...

1) I have a theory for the strange cadence pattern,  if you buy me a beer and supply a white board plus a few markers I'll explain it.

Disproven Ideas

RHEL7/Lustre-2.10 Idea

This idea proposes that the increased system CPU usage on the MDS is caused by RHEL7 but more specificaly Lustre-2.10.  In the 1-year CPU graph of aocmds you can clearly see a large increase in system time starting around mid October 2019.  There is a very similar increase in user/system CPU time on nmpost061 through nmpost070.

...