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113 lines
3.1 KiB
Groff
113 lines
3.1 KiB
Groff
.\" Copyright (c) 2000 Kelly Yancey
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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 January 3, 2000
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.Dt MICROTIME 9
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.Os FreeBSD
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.Sh NAME
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.Nm microtime ,
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.Nm getmicrotime ,
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.Nm nanotime ,
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.Nm getnanotime
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.Nd get the current time
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.Sh SYNOPSIS
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.Fd #include <sys/time.h>
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.Ft void
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.Fn microtime "struct timeval *tv"
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.Ft void
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.Fn getmicrotime "struct timeval *tv"
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.Ft void
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.Fn nanotime "struct timespec *ts"
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.Ft void
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.Fn getnanotime "struct timespec *tsp"
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.Sh DESCRIPTION
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The
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.Fn microtime
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and
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.Fn getmicrotime
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functons stores the system time as a
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.Ft struct timeval
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at the address specified by
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.Fa tv .
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The
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.Fn nanotime
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and
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.Fn getnanotime
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functions perform the same utility, but record the time as a
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.Ft struct timespec
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instead.
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.Pp
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.Fn Microtime
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and
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.Fn nanotime
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always query the timecounter to return the current time as precisely as
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possible.
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Whereas
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.Fn getmicrotime
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and
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.Fn getnanotime
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functions are abstractions which can alternately return a less precise, but
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faster to obtain, time.
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This behaviour can be toggled via the
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kern.timecounter.method sysctl variable:
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.Bl -tag -width ABC
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.It Dv 0
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sacrifice precision in favor of faster code execution
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.It Dv 1
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return the more precise time (the same as calling
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.Fn microtime
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or
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.Fn nanotime ) .
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.El
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.Pp
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The intent of the
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.Fn getmicrotime
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and
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.Fn getnanotime
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functions is to enforce the user's preference for timer accuracy versus
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execution time.
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.Sh SEE ALSO
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.Xr getmicrouptime 9 ,
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.Xr getnanouptime 9 ,
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.Xr microuptime 9 ,
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.Xr nanouptime 9 ,
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.Xr tvtohz 9
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.Sh DIAGNOSTICS
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Buggy hardware can cause "calcru negative..." when kern.timecounter.method
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is set to 0.
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.Sh HISTORY
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The
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.Nm microtime
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and
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.Nm nanotime
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functions first appeared in
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.Fx 3.0
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but existed in other incarnations since
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.Bx 4.4
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.Sh AUTHORS
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This manual page was written by
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.An Kelly Yancey Aq kbyanc@posi.net .
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