Re: [Xen-users] Domain-0

["Austin S. Hemmelgarn" <ahferroin7@xxxxxxxxx>]

On 2016-01-27 11:27, Ian Campbell wrote:
> On Wed, 2016-01-27 at 16:18 +0000, Chris Arnold wrote:
> > > On Jan 27, 2016, at 11:05 AM, Ian Campbell <ian.campbell@xxxxxxxxxx>
> > > wrote:
> > >
> > > See the first hit on google for "xen domain 0" which is http://wiki.xen
> > > proj
> > > ect.org/wiki/Dom0 . It is the control domain, i.e. the thing which is
> > > launched by Xen on boot where the tools reside, I think it is probably
> > > what
> > > you are referring to as the "physical OS".
> > >
> > > It is very much a required part of the system. As to why it only showed
> > > up
> > > now I don't know (it's possible older libvirt shielded you from it) and
> > > what that has to do with your performance issues neither. I'd suggest
> > > that
> > > you persist with SLES support.
> > Yea, I just read that domain-0 is a major piece and I should not shut it
> > down and delete. So is there a config file for xen domain-0 that I can
> > adjust the RAM usage? I realize suse does different things to your
> > software but if I have the xen config file for domain-0 I could find it
> > if suse puts it somewhere else.
> There is no config file.
>
> The amount of RAM which dom0 has can be set form the hypervisor command
> line (search for "dom0_mem" in the hypervisor command line docs).
>
> You can also adjust it later by using the same tools as you would use to
> change the current memory assigned to a domU, assuming those tools aren't
> hiding it from you for some reason.
I'd be willing to bet though that the actual amount of RAM assigned to 
Domain-0 hasn't changed though due to the upgrade, it's just that it's 
actually being visibly accounted now.  Lowering that will lower the 
amount of RAM that your host/physical OS sees, which will likely impact 
your I/O performance for you other VM's.

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