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.\" Copyright (c) 2000 Mark R V Murray
.\" All rights reserved.
.\"
.\" 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 AUTHOR AND CONTRIBUTORS ``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 AUTHOR OR CONTRIBUTORS 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.
.\"
.\" $FreeBSD$
.\"
.Dd November 20, 2000
.Dt GET_CYCLECOUNT 9
.Os
.Sh NAME
.Nm get_cyclecount
.Nd get the CPU's fast counter register contents
.Sh SYNOPSIS
.In sys/param.h
.In sys/systm.h
.In machine/cpu.h
.Ft u_int64_t
.Fn get_cyclecount "void"
.Sh DESCRIPTION
The
.Fn get_cyclecount
function uses a register
available in most modern CPUs
to return a value
that is monotonically increasing
inside each CPU.
.Pp
On SMP systems,
there will be a number of
separate monotonic sequences,
one for each CPU running.
The value in the SMP case is
selected from one of these sequences,
dependent on which CPU
was scheduled to service the request.
.Pp
The speed and the maximum value
of each counter
is CPU-dependent.
Some CPUs
(such as the
.Tn Intel
80386 and 80486)
do not have such a register,
so
.Fn get_cyclecount
on these platforms
returns the number of nanoseconds
represented by the
structure returned by
.Xr nanotime 9 .
.Pp
The
.Tn Pentium
processors all use the
.Li TSC
register.
.Pp
The
.Tn Alpha
processors use the
.Li PCC
register.
.Pp
The
.Tn IA64
processors use the
.Li AR.ITC
register.
.Sh SEE ALSO
.Xr nanotime 9
.Sh HISTORY
The
.Fn get_cyclecount
function first appeared in
.Fx 5.0 .
.Sh AUTHORS
This manual page was written by
.An Mark Murray Aq markm@FreeBSD.org .
|
