Re: domU to dom0 switch question

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 04/02/2010 04:02 PM, George Valzcig wrote:
> I have two questions on between a switch one dom to another dom in 
> Xen. I hope this is the right forum to ask these questions ...
>
> 1) other than I / O, there is no reason to switch from one domU to 
> dom0 (memory page remapping etc)? If I have a 1 CPU in my physical 
> machine and I run a domU with while loop that does nothing but use 
> CPU, there is no reason to switch to dom0?
> 2) In Xen PV is the hyper call entry page in the address space of the 
> domU - so call to a mapped hyper call not cause context switch - yes?

I don't follow your questions.

"Dom0" is the domain started by Xen automatically at boot time, which is 
privileged and is typically used for its hardware device drivers and 
systemwide administrative functions.  "DomU" is a less privileged 
"guest" domain, which may be either paravirtualized (PV) or using 
hardware virtualization features (HVM).

Note that "dom0" and "domU" are just roles; a single (pvops Linux) 
kernel image can be used unchanged as dom0, PV domU or HVM domU.

You seem to be using the terms "dom0" and "domU" in some other way, so I 
think you need to clarify the question before you get the answer you're 
looking for.

     J