Subject: Converted power-mgmt docs
To: None <netbsd-docs@netbsd.org>
From: None <dsieger@techfak.uni-bielefeld.de>
List: netbsd-docs
Date: 04/04/2007 18:38:18
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Hi.
Attach is a converted htdocs/Documentation/power-mgmt/index.list and
associated patch.
Regards,
Daniel
--
Daniel Sieger
Faculty of Technology
Bielefeld University
wwwhomes.uni-bielefeld.de/dsieger
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Index: Makefile
===================================================================
RCS file: /cvsroot/htdocs/Documentation/power-mgmt/Makefile,v
retrieving revision 1.5
diff -u -r1.5 Makefile
--- Makefile 14 Oct 2005 08:59:56 -0000 1.5
+++ Makefile 4 Apr 2007 16:33:42 -0000
@@ -1,5 +1,5 @@
# $NetBSD: Makefile,v 1.5 2005/10/14 08:59:56 rillig Exp $
-LISTDOCS+= index.list
+XMLDOCS+= index
.include "../../share/mk/web.site.mk"
Index: layout.xml
===================================================================
RCS file: /cvsroot/htdocs/layout.xml,v
retrieving revision 1.231
diff -u -r1.231 layout.xml
--- layout.xml 4 Apr 2007 08:21:51 -0000 1.231
+++ layout.xml 4 Apr 2007 16:34:11 -0000
@@ -99,6 +101,7 @@
<tocentry page="Documentation/network/ipv6/index.xml" dir="ipv6" filename="."/>
<tocentry page="Documentation/network/isdn/index.xml" dir="isdn" filename="."/>
</tocentry>
+ <tocentry page="Documentation/power-mgmt/index.xml" dir="power-mgmt" filename="."/>
<tocentry page="Documentation/research/index.xml" dir="research" filename="."/>
<tocentry page="Documentation/software/index.xml" dir="software" filename=".">
<tocentry page="Documentation/software/compiling.xml" filename="compiling.html"/>
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Content-Disposition: attachment; filename="index.xml"
<?xml version="1.0"?>
<!DOCTYPE webpage
PUBLIC "-//NetBSD//DTD Website-based NetBSD Extension//EN"
"http://www.NetBSD.org/XML/htdocs/lang/share/xml/website-netbsd.dtd">
<webpage id="Documentation-power-mgmt">
<config param="desc" value="NetBSD Documentation: Power Managment"/>
<config param="cvstag" value="$NetBSD: $"/>
<config param="rcsdate" value="$Date: $"/>
<head>
<!-- Copyright (c) 1994-2007
The NetBSD Foundation, Inc. ALL RIGHTS RESERVED. -->
<title>&os; Documentation: Power Managment</title>
</head>
<sect1 role="toc">
<sect2 id="power_managment">
<title>Power Management for Laptops</title>
<sect3 id="introduction">
<title>Introduction</title>
<para>This documentation describes some of the power
management facilities available in &os;, including the
Advanced Power Management (APM) support found in most modern
laptops.</para>
<para>Currently most of the information on this page is i386
specific. When &os; starts supporting more laptop
architectures, then this documentation will be expanded to
cover the power management features for those
architectures.</para>
</sect3>
<sect3 id="basics">
<title>The Basics of Power Management</title>
<para>The core of laptop power management is centered around
Advanced Power Management, or APM for short. This is a set
of BIOS provided service routines that provide an interface
to the laptop hardware power management features. It is via
this interface that &os; receives APM events (such as
suspend requests) or makes power management requests or
queries (such as the current battery level).</para>
<para>APM specifies two different power saving modes: standby
and suspend. What this actually does at a hardware level is
dependent on the particular laptop being
used. <quote>standby</quote> typically means a light sleep,
which consumes more power and is quicker to restore from
than the <quote>suspend</quote> mode. Typically the APM
timers for standby and suspend mode are configured in a
machine's BIOS. After a machine has been determined
<quote>idle</quote> for the appropriate period of time, the
BIOS will request that the operating system go into the
appropriate power saving mode.</para>
<para>At the &os; level, there are three components to APM
support. The kernel driver, which is the interface to the
APM BIOS, the apm daemon <application>apmd</application>,
which interfaces with the APM kernel driver and runs the
userland event scripts, and the command line program
<command>apm</command>, which interfaces to
<application>apmd</application> and can be used to query
battery level or initiate a system suspend.</para>
<para>The way power management events generally flow
is:</para>
<orderedlist>
<listitem>The APM BIOS determines a machine has been idle
for the appropriate amount of time, and queues a
standby/suspend request.</listitem>
<listitem>The APM kernel driver gets the request event the
next time it polls the APM BIOS (typically once per
