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Re: [Xen-devel] [XEN-3.4] pv_ops dom0 time/clock handling

To: Daniel Schroeder <sec@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [XEN-3.4] pv_ops dom0 time/clock handling
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 26 May 2009 21:08:01 -0700
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Daniel Schroeder wrote:
this works for OpenSUSE 2.6.29.X XEN dom0 Kernel...
...i have tested latest git-next repo .30-rc6 and the pv domU is two
hours ahead.
I have checked the following:

dom0 ntpd working, correct time and /etc/localtime is correct
(Europe/Berlin)

domU no ntpd and correct timezone and /etc/localtime (Europe/Berlin)
"localtime = 0" in pv domU config file...

it seems to me, that the domU gets not UTC as basetime...
This could plausibly be a pv_ops bug. I fthe only thing you change is the
kernel -- keeping all configuration the same -- then dom0 will be providing
exactly the same time info to both kernels.

checked with OpenSUSE 2.6.29.X xenified dom0...pv domU has the right
time...booted pvops .30-rc6, pv domU gets probably localtime as
basetime, so domU is two hours in the future...

Time is pretty straightforward, and there's no TZ calculation involved at any points. Its hard to see how you'd get a two hour delta (is it exactly 2 hours?).

One difference between pvops time handling and the -xen kernels, is that they defaulted to slaving the domU time off the hypervisor at all times, so a system time change would propagate into guests. I don't implement that in pvops kernels, so they'll maintain independent time unless you explicitly sync with some mechanism like ntp.

   J

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