[collectd] [plugin:virt] - Confusing metrics value type.

[Gaël THEROND]

Hi everyone,

I'm currently building some monitoring pages for our Openstack platform.
To do so I leverage collectd with collectd-virt plugin and write_prometheus
plugin.

Everything is fine, I'm receiving all metrics and I'm able to graph them
from Grafana using prometheus as our datasource.

The only issue that I'm facing is to manipulate those metrics.
Our platform is CentOS 8 based and uses Collectd 5.11 provided by CentOS.

The first issue that I've got is that few metrics labels exposed to
prometheus aren't listed in here or are having a different name (We do not
relabeled them yet): https://collectd.org/wiki/index.php/Plugin:virt

The second issue that I face is to find out the appropriate unit type of
those metrics as, yes, I've the data type, but are those float and int
expressing ms? ns? ms/s? time since epoch? or something else?

Here are the problematic metrics:
collectd_virt_virt_cpu_total_total - prometheus type counter
collectd_virt_ps_cputime_user_total - prometheus type counter
collectd_virt_ps_cputime_syst_total - prometheus type counter

Subsidiary question:
Is there any way to get the vm internal memory usage?
Because within the wiki page there is memory-rss etc but our collectd with
collectd-virt plugin is just exposing allocated memory.

Additional information:
OS Version: CentOS 8.4.2105
Kernel: 4.18.0-305.7.1
Collectd: 5.11.0-2
Collectd-virt: 5.11.0-2
Collectd-write_prometheus: 5.11.0-2

Feel free to tell me if I missed something important.
Cheers!
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