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_CYCLECOUNT 9 29.Os 30.Sh NAME 31.Nm get_cyclecount 32.Nd get the CPU's fast counter register contents 33.Sh SYNOPSIS 34.In sys/param.h 35.In sys/systm.h 36.In machine/cpu.h 37.Ft u_int64_t 38.Fn get_cyclecount "void" 39.Sh DESCRIPTION 40The 41.Fn get_cyclecount 42function uses a register 43available in most modern CPUs 44to return a value 45that is monotonically increasing 46inside each CPU. 47.Pp 48On SMP systems, 49there will be a number of 50separate monotonic sequences, 51one for each CPU running. 52The value in the SMP case is 53selected from one of these sequences, 54dependent on which CPU 55was scheduled to service the request. 56.Pp 57The speed and the maximum value 58of each counter 59is CPU-dependent. 60Some CPUs 61(such as the 62.Tn Intel 6380486) 64do not have such a register, 65so 66.Fn get_cyclecount 67on these platforms 68returns the number of nanoseconds 69represented by the 70structure returned by 71.Xr nanotime 9 . 72.Pp 73The 74.Tn Pentium 75processors all use the 76.Li TSC 77register. 78.Pp 79The 80.Tn Alpha 81processors use the 82.Li PCC 83register. 84.Pp 85The 86.Tn IA64 87processors use the 88.Li AR.ITC 89register. 90.Sh SEE ALSO 91.Xr nanotime 9 92.Sh HISTORY 93The 94.Fn get_cyclecount 95function first appeared in 96.Fx 5.0 . 97.Sh AUTHORS 98This manual page was written by 99.An Mark Murray Aq markm@FreeBSD.org . 100