Re: [Xen-users] Using custom domU kernels with Fedora,Debian,SUSE

["Luke S. Crawford" <lsc@xxxxxxxxx>]

On Thu, 1 Mar 2007, Peter Braun wrote:
> I would like to ask people here who is using xen in production/hosting
> enviroment.
I'm running a hosting service (right now, it's descending into 'broken toy' 
status;  I've not met my SLA (or charged people) in several months, mostly 
because it needs some kernel hacker attention, and I'm the closest thing 
we have to a kernel hacker, and I have been focusing on my consulting 
clients)  I also do consulting, and my client's systems run much better 
than my own.  (my clients also use distro-specific kernels)
> Have you ever experienced problems with para-virtualized guest while
> using non-distribution kernels?
It's a lot like running a non-distribution kernel on a normal install; 
some things work, other things not so much.  switching from a 2.4 to a 2.6 
kernel requires new module-init-tools packages.
> Current official xen kernel is 2.6.16. I have self compiled kernel for
> domU - non-privileged.
>
> Am using this kernel for wide range of guests like
> fedora,debian,gentoo,opensuse without problems. Have you ever
> experienced problems while using non distribution kernel in some
> distribution?
Like I said, the biggest gotcha is if you are running a distro that 
expects 2.4 kernels and you are using a 2.6 kernel, you need to install a 
new module-init-tools;  customers become annoyed when they cannot install 
modules.  Also remember to compile all the default modules and leave them 
in /lib/modules/ within the DomU.
> I tried to use fedora distribution xen guest kernel and its working but its 
> fc5.
> There is no available 2.6.16 based xen kernel for fc6.
If it's a Xen3 paravirt kernel, it should work even if it's not 2.6.16. 
One of my clients uses RHEL3 guests, and we use the xensource-provided 
linux 2.4 RHEL3 xenU kernel that you can find at 
http://xenbits.xensource.com/kernels   It works great for them.  (thanks 
Xensource!)  The dom0s in this case use the standard xen 2.6.16 kernel. 
Since 3.0.3, we've not had any difficulties with this setup.
At my hosting business, we even run NetBSD XenU kernels, which work 
even though our Dom0s use the standard linux 2.6.16 kernels.  (we have had 
some problems with these, but I am unsure those problems are related to 
the xen0/xenU differences.  We've had lots of problems on my hosting setup 
in general)
(note, there are differences between Xen3.0.2 and 3.0.3 that cause 
issues;  you probably want your xen0 and xenu kernels on the same side of 
that line)

> According to fedora xen kernels - since fc5 - there arent separete xen
> kernels for dom0 and domUs?
you can use the same kernel for Dom0 as DomU;  all you get out of a 
seperate DomU kernel is saving some space and compile time (as it doesn't 
need the Dom0 specific code or any of the hw drivers)  By default I use 
the Dom0 boot kernel for my guest xenU kernel unless they request 
otherwise.
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