Cloned specifically to track possible future nova.conf enhancement to support CPU flags specification. eg ability to set something like this: cpu_model=Haswell cpu_model_extra_flags="pdpe1gb" to enable use of 1GB huge pages with Haswell model as one use case for extra flags.
This RFE has much greater urgency/severity given the Meltdown fixes. People running Westmere, SandyBridge, IvyBridge named CPU models have a critical performance need to be able to set cpu_model_extra_flags="+pcid"
(In reply to Daniel Berrange from comment #2) > This RFE has much greater urgency/severity given the Meltdown fixes. People > running Westmere, SandyBridge, IvyBridge named CPU models have a critical > performance need to be able to set cpu_model_extra_flags="+pcid" I recall some discussion that not all Intel Westmere CPUs have PCID. Do we know for sure which models contain the PCID feature and which doesn't? From here[*], there are five variants of 'Westmere': Arrandale, Clarksdale, Gulftown, Westmere-EP and Westmere-EX. [*] https://software.intel.com/en-us/articles/intel-architecture-and-processor-identification-with-cpuid-model-and-family-numbers
I don't recall which variants have pcid and which don't but it doesn't really matter from POV of fixing this. It is upto admin to decide whether to enable the pcid feature. They may not want to enable it, even if they have it on some hosts, in order to maintain migrate compat across hosts.
The first part of this, to addressed the "Meltdown" performance degradation is merged upstream (Git master, Pike, and Queens): https://review.openstack.org/#/q/topic:bug/1750829+(status:open+OR+status:merged) http://git.openstack.org/cgit/openstack/nova/commit/?id=6b601b7&h=stable%2Fqueens The second part would be to lift this restriction, so that broader set of CPU flags are allowed.
Test procedure to verify this is written up here: https://bugzilla.redhat.com/show_bug.cgi?id=1570605#c5
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHEA-2019:0045