profhz(9) [netbsd man page]

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 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 avail-
     able, 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-depen-
     dent; 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

tickadj(1)						      General Commands Manual							tickadj(1)

NAME

       tickadj - set time-related kernel variables

SYNOPSIS

       tickadj [ -Aqs ] [ -a tickadj  ] [ -t tick  ]

DESCRIPTION

       The  tickadj   program  reads,  and  optionally modifies, several timekeeping-related variables in the running kernel in some machines, via
       /dev/kmem . The particular variables it is concerned with are tick , which is the number of microseconds added to the system time during  a
       clock  interrupt,  tickadj  , which sets the slew rate and resolution used by the adjtime  system call, and dosynctodr , which indicates to
       the kernels on some machines whether they should internally adjust the system clock to keep it in line with time-of-day clock or not.

       By default, with no arguments, tickadj  reads the variables of interest in the kernel and displays them. At the same time, it determines an
       "optimal" value for the value of the tickadj  variable if the intent is to run the ntpd Network Time Protocol (NTP) daemon, and prints this
       as well. Since the operation of tickadj	when reading the kernel mimics the operation of similar parts of the ntpd  program fairly closely,
       this can be useful when debugging problems with ntpd .

       Note  that tickadj  should be run with some caution when being used for the first time on different types of machines. The operations which
       tickadj	tries to perform are not guaranteed to work on all Unix machines and may in rare cases cause the kernel to crash.

COMMAND LINE OPTIONS

       -a      tickadj Set the kernel variable tickadj	to the value tickadj  specified.

       -A      Set the kernel variable tickadj	to an internally computed "optimal" value.

       -t      tick Set the kernel variable tick  to the value tick   specified.

       -s      Set the kernel variable dosynctodr  to zero, which disables the hardware time-of-year clock, a prerequisite for	running  the  ntpd
	       daemon under SunOS4.

       -q      Normally, tickadj  is quite verbose about what it is doing. The -q  flag tells it to shut up about everything except errors.

FILES

       /vmunix

       /unix

       /dev/kmem

BUGS

       Fiddling  with  kernel  variables at run time as a part of ordinary operations is a hideous practice which is only necessary to make up for
       deficiencies in the implementation of adjtime  in many kernels and/or brokenness of the system clock in some vendors' kernels. It would	be
       much better if the kernels were fixed and the tickadj  program went away.

SEE ALSO

       More documentation is available in the package ntp-doc.

AUTHOR

       David L. Mills <mills@udel.edu>

ntp 4.1.1b-r5																tickadj(1)