[Engine-devel] host cpu feature

[Yaniv Kaul]

On 12/05/2012 01:46 PM, Laszlo Hornyak wrote:
>
> ----- Original Message -----
>> From: "Yaniv Kaul" <ykaul at redhat.com>
>> To: "Laszlo Hornyak" <lhornyak at redhat.com>
>> Cc: "engine-devel" <engine-devel at ovirt.org>
>> Sent: Wednesday, December 5, 2012 12:23:47 PM
>> Subject: Re: [Engine-devel] host cpu feature
>>
>> On 12/05/2012 12:32 PM, Laszlo Hornyak wrote:
>>> Hi,
>>>
>>> CPU-Host support allows the virtual machines to see and utilize the
>>> host's CPU flags, this enables better performance in VM's, at the
>>> price of worse portablity.
>>>
>>> http://www.ovirt.org/Features/Cpu-host_Support
>>>
>>> Your feedback is welcome!
>>>
>>> Thank you,
>>> Laszlo
>>> _______________________________________________
>>> Engine-devel mailing list
>>> Engine-devel at ovirt.org
>>> http://lists.ovirt.org/mailman/listinfo/engine-devel
>> - I assume that when you allow migration, you'd use host-model? This
>> is
>> not clear from the design. It seems like we VDSM developers can
>> choose
>> to use either this or passthrough, while in practice we should
>> support both.
> If AllowMigrateCPUHost is set to true (in case you have the same cpu model everywhere in your DC) migration of such hsots will be enabled. Otherwise it will not be enabled.

It's not going to help just enabling it - you need to use 'host-model' 
and not 'host-passthrough', so there'll be a reasonable chance to 
succeed the migration, AFAIK.

>
>> - I'm still convinced and commented on both relevat oVirt and libvirt
>> BZs that we need to add x2apic support to the CPU, regardless of what
>> the host CPU exposes.
>> AFAIK, the KVM developers agree with me.
> Not quite sure how is this related... could you send some URL's for the bugreports?

It's related because x2apic improves performance, and so does '-cpu 
host', but that doesn't enable x2apic implicitly.
https://bugzilla.redhat.com/show_bug.cgi?id=838469#c7
https://bugzilla.redhat.com/show_bug.cgi?id=700272#c28

Y.

>
>> Y.
>>
>>