Microkernel CPU Instrumentation

The C_OS implements the microkernel CPU instrumentation via the sysctl kern.mkstats.cpu node.

Instrumentation related to microkernel CPU use comprises the following measurements:

Function	Instrument Type	Description
`total_cpu()`	Counter	Measures the number of milliseconds CPU has been used since boot
`external()`	Counter	Measures the number of milliseconds the CPU has been used outside execution actor since boot (similar to UNIX supervisor mode)
`internal()`	Counter	Measures the number of milliseconds the CPU has been used inside execution actor supervisor mode since boot (similar to UNIX user mode)

This basic instrumentation provides only raw measurements on top of which applications can compute ratios of CPU use according to their needs.