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

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

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 ?

Ian.

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