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



On 04/25/2013 03:41 AM, Guannan Ren wrote:
> On 04/24/2013 11:39 AM, Guannan Ren wrote:
>> 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.
> 
>       Hi Cole,
> 
>          What's your ideas? If you decide to restore the 'copy' button, I will
> do it.
> 
>       Guannan

Yeah I think we should restore the button behavior, sorry I know its a pain.
I'd rather see what host-model improvements Jiri plans hit a libvirt release
and then we can re-evaluate.

- Cole


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