[Fedora-xen] Re: What are the minimal required FC6 packages for Dom0?

[Mathew Brown]

Hi,
  Actually, just a small point of clarification.  Guest OSes can know if
  they're running in a hypervisor in hardware virtualization.  If you're
  using AMD-V, there's an instruction called VMMCALL that allows the
  guest OS to check to see if it's running under a hypervisor or not. 
  On Intel, the equivalent instruction is VMCALL.  This is useful
  because if it finds that it is running under a hypervisor, it can do
  things such as ask for more memory if it's running out of memory or
  ask for more disk space.  Here's an article about if:  
  http://developer.amd.com/articles.aspx?id=15&num=3  You can also
  search google for VMMCALL or VMCALL :)

PS.  Of course, the guest OS would have to have the ability to do this
check.  I'm not sure how complicated it would be.  Probably a patch to
the kernel or something.

> On Sat, Oct 07, 2006 at 11:12:00PM +0200, Aryanto Rachmad wrote:
> > ----- Original Message ----- 
> > From: "Daniel P. Berrange" <berrange redhat com>
> > To: "Aryanto Rachmad" <aryanto chello at>
> > Cc: <fedora-xen redhat com>
> > Sent: Saturday, October 07, 2006 10:43 PM
> > Subject: Re: [Fedora-xen] What are the minimal required FC6 packages for Dom0?
> > 
> > 
> > >
> > > Fully-virt just lets you run unmodified operating systems (notably Windows,
> > > or older versions of Linux for which there is no Xen kernel available).
> > > If you only care about running modern Xen enabled Linux  kernels then
> > > you have on need for fully-virt. As a general rule, if there is a paravirt
> > > version of your desired OS available, using that will always be preferrable
> > > to fullyvirt. The network & disk I/O is much faster in paravirt, and since
> > > the kernel is informed when the hypervisor re-schedules it, it can do much
> > > more accurate process accounting in the guest. It is basically impossible
> > > to do accurate process scheduling in fully-virt, since the guest kernel
> > > has no knowledge of the fact that its running under a hypervisor.
> > >
> > 
> > Thanks a lot Dan,
> > 
> > I am actually planning to use Windows XP on one of the guests. So in this case I can not
> > do that, cann't I? But on the other hand, I prefer para-virtualised as it has more
> > advantages as you explained.
> 
> Yeah, for Windows XP you'll need an Intel-VT or AMD-V  capable CPU.
> 
> Regards,
> Dan.
> --
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-- 
  Mathew Brown
  mathewbrown at fastmail.fm

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