RE: [Xen-devel] Re: [Xen-users] ntpd under Xen Dom0 exhibits extremely high jitter/noise? runs stable/quiet under non-xen kernel.

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

I'm away from the office right now so can't easily look this up
but the following patch was submitted by Tim Deegan in March 2009
and may be relevant.  Likely it is in Xen's dom0 but not in
the dom0 of the distro you are using.

Apologies if I've missed an important point as I'm only
skimming email today and just happened to have Tim's
March email in a folder.

Re: [Xen-devel] [PATCH] linux-2.6.18-xen.hg: fix interaction of NTP and 
dom0->xen time updates

> -----Original Message-----
> From: mail ignored [mailto:0.bugs.only.0@xxxxxxxxx]
> Sent: Sunday, January 17, 2010 4:53 PM
> To: Keir Fraser
> Cc: Fajar A. Nugraha; xen-devel@xxxxxxxxxxxxxxxxxxx; Xen User-List
> Subject: [Xen-devel] Re: [Xen-users] ntpd under Xen Dom0 exhibits
> extremely high jitter/noise? runs stable/quiet under non-xen kernel.
> 
> 
> On Sun, Jan 17, 2010 at 1:33 PM, Keir Fraser 
> <keir.fraser@xxxxxxxxxxxxx> wrote:
> > Tbh I don't think we've ever done a detailed
> > analysis of ntp performance on Xen before -- this is 
> something we might be
> > able to improve.
> 
> just fyi -- this may be all old info for you -- this
> 
>  "Kernel Model for Precision Timekeeping"
>   http://www.eecis.udel.edu/~mills/ntp/html/kern.html
> 
> and the site/info around it, seem to be the authoritative resource on
> timekeeping with ntp (function, debugging, etc).
> 
> it's been a great resource in understanding the expected 
> behavior of ntp.
> 
> i also found good general guidance in
> 
>  "Network Time Protocol (NTP) Overview and Configuration: An 
> Internet2 Cookbook"
>   http://e2epi.internet2.edu/npw/binder-docs/ntp-cookbook.pdf
> 
> although it does include a # of quotes/references to Mills' bias
> against Linux, e.g.,
> 
>   “I have confronted Linux many, many times with broken this and that
> and concluded I will not attempt to examine, fix, or judge anything
> Linux. You are on your own.” —David L. Mills, 2004-10-20
> 
> so it's not clear, at least to me, if there are in fact 'deeper'
> issues with ntp at hand.  hopefully that's gotten better over the
> years ...
> 
> hth.
> 
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>

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