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

[mail ignored <0.bugs.only.0@xxxxxxxxx>]

On Thu, Jan 14, 2010 at 6:19 PM, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:
> Your original problem was that ntpd experience high noise/jitter. IMHO
> dedicated dom0 cpu is not the fix for that, so that's two different
> issues.

It certainly did not appear to make a difference.

> First, about ntpd. Since you're using Opensuse kernel, your best bet
> is novell guys, since users on this list does not know what cause or
> fix that issue.

As per my OP, "Already reported this downstream; everybody's "stumped".

I.e., it's already been filed at novell, and discussed ad nauseum.  No
solution/progress there, simply statements that they can't reproduce
the problem; of course, that's with not identical environments.  I
*am* able to reproduce this issue on 5 different boxes, so I'm hard
pressed to believe that its any one box that's at fault.,

There have been suggestions to come 'here', though.  And, there are
@novell types on these lists -- if more prominently on xen-devel

> Second, about dom0 cpu. It's generally best to assign at least one
> physical core/cpu exclusive for dom0 usage. What I did is use this on
> grub.conf
>
>        kernel /xen.gz-3.4.1 com2=115200,8n1 console=vga,com2 dom0_mem=768M
> dom0_vcpus_pin
...
> The difference between this approach and the one you're trying to use:
> - I hard-limit dom0 memory.

you'll note from above that i already *have*limited dom0 memory, in grub,

kernel /xen.gz loglvl=all loglvl_guest=all dom0_mem=1024M
vga=gfx-1280x1024x32 console=vga,com1 com1=57600,8n1 iommu=1
cpufreq=xen:performance cpuidle dom0_max_vcpus=2 dom0_vcpus_pin
sched=credit

have already disabled ballooning in xend-config.sxp,

   (enable-dom0-ballooning no)
   (dom0-cpus 0),

and, have already isolated guests to the 'other' cpus, e.g., in test_guest.cfg
 ...
 cpus      = '2-3'
 vcpus     = 2
 ...

with this config I verify 2 cpus available to Dom0

 cat /proc/cpuinfo | grep processor
  processor       : 0
  processor       : 1

with 2 vcpus using those two cpus,

xm vcpu-list Domain-0
 Name                                ID  VCPU   CPU State   Time(s) CPU Affinity
 Domain-0                             0     0     0   -b-      31.5 0
 Domain-0                             0     1     1   r--      24.6 1

and @ the guest, the 'other' two cpus being used,

xm vcpu-list test_guest
 Name                              ID  VCPU   CPU State   Time(s) CPU Affinity
 test_guest                         1     0     3   -b-       5.0 2-3
 test_guest                         1     1     2   -b-       2.4 2-3

> This might be the reason why novell guys recommended against it.
> You'll have to ask them for the details though.

already have ... waiting for clarification

> Note that "unsupported" does not allways mean it won't work :D

that's certainly true!

the point remains, however, that ntpd withOUT xen's presence, on
any/all hardware I have, runs quiet & stable.  clearly, "xen" is
involved.  whether it's the opensuse implementation of kernel-xen or
Xen, or something inherent in Xen's design, is unknown atm ...

thanks.

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