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Re: xen advice

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 <> 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.

> 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 :)

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference

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