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



On 04/23/2013 11:20 PM, Jiri Denemark wrote:
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.


Actually, virt-manager cached the cpu model and features via VIR_DOMAIN_XML_UPDATE_CPU
   after toggling host-model checkbox.
We can give a hint to user if host cpu changed after destroy/start/migration: one is to keep guest OS running safely with cached host-model cpu (convert to custom mode automatically), the other
   is to use newest host-model cpu.

   "copy XML" is the safest way, but not with best performance.
   Either is okay,  rolling back is last choice.

   Guannan


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