svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
eventtimers(4)
EVENTTIMERS(4) BSD Kernel Interfaces Manual EVENTTIMERS(4)
NAME
eventtimers — kernel event timers subsystem
SYNOPSIS
Kernel uses several types of time-related devices, such as: real time
clocks, time counters and event timers. Real time clocks responsible for
tracking real world time, mostly when system is down. Time counters are
responsible for generation of monotonically increasing timestamps for
precise uptime tracking purposes, when system is running. Event timers
are responsible for generating interrupts at specified time or periodi‐
cally, to run different time-based events. This page is about the last.
DESCRIPTION
Kernel uses time-based events for many different purposes: scheduling,
statistics, time keeping, profiling and many other things, based on
callout(9) mechanism. These purposes now grouped into three main call‐
backs:
hardclock() callout(9) and timekeeping events entry. Called with fre‐
quency defined by hz variable, usually 1000Hz.
statclock() statistics and scheduler events entry. Called with fre‐
quency about 128Hz.
profclock() profiler events entry. When enabled, called with frequency
about 8KHz.
Different platforms provide different kinds of timer hardware. The goal
of the event timers subsystem is to provide unified way to control that
hardware, and to use it, supplying kernel with all required time-based
events.
Each driver implementing event timers, registers them at the subsystem.
It is possible to see the list of present event timers, like this, via
kern.eventtimer sysctl:
kern.eventtimer.choice: HPET(550)LAPIC(400)i8254(100)RTC(0)
kern.eventtimer.et.LAPIC.flags: 15
kern.eventtimer.et.LAPIC.frequency: 0
kern.eventtimer.et.LAPIC.quality: 400
kern.eventtimer.et.i8254.flags: 1
kern.eventtimer.et.i8254.frequency: 1193182
kern.eventtimer.et.i8254.quality: 100
kern.eventtimer.et.RTC.flags: 17
kern.eventtimer.et.RTC.frequency: 32768
kern.eventtimer.et.RTC.quality: 0
kern.eventtimer.et.HPET.flags: 7
kern.eventtimer.et.HPET.frequency: 14318180
kern.eventtimer.et.HPET.quality: 550
where:
kern.eventtimer.et.X.flags is a bitmask, defining event timer capabili‐
ties:
1 periodic mode supported,
2 one-shot mode supported,
4 timer is per-CPU,
8 timer may stop when CPU goes to sleep state,
16 timer supports only power-of-2 divisors.
kern.eventtimer.et.X.frequency is a timer base frequency,
kern.eventtimer.et.X.quality is an integral value, defining how good is
this timer, comparing to others.
Timers management code of the kernel chooses one timer from that list.
Current choice can be read and affected via kern.eventtimer.timer tun‐
able/sysctl. Several other tunables/sysctls are affecting how exactly
this timer is used:
kern.eventtimer.periodic allows to choose periodic and one-shot operation
mode. In periodic mode, periodic interrupts from timer hardware are
taken as the only source of time for time events. One-shot mode instead
uses currently selected time counter to precisely schedule all needed
events and programs event timer to generate interrupt exactly in speci‐
fied time. Default value depends of chosen timer capabilities, but one-
shot mode is preferred, until other is forced by user or hardware.
kern.eventtimer.singlemul in periodic mode specifies how much times
higher timer frequency should be, to not strictly alias hardclock() and
statclock() events. Default values are 1, 2 or 4, depending on config‐
ured HZ value.
kern.eventtimer.idletick makes each CPU to receive every timer interrupt
independently of whether they busy or not. By default this options is
disabled. If chosen timer is per-CPU and runs in periodic mode, this
option has no effect - all interrupts are always generating.
SEE ALSO
apic(4), atrtc(4), attimer(4), hpet(4), timecounters(4), eventtimers(9)
BSD March 13, 2012 BSD