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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.08.12 at 12:02, Andre Przywara <andre.przywara@xxxxxxx> wrote:
> On 08/01/2012 06:16 PM, Dario Faggioli wrote:
>> Hi everyone,
>>
>> With automatic placement finally landing into xen-unstable, I stated
>> thinking about what I could work on next, still in the field of
>> improving Xen's NUMA support. Well, it turned out that running out of
>> things to do is not an option! :-O
>>
>> In fact, I can think of quite a bit of open issues in that area, that I'm
>> just braindumping here.
> 
>> ...
>>
>>         * automatic placement of Dom0, if possible (my current series is
>>           only affecting DomU)
> 
> I think Dom0 NUMA awareness should be one of the top priorities. If I 
> boot my 8-node box with Xen, I end up with a NUMA-clueless Dom0 which 
> actually has memory from all 8 nodes and thinks it's memory is flat.
> There are some tricks to confine it to node 0 (dom0_mem=<memory of 
> node0> dom0_vcpus=<cores in node0> dom0_vcpus_pin), but this requires 
> intimate knowledge of the systems parameters and is error-prone.

How about "dom0_mem=node<n> dom0_vcpus=node<n>" as
an extension to the current options?

> Also this does not work well with ballooning.
> Actually we could improve the NUMA placement with that: By asking the 
> Dom0 explicitly for memory from a certain node.

Yes, passing sideband information to the balloon driver was
always a missing item, not only for NUMA support, but also
for address restricted memory (e.g. such needed to start
32-bit PV guests on big systems).

Jan


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