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

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Jan 13, 2010 at 08:44:08AM -0800, mail ignored wrote:
> hi
> 
> On Tue, Jan 12, 2010 at 11:13 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> > How many vcpus does your dom0 have?
> 
> 4, atm,
> 
> xm vcpu-list Domain-0
>  Name                                ID  VCPU   CPU State   Time(s) CPU 
> Affinity
>  Domain-0                             0     0     0   r--     273.0 any cpu
>  Domain-0                             0     1     1   -b-     202.4 any cpu
>  Domain-0                             0     2     3   -b-     179.1 any cpu
>  Domain-0                             0     3     2   -b-     199.9 any cpu
> 
> > Have you configured domain weights (ie. guaranteed cpu time for dom0?)
> 
> no, i didn't realize that was available.  how is that explicitly done?
>  is that done using the CreditScheduler?
> 

Yes, it's done using Xen Credit Scheduler:
http://wiki.xensource.com/xenwiki/CreditScheduler

Use this to check the current settings:
        xm sched-credit -d Domain-0

And this to configure the weight:
        xm sched-credit -d Domain-0 -w <weight>

You might want to give dom0 for example weight of 384 or 512, 
so it'll have more weight than the guests (the default weight is 256).


> > Have you tried dedicating a single cpu core only for dom0?
> 
> no, not yet.  clearly, i could set maxcpus=1 @ grub.  would i also
> need to pin the Dom0 cpu to a specific cpu, shomehow?
> 

You can use this for xen.gz in grub.conf:
dom0_vcpus=1 dom0_vcpus_pin

And then make sure the other domains (guests) don't use pcpu 0, using
cpus=1-3 parameter in /etc/xen/<guest> cfgfiles.

Also you might want to dedicate dom0 fixed amount of memory, for example
512MB using dom0_mem=512M options for xen.gz, and then disable dom0
ballooning totally by specifying (dom0-min-mem 512) in /etc/xen/xend-config.sxp 


-- Pasi

> On Tue, Jan 12, 2010 at 11:37 PM, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:
> > which kernel is it? vanilla? distro-provided? gentoo-xen kernel?
> 
> it's distro-provided -- opensuse 11.2's,
> 
>  uname -a
>   Linux test 2.6.31.8-0.1-xen #1 SMP 2009-12-15 23:55:40 +0100 x86_64
> x86_64 x86_64 GNU/Linux
> 
>  lsb_release -a
>   LSB Version:
> core-2.0-noarch:core-3.2-noarch:core-4.0-noarch:core-2.0-x86_64:core-3.2-x86_64:core-4.0-x86_64:desktop-4.0-amd64:desktop-4.0-noarch:graphics-2.0-amd64:graphics-2.0-noarch:graphics-3.2-amd64:graphics-3.2-noarch:graphics-4.0-amd64:graphics-4.0-noarch
>   Distributor ID: SUSE LINUX
>   Description:    openSUSE 11.2 (x86_64)
>   Release:        11.2
>   Codename:       n/a
> 
>  rpm -qa | grep -i ^xen-3
>   xen-3.4.1_19718_04-28.1.x86_64
> 
> > FWIW, a quick workaround is to use kernel 2.6.18. I've been using
> > RHEL's kernel-xen (2.6.18-164.2.1.el5xen) and it works great WRT
> > time/ntp.
> 
> good to know. although @downstream, they're unable to reproduce this
> problem, i'm able to on, as above, 5 different mobos from 3 different
> vendors.
> 
> commonalities are (1) opensuse 11.2, (2) similar install profiles, (3)
> AMD Deneb cores (Phenom II X4s)
> 
> whether this is an issue due to my local environmentS, opensuse or
> xen, i'd like to find/fix it.

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