diff --git a/share/man/man9/hz.9 b/share/man/man9/hz.9 index d0e5d1b1ff3e..73efcf3b0da3 100644 --- a/share/man/man9/hz.9 +++ b/share/man/man9/hz.9 @@ -1,114 +1,159 @@ .\" .\" 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 +.Dd July 1, 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 stathz; .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. +These clocks regulate periodic events in the system. .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 +and to pace periodic system processing as documented in .Xr hardclock 9 . -That routine will be called approximately +That routine may be called once every 1 / .Va hz -times per second. +seconds, though the call is omitted if no work is needed in the next tick and it +has not been 0.5 seconds since the last call. .Pp -The second clock, running at either +The stat clock running at .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 . +gathers statistics on the system and its processes. +It computes values for +.Xr getrusage 2 +and statistics displayed by +.Xr ps 1 +and +.Xr top 1 . +.Pp +Finally, a profiling clock may run at +.Vt profhz +to sample user program counter values for profiling purposes. +This profiling mechanism has been replaced by the more functional +.Xr hwpmc 4 +and may be removed in a future version of +.Fx . .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 current global and per-CPU CPU time usage is returned to the user in units +of 1 / +.Va stathz +ticks in the +.Sy kern.cp_time +and +.Sy kern.cp_times +sysctl MIBs. +.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 ps 1 , +.Xr top 1 , .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 +.Sh IMPLEMENTATION NOTES +Historically, both the +.Va stathz +and +.Va profhz +clocks have run off the same physical timer running at the slower rate when no +process is using the profile features, or at the higher rate when at least one +process is using it. +Although the interface is deprecated by +.St -p1003.1-2008 +in favor of +.Xr timer_settime 2 , +several programs still use +.Xr setitimer 2 +and +.Va ITIMER_PROF +for a higher-resolution periodic interrupt than has been traditionally +available. +.Pp +Historically, +.Xr hardclock 9 +has also been run off a separate interrupt, except on constrained platforms that +lack enough periodic interrupt sources. +.Fx +uses +.Xr eventtimers 9 +to abstract these details away, though some old code may still harbor +assumptions that are an imperfect fit to this abstraction. +.Pp +.Xr timecounters 9 +are limited to 32-bits and wrap after about a second, so we must update the +time hands they maintain at least every half second to get the proper wrapping +math. +In addition, +.Va kern.cp_times +needs to updated at least once a second so that the values displayed by +.Xr top 1 +update every second.