OS CPU monitoring

LPAR2RRD monitors physical CPU usage based on HMC utilization data.
It is like physical CPU core allocation.

The OS is further able to "virtualize" CPU core and run tasks in parallel. That technology is called SMT (simultaneous multithreading).
Therefore the OS can still have free CPU resources although it runs on all CPU cores which it is able to allocate.

LPAR2RRD OS agent use vmstat for obtaining CPU utilization data

$ vmstat 60 1

System configuration: lcpu=8 mem=1536MB ent=0.20

kthr    memory              page              faults              cpu
----- -----------   ------------------------ ------------ -----------------------
 r  b   avm   fre   re  pi  po  fr   sr  cy  in   sy  cs  us sy id wa    pc    ec
 0  0 384410 11652   0   0   0   0    0   0   4 2038 2079  5 13 82  0  0.06  30.9

• us - user utilization
• sy - system utilization
• id - idle
• wa - CPU is waiting for IO

You can read Nigel's blog where he explains that as well: Why are the PCPU_ALL graphs lower?