Summary
The "GBL_ACTIVE_CPU" metric and the output of the comand “lscfg” do not match on an SMT enabled server.
Error
When checking with metrics "GBL_ACTIVE_CPU" the number is 4, but when running the command “lscfg”, the number is 2.
Cause
From the perfstat output, it is evident that the system has 4 CPUs:
Type : Dedicated-SMT
Online Virtual CPUs : 2
SMT is enabled and 2 virtual CPUs are configured. When SMT is enabled, the number of CPUs become twice since SMT enables another execution thread for each CPU core.
Fix
On AIX, there are two set of metrics introduced since PA 4.60 – Logical and Physical. Logical metrics will not match the system command outputs when SMT is enabled on a System. It should be compared with the Physical metrics. These metrics have similar names as logical but they have _PHYS_ in between. For example, GBL_PHYS_ACTIVE_CPU.