The
hardclock()
function is called periodically based on pending work.
The rate ranges from
hz
times per second on a very busy system, to twice a second on an idle system.
The
cnt
argument reports an estimate of the number of ticks since the last call.
Over long timescales, the average sum of
cnt
over one second is
hz.
See
hz(9)
for important details over shorter time scales.
The
usermode
argument is non-zero when
hardclock()
is called from an context that interrupted usermode execution.
hardclock()
may perform different tasks such as:
- Run the current process's virtual and profile time (decrease the
corresponding timers, if they are activated, and generate
SIGVTALRM
or
SIGPROF,
respectively).
- Increment the time-of-day, taking care of any
ntpd(8)
or
adjtime(2)
induced changes and leap seconds, as well as any necessary
compensations to keep in sync with PPS signals or external clocks, if
supported by the kernel.
- Schedule softclock interrupts
(
swi(9)
)
processing.
- Collect
hwpmc(4)
statistics.
- Do device polling, when enabled
(
see
polling(4)
).
- Implement software
watchdog(9)
processing.
- Enqueue
epoch(9)
processing.
