.\" .\" 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. .\" .\" $FreeBSD: src/share/man/man7/clocks.7,v 1.9.2.5 2001/12/17 11:30:15 ru Exp $ .\" .Dd January 5, 2019 .Dt CLOCKS 7 .Os .Sh NAME .Nm clocks .Nd various system timers .Sh SYNOPSIS .In time.h .Sh DESCRIPTION .Ql HZ is not part of the application interface in .Bx . .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 .Dx . 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 .Dx . 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 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 .Bx 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 .Bx applications. .It 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. .It 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 .Va hw.tsc_frequency and its presence via .Va hw.tsc_present . It is used to interpolate between values of the scheduling clock. It is only available to applications in a purely machine-dependent manner. .It The HPET (High Precision Event Timers). Only main counter is used currently. This CPU timer is expected to be faster than ACPI-fast24 and ACPI-safe, so it should be given higher priority. HPET is not enabled by default. To enable it, you should add .Li debug.acpi.enabled="hpet" to your .Pa /boot/loader.conf . If the HPET is detected and attached, .Va kern.cputimer.name will report .Li HPET . .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 , .Xr loader.conf 5 .Sh AUTHORS .An -nosplit This man page has been written by .An J\(:org Wunsch after a description posted by .An Bruce Evans .