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Re: [Xen-users] xen and smp

  • To: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
  • From: Shahzad Chohan <shahzad.chohan@xxxxxxxxx>
  • Date: Thu, 4 Aug 2005 10:24:58 +0100
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 04 Aug 2005 09:23:24 +0000
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On 8/4/05, Mark Williamson <mark.williamson@xxxxxxxxxxxx> wrote:
> > I noticed that the xen has support for smp in the xen0 kernel. However
> > once I boot up with it I can only see 1 cpu. I understand this to be
> > that xen0 is a guest within xen, but what does this actully mean,
> > where is xen in realtion to the xen0 kernel?
> Xen lives under *everything* in the system.  It is responsible for sharing CPU
> and memory between *all* domains, including dom0.  Although dom0 controls IO
> devices and Xen's control interface, it's still Xen itself that sits at the
> lowest layer and manages sharing.
> Xen 2.0.x:
> * Domains (including dom0) can only run on one CPU.
> * Xen can handle multiple CPUs, so by running multiple domains you can still
> use all your CPUs.
> Xen 3.0:
> * Domains can run on multiple CPUs.  This can be more or less than the number
> of real CPUs.
> * Dom0 must boot initially on the number of CPUs in the machine, although I
> believe it can subsequentially relinquish them.
> * Xen is SMP and responsible for the low-level time sharing of the real CPUs
> between virtual CPUs running on them.
> Cheers,
> Mark
Thanks for that Mark

It's made things clearer. I'm just writing a simple document about xen
and how to install it, and this aspect came up. Looks a lot clearer


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