Re: [Xen-users] Clock wobble

[Nathan Stratton <nathan@xxxxxxxxxxxx>]

On Mon, 5 Jan 2009, Nathan Stratton wrote:

> We are building video/audio applications running on xen and have run into 
> some major timing issues due to xen DomU clock wobble. My routers in each 
> city act as NTP servers to the Dom0s. If I watch the clocks with ntpdate -q 
> {cisco NTP server} I see wobble of 2 - 4 ms on the Dom0s. However with 
> xen.independent_wallclock=0 I see wobble from -5 to -150 ms. I have tried to 
> set xen.independent_wallclock=1 and use NTP, but that does not help because 
> the clock still drifts between NTP updates.
> My issue is drifting back and forth over the window between when the Dom0 
> updates the DomU or between NTP updates if xen.independent_wallclock is set 
> to 1. It does not look like it matters if it is a full or para DomU.
> I have been looking at running a real time kernel, but so far have not been 
> able to get that to run on xen.
> Any ideas? Overall my clocks don't drift more then 200 ms, but when your 
> mixing audio and video that is a big deal.
> P.S. I also have played around with permitted_clock_jitter, but it does not 
> seam to do anything.
Sorry to reply to my own post... We are running Centos 5.2 
2.6.18-92.1.18.el5xen for Dom0 and DomUs with Xen 3.3.0.
> <>
Nathan Stratton                                CTO, BlinkMind, Inc.
nathan at robotics.net                         nathan at blinkmind.com
http://www.robotics.net                        http://www.blinkmind.com

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