The CPU bar showed the average since the host booted, read for every
compute on every load of the VM list. The dialog now reads each compute's
graph endpoint (load over one second) when it opens, two computes at a
time so the reads hold at most two workers, and ignores answers of an
earlier opening. A host that cannot be read shows a dash. The since-boot
reading had no other caller and is removed.
Each poll of a host's overview graph held a worker for one second between
two CPU samples. The answer now carries its sample, signed with the time
and the compute; the next poll sends it back and the usage is taken since
then, so a point is the average since the previous one (normally 5 s, at
most 15 s). Without a sample, or with one that is altered, older or from
another host, or when the host restarted, it is measured over one second
as before.
A sample is one reading; the busy share was mixed from separate readings,
counted guest time twice (it is part of user) and added half a percent.
A host that cannot be read leaves a gap in both graphs instead of a zero
CPU point and a broken memory axis.
