XenAPI vCPU Topology

XenAPI vCPU Topology

https://blueprints.launchpad.net/nova/+spec/xenapi-vcpu-topology

The proposal is to add support for vCPU topology for XenAPI. It will utilize the work done on the virt-driver-vcpu-toplogy blueprint. Most of this blueprint has been copied from the virt-driver-vcpu-topology blueprint as they align well but differ slightly on implementations per hypervisor.

Problem description

See Virt Driver VCPU Topology spec referenced at the end of blueprint.

Proposed change

See Virt Driver VCPU Topology spec referenced at the end of blueprint.

For XenServer implementation the following configurations will be used:

  • hw:cpu_sockets=NN - preferred number of sockets to expose to the guest

  • hw:cpu_cores=NN - preferred number of cores to expose to the guest

  • hw:cpu_max_sockets=NN - maximum number of sockets to expose to the guest

  • hw:cpu_max_cores=NN - maximum number of cores to expose to the guest

At the image level the exact same set of parameters will be permitted, with the exception that image properties will use underscores throughout instead of an initial colon.

  • hw_cpu_sockets=NN - preferred number of sockets to expose to the guest

  • hw_cpu_cores=NN - preferred number of cores to expose to the guest

  • hw_cpu_max_sockets=NN - maximum number of sockets to expose to the guest

  • hw_cpu_max_cores=NN - maximum number of cores to expose to the guest

Note that XenServer does not have a specific setting for number of threads so setting threads will not function on XenServer currently.

Alternatives

None, will utilize existing work done in virt-driver-vcpu-topology blueprint

Data model impact

No impact.

The new properties will use the existing flavor extra specs and image property storage models.

REST API impact

No impact.

The new properties will use the existing flavor extra specs and image property API facilities.

Security impact

The choice of sockets vs cores can have an impact on host resource utilization when NUMA is involved, since over use of cores will prevent a guest being split across multiple NUMA nodes. This feature addresses this by allowing the flavor administrator to define hard caps, and ensuring the flavor will always take priority over the image settings.

Notifications impact

No impact.

There is no need for this feature to integrate with notifications.

Other end user impact

The user will gain the ability to control aspects of the vCPU topology used by their guest. They will achieve this by setting image properties in glance.

Performance Impact

The cores vs sockets vs threads decision does not involve any scheduler interaction, since this design is not attempting to match host topology to guest topology. A later blueprint on CPU pinning will make it possible todo such host to guest topology matching, and its performance impact will be considered there.

Other deployer impact

The flavor extra specs will gain new parameters in extra specs which a cloud administrator can choose to use. If none are set then the default behaviour is unchanged from previous releases.

Developer impact

Implementation will add support for XenAPI drivers.

Implementation

Assignee(s)

Primary assignees:

antonym johngarbutt

Work Items

  • Add XenAPI driver support for choosing a CPU topology solution based on the given hw_cpu_* parameters.

Dependencies

No external dependencies

Testing

Testing of this feature will be covered by the XenServer CI.

Documentation Impact

The new flavor extra specs and image properties will need to be documented. Guidance should be given to cloud administrators on how to make most effective use of the new features. Guidance should be given to the end user on how to use the new features to address their use cases.

References

Creative Commons Attribution 3.0 License

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nova-specs