[ops][nova] Quick show of hands: any use Intel (non-CMT) `perf` events?
Heya folks, While removing some dead code I was wondering if anyone here uses "non-CMT" (Cache Monitoring Technology) performance events events? I'm referring to the events here[0], besides the first three, which are CMT-related. Background ---------- The Intel CMT events (there are three of them) were deprecated during the Rocky release, in this[1] commit, and with this rationale: 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. Now we're removing[2] support for CMT events altogether. Question -------- What I'm wondering now is the answer to the last sentence in the above quoted commit: "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". If we know that "no one" (as if we can tell for sure) is using them, we can get rid of more dead code. So, any operators using the non-CMT events from here[0]? [0] https://libvirt.org/formatdomain.html#elementsPerf [1] https://opendev.org/openstack/nova/commit/fc4794acc6 —libvirt: Deprecate support for monitoring Intel CMT `perf` events [2] https://review.opendev.org/669129 — libvirt: Remove support for Intel CMT `perf` event -- /kashyap
Sorry for reply late. + ceilometer The ceilometer is still using the cmt meter https://github.com/openstack/ceilometer/blob/master/ceilometer/compute/virt/... should we deprecate them? And there are some other meter depend on perf feature https://github.com/openstack/ceilometer/blob/master/ceilometer/compute/virt/... So sounds like we shouldn't remove the whole perf feature. Thanks Alex Kashyap Chamarthy <kchamart@redhat.com> 于2019年7月4日周四 下午6:37写道：
Heya folks,
While removing some dead code I was wondering if anyone here uses "non-CMT" (Cache Monitoring Technology) performance events events? I'm referring to the events here[0], besides the first three, which are CMT-related.
Background ----------
The Intel CMT events (there are three of them) were deprecated during the Rocky release, in this[1] commit, and with this rationale:
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.
Now we're removing[2] support for CMT events altogether.
Question --------
What I'm wondering now is the answer to the last sentence in the above quoted commit: "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".
If we know that "no one" (as if we can tell for sure) is using them, we can get rid of more dead code.
So, any operators using the non-CMT events from here[0]?
[0] https://libvirt.org/formatdomain.html#elementsPerf [1] https://opendev.org/openstack/nova/commit/fc4794acc6 —libvirt: Deprecate support for monitoring Intel CMT `perf` events [2] https://review.opendev.org/669129 — libvirt: Remove support for Intel CMT `perf` event
-- /kashyap
participants (2)
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Alex Xu
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Kashyap Chamarthy