Public bug reported: Upstream Linux kernel has removed[*] the 'perf cqm' (Cache Quality-of-Service Monitoring) from the following kernels onwards:
[linux]$> git tag --contains c39a0e2 v4.14 Impact for OpenStack / Nova --------------------------- Quoting the summary from Dan Berrangé from a downstream bug (with some edits, references and formatting): - Libvirt supports enabling perf event reporting per guest using <perf ../> XML in guest XML https://libvirt.org/formatdomain.html#elementsPerf - OpenStack has abiity to enable this support by using /etc/nova/nova.conf setting "enabled_perf_events" in [libvirt] section - Although libvirt supports many events, OpenStack only supports the 'cmt', 'mbmt' and 'mbml' perf events - Upstream Linux kernel decided the perf framework integration with 'cmt', 'mbmt' and 'mbml' events was broken by design and entirely deleted it[*] - Upstream kernel has provided a new approach to 'cmt', 'mbmt' and 'mbml' info reporting that is *not* using perf framework - There's unlikely to be any way for libvirt to make this functionality magically re-appear, given the kernel changes. The new approach is completely incompatible with what was done before. IOW, if someone has set "enabled_perf_events" in /etc/nova/nova.conf previously, they will be unable to start any guest, once they upgrade to any kernels that has backported the commit: c39a0e2 ("x86/perf/cqm: Wipe out perf based cqm")[*]. [*] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c39a0e2 ** Affects: nova Importance: Undecided Status: New ** Tags: libvirt ** Tags added: libvirt -- You received this bug notification because you are a member of Yahoo! Engineering Team, which is subscribed to OpenStack Compute (nova). https://bugs.launchpad.net/bugs/1751073 Title: [Regression] Nova's 'enabled_perf_events' feature will be broken with Linux Kernel 4.14+ Status in OpenStack Compute (nova): New Bug description: Upstream Linux kernel has removed[*] the 'perf cqm' (Cache Quality-of-Service Monitoring) from the following kernels onwards: [linux]$> git tag --contains c39a0e2 v4.14 Impact for OpenStack / Nova --------------------------- Quoting the summary from Dan Berrangé from a downstream bug (with some edits, references and formatting): - Libvirt supports enabling perf event reporting per guest using <perf ../> XML in guest XML https://libvirt.org/formatdomain.html#elementsPerf - OpenStack has abiity to enable this support by using /etc/nova/nova.conf setting "enabled_perf_events" in [libvirt] section - Although libvirt supports many events, OpenStack only supports the 'cmt', 'mbmt' and 'mbml' perf events - Upstream Linux kernel decided the perf framework integration with 'cmt', 'mbmt' and 'mbml' events was broken by design and entirely deleted it[*] - Upstream kernel has provided a new approach to 'cmt', 'mbmt' and 'mbml' info reporting that is *not* using perf framework - There's unlikely to be any way for libvirt to make this functionality magically re-appear, given the kernel changes. The new approach is completely incompatible with what was done before. IOW, if someone has set "enabled_perf_events" in /etc/nova/nova.conf previously, they will be unable to start any guest, once they upgrade to any kernels that has backported the commit: c39a0e2 ("x86/perf/cqm: Wipe out perf based cqm")[*]. [*] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c39a0e2 To manage notifications about this bug go to: https://bugs.launchpad.net/nova/+bug/1751073/+subscriptions -- Mailing list: https://launchpad.net/~yahoo-eng-team Post to : yahoo-eng-team@lists.launchpad.net Unsubscribe : https://launchpad.net/~yahoo-eng-team More help : https://help.launchpad.net/ListHelp