.\"
.\" Copyright (c) 1996 Joerg Wunsch
.\"
.\" All rights reserved.
.\"
.\" This program is free software.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $Id: clocks.7,v 1.7 1997/09/04 20:59:33 jdp Exp $
.\" "
.Dd April 1, 1996
.Os
.Dt CLOCKS 7
.Sh NAME
.Nm clocks
.Nd various system timers
.Sh SYNOPSIS
.Fd #include <time.h>
.Sh DESCRIPTION
.Ql HZ
is not part of the application interface in BSD.
.Pp
There are many different real and virtual (timekeeping) clocks with
different frequencies:
.Bl -bullet -offset XXX
.It
The scheduling clock.  This is a real clock with frequency that
happens to be 100.  It isn't available to applications.
.It
The statistics clock.  This is a real clock with frequency that
happens to be 128.  It isn't directly available to applications.
.It
The clock reported by
.Xr clock 3 .
This is a virtual clock with a frequency that happens to be 128.  Its
actual frequency is given by the macro 
.Dv CLOCKS_PER_SEC .  
Note that
.Dv CLOCKS_PER_SEC
may be floating point.  Don't use 
.Fn clock
in new programs under
.Tn FreeBSD .
It is feeble compared with
.Xr getrusage 2 .
It is provided for ANSI conformance.  It is implemented by calling
.Fn getrusage
and throwing away information and resolution.
.It
The clock reported by
.Xr times 3 .
This is a virtual clock with a frequency that happens to be 128.  Its
actual frequency is given by the macro
.Dv CLK_TCK
(deprecated; don't use) and by 
.Fn sysconf SC_CLK_TCK
and by
.Xr sysctl 3 .
Note that its frequency may be different from
.Dv CLOCKS_PER_SEC .
Don't use 
.Xr times 3
in new programs under
.Tn FreeBSD .
It is feeble compared with
.Xr gettimeofday 2
together with 
.Fn getrusage .
It is provided for POSIX
conformance.  It is implemented by calling 
.Fn gettimeofday
and
.Fn getrusage
and throwing away information and resolution.
.It
The profiling clock.  This is a real clock with frequency 1024.
It is used mainly by
.Xr moncontrol 3 ,
.Xr kgmon 8
and
.Xr gprof 1 .
Applications should determine its actual frequency using
.Xr sysctl 3
or by reading it from the header in the profiling data file.
.It
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.
.It
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
.Xr getrusage 2 ,
.Xr gettimeofday 2 ,
.Xr select 2 ,
.Xr getitimer 2 ,
etc...  This is the clock that should normally be used
by BSD applications.
.It
the i8254 clock.  This is a real clock with a nominal frequency of
1193182.  It is divided down to give the scheduling clock.  It isn't
available to applications.
.It
the i586 clock on i586 systems.  This is a real clock with a frequency
of up to 200000000.  It is used to interpolate between values of the
scheduling clock.  It isn't available to applications.
.El
.Pp
Summary: if
.Ql HZ
isn't 1000000 then the application is probably using the wrong clock.
.Sh SEE ALSO
.Xr gprof 1 ,
.Xr getitimer 2 ,
.Xr getrusage 2 ,
.Xr gettimeofday 2 ,
.Xr select 2 ,
.Xr clock 3 ,
.Xr moncontrol 3 ,
.Xr times 3
.Sh AUTHORS
This man page has been written by
.ie t J\(:org Wunsch
.el Joerg Wunsch
after a description posted by
.An Bruce Evans .