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

NAME
     hz, tick, tickadj, stathz, profhz -- system time model

SYNOPSIS
     extern int hz;
     extern int tick;
     extern int tickadj;
     extern int stathz;
     extern int profhz;

DESCRIPTION
     The system is driven by hardclock(9) interrupts, which occur at hz fre-
     quency, and are used to keep track of real time.

     On systems where another independent clock is available, it is set at
     stathz frequency, and used to gather timing statistics.  Ideally, it
     would be better to drive stathz with a slightly randomized clock, that is
     still a fixed number on average, as this would prevent malicious pro-
     cesses from working around the scheduler.  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 must be a multiple of stathz.  This
     will give higher resolution profiling information.

     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, but by no more than ten times tickadj.

     Those systems variables are available as a struct clockinfo from
     sysctl(3).

SEE ALSO
     adjtime(2), clock_getres(2), sysctl(3), hardclock(9), microtime(9)

BSD                              May 31, 2007                              BSD