[virt-tools-list] [PATCH v2 0/3] add cpu mode 'host-model' support

[Jiri Denemark]

On Tue, Apr 23, 2013 at 10:47:58 -0400, Cole Robinson wrote:
> On 04/23/2013 08:06 AM, Martin Kletzander wrote:
> > On 04/23/2013 01:56 PM, Guannan Ren wrote:
> >> On 04/23/2013 07:37 PM, Martin Kletzander wrote:
> >>> On 04/20/2013 10:09 PM, Cole Robinson wrote:
> >>>> On 04/18/2013 03:47 AM, Guannan Ren wrote:
> >>>>> v1 to v2:
> >>>>>    removed UPDATE_CPU flag checking
> >>>>>    renamed helper function name from reset() to clear_attrs()
> >>>>>    change the check box to be labeled 'Use host CPU model'
> >>>>>    remove the lightbulb icon, use tooltip instead
> >>>>>    reword the tooltip from Cole's
> >>>>>    remove the WARN image icon from UI
> >>>>>
> >>>>> Add a checkbox for 'host-model' mode and removed 'Copy host CPU
> >>>>> configuration'
> >>>>> button.
> >>>>>
> >>> Sorry for not catching this thread earlier, but IIUC, the 'host-model'
> >>> doesn't make up for the button.  XML is saved with 'host-model' then,
> >>> right?
> >>>
> >>> Unfortunately, I can't see that easily right now as git virt-manager
> >>> consistently crashes for me on all VMs and bare metal as well and I made
> >>> that one of my priorities in order to speed up the bug hunt on it.
> >>>
> >>
> >>     Martin, I am using virt-manager git head now, it seems fine for me.
> >>     Is there anything wrong about 'host-model', I can't quite follow you
> >> here.
> >>
> >>     Guannan
> >>
> > 
> > I was just wondering if dropping the button isn't a bad idea, some guest
> > OS might have problems when it is ran on different CPU, which is what
> > might happen with host-model after destroy/start, but would be avoided
> > with 'Copy host configuration'.  I'm not saying 'host-model' is wrong,
> > we definitely want the support for that.
> > 
> 
> Hmm, how would host-model change CPU between destroy/start... like a libvirt
> update supporting more flags? I didn't think about that, and it is
> problematic. Libvirt goes to great lengths to try and preserve hardware config
> for a VM across libvirt updates, host-model potentially throws that out the
> window...
> 
> Unless there's some clever way of getting around that it makes me think
> host-model just doesn't fit in the UI. Trying to explain all the nuances of
> this stuff in the current UI is impossible, so until we come up with something
> different we should go with the safest bet, which is only providing the old
> button press behavior.

I agree that currently copying host CPU XML into guest CPU is safest
than using host-model (which is just a shortcut for it but the config is
not preserved after domain shutdown). However, host-model will be
improved (hopefully soon) to provide more. And I think we (libvirt)
should come up with something that would preserve the configuration,
too.

Jirka