Date: Tue, 22 Apr 2014 20:51:07 +0000 (UTC) From: Christian Brueffer <brueffer@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r264775 - stable/10/share/man/man4 Message-ID: <201404222051.s3MKp7qQ025745@svn.freebsd.org>
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Author: brueffer Date: Tue Apr 22 20:51:07 2014 New Revision: 264775 URL: http://svnweb.freebsd.org/changeset/base/264775 Log: MFC: r264384, r264415 mdoc and language improvements. Modified: stable/10/share/man/man4/timecounters.4 Directory Properties: stable/10/ (props changed) Modified: stable/10/share/man/man4/timecounters.4 ============================================================================== --- stable/10/share/man/man4/timecounters.4 Tue Apr 22 20:37:07 2014 (r264774) +++ stable/10/share/man/man4/timecounters.4 Tue Apr 22 20:51:07 2014 (r264775) @@ -24,27 +24,27 @@ .\" .\" $FreeBSD$ .\" -.Dd December 20, 2011 +.Dd April 12, 2014 .Dt TIMECOUNTERS 4 .Os .Sh NAME .Nm timecounters .Nd kernel time counters subsystem .Sh SYNOPSIS -Kernel uses several types of time-related devices, such as: real time clocks, +The 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 +Real time clocks are responsible for tracking real world time, mostly when the system is down. -Time counters are responsible for tracking purposes, when system is running. -Event timers are responsible for generating interrupts at specified time or +Time counters are responsible for tracking purposes, when the system is running. +Event timers are responsible for generating interrupts at a specified time or periodically, to run different time-based events. This page is about the second. .Sh DESCRIPTION -Time counters are the lowest level of time tracking in kernel. +Time counters are the lowest level of time tracking in the kernel. They provide monotonically increasing timestamps with known width and update frequency. -They can overflow, drift, etc and so in raw form used only in very limited -performance-critical places like process scheduler. +They can overflow, drift, etc and so in raw form can be used only in very limited +performance-critical places like the process scheduler. .Pp More usable time is created by scaling the values read from the selected time counter and combining it with some offset, regularly updated by @@ -54,13 +54,14 @@ on invocation. .Pp Different platforms provide different kinds of timer hardware. -The goal of the time counters subsystem is to provide unified way to access +The goal of the time counters subsystem is to provide a unified way to access that hardware. .Pp -Each driver implementing time counters, registers them at the subsystem. -It is possible to see the list of present time counters, like this, via +Each driver implementing time counters registers them with the subsystem. +It is possible to see the list of present time counters, via the .Va kern.timecounter -sysctl: +.Xr sysctl 8 +variable: .Bd -literal kern.timecounter.choice: TSC-low(-100) HPET(950) i8254(0) ACPI-fast(900) dummy(-1000000) kern.timecounter.tc.ACPI-fast.mask: 16777215 @@ -81,7 +82,7 @@ kern.timecounter.tc.TSC-low.frequency: 1 kern.timecounter.tc.TSC-low.quality: -100 .Ed .Pp -where: +The output nodes are defined as follows: .Bl -inset .It Va kern.timecounter.tc. Ns Ar X Ns Va .mask is a bitmask, defining valid counter bits, @@ -90,13 +91,13 @@ is a present counter value, .It Va kern.timecounter.tc. Ns Ar X Ns Va .frequency is a counter update frequency, .It Va kern.timecounter.tc. Ns Ar X Ns Va .quality -is an integral value, defining how good is this time counter, -comparing to others. -Negative value means that this time counter is broken and should not be used. +is an integral value, defining the quality of this time counter +compared to others. +A negative value means this time counter is broken and should not be used. .El .Pp -Time management code of the kernel chooses one time counter from that list. -Current choice can be read and affected via +The time management code of the kernel chooses one time counter from that list. +The current choice can be read and affected via the .Va kern.timecounter.hardware tunable/sysctl. .Sh SEE ALSO
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