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Features/Cpu-host Support


CPU-Host Support


CPU-Host support allows the virtual machines to see and utilize the host's CPU flags, this enables better performance in VM's, at the price of worse portablity.


Current status

  • Merged
  • Last updated date: 19 Dec 2012

Detailed Description

Since with host-passthrough gives the host cpu-capabilities to the VM's CPU, migration can not happen to different CPU-models. This could still be acceptable if all the hosts are all uniform in the cluster.

  • engine modifications:
    • modify VmStatic, add useHostCpuFlags boolean property
      • database schema modification in tables, views and stored procedures
      • DAO modifications
    • modify the Add/Edit VM dialog, add 'use host cpu flags' checkbox - it should be enabled only when Vm is pinned to host


  • vdsm modifications:
  • rest-api:
    • Add new element cpu_mode with values custom, host_model and host_passthrough to CPU
    • example
<cpu><topology cores="1" sockets="1"/><cpu_mode>HOST_PASSTHROUGH</cpu_mode></cpu>

Label should be "Pass through host CPU". When this is set the VM should be marked as non-migratable

Benefit to oVirt

Allows the users to get better performance from their VM's through using all CPU capabilities - including the ones not handled by qemu/kvm

Dependencies / Related Features

Documentation / External references

Comments and Discussion