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

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

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...


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

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