Nova's libvirt driver now allows the specification of granular CPU feature flags when configuring CPU models.
One benefit of this change is the alleviation of a performance degradation experienced on guests running with certain Intel-based virtual CPU models after application of the "Meltdown" CVE fixes. This guest performance impact is reduced by exposing the CPU feature flag 'PCID' ("Process-Context ID") to the *guest* CPU, assuming that the PCID flag is available in the physical hardware itself.
For more details, refer to the documentation of ``[libvirt]/cpu_model_extra_flags`` in ``nova.conf`` for usage details.
The patch [*] is already in RHOS-13:
$> git branch --contains 95ca7cdbd
rhos-13.0-patches
[*] From RHOS-13 branch:
$ git show 95ca7cdbd
commit 95ca7cdbd2479df14b6368c565ebf21042aa05de
Author: Rajesh Tailor <ratailor>
Date: Wed Apr 11 17:11:15 2018 +0530
Handle libvirt/cpu_model_extra_flags option
This allows for specifying granular CPU feature flags when specifying
CPU models.
It should be set only if 'cpu_mode' and 'cpu_model' attributes are set
and cpu_mode attribute value is set to "custom".
NOTE: The related nova changes are done in change:
I6bb956808aa3df58747c865c92e5b276e61aff44
Change-Id: Id4f2cad2e0b0c34a7a68d0b3a6f69b44816f4cd9
(cherry picked from commit c12e3580287911a355de8bdf2fdd4c37c38d7fec)
The patch [*] is already in RHOS-13: $> git branch --contains 95ca7cdbd rhos-13.0-patches [*] From RHOS-13 branch: $ git show 95ca7cdbd commit 95ca7cdbd2479df14b6368c565ebf21042aa05de Author: Rajesh Tailor <ratailor> Date: Wed Apr 11 17:11:15 2018 +0530 Handle libvirt/cpu_model_extra_flags option This allows for specifying granular CPU feature flags when specifying CPU models. It should be set only if 'cpu_mode' and 'cpu_model' attributes are set and cpu_mode attribute value is set to "custom". NOTE: The related nova changes are done in change: I6bb956808aa3df58747c865c92e5b276e61aff44 Change-Id: Id4f2cad2e0b0c34a7a68d0b3a6f69b44816f4cd9 (cherry picked from commit c12e3580287911a355de8bdf2fdd4c37c38d7fec)