PERF feature provides an API to share the system timer (clock) in two modes:
A free-running mode, which causes the timer to overflow after reaching its maximum value and continue to count up from its minimum value. This mode can be used for fine grained execution measurement. This deactivates the system clock.
A periodic mode, where the system timer is shared between the application and the system tick. The timer will generate an interrupt at a set interval. The application handler will be invoked at the required period. This mode can be used by applications such as profilers.
PERF API closely follows the timer(9DDI) device driver interface.
For more details see PERF(5FEA).