xref: /freebsd/share/man/man9/microtime.9 (revision 1111b49c35645b9561e28458a445684ef38c0881)

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.Dd January 3, 2000
.Dt MICROTIME 9
.Os FreeBSD
.Sh NAME
.Nm microtime ,
.Nm getmicrotime ,
.Nm nanotime ,
.Nm getnanotime
.Nd get the current time
.Sh SYNOPSIS
.Fd #include <sys/time.h>
.Ft void
.Fn microtime "struct timeval *tv"
.Ft void
.Fn getmicrotime "struct timeval *tv"
.Ft void
.Fn nanotime "struct timespec *ts"
.Ft void
.Fn getnanotime "struct timespec *tsp"
.Sh DESCRIPTION
The
.Fn microtime
and
.Fn getmicrotime
functons stores the system time as a
.Ft struct timeval
at the address specified by
.Fa tv .
The
.Fn nanotime
and
.Fn getnanotime
functions perform the same utility, but record the time as a
.Ft struct timespec
instead.
.Pp
.Fn Microtime
and
.Fn nanotime
always query the timecounter to return the current time as precisely as
possible.
Whereas
.Fn getmicrotime
and
.Fn getnanotime
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 microtime
or
.Fn nanotime ) .
.El
.Pp
The intent of the
.Fn getmicrotime
and
.Fn getnanotime
functions is to enforce the user's preference for timer accuracy versus
execution time.
.Sh SEE ALSO
.Xr getmicrouptime 9 ,
.Xr getnanouptime 9 ,
.Xr microuptime 9 ,
.Xr nanouptime 9 ,
.Xr tvtohz 9
.Sh DIAGNOSTICS
Buggy hardware can cause "calcru negative..." when kern.timecounter.method
is set to 0.
.Sh HISTORY
The
.Nm microtime
and
.Nm nanotime
functions first appeared in
.Fx 3.0
but existed in other incarnations since
.Bx 4.4
.Sh AUTHORS
This manual page was written by
.An Kelly Yancey Aq kbyanc@posi.net .