Re: xen advice

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

On Thu, 21 Feb 2008 23:45:17 +0100
Manuel Bouyer <bouyer%antioche.eu.org@localhost> wrote:

> On Wed, Feb 20, 2008 at 03:14:25AM +0000, Steven M. Bellovin wrote:
> > On Tue, 19 Feb 2008 21:57:40 -0500
> > Greg Troxel <gdt%ir.bbn.com@localhost> wrote:
> > 
> > > I'm not sure if you can run MP under xen.  Probably you want to
> > > start with xen3, and then you run the XEN3_DOM0 kernel.
> > > 
> > 
> > As far as I know, not on NetBSD, but you can on Linux.  Manuel?
> 
> Yes, A NetBSD dom0 or domU won't use more than one CPU at this time.
> But with NetBSD as dom0, the hypervisor will still see all the CPUs,
> and you can run a linux domU with all the CPUs for example.
> > 
> > I have a dual-core dom0.  Here's what my dom0 says:
> > 
> >     cpu0 at mainbus0: apid 0 (boot processor)
> >     cpu1 at mainbus0: apid 1 (application processor)
> > 
> > I'm not sure I know what that means...  The top command only shows
> > one CPU, unlike on my -current dual-core amd64.
> > 
> > The domUs show
> > 
> >     vcpu0 at hypervisor0: (uniprocessor)
> 
> Dom0 should also shows you one vcpu. Dom0 sees what the hardware is,
> and eventually needs to know about it to properly route interrupts
> (most of the ACPI interrupt setup is done by the dom0), but the dom0
> really runs on the vcpus provided by the hypervisor.
> 
Ah, yes, I see the vcpu line now.
> 
> > 
> > but on Linux one can specify how many CPUs to give to the domUs.
> > (That's the main reason I've wondered about running a Linux dom0.)
> 
> You don't really need much CPU power in dom0, unless you want to do
> other things than managing domUs :)
> I have NetBSD dom0 on 8-ways systems, for make -j<a lot> I use a linux
> domU :)
> 
My concern is being able to use both cores of the underlying hardware.
It would be nice if a single NetBSD domU could do so -- one of my VMs
is a build machine -- but if the other CPU is available for the other
domUs, I'm reasonably content for now.


                --Steve Bellovin, http://www.cs.columbia.edu/~smb