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Upstream Linux kernel has deleted[*] the `perf` framework integration with Intel CMT (Cache Monitoring Technology; or "CQM" in Linux kernel parlance), because the feature was broken by design -- an incompatibility between Linux's `perf` infrastructure and Intel CMT hardware support. It was removed in upstream kernel version v4.14; but bear in mind that downstream Linux distributions with lower kernel versions than 4.14 have backported the said change. Nova supports monitoring of the above mentioned Intel CMT events (namely: 'cmt', 'mbm_local', and 'mbm_total') via the configuration attribute `[libvirt]/enabled_perf_events`. Given that the underlying Linux kernel infrastructure for Intel CMT is removed, we should remove support for it in Nova too. Otherwise enabling them in Nova, and updating to a Linux kernel 4.14 (or above) will result in instances failing to boot. To that end, deprecate support for the three Intel CMT events in "Rocky" release, with the intention to remove support for it in the upcoming "Stein" release. Note that we cannot deprecate / remove `enabled_perf_events` config attribute altogether -- since there are other[+] `perf` events besides Intel CMT. Whether anyone is using those other events with Nova is a good question to which we don't have an equally good answer for, if at all. [*] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c39a0e2 [+] https://libvirt.org/formatdomain.html#elementsPerf Closes-Bug: #1751073 Change-Id: I7e77f87650d966d605807c7be184e670259a81c1 Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
18 lines
920 B
YAML
18 lines
920 B
YAML
---
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deprecations:
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- |
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Support to monitor performance events for Intel CMT (Cache
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Monitoring Technology, or "CQM" in Linux kernel parlance) -- namely
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``cmt``, ``mbm_local`` and ``mbm_total`` -- via the config attribute
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``[libvirt]/enabled_perf_events`` is now *deprecated* from Nova, and
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will be *removed* in the "Stein" release. Otherwise, if you have
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enabled those events, and upgraded to Linux kernel 4.14 (or suitable
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downstream version), it will result in instances failing to boot.
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That is because the Linux kernel has deleted the `perf` framework
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integration with Intel CMT, as the feature was broken by design --
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an incompatibility between Linux's `perf` infrastructure and Intel
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CMT. It was removed in upstream Linux version v4.14; but bear in
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mind that downstream Linux distributions with lower kernel versions
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than 4.14 have backported the said change.
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