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From Chiradeep Vittal <Chiradeep.Vit...@citrix.com>
Subject Re: [ACS41] System VMs not syncing time - does this block the release?
Date Wed, 15 May 2013 18:22:17 GMT
The normal S3 time sync is 15 minutes. I can't imagine a drift of 15
minutes in a few days of operation? I logged into 3 system vms running on
Xen and saw this drift:

r-9-VM 17:52:37 up 29 days, 10:33,
domU: Wed May 15 17:52:37 UTC 2013
dom0: Wed May 15 10:52:37 PDT 2013

r-535-VM 18:13:46 up 43 days, 20:49,
domU: Wed May 15 18:13:46 UTC 2013
dom0: Wed May 15 11:14:47 PDT 2013

r-247793-VM 18:18:20 up 43 days, 20:53,
domU: Wed May 15 18:18:20 UTC 2013
dom0: Wed May 15 11:18:33 PDT 2013


A PV kernel such as the systemvm's automatically maintains the clock sync
with dom0.


On 5/15/13 10:30 AM, "John Burwell" <jburwell@basho.com> wrote:

>Chiradeep,
>
>The issue I am experiencing is that the system VMs are not syncing to dom0
>on devcloud (i.e. the dom0 clock and the SSVM clock are different).  As I
>mentioned earlier in this thread, the syncing was working previously which
>seems to jibe with your findings.  What mechanism is used to sync the dom0
>and domU clocks (e.g. NTP, kernel driver, etc)?  It may be a situation
>where the pieces are present, but they aren't configured properly or
>simply
>not running.
>
>As an aside, we can not run VirtualBox Additions on devcloud due a
>conflict
>with the Xen kernel.  Therefore, I hard execute "ntpdate pool.ntp.org"
>periodically on the devcloud host to keep the clock synced with the "real
>world".  Another approach is to configure NTP with a very large drift and
>increase check frequency to accomodate the large clock swings that can
>occur.
>
>Thanks,
>-John
>
>
>On Wed, May 15, 2013 at 1:21 PM, Chiradeep Vittal <
>Chiradeep.Vittal@citrix.com> wrote:
>
>> Perhaps this is a problem with DevCloud?
>> 
>>http://nerdboys.com/2011/03/15/how-to-fix-virtualbox-time-synchonization-
>>pr
>> oblems/
>>
>>
>>
>> On 5/15/13 10:17 AM, "Chiradeep Vittal" <Chiradeep.Vittal@citrix.com>
>> wrote:
>>
>> >According to our resident Xen expert, any PV kernel automatically
>>syncs to
>> >the hardware clock on dom0.
>> >
>> >On 5/15/13 9:50 AM, "John Burwell" <jburwell@basho.com> wrote:
>> >
>> >>Marcus,
>> >>
>> >>Agreed.  I think we need to add a set of hypervisor agnostic  time
>> >>keeping guidelines to the documentation.  I just wanted to make sure
>> >>there wasn't anything KVM specific that should be added as well.
>> >>
>> >>Thanks,
>> >>-John
>> >>
>> >>On May 15, 2013, at 12:48 PM, Marcus Sorensen <shadowsor@gmail.com>
>> >>wrote:
>> >>
>> >>> Just the general one that system vms sync their time to the
>> >>> hypervisor, thus admins need to keep the hypervisor time correct. It
>> >>> sounds like that will be the case for all three, if we can manage
>>it.
>> >>>
>> >>> On Wed, May 15, 2013 at 10:44 AM, John Burwell <jburwell@basho.com>
>> >>>wrote:
>> >>>> Marcus,
>> >>>>
>> >>>> Excellent.  So, it looks like we have KVM resolved.  We just need
>>to
>> >>>>address Xen and VMWare now.  Do you think we need to any guidance
to
>> >>>>the documentation regarding KVM time keeping (e.g. environmental
>> >>>>prerequisites)?
>> >>>>
>> >>>> Thanks,
>> >>>> -John
>> >>>>
>> >>>>
>> >>>>
>> >>>> On May 15, 2013, at 12:39 PM, Marcus Sorensen <shadowsor@gmail.com>
>> >>>>wrote:
>> >>>>
>> >>>>> KVM LibvirtComputingResource has been patched in master. Tested
on
>> >>>>> master, 4.1, and both the acton and current system vm templates.
>>This
>> >>>>> patch makes system vms use 'kvmclock' for their timer, which
is a
>>vm
>> >>>>> driver that gets it's time from the hypervisor. No change to
the
>> >>>>> system vm template itself.
>> >>>>>
>> >>>>> bfc5887a1bf6b41e88dd7a8f9987fcee8d3d9175
>> >>>>>
>> >>>>> On Wed, May 15, 2013 at 9:08 AM, Chip Childers
>> >>>>> <chip.childers@sungard.com> wrote:
>> >>>>>> On Wed, May 15, 2013 at 11:03:16AM -0400, John Burwell wrote:
>> >>>>>>> Chip,
>> >>>>>>>
>> >>>>>>> One other item I neglected to mention was that clock
sync, at
>>least
>> >>>>>>>for Xen system VMs, wasn't an issue in the Jan-Feb timeframe.
>> >>>>>>>Previously when I encountered these issues, syncing the
host's
>>clock
>> >>>>>>>and rebuilding the system VMs addressed the issue.  I
assumed,
>>but
>> >>>>>>>never verified, that the SSVM was syncing back against
the host's
>> >>>>>>>clock through hypervisor.  During my testing yesterday,
aside
>>from
>> >>>>>>>hard setting the clock, I was unable to force clock sync
on the
>> >>>>>>>SSVM.
>> >>>>>>>
>> >>>>>>> Thanks,
>> >>>>>>> -John
>> >>>>>>
>> >>>>>> I think that's our issue right now...  answering the question:
>>Why
>> >>>>>>is
>> >>>>>> this only an issue now?  Did we just get lucky up to this
point?
>> >>>>>>Since
>> >>>>>> the SSVMs are the same template as the timeframe you mention,
I
>>tend
>> >>>>>>to
>> >>>>>> believe that you / we were just lucky.
>> >>>>>>
>> >>>>>> Anyone else have thoughts?
>> >>>>>>
>> >>>>>>>
>> >>>>>>> On May 15, 2013, at 10:18 AM, Chip Childers
>> >>>>>>><chip.childers@sungard.com> wrote:
>> >>>>>>>
>> >>>>>>>> Starting a thread on this specific issue.
>> >>>>>>>>
>> >>>>>>>> CLOUDSTACK-2492 was opened, which is basically the
fact that
>>the
>> >>>>>>>>System
>> >>>>>>>> VMs aren't syncing time to the host or to an NTP
server.  The
>>S3
>> >>>>>>>> integration is broken because of this problem, and
therefore
>>could
>> >>>>>>>>not
>> >>>>>>>> be considered a function available in 4.1 if we
release as is.
>> >>>>>>>>
>> >>>>>>>> We need input from people that know about the current
system
>>VMs
>> >>>>>>>>(the
>> >>>>>>>> 3.x VMs), as well as the possibility of using the
newer ones
>>that
>> >>>>>>>>we
>> >>>>>>>> have been considering experimental for 4.1.0.
>> >>>>>>>>
>> >>>>>>>> What should we do?
>> >>>>>>>>
>> >>>>>>>> -chip
>> >>>>>>>
>> >>>>>>>
>> >>>>
>> >>
>> >
>>
>>


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