Re: NUMA problem with AMD G34 system

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

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