Re: [Xen-devel] [PATCH 2/4] [HVM] introduce CPU affinity for allocate_physmap call

["Andre Przywara" <andre.przywara@xxxxxxx>]

Ryan Harper wrote:
> One concern has been the static nature of the ACPI SRAT data versus the
> dynamic ability of the vcpu to cpu mapping.  If the scheduler is
> migrating the guest vcpu to various cpus, then the SRAT information is
> likely to be incorrect.
I think this is a problem even for the native OSes when you think of 
CPU- and/or memory-hotplugging. Although Linux can do CPU hotplugging, 
AFAIK NUMA isn't currently considered in this process. I think the most 
feasible approach would be to rebuild all affected structures when the 
hotplug event occurs. This will probably considered quite rare and thus 
could be potentially more costly, so I this is not something you want to 
do every time Xen decides to reschedule a VCPU. So IMHO pinning VCPUs to 
a certain node (actually all cores within this node) is OK for now.
> That said, if one creates a vnode, and it sufficiently restricts the
> vcpu affinity, then accurate SRAT information can be exported for the
> guest to utilize.
My patch does this automatically. CPU affinity information from the 
config file is ignored and each VCPUs affinity is set to match the NUMA 
topology.
Regards,
Andre.

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Andre Przywara
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