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CLOCKS(7)          FreeBSD Miscellaneous Information Manual          CLOCKS(7)

NAME
     clocks - various system timers

SYNOPSIS
     #include <time.h>

DESCRIPTION
     `HZ' is not part of the application interface in BSD.

     There are many different real and virtual (timekeeping) clocks with
     different frequencies:

        +o   The scheduling clock.  This is a real clock with frequency that
            happens to be 100.  It isn't available to applications.

        +o   The statistics clock.  This is a real clock with frequency that
            happens to be 128.  It isn't directly available to applications.

        +o   The clock reported by clock(3).  This is a virtual clock with a
            frequency that happens to be 128.  Its actual frequency is given
            by the macro CLOCKS_PER_SEC.  Note that CLOCKS_PER_SEC may be
            floating point.  Don't use clock() in new programs under FreeBSD.
            It is feeble compared with getrusage(2).  It is provided for ANSI
            conformance.  It is implemented by calling getrusage() and
            throwing away information and resolution.

        +o   The clock reported by times(3).  This is a virtual clock with a
            frequency that happens to be 128.  Its actual frequency is given
            by the macro CLK_TCK (deprecated; don't use) and by
            sysconf(SC_CLK_TCK) and by sysctl(3).  Note that its frequency may
            be different from CLOCKS_PER_SEC.  Don't use times(3) in new
            programs under FreeBSD.  It is feeble compared with
            gettimeofday(2) together with getrusage().  It is provided for
            POSIX conformance.  It is implemented by calling gettimeofday()
            and getrusage() and throwing away information and resolution.

        +o   The profiling clock.  This is a real clock with frequency 1024.
            It is used mainly by moncontrol(3), kgmon(8) and gprof(1).
            Applications should determine its actual frequency using sysctl(3)
            or by reading it from the header in the profiling data file.

        +o   The mc14618a clock.  This is a real clock with a nominal frequency
            of 32768.  It is divided down to give the statistic clock and the
            profiling clock.  It isn't available to applications.

        +o   The microseconds clock.  This is a virtual clock with frequency
            1000000.  It is used for most timekeeping in BSD and is exported
            to applications in getrusage(2), gettimeofday(2), select(2),
            getitimer(2), etc...  This is the clock that should normally be
            used by BSD applications.

        +o   The i8254 clock.  This is a real clock/timer with a nominal
            frequency of 1193182.  It is divided down to give the scheduling
            clock.  It isn't available to applications.

        +o   The TSC clock (64-bit register) on fifth-generation or later x86
            systems.  This is a real clock with a frequency that is equivalent
            to the number of cycles per second of the CPU(s).  Its frequency
            can be found using the sysctl machdep.tsc_freq.  It is used to
            interpolate between values of the scheduling clock.  It is only
            available to applications in a purely machine-dependent manner.

     Summary: if `HZ' isn't 1000000 then the application is probably using the
     wrong clock.

SEE ALSO
     gprof(1), getitimer(2), getrusage(2), gettimeofday(2), select(2),
     clock(3), moncontrol(3), times(3)

AUTHORS
     This man page has been written by Jorg Wunsch after a description posted
     by Bruce Evans.

FreeBSD 11.0-PRERELEASE          April 1, 1996         FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | AUTHORS

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