debian: seeing extra cgroups for collectd plugins

[Jim Gauld]

Brief Description
-----------------
Seeing extra 'could not find cgroup' logs for collectd cpu and memory plugins. There are new cgroup directories for *.mount and *.scope see under /sys/fs/cgroup/* that should not be picked up by these plugins. This gives flood of useless logs.

Severity
--------
Provide the severity of the defect.
Minor: Feature usable, but has poor optics and log flooding.

Steps to Reproduce
------------------
Debian fresh install. Look at /var/log/collectd.log .

Expected Behavior
------------------
Should only see output like this (for cpu and memory plugins):
collectd[900868]: info platform memory usage: Usage: 52.4%; Reserved: 8000.0 MiB, Platform: 4193.8 MiB (Base: 3088.7, k8s-system: 1105.1), k8s-addon: 0.0
collectd[900868]: info 4K memory usage: Anon: 21.4%, Anon: 4071.0 MiB, cgroup-rss: 4208.3 MiB, Avail: 14936.1 MiB, Total: 19007.1 MiB
collectd[900868]: info 4K numa memory usage: node0, Anon: 20.92%, Anon: 4071.0 MiB, Avail: 15389.6 MiB, Total: 19460.6 MiB
collectd[900868]: info platform cpu usage plugin Usage: 16.2% (avg per cpu); cpus: 4, Platform: 15.8% (Base: 11.8, k8s-system: 4.0), k8s-addon: 0.0

Actual Behavior
----------------
e.g., flood of logs every 30 seconds like this for both cpu and memory plugin
2022-06-14T19:01:28.826 controller-0 collectd[646921]: info platform memory usage: could not find cgroup: sys-fs-fuse-connections.mount

Reproducibility
---------------
100%, is due to new cgroup configuration on Debian

System Configuration
--------------------
All systems.

Branch/Pull Time/Commit
-----------------------
BUILD_ID="2022-06-11_22-00-50"
+ Required Joao Paulo Taveras Musico's in-progress-work to enable collectd plugins.

Last Pass
---------
Worked on CentOS, this is new in Debian.

Timestamp/Logs
--------------
na

Test Activity
-------------
Developer testing

Workaround
----------
None, code changes required.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/monitoring/+/845821

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/monitoring/+/845821
Committed: https://opendev.org/starlingx/monitoring/commit/201c9524d097d3443759bee8a230658bf340b22a
Submitter: "Zuul (22348)"
Branch: master

commit 201c9524d097d3443759bee8a230658bf340b22a
Author: Jim Gauld <email address hidden>
Date: Tue Jun 14 16:30:18 2022 -0400

    debian: exclude unused cgroup directores from collectd plugins

    The cpu and memory plugins walk the tree under /sys/fs/cgroups
    and pick up unused cgroup sub-directories. This update specifically
    excludes any high-level directores named *.mount or *.scope since
    they are not used in monitoring accounting.

    Closes-Bug: 1978732

    TESTPLAN:
    Debian
    PASS: Inspect /var/log/collectd.log does not have extraneous
          *.mount, *.scope logs for cpu and memory plugins.

    CentOS:
    PASS: Inspect /var/log/collectd.log has expected output
          i.e., platform cpu and memory logs

    Signed-off-by: Jim Gauld <email address hidden>
    Change-Id: Iaa31e7a124671368de06bab59a4cdc86c8f8570e