---
deprecations:
  - |
    Support to monitor performance events for Intel CMT (Cache
    Monitoring Technology, or "CQM" in Linux kernel parlance) -- namely
    ``cmt``, ``mbm_local`` and ``mbm_total`` -- via the config attribute
    ``[libvirt]/enabled_perf_events`` is now *deprecated* from Nova, and
    will be *removed* in the "Stein" release.  Otherwise, if you have
    enabled those events, and upgraded to Linux kernel 4.14 (or suitable
    downstream version), it will result in instances failing to boot.

    That is because the Linux kernel has deleted the `perf` framework
    integration with Intel CMT, as the feature was broken by design --
    an incompatibility between Linux's `perf` infrastructure and Intel
    CMT.  It was removed in upstream Linux version v4.14; but bear in
    mind that downstream Linux distributions with lower kernel versions
    than 4.14 have backported the said change.
