Re: [Xen-devel] Xen hypervisor dom0_vcpus option broken in Xen 3.4 ?

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Jan 13, 2010 at 09:54:56PM +0000, Andrew Lyon wrote:
> On Wed, Jan 13, 2010 at 9:52 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> > On Wed, Jan 13, 2010 at 09:47:38PM +0000, Andrew Lyon wrote:
> >> On Wed, Jan 13, 2010 at 9:38 PM, Andrew Lyon <andrew.lyon@xxxxxxxxx> wrote:
> >> > On Wed, Jan 13, 2010 at 8:36 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> >> >> Hello,
> >> >>
> >> >> while discussing things on xen-users we noticed this:
> >> >>
> >> >> (XEN) Xen version 3.4.2 (root@(none)) (gcc version 4.4.2 20091027 
> >> >> (RedHat 4.4.2-7) (GCC) ) Mon Dec 14 06:53:18 EET 2009
> >> >> (XEN) Latest ChangeSet: unavailable
> >> >> (XEN) Command line: dom0_mem=1G loglvl=all guest_loglvl=all 
> >> >> com1=38400,8n1 console=com1 dom0_vcpus=1
> >> >> ..
> >> >> (XEN) Dom0 has maximum 4 VCPUs
> >> >> ..
> >> >>
> >> >> Has dom0_vcpus option name changed, or is it just broken?
> >> >>
> >> >> -- Pasi
> >> >>
> >> >>
> >> >> _______________________________________________
> >> >> Xen-devel mailing list
> >> >> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >> >> http://lists.xensource.com/xen-devel
> >> >>
> >> >
> >> > Looks like it is called dom0_max_vcpus in 3.4.2:
> >> >
> >> > cat xen-3.4.2.gz |gzip -d | strings | grep cpus | grep dom0
> >> > dom0_vcpus_pin
> >> > dom0_max_vcpus
> >> >
> >> > Andy
> >> >
> >>
> >> Also see this thread
> >> http://article.gmane.org/gmane.comp.emulators.xen.devel/69017, which
> >> seems to suggest that  dom0_max_vcpus is parameter for the Xen
> >> hypervisor (xen.gz) itself, while dom0_vcpus is for the dom0 kernel
> >> and causes it to hot-unplug the "extra" cpu's so that they can be
> >> (re)added later.
> >>
> >> I believe the xen 2.6.18 kernel also supports booting pv domUs with
> >> more max-cpus than active at startup, again so that they can be added
> >> later.
> >>
> >> I guess dom0_vcpus only works with Xen 2.6.18, I can find no trace of
> >> it in the openSUSE Xen kernel source.
> >>
> >
> > I've been using dom0_vcpus for Xen *hypervisor* with RHEL5/CentOS5 (which 
> > includes Xen 3.1.2.)
> >
> > I think you mixed that up with xend-config.sxp dom0-cpus option, which
> > is totally different thing, like Keir explains in that thread.
> 
> If you google dom0-cpus there are examples of other users passing the
> argument to Xen or dom0, but yeh, good chance they are confused too
> :-)
> 

Indeed :)

I just verified with Xen 3.4.2, setting dom0_max_vcpus=1 for xen.gz in 
grub.conf 
works OK and limits the amount of vcpus for dom0 to 1.

So now let's put the other related settings here aswell, for google archives:

Xen 3.4 hypervisor (xen.gz) boot time options for grub.conf:
        dom0_max_vcpus=X
        dom0_vcpus_pin
        dom0_mem=512M

Xend configuration options in /etc/xen/xend-config.sxp:
        (dom0-cpus 1)
        (dom0-min-mem 512)
        (enable-dom0-ballooning no)

Hopefully this helps future google searches :)

-- Pasi


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