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[Thierry Carrez <thierry.carrez+lp@xxxxxxxxx>]

** Changed in: nova
       Status: Fix Committed => Fix Released

** Changed in: nova
    Milestone: None => kilo-2

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https://bugs.launchpad.net/bugs/1400315

Title:
  Add hyper-v timer enlightenments for windows guests

Status in OpenStack Compute (Nova):
  Fix Released

Bug description:
  Back in Folsom we added some special timer settings to improve the
  reliability of guest time keeping and performance

    https://bugs.launchpad.net/nova/+bug/1011848

  These were useful for both Windows and Linux guests,  but since that
  time, KVM has gained support for a number of further tunables that
  specifically help Windows guests supporting Hyper-V enlightenments.
  Setting these for all windows guests will improve time keeping
  reliability and performance of windows guests. There is no harm to
  setting them with old windows versions which lack support for this,
  since they'll simply ignore the extra feature with no negative impact.

  The recommended qemu configuration is from QEMU maintainers is:

     -cpu ...,hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time

  Which maps to the libvirt XML:

     <features>
       <hyperv>
         <relaxed state='on'/>
         <vapic state='on'/>
         <spinlocks state='on' retries='8191'/>
       </hyperv>
     <features/>

     <clock ...>
       <timer name='hypervclock' present='yes'/>
     </clock>

  Though there are some version caveats here:
  - relaxed state='on' libvirt 1.0.0+, qemu 1.1+
  - vapic, spinlocks requires libvirt 1.1.0+, qemu 1.1+
  - hypervclock requires libvirt 1.2.2+, qemu 2.0.0+

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