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.\" $FreeBSD$ 26.\" 27.Dd November 20, 2000 28.Dt GET_CYCLECOUNTER 9 29.Os 30.Sh NAME 31.Nm get_cyclecounter 32.Nd get the CPU's fast counter register contents 33.Sh SYNOPSIS 34.In sys/param.h 35.In sys/queue.h 36.In machine/cpufunc.h 37.In machine/cpu.h 38.Ft u_int64_t 39.Fn get_cyclecounter "void" 40.Sh DESCRIPTION 41The 42.Fn get_cyclecounter 43functon uses a register 44available in most modern CPUs 45to return a value 46that is monotonically increasing 47inside each CPU. 48.Pp 49In SMP systems, 50there will be a number of 51separate monotonic sequences, 52one for each CPU running. 53The value in the SMP case is 54selected from one of these sequences, 55dependent on which CPU 56was scheduled to service the request. 57.Pp 58The speed and maximum value 59of each counter 60is CPU-dependent. 61Some CPUs 62(such as the 63.Tn Intel 6480386 and 80486) 65do not have such a register, 66so 67.Fn get_cyclecounter 68on these platforms 69returns the number of nanoseconds 70represented by the 71structure returned by 72.Xr nanotime 9 . 73.Pp 74The 75.Tn Pentium 76processors all use the 77.Li TSC 78register. 79.Pp 80The 81.Tn Alpha 82processors use the 83.Li PCC 84register. 85.Pp 86The 87.Tn IA64 88processors use the 89.Li AR.ITC 90register. 91.Sh SEE ALSO 92.Xr nanotime 9 93.Sh HISTORY 94The 95.Fn get_cyclecounter 96function first appeared in 97.Fx 5.0 . 98.Sh AUTHORS 99This manual page was written by 100.An Mark Murray Aq markm@FreeBSD.org . 101