Re: [Xen-devel] NUMA TODO-list for xen-devel

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.08.12 at 11:48, Andre Przywara <andre.przywara@xxxxxxx> wrote:
> On 08/03/2012 11:23 AM, Jan Beulich wrote:
>>>>> On 02.08.12 at 18:36, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
>>> On Thu, Aug 2, 2012 at 2:34 PM, Dario Faggioli <raistlin@xxxxxxxx> wrote:
>>>> On Thu, 2012-08-02 at 10:43 +0100, Jan Beulich wrote:
>>>>>>>> On 01.08.12 at 18:16, Dario Faggioli <raistlin@xxxxxxxx> wrote:
>>>>>>      - Virtual NUMA topology exposure to guests (a.k.a guest-numa). If a
>>>>>>        guest ends up on more than one nodes, make sure it knows it's
>>>>>>        running on a NUMA platform (smaller than the actual host, but
>>>>>>        still NUMA). This interacts with some of the above points:
>>>>>
>>>>> The question is whether this is really useful beyond the (I would
>>>>> suppose) relatively small set of cases where migration isn't
>>>>> needed.
>>>>>
>>>> Mmm... Not sure I'm getting what you're saying here, sorry. Are you
>>>> suggesting that exposing a virtual topology is not a good idea as it
>>>> poses constraints/prevents live migration?
> 
> Honestly, what would be the problems with migration? NUMA awareness is 
> actually a software optimization, so we will not really break something 
> if the advertised topology isn't the real one.

Sure, nothing would break, but the purpose of the whole feature
is improving performance, and that might get entirely lost (or
even worse) after a migration to a different topology host.

Jan


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