Vanilla Xen total CPU %

[Nick Calvert <nick.calvert@xxxxxxxxx>]

Hi everyone,

I am interested in calculating the approximate total CPU runtime % of
a vanilla Xen project host (without any of the bells and whistles of
XCP-ng or Xen Server). What I have at my disposal is Ubuntu, Xen and
the xl tool stack.

I have been experimenting with writing a parser for xentop output in
batch mode, this is a fairly easy task and I can see other attempts at
parsers across dead and dying github projects... my issue around this
is the precise meaning of the 'CPU/sec' metric given by xentop and how
I could use it to infer a total cpu time.

The docs for xentop say "CPU(sec) CPU time which the guest OS has
consumed(cumulated)".

My confusion is around how CPU 'seconds' actually relat to vCPUs, real
cores etc in this context. I can also see a couple of attempts at
figuring out total CPU %, but none look quite right.

If I were able to derive both the CPU seconds for each domu in an
interval, the aggregate CPU seconds in this interval and both total
vCPUs and physical cores what would be the correct formula for
approximating a total CPU runtime %?

Also if I am missing a trick and there is an easier way of calculating
this I would be extremely happy to hear it, as simple is nice :)

Thank you.