrote: Hey, linode people! Any chance we could get an internal ntp server to sync to? :)
Aside from jtsage's link, there are other public NTP servers hosted on Linodes, too; some are in the stratum 2 list.

kbrantley wrote: edit: hey linode people! How about opening up the ntp daemon on the hosts to the VMs they support? I like that idea even better.
It already is. Try it. There are no service guarantees, though.

jeffml wrote: The statistics geek in me would love to see a graph of requests for the top of the minute requests. It would seem that the spike would relate to the amount of drift in clocks for those that request them. Probably more like a prolonged 15 second spike on each side of the top of the minute?
I don't have any graphs, but in my experience, the spike peaks about 4 seconds after the hour. Traffic may have started increasing a few seconds before the hour, but not very significantly. It stays unusually high for at least a few minutes, and, of course, there are smaller spikes every minute. (The spike 1 minute after the hour is pretty significant, too.)

[H3LR4ZR]

Just use the pool. Thats what its there for.

http://www.pool.ntp.org/en/use.html

You could also add time.xenscale.com as well. Its a Linode in Dallas and a pool contributor.

[kbrantley]

mnordhoff wrote: kbrantley wrote: edit: hey linode people! How about opening up the ntp daemon on the hosts to the VMs they support? I like that idea even better.
It already is. Try it. There are no service guarantees, though.

Check that out.

*is perfectly happy*