[Pkg-xen-devel] Re: Xen and PAE

[Roberto C. Sánchez]

I thought this might be of interest to the list.  I am only running Xen
on amd64, so I am not sure how intelligently I can help out.   Probably
best to CC urs, since I don't imagine he is subscribed to the list.

Regards,

-Roberto

On Wed, Mar 21, 2007 at 07:26:26PM +0100, Urs Thuermann wrote:
> I have two separate questions, actually, concerning Xen and PAE:
> 
> Today, I installed Xen on a Pentium4 machine running Debian testing.
> I did
> 
>     aptitude install xen-linux-system-2.6.18-4-xen-686
> 
> which installed besides others the two debian packages
> 
>     xen-hypervisor-3.0.3-1-i386-pae and linux-image-2.6.18-4-xen-686
> 
> The description of the first of these packages says
> 
>     This version of the hypervisor is built with PAE enabled, in order
>     to support systems with more than 4GB of memory.  If you have less
>     than that you should probably choose the non -pae version.
> 
> However, the xen-linux-system-2.6.18-4-xen-686 depends on the -pae
> version and the kernel linux-image-2.6.18-4-xen-686 cannot run with
> the non -pae xen hypervisor.  An older version of xen-linux-system
> seems not be available anymore in Debian testing.
> 
> Therefore, I run the -pae version now but I wonder how much
> unnecessary overhead and performance impact this might have on my
> system with only 512 MB of RAM.  And will there be a version of the
> 2.6.18-4 kernel for Xen but without -pae?
> 
> 
> 
> 
> On another system I had Xen installed for quite a while now.  It had
> xen-linux-system-2.6.18-3-xen-686 which depends on the non -pae
> hypervisor and kernel found in the packages
> 
>     xen-hypervisor-3.0.3-1-i386 and xen-linux-system-2.6.18-3-xen-686
> 
> Today, I installed additionally xen-linux-system-2.6.18-4-xen-686
> because I thought this has a newer kernel and not being aware this has
> -pae compiled in.  The installation also called update-grub which then
> produced 4 boot entries for Xen/Linux, two of which can't boot
> successfully.  The 4 entries are
> 
>     title           Xen 3.0.3-1-i386-pae / Debian GNU/Linux, kernel 2.6.18-4-xen-686
>     ...
>     
>     title           Xen 3.0.3-1-i386 / Debian GNU/Linux, kernel 2.6.18-4-xen-686
>     ...
>     
>     title           Xen 3.0.3-1-i386-pae / Debian GNU/Linux, kernel 2.6.18-3-xen-686
>     ...
>     
>     title           Xen 3.0.3-1-i386 / Debian GNU/Linux, kernel 2.6.18-3-xen-686
>     ...
> 
> 
> where the 2nd and the 3rd don't boot because they combine a non-pae
> Xen hypervisor with a pae kernel or vice versa.  Even worse, the 2nd
> entry was made the default for some reason.
> 
> Couldn't grub somehow recognize this problem and leave out those bad
> combinations which don't boot?
> 
> 

-- 
Roberto C. Sánchez
http://people.connexer.com/~roberto
http://www.connexer.com
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