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xen-devel
Re: [Xen-devel] [PATCH 2/4] [HVM] introduce CPU affinity for allocate_ph
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.
--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 277-84917
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