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Index: share/man/man9/Makefile
===================================================================
--- share/man/man9/Makefile
+++ share/man/man9/Makefile
@@ -159,10 +159,12 @@
g_provider_by_name.9 \
groupmember.9 \
g_wither_geom.9 \
+ hardclock.9 \
hash.9 \
hashinit.9 \
hexdump.9 \
hhook.9 \
+ hz.9 \
ieee80211.9 \
ieee80211_amrr.9 \
ieee80211_beacon.9 \
@@ -1125,6 +1127,10 @@
hhook.9 hhook_run_hooks.9 \
hhook.9 HHOOKS_RUN_IF.9 \
hhook.9 HHOOKS_RUN_LOOKUP_IF.9
+MLINKS+=hz.9 profhz.9 \
+ hz.9 stathz.9 \
+ hz.9 tick.9 \
+ hz.9 tickadj.9
MLINKS+=ieee80211.9 ieee80211_ifattach.9 \
ieee80211.9 ieee80211_ifdetach.9
MLINKS+=ieee80211_amrr.9 ieee80211_amrr_choose.9 \
Index: share/man/man9/hardclock.9
===================================================================
--- /dev/null
+++ share/man/man9/hardclock.9
@@ -0,0 +1,100 @@
+.\" $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.
+.\"
+.Dd March 25, 2010
+.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
+function is called
+.Xr hz 9
+times per second.
+It implements the real-time system clock.
+The argument
+.Va cnt
+is the estimated number of ticks since the last call to
+.Fn hardclock .
+The argument
+.Va usermode
+is none-zero when
+.Fn hardclock
+is called from a user-mode context.
+.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 callout 9 ,
+.Xr hz 9
Index: share/man/man9/hz.9
===================================================================
--- /dev/null
+++ share/man/man9/hz.9
@@ -0,0 +1,99 @@
+.\"
+.\" Copyright (c) 2021 Netflix, Inc.
+.\"
+.\" 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.
+.\"
+.Dd June 18, 2021
+.Dt HZ 9
+.Os
+.Sh NAME
+.Nm hz ,
+.Nm tick ,
+.Nm stathz ,
+.Nm profhz
+.Nd system time model
+.Sh SYNOPSIS
+.In sys/kernel.h
+.Pp
+.Vt extern int hz;
+.Vt extern int tick;
+.Vt extern int stathz;
+.Vt extern int profhz;
+.Sh DESCRIPTION
+.Fx
+utilizes periodic, one-shot, global or per-CPU
+timing hardware using
+.Xr eventtimers 9
+to produce traditional clock behavior.
+.Pp
+The main clock is used to keep track of wall time and to pace periodic system
+callbacks.
+.Xr hardclock 9
+will be called approximately
+.Va hz
+times per second.
+.Pp
+The second clock is used to gather timing statistics, and kernel or user
+profiling.
+It fires randomly with a mean frequency of
+.Va stathz
+to avoid aliasing between it and the main clock.
+.Pp
+When profiling is enabled,
+.Xr setitimer 2
+with
+.Va ITIMER_PROF
+will fire at up to
+.Va profhz
+to produce higher resolution profiling information.
+.Pp
+.Va tick
+is the length of time in microseconds of one system tick.
+.Pp
+These system variables are also available as
+.Em struct clockinfo
+from
+.Xr sysctl 3
+and
+.Sy kern.clockrate
+from
+.Xr sysctl 8 .
+.Pp
+The
+.Va hz
+rate may be overridden by defining
+.Dv HZ
+in the kernel configuration file or setting
+.Sy kern.hz
+system tuneable via
+.Xr loader.conf 5 .
+.Pp
+The current default is 1000 Hz for a tick of 1 ms for real hardware.
+For virtual machine guests, the default is 100 Hz for a tick of 10 ms.
+Only override the default value if you really know what you are doing.
+.Sh SEE ALSO
+.Xr setitimer 2 ,
+.Xr loader.conf 5 ,
+.Xr eventtimers 9 ,
+.Xr hardclock 9 ,
+.Xr microtime 9 ,
+.Xr time_second 9

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