git: 4c0bc591466f - main - man9: add hz(9) and hardclock(9)
Warner Losh
imp at FreeBSD.org
Fri Jun 18 14:43:50 UTC 2021
The branch main has been updated by imp:
URL: https://cgit.FreeBSD.org/src/commit/?id=4c0bc591466fd2731ba892269260b7dab74cfbad
commit 4c0bc591466fd2731ba892269260b7dab74cfbad
Author: Warner Losh <imp at FreeBSD.org>
AuthorDate: 2021-06-18 14:39:42 +0000
Commit: Warner Losh <imp at FreeBSD.org>
CommitDate: 2021-06-18 14:42:51 +0000
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
---
share/man/man9/Makefile | 3 ++
share/man/man9/hardclock.9 | 100 +++++++++++++++++++++++++++++++++++++++
share/man/man9/hz.9 | 114 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 217 insertions(+)
diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index 179f79b39573..f7d72ad8cd8f 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -159,10 +159,12 @@ MAN= accept_filter.9 \
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 +1127,7 @@ MLINKS+=hhook.9 hhook_head_register.9 \
hhook.9 hhook_run_hooks.9 \
hhook.9 HHOOKS_RUN_IF.9 \
hhook.9 HHOOKS_RUN_LOOKUP_IF.9
+MLINKS+=hz.9 tick.9
MLINKS+=ieee80211.9 ieee80211_ifattach.9 \
ieee80211.9 ieee80211_ifdetach.9
MLINKS+=ieee80211_amrr.9 ieee80211_amrr_choose.9 \
diff --git a/share/man/man9/hardclock.9 b/share/man/man9/hardclock.9
new file mode 100644
index 000000000000..2aab68cb5f85
--- /dev/null
+++ b/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
diff --git a/share/man/man9/hz.9 b/share/man/man9/hz.9
new file mode 100644
index 000000000000..d0e5d1b1ff3e
--- /dev/null
+++ b/share/man/man9/hz.9
@@ -0,0 +1,114 @@
+.\"
+.\" 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; /* deprecated */
+.Vt extern int profhz; /* deprecated */
+.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 update the system's notion of time via
+.Xr timecounters 9
+and to pace periodic system callbacks via
+.Xr callout 9 ,
+.Xr epoch 9 ,
+and other methods documented in
+.Xr hardclock 9 .
+That routine will be called approximately
+.Va hz
+times per second.
+.Pp
+The second clock, running at either
+.Va stathz
+or
+.Va profhz
+was used to gather timing statistics, but has been replaced with the more
+functional
+.Xr hwpmc 4 .
+These values are returned for
+.Qq compatibility
+with
+.Bx 4.4 ,
+.St -p1003.1-2001
+and the
+.Xr setitimer 2
+.Va ITIMER_PROF
+flag, which were deprecated in
+.St -p1003.1-2008
+in favor of
+.Xr timer_settime 2 .
+.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.
+Due to the adaptive nature of timeouts, changing this value has less effect than
+it had in the past.
+.Sh SEE ALSO
+.Xr setitimer 2 ,
+.Xr timer_settime 2 ,
+.Xr loader.conf 5 ,
+.Xr callout 9 ,
+.Xr eventtimers 9 ,
+.Xr hardclock 9 ,
+.Xr microtime 9 ,
+.Xr time_second 9 ,
+.Xr timecounters 9
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