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Re: [Xen-devel] NUMA problem with AMD G34 system

To: Brian Marcotte <marcotte@xxxxxxxxx>
Subject: Re: [Xen-devel] NUMA problem with AMD G34 system
From: Andre Przywara <andre.przywara@xxxxxxx>
Date: Mon, 21 Feb 2011 14:42:59 +0100
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Brian Marcotte wrote:
I prepared Xen to handle this situation (nodes without memory)
before the M-C launch, before that it simply crashed. I agree that
it is not obvious that you need to populate at least 4 DIMMs per
CPU.

I suppose that Xen could arrange the cpu to node mapping such that
the memoryless CPUs were assigned to the "nearest" node making it so
you could benefit from the shared L3 cache.

I don't know that it's worth anyone's time though. Perhaps a warning
would suffice?
I also considered more possible action back then, but found that it is probably not worth the effort, as this kind of configuration was considered kind of bogus. But a warning message sounds like a good idea.


Do you have only 4 DIMMs?

Yes, but I don't expect that to last too long. We find that over the
lifetime of a machine, we max out the RAM slots long before we run out
of CPU. The second CPU is mostly just so we can (eventually) fill all
the RAM slots. It's not a problem to run with one CPU for while. I may
also just pin the domains to particular CPU cores rather than pull the
CPU.
Yes, just put all the DIMMs in the blue slots of the first CPU and boot Xen with maxcpus=8. This should give you the best results without much fiddling with the hardware.

Regards,
Andre.

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



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