Re: [PATCH 1 of 3 v5/leftover] libxl: enable automatic placement of guests on NUMA nodes [and 1 more messages]

[Andre Przywara <andre.przywara@amd.com>]

On 07/19/2012 04:43 PM, Ian Jackson wrote:
> Andre Przywara writes ("Re: [PATCH 1 of 3 v5/leftover] libxl: enable automatic placement of guests on NUMA nodes [and 1 more messages]"):
>> On 07/18/2012 01:00 PM, Ian Jackson wrote:
>>> What is the maximum number of NUMA nodes we might expect to see on a
>>> single system in the next five years?  I would argue that 32 is too
>>> optimistic.  128 or 256 seem like more reasonable upper bounds.
>>
>> Wow, what are you talking about?
>> To calm this down from the AMD side:
>> The current Opteron NUMA architecture is limited to exactly 8 nodes.
>> This has ever been the case since the release of Opteron and changing
>> this is not trivial and will not happen in any near future. In general I
>> don't think we will see much bigger NUMA systems, but more cluster like
>> architectures.
>
> One of these `more cluster like architectures', if it has shared
> memory at all, may well end up being most easily represented in the
> model supported by Xen as a NUMA host with a large number of nodes.
>
> We need to plan for the software that we are writing today to work for
> at least the next 5 years /even if we intend to replace the algorithm
> in the next release/.  It is very difficult to foresee what might
> happen to hardware in that time.
>
> But it's OK, we don't need to panic.  We just need a safety catch
> which stops this algorithm running in situations where it won't work.
> Following a discussion with Dario, AIUI he plans to implement a rule
> that it will bail on systems with more than 8 NUMA nodes.
>
> That is releasable in 4.2 and ought to be satisfactory for you ?

Absolutely, that's fine. I just wanted to make sure that we don't drop 
the patches at all because of the theoretical fear of a large NUMA box 
lingering somewhere around the corner...

Thanks,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany