6329ca325e
Refine mistakes from adaptaton of NetBSD's hardclock man page to FreeBSD: o clarify what usermode means o clarify how often hardclock is called o remove Xr callout(9) since that's done elsewhere Reviewed by: mav@ Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D30982
107 lines
3.0 KiB
Groff
107 lines
3.0 KiB
Groff
.\" $NetBSD: hardclock.9,v 1.3 2010/03/25 15:17:38 jruoho Exp $
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.\"
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.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Thomas Klausner.
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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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd July 1, 2021
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.Dt HARDCLOCK 9
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.Os
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.Sh NAME
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.Nm hardclock
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.Nd real-time timer
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.Sh SYNOPSIS
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.Ft void
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.Fn hardclock "int cnt" "int usermode"
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.Sh DESCRIPTION
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The
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.Fn hardclock
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function is called periodically based on pending work.
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The rate ranges from
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.Va hz
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times per second on a very busy system, to twice a second on an idle system.
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The
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.Va cnt
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argument reports an estimate of the number of ticks since the last call.
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The sum of
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.Va cnt
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over a second averages
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.Va hz
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over the long haul.
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See
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.Xr hz 9
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for important details over shorter time scales.
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The argument
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.Va usermode
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is none-zero when
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.Fn hardclock
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is called from an context that interrupted usermode execution.
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.Pp
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.Fn hardclock
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may perform different tasks such as:
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.Bl -bullet -offset indent
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.It
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Run the current process's virtual and profile time (decrease the
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corresponding timers, if they are activated, and generate
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.Li SIGVTALRM
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or
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.Li SIGPROF ,
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respectively).
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.It
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Increment the time-of-day, taking care of any
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.Xr ntpd 8
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or
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.Xr adjtime 2
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induced changes and leap seconds, as well as any necessary
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compensations to keep in sync with PPS signals or external clocks, if
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support for this is in the kernel (see
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.Xr options 4 ) .
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.It
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Schedule softclock interrupts (
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.Xr swi 9 )
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processing.
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.It
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Collect
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.Xr hwpmc 4
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statistics.
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.It
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Do device polling, when enabled.
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.It
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Implement software
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.Xr watchdog 9
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processing.
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.It
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Enqueue
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.Xr epoch 9
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processing.
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.El
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.Sh SEE ALSO
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.Xr adjtime 2 ,
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.Xr ntp_adjtime 2 ,
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.Xr signal 3 ,
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.Xr ntpd 8 ,
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.Xr hz 9
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