[libvirt] specifying cirrus ram size

[Gerd Hoffmann]

On Mi, 2014-03-19 at 10:22 +0000, Daniel P. Berrange wrote:
> On Wed, Mar 19, 2014 at 12:49:06AM -0500, Serge Hallyn wrote:
> > Quoting Eric Blake (eblake at redhat.com):
> > > On 03/18/2014 03:59 PM, Serge Hallyn wrote:
> > > > Hi,
> > > > 
> > > > In order to migrate a VM from an older system with qemu-kvm to a newer
> > > > one with qemu, the newer qemu needs to be told to use the same vga
> > > > ram size as qemu-kvm used, 8M.
> > > > 
> > > > virsh domxml-from-native suggests that the way to specify a
> > > > 8mb cirrus vga ram size would be to add

In theory this should not be needed, -M pc-$version and compat
properties should take care.  In practice there probably is a hickup due
to upstream qemu using 8M by default and qemu-kvm using 16M by default.

> > tbh I originally expected <model type='cirrus' vram='8192'> to work,
> > but it seemed to be ignored.
> 
> Yes, that ought to work but it is possible we only ever plumbed it
> in for QXL, since historically you couldn't change ram for other
> drivers.

For cirrus this is pretty pointless.  We emulate old, existing hardware
here and increasing the memory size buys you nothing as real cirrus
hardware isn't able to address more memory.  Even the 16M we have today
are more than cirrus is able to handle and it being there is more or
less a historic accident:  qemu-kvm bumped video memory from 8 to 16 MB
for both stdvga and cirrus without checking how useful that is.

For stdvga I have a rfe bug open ;)

cheers,
  Gerd