Re: [Xen-devel] Xen 3.4.1 NUMA support

[Andre Przywara <andre.przywara@xxxxxxx>]

George Dunlap wrote:
> Andre Przywara wrote:
> > BTW: Shouldn't we set finally numa=on as the default value?
> >   
> Is there any data to support the idea that this helps significantly on 
> common systems?
I don't have any numbers handy, but I will try if I can generate some.

Looking from a high level perspective it is a shame that it's not the 
default: With numa=off the Xen domain loader will allocate physical 
memory from some node (maybe even from several nodes) and will schedule 
the guest on some other (even rapidly changing) nodes. According to 
Murphy's law you will end up with _all_ the memory access of a guest to 
be remote. But in fact a NUMA architecture is really beneficial for 
virtualization: As there are close to zero cross domain memory accesses 
(except for Dom0), each node is more or less self contained and each 
guest can use the node's memory controller almost exclusively.
But this is all spoiled as most people don't know about Xen's NUMA 
capabilities and don't set numa=on. Using this as a default would solve 
this.
Regards,
Andre.

--
Andre Przywara
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