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.\" $FreeBSD$ 29.\" " 30.Dd January 18, 2008 31.Dt CLOCKS 7 32.Os 33.Sh NAME 34.Nm clocks 35.Nd various system timers 36.Sh SYNOPSIS 37.In time.h 38.Sh DESCRIPTION 39.Dv HZ 40is not part of the application interface in 41.Bx . 42.Pp 43There are many different real and virtual (timekeeping) clocks with 44different frequencies: 45.Bl -bullet 46.It 47The scheduling clock. 48This is a real clock with frequency that happens to be 100. 49It is not available to applications. 50.It 51The statistics clock. 52This is a real clock with frequency that happens to be 128. 53It is not directly available to applications. 54.It 55The clock reported by 56.Xr clock 3 . 57This is a virtual clock with a frequency that happens to be 128. 58Its actual frequency is given by the macro 59.Dv CLOCKS_PER_SEC . 60Note that 61.Dv CLOCKS_PER_SEC 62may be floating point. 63Do not use 64.Xr clock 3 65in new programs under 66.Fx . 67It is feeble compared with 68.Xr getrusage 2 . 69It is provided for 70.Tn ANSI 71conformance. 72It is implemented by calling 73.Xr getrusage 2 74and throwing away information and resolution. 75.It 76The clock reported by 77.Xr times 3 . 78This is a virtual clock with a frequency that happens to be 128. 79Its actual frequency is given by the macro 80.Dv CLK_TCK 81(deprecated; do not use) and by 82.Fn sysconf _SC_CLK_TCK 83and by 84.Xr sysctl 3 . 85Note that its frequency may be different from 86.Dv CLOCKS_PER_SEC . 87Do not use 88.Xr times 3 89in new programs under 90.Fx . 91It is feeble compared with 92.Xr gettimeofday 2 93together with 94.Xr getrusage 2 . 95It is provided for 96.Tn POSIX 97conformance. 98It is implemented by calling 99.Xr gettimeofday 2 100and 101.Xr getrusage 2 102and throwing away information and resolution. 103.It 104The profiling clock. 105This is a real clock with frequency 1024. 106It is used mainly by 107.Xr moncontrol 3 , 108.Xr kgmon 8 109and 110.Xr gprof 1 . 111Applications should determine its actual frequency using 112.Xr sysctl 3 113or by reading it from the header in the profiling data file. 114.It 115The mc146818a clock. 116This is a real clock with a nominal frequency of 32768. 117It is divided down to give the statistic clock and the profiling clock. 118It is not available to applications. 119.It 120The microseconds clock. 121This is a virtual clock with frequency 1000000. 122It is used for most timekeeping in 123.Bx 124and is exported to applications in 125.Xr getrusage 2 , 126.Xr gettimeofday 2 , 127.Xr select 2 , 128.Xr getitimer 2 , 129etc. 130This is the clock that should normally be used by 131.Bx 132applications. 133.It 134The i8254 clock. 135This is a real clock/timer with a nominal frequency of 1193182. 136It has three independent time counters to be used. 137It is divided down to give the scheduling clock. 138It is not available to applications. 139.It 140The TSC clock (64-bit register) on fifth-generation or later x86 systems. 141This is a real clock with a frequency that is equivalent to the number of 142cycles per second of the CPU(s). 143Its frequency can be found using the 144.Va machdep.tsc_freq 145sysctl, if it is available. 146It is used to interpolate between values of the scheduling clock. 147It can be accessed using the 148.Dv PMIOTSTAMP 149request of 150.Xr perfmon 4 . 151.It 152The ACPI clock. 153This is a real clock/timer with a nominal frequency of 3579545. 154It is accessed via a 24 or 32 bit register. 155Unlike the TSC clock, it maintains a constant tick rate even when the CPU 156sleeps or its clock rate changes. 157It is not available to applications. 158.El 159.Pp 160Summary: if 161.Dv HZ 162is not 1000000 then the application is probably using the wrong clock. 163.Sh SEE ALSO 164.Xr gprof 1 , 165.Xr clock_gettime 2 , 166.Xr getitimer 2 , 167.Xr getrusage 2 , 168.Xr gettimeofday 2 , 169.Xr select 2 , 170.Xr clock 3 , 171.Xr moncontrol 3 , 172.Xr times 3 173.Sh AUTHORS 174.An -nosplit 175This manual page was written by 176.An J\(:org Wunsch 177after a description posted by 178.An Bruce Evans . 179