.\" Copyright (c) 2000 Kelly Yancey
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.\"    $FreeBSD: src/share/man/man9/microuptime.9,v 1.2.2.2 2001/12/17 11:30:18 ru Exp $
.\"    $DragonFly: src/share/man/man9/microuptime.9,v 1.3 2006/02/17 19:37:10 swildner Exp $
.\"
.Dd January 3, 2000
.Dt MICROUPTIME 9
.Os
.Sh NAME
.Nm microuptime ,
.Nm getmicrouptime ,
.Nm nanouptime ,
.Nm getnanouptime
.Nd get the time elapsed since boot
.Sh SYNOPSIS
.In sys/time.h
.Ft void
.Fn microuptime "struct timeval *tv"
.Ft void
.Fn getmicrouptime "struct timeval *tv"
.Ft void
.Fn nanouptime "struct timespec *ts"
.Ft void
.Fn getnanouptime "struct timespec *tsp"
.Sh DESCRIPTION
The
.Fn microuptime
and
.Fn getmicrouptime
functions store the time elapsed since boot as a
.Ft struct timeval
at the address specified by
.Fa tv .
The
.Fn nanouptime
and
.Fn getnanouptime
functions perform the same utility, but record the elapsed time as a
.Ft struct timespec
instead.
.Pp
.Fn Microuptime
and
.Fn nanouptime
always query the timecounter to return the current time as precisely as
possible.
Whereas
.Fn getmicrouptime
and
.Fn getnanouptime
functions are abstractions which can alternately return a less precise, but
faster to obtain, time.
This behaviour can be toggled via the
kern.timecounter.method sysctl variable:
.Bl -tag -width ABC
.It Dv 0
sacrifice precision in favor of faster code execution
.It Dv 1
return the more precise time (the same as calling
.Fn microuptime
or
.Fn nanouptime ) .
.El
.Pp
The intent of the
.Fn getmicrouptime
and
.Fn getnanouptime
functions is to enforce the user's preference for timer accuracy versus
execution time.
.Sh DIAGNOSTICS
Buggy hardware can cause "calcru negative..." when kern.timecounter.method
is set to 0.
.Sh SEE ALSO
.Xr getmicrotime 9 ,
.Xr getnanotime 9 ,
.Xr microtime 9 ,
.Xr nanotime 9 ,
.Xr tvtohz 9
.Sh AUTHORS
This manual page was written by
.An Kelly Yancey Aq kbyanc@posi.net .