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freebsd-nq/share/man/man9/hardclock.9

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man9: add hz(9) and hardclock(9) Document aspects of system time keeping. Hz is the nominal rate that we interrupt the system and is known and the 'tick' period of 1 / hz. hardclock is the routine that does various bits of timekeeping. stathz and profhz are documented as historical relics that are deprecated and replaced by hwpmc.4 and others. Reviewed by: phk@, mav@ and gnn@ (previous version) Obtained from: hardclock.9 from NetBSD (with FreeBSD adjustments) Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D30802
2021-06-18 14:39:42 +00:00
.\" $NetBSD: hardclock.9,v 1.3 2010/03/25 15:17:38 jruoho Exp $
.\"
.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Thomas Klausner.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
hardclock.9: Refine some details 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
2021-07-02 23:09:19 +00:00
.Dd July 1, 2021
man9: add hz(9) and hardclock(9) Document aspects of system time keeping. Hz is the nominal rate that we interrupt the system and is known and the 'tick' period of 1 / hz. hardclock is the routine that does various bits of timekeeping. stathz and profhz are documented as historical relics that are deprecated and replaced by hwpmc.4 and others. Reviewed by: phk@, mav@ and gnn@ (previous version) Obtained from: hardclock.9 from NetBSD (with FreeBSD adjustments) Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D30802
2021-06-18 14:39:42 +00:00
.Dt HARDCLOCK 9
.Os
.Sh NAME
.Nm hardclock
.Nd real-time timer
.Sh SYNOPSIS
.Ft void
.Fn hardclock "int cnt" "int usermode"
.Sh DESCRIPTION
The
.Fn hardclock
hardclock.9: Refine some details 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
2021-07-02 23:09:19 +00:00
function is called periodically based on pending work.
The rate ranges from
.Va hz
times per second on a very busy system, to twice a second on an idle system.
The
man9: add hz(9) and hardclock(9) Document aspects of system time keeping. Hz is the nominal rate that we interrupt the system and is known and the 'tick' period of 1 / hz. hardclock is the routine that does various bits of timekeeping. stathz and profhz are documented as historical relics that are deprecated and replaced by hwpmc.4 and others. Reviewed by: phk@, mav@ and gnn@ (previous version) Obtained from: hardclock.9 from NetBSD (with FreeBSD adjustments) Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D30802
2021-06-18 14:39:42 +00:00
.Va cnt
hardclock.9: Refine some details 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
2021-07-02 23:09:19 +00:00
argument reports an estimate of the number of ticks since the last call.
The sum of
.Va cnt
over a second averages
.Va hz
over the long haul.
See
.Xr hz 9
for important details over shorter time scales.
man9: add hz(9) and hardclock(9) Document aspects of system time keeping. Hz is the nominal rate that we interrupt the system and is known and the 'tick' period of 1 / hz. hardclock is the routine that does various bits of timekeeping. stathz and profhz are documented as historical relics that are deprecated and replaced by hwpmc.4 and others. Reviewed by: phk@, mav@ and gnn@ (previous version) Obtained from: hardclock.9 from NetBSD (with FreeBSD adjustments) Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D30802
2021-06-18 14:39:42 +00:00
The argument
.Va usermode
is none-zero when
.Fn hardclock
hardclock.9: Refine some details 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
2021-07-02 23:09:19 +00:00
is called from an context that interrupted usermode execution.
man9: add hz(9) and hardclock(9) Document aspects of system time keeping. Hz is the nominal rate that we interrupt the system and is known and the 'tick' period of 1 / hz. hardclock is the routine that does various bits of timekeeping. stathz and profhz are documented as historical relics that are deprecated and replaced by hwpmc.4 and others. Reviewed by: phk@, mav@ and gnn@ (previous version) Obtained from: hardclock.9 from NetBSD (with FreeBSD adjustments) Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D30802
2021-06-18 14:39:42 +00:00
.Pp
.Fn hardclock
may perform different tasks such as:
.Bl -bullet -offset indent
.It
Run the current process's virtual and profile time (decrease the
corresponding timers, if they are activated, and generate
.Li SIGVTALRM
or
.Li SIGPROF ,
respectively).
.It
Increment the time-of-day, taking care of any
.Xr ntpd 8
or
.Xr adjtime 2
induced changes and leap seconds, as well as any necessary
compensations to keep in sync with PPS signals or external clocks, if
support for this is in the kernel (see
.Xr options 4 ) .
.It
Schedule softclock interrupts (
.Xr swi 9 )
processing.
.It
Collect
.Xr hwpmc 4
statistics.
.It
Do device polling, when enabled.
.It
Implement software
.Xr watchdog 9
processing.
.It
Enqueue
.Xr epoch 9
processing.
.El
.Sh SEE ALSO
.Xr adjtime 2 ,
.Xr ntp_adjtime 2 ,
.Xr signal 3 ,
.Xr ntpd 8 ,
.Xr hz 9
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