Re: [Xen-users] xen and smp

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> 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

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