1.\" 2.\" Copyright (c) 1996 Joerg Wunsch 3.\" 4.\" All rights reserved. 5.\" 6.\" This program is free software. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 18.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 21.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27.\" 28.\" $Id$ 29.\" " 30.Dd April 1, 1996 31.Os 32.Dt CLOCKS 7 33.Sh NAME 34.Nm clocks 35.Nd various system timers 36.Sh SYNOPSIS 37.Fd #include <time.h> 38.Sh DESCRIPTION 39.Ql HZ 40is not part of the application interface in BSD. 41.Pp 42There are many different real and virtual (timekeeping) clocks with 43different frequencies: 44.Bl -bullet -offset XXX 45.It 46The scheduling clock. This is a real clock with frequency that 47happens to be 100. It isn't available to applications. 48.It 49The statistics clock. This is a real clock with frequency that 50happens to be 128. It isn't directly available to applications. 51.It 52The clock reported by 53.Xr clock 3 . 54This is a virtual clock with a frequency that happens to be 128. It's 55actual frequency is given by the macro 56.Dv CLOCKS_PER_SEC . 57Note that 58.Dv CLOCKS_PER_SEC 59may be floating point. Don't use 60.Fn clock 61in new programs under FreeBSD. It is feeble compared with 62.Xr getrusage 2 . 63It is provided for ANSI conformance. It is implemented by calling 64.Fn getrusage 65and throwing away information and resolution. 66.It 67The clock reported by 68.Xr times 3 . 69This is a virtual clock with a frequency that happens to be 128. It's 70actual frequency is given by the macro 71.Dv CLK_TCK 72(deprecated; don't use) and by 73.Fn sysconf SC_CLK_TCK 74and by 75.Xr sysctl 3 . 76Note that its frequency may be different from 77.Dv CLOCKS_PER_SEC . 78Don't use 79.Xr times 3 80in new programs under FreeBSD. It is feeble compared with 81.Xr gettimeofday 2 82together with 83.Fn getrusage . 84It is provided for POSIX 85conformance. It is implemented by calling 86.Fn gettimeofday 87and 88.Fn getrusage 89and throwing away information and resolution. 90.It 91The profiling clock. This is a real clock with frequency 1024. 92It is used mainly by 93.Xr moncontrol 3 , 94.Xr kgmon 8 95and 96.Xr gprof 1 . 97Applications should determine its actual frequency using 98.Xr sysctl 3 99or by reading it from the header in the profiling data file. 100.It 101The mc14618a clock. This is a real clock with a nominal frequency of 10232768. It is divided down to give the statistic clock and the profiling 103clock. It isn't available to applications. 104.It 105The microseconds clock. This is a virtual clock with frequency 1061000000. It is used for most timekeeping in BSD and is exported 107to applications in 108.Xr getrusage 2 , 109.Xr gettimeofday 2 , 110.Xr select 2 , 111.Xr getitimer 2 , 112etc... This is the clock that should normally be used 113by BSD applications. 114.It 115the i8254 clock. This is a real clock with a nominal frequency of 1161193182. It is divided down to give the scheduling clock. It isn't 117available to applications. 118.It 119the i586 clock on i586 systems. This is a real clock with a frequency 120of up to 200000000. It is used to interpolate between values of the 121scheduling clock. It isn't available to applications. 122.El 123.Pp 124Summary: if 125.Ql HZ 126isn't 1000000 then the application is probably using the wrong clock. 127.Sh SEE ALSO 128.Xr gprof 1 , 129.Xr getitimer 2 , 130.Xr getrusage 2 , 131.Xr gettimeofday 2 , 132.Xr select 2 , 133.Xr clock 3 , 134.Xr moncontrol 3 , 135.Xr times 3 136.Sh AUTHORS 137This man page has been written by 138.ie t J\(:org Wunsch 139.el Joerg Wunsch 140after a description posted by Bruce Evans. 141