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: clocks.7,v 1.6 1997/03/21 20:14:09 mpp Exp $ 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. Its 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 62.Tn FreeBSD . 63It is feeble compared with 64.Xr getrusage 2 . 65It is provided for ANSI conformance. It is implemented by calling 66.Fn getrusage 67and throwing away information and resolution. 68.It 69The clock reported by 70.Xr times 3 . 71This is a virtual clock with a frequency that happens to be 128. Its 72actual frequency is given by the macro 73.Dv CLK_TCK 74(deprecated; don't use) and by 75.Fn sysconf SC_CLK_TCK 76and by 77.Xr sysctl 3 . 78Note that its frequency may be different from 79.Dv CLOCKS_PER_SEC . 80Don't use 81.Xr times 3 82in new programs under 83.Tn FreeBSD . 84It is feeble compared with 85.Xr gettimeofday 2 86together with 87.Fn getrusage . 88It is provided for POSIX 89conformance. It is implemented by calling 90.Fn gettimeofday 91and 92.Fn getrusage 93and throwing away information and resolution. 94.It 95The profiling clock. This is a real clock with frequency 1024. 96It is used mainly by 97.Xr moncontrol 3 , 98.Xr kgmon 8 99and 100.Xr gprof 1 . 101Applications should determine its actual frequency using 102.Xr sysctl 3 103or by reading it from the header in the profiling data file. 104.It 105The mc14618a clock. This is a real clock with a nominal frequency of 10632768. It is divided down to give the statistic clock and the profiling 107clock. It isn't available to applications. 108.It 109The microseconds clock. This is a virtual clock with frequency 1101000000. It is used for most timekeeping in BSD and is exported 111to applications in 112.Xr getrusage 2 , 113.Xr gettimeofday 2 , 114.Xr select 2 , 115.Xr getitimer 2 , 116etc... This is the clock that should normally be used 117by BSD applications. 118.It 119the i8254 clock. This is a real clock with a nominal frequency of 1201193182. It is divided down to give the scheduling clock. It isn't 121available to applications. 122.It 123the i586 clock on i586 systems. This is a real clock with a frequency 124of up to 200000000. It is used to interpolate between values of the 125scheduling clock. It isn't available to applications. 126.El 127.Pp 128Summary: if 129.Ql HZ 130isn't 1000000 then the application is probably using the wrong clock. 131.Sh SEE ALSO 132.Xr gprof 1 , 133.Xr getitimer 2 , 134.Xr getrusage 2 , 135.Xr gettimeofday 2 , 136.Xr select 2 , 137.Xr clock 3 , 138.Xr moncontrol 3 , 139.Xr times 3 140.Sh AUTHORS 141This man page has been written by 142.ie t J\(:org Wunsch 143.el Joerg Wunsch 144after a description posted by Bruce Evans. 145