NAME
hz,
tick,
tickadj,
stathz,
profhz —
system time model
SYNOPSIS
#include <sys/kernel.h>
extern int hz;
extern int tick;
extern int tickadj;
extern int stathz;
extern int profhz;
DESCRIPTION
The essential clock handling routines in
NetBSD are
written to operate with two timers that run independently of each other. The
main clock, running
hz times per second, is used to keep
track of real time.
In another words,
hz specifies the number of times the
hardclock(9) timer ticks per
second. Normally
hardclock(9)
increments time by
tick each time it is called. If the
system clock has drifted,
adjtime(2) may be used to skew
this increment based on the rate of
tickadj.
The second timer is used to gather timing statistics. It also handles kernel and
user profiling. If the second timer is programmable, it is randomized to avoid
aliasing between the two clocks. The mean frequency of the second timer is
stathz. If a separate clock is not available,
stathz is set to
hz.
If profiling is enabled, the clock normally used to drive
stathz may be run at a higher rate
profhz, which is required to be a multiple of
stathz. This will give higher resolution profiling
information.
These system variables are also available as
struct clockinfo
from
sysctl(3) and
kern.clockrate from
sysctl(8). The
hz is hardware-dependent; it can be overridden (if the
machine dependent code supports this) by defining
HZ
in the kernel configuration file (see
options(4)). Only override the
default value if you really know what you are doing.
SEE ALSO
adjtime(2),
callout(9),
hardclock(9),
microtime(9),
time_second(9)