1.\" Copyright (c) 2000 Mark R V Murray 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.Dd March 15, 2011 26.Dt GET_CYCLECOUNT 9 27.Os 28.Sh NAME 29.Nm get_cyclecount 30.Nd get the CPU's fast counter register contents 31.Sh SYNOPSIS 32.In sys/param.h 33.In sys/systm.h 34.In machine/cpu.h 35.Ft uint64_t 36.Fn get_cyclecount "void" 37.Sh DESCRIPTION 38The 39.Fn get_cyclecount 40function uses a register 41available in most modern CPUs 42to return a value 43that is monotonically increasing 44inside each CPU. 45.Pp 46On SMP systems, 47there will be a number of 48separate monotonic sequences, 49one for each CPU running. 50The value in the SMP case is 51selected from one of these sequences, 52dependent on which CPU 53was scheduled to service the request. 54.Pp 55The speed and the maximum value 56of each counter 57is CPU-dependent. 58Some CPUs 59(such as the 60.Tn Intel 6180486) 62do not have such a register, 63so 64.Fn get_cyclecount 65on these platforms 66returns a (monotonic) combination of numbers 67represented by the 68structure returned by 69.Xr binuptime 9 . 70.Pp 71The 72.Tn AMD64 73and 74.Tn Intel 64 75processors use the 76.Li TSC 77register. 78.Sh SEE ALSO 79.Xr binuptime 9 80.Sh HISTORY 81The 82.Fn get_cyclecount 83function first appeared in 84.Fx 5.0 . 85.Sh AUTHORS 86This manual page was written by 87.An Mark Murray Aq Mt markm@FreeBSD.org . 88