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Re: [Xen-users] Same pv-ops kernel for dom0 and domU ?

On Fri, Jun 11, 2010 at 1:40 AM, Bruce Edge <bruce.edge@xxxxxxxxx> wrote:
> I read that this is one of the benefits of pv-ops,

Actually, domU can use dom0's kernel whether it's -xen kernel or pv_ops kernel.
The different with pv_ops is that it can also be used to boot native
(non-xen) or full-virtualization.

> but is it really good
> practice to use the same kernel options for both dom0 and domUs?

Depends on what you need, and who you ask.
As an illustration, Redhat uses the same kernel-xen rpm for both dom0
and domU. The benefit is that you only have to maintain small number
of kernel package (only kernel and kernel-xen).

Ubuntu, on the other hand, have several different kernel package for
different purposes. linux-image-server is the general kernel package
suitable for common server purposes. However, there's also
linux-image-virtual, which contains much fewer modules and suitable
for domU/HVM kernel, thus can result to smaller installation size and
(slightly) faster boot times (due to the smaller initrd).

> If not, what options should differ between dom0 and domU pv-ops kernels?
> I'm using jeremy's 2.6.32.x tree and dom0/domU are ubuntu 10.04.

If you want to go with "smallest kernel possible for commonly used PV
domU" then you could start by excluding most drivers (disk, network,
multimedia, etc.). PV domU's hardware is pretty common, so you should
only need drivers for Xen frontend disk, network, console, and
(optionally) virtual frame buffer.

If you want to reduce it even further, you can also remove some packet
filtering support. I usually have dedicated firewall box or
specialized domUs for firewall, so most of my domUs won't need packet
filtering support. Same thing goes with raid (as I usually do raid in
dom0 or hadware).

Then you can also remove xen dom0 and backend support, although I'm
not sure how big the size reduction would be for this one.


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