100 lines
2.6 KiB
Groff
100 lines
2.6 KiB
Groff
.\" Copyright (c) 2000 Mark R V Murray
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd November 20, 2000
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.Dt GET_CYCLECOUNT 9
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.Os
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.Sh NAME
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.Nm get_cyclecount
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.Nd get the CPU's fast counter register contents
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/systm.h
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.In machine/cpu.h
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.Ft u_int64_t
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.Fn get_cyclecount "void"
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.Sh DESCRIPTION
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The
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.Fn get_cyclecount
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function uses a register
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available in most modern CPUs
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to return a value
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that is monotonically increasing
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inside each CPU.
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.Pp
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On SMP systems,
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there will be a number of
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separate monotonic sequences,
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one for each CPU running.
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The value in the SMP case is
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selected from one of these sequences,
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dependent on which CPU
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was scheduled to service the request.
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.Pp
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The speed and the maximum value
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of each counter
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is CPU-dependent.
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Some CPUs
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(such as the
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.Tn Intel
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80386 and 80486)
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do not have such a register,
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so
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.Fn get_cyclecount
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on these platforms
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returns the number of nanoseconds
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represented by the
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structure returned by
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.Xr nanotime 9 .
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.Pp
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The
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.Tn Pentium
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processors all use the
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.Li TSC
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register.
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.Pp
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The
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.Tn Alpha
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processors use the
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.Li PCC
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register.
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.Pp
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The
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.Tn IA64
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processors use the
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.Li AR.ITC
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register.
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.Sh SEE ALSO
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.Xr nanotime 9
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.Sh HISTORY
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The
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.Fn get_cyclecount
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function first appeared in
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.Fx 5.0 .
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.Sh AUTHORS
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This manual page was written by
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.An Mark Murray Aq markm@FreeBSD.org .
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