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NetBSD 6.1.5 - man page for profhz (netbsd section 9)

HZ(9)				  BSD Kernel Developer's Manual 			    HZ(9)

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 pro-
     filing.  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 pro-
     filing 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)

BSD					  March 25, 2010				      BSD


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