second) and queues the standby/suspend request to the apm
daemon.</listitem>
<listitem>The apm daemon determines whether or not to accept
this request, based on the current power source and the
daemon configuration. If the request is accepted, it
performs any standby/suspend activities, then sends the
accept/reject notice back to the kernel driver.</listitem>
<listitem>The kernel driver sends the accept/reject notice
to the APM BIOS.</listitem>
<listitem>If the event request was accepted, the APM BIOS
places the hardware in the specified mode.</listitem>
</orderedlist>
</sect3>
<sect3 id="configuring">
<title>Configuring &os; APM Support</title>
<para>First off, you need to compile a kernel with the APM
driver enabled. Add (or uncomment) the following line in
your kernel configuration file:</para>
<programlisting>
apm0 at mainbus0 # Advanced power management</programlisting>
<para>See <ulink url="../../guide/en/chap-kernel.html">how to
build a kernel</ulink> for details on how to build your own
kernels.</para>
<para>Once you have a kernel with the APM kernel driver built,
run the apm daemon (<application>apmd</application>) at boot
time by setting the <code>apmd</code> variable
<filename>/etc/rc.conf</filename> to
<code>YES</code>.</para>
<para>Once you've done both of these steps, you can use the
<application>apm</application> utility to interface with the
APM system. For example:</para>
<programlisting>
% apm
Battery charge state: high
Battery remaining: 98 percent
A/C adapter state: not connected
Power management enabled</programlisting>
<para>Read &man.apm.8; and &man.apmd.8; for more detailed
information on how to use the APM support.</para>
</sect3>
<sect3 id="hints">
<title>Power Management Hints and Tricks</title>
<para>The primary interfaces for power management events are
the scripts in <filename>/etc/apm</filename>:
<filename>standby</filename>, <filename>suspend</filename>,
and <filename>resume</filename>. <filename>apmd</filename>
will run these scrips when it receives the appropriate APM
event.</para>
<para>Some things you might want to do in a
<filename>standby</filename> or <filename>suspend</filename>
script are:</para>
<itemizedlist>
<listitem>Turn off power to a network interface card. If
you are using PCMCIA network interface cards, you can do
this by <code>ifconfig <interface>
down</code>.</listitem>
<listitem>Unmount network filesystems (if you plan on
resuming a laptop in a place where that filesystem might
not be accessible).</listitem>
<listitem>Stop running <command>dhclient</command> or
<command>pppd</command>.</listitem>
</itemizedlist>
<para>Conversely, you can run all the appropriate commands to
undo all of the things you did at standby or suspend time in
your <filename>resume</filename> script.</para>
<para>New in &os; 1.4 is the <command>atactl</command>
command. This command can be used to control power
management features of ATA devices (more commonly known as
IDE). You can use the <option>setidle</option> option of
<command>atactl</command> to set the standby timer used to
control disk spindown. See &man.atactl.8; for more specific
information.</para>
<para>If you're wondering what value to set for the ATA
standby timer, I would recommend reading the following
papers:</para>
<itemizedlist>
<listitem>
<quote>A Quantitative Analysis of Disk Drive Power
Management in Portable Computers</quote>, Kester Li,
Roger Kumpf, Paul Horton, Thomas Anderson, Computer
Science Division, University of California, Berkeley,
Winter 1994 Usenix.
</listitem>
<listitem>
<quote>Thwarting the Power-Hungry Disk</quote>, Fred
Douglas, P. Krishnan, Brian Marsh, Matsushita
Information Technology Laboratory, Winter 1994
Usenix.
</listitem>
</itemizedlist>
<para>These papers both recommend low values for a standby
timer, on the order of 2 to 8 seconds.</para>
<para>One problem with setting a low value for the standby
timer is that by default &os; writes to the disk often
enough that the disk is constantly spinning up (at least
once every 30 seconds, or however often
<command>update</command> runs). It turns out the most
common cause of this is the filesystem updating the last
access timestamps on files and the last modified time on
device special files (such as pseudo-ttys). This behavior
can be suppressed by the &man.mount.8; options
<option>noatime</option> and (new in &os; 1.4)
<option>nodevmtime</option>. If you decide to do this as
well, you might want to also change or remove completely the
<command>atrun</command> job inside of
<application>cron</application> - by default it will run
once every 10 minutes and append an entry to the
<application>cron</application> log file, causing a disk
spinup.</para>
<para>It is also desirable in some circumstances to use
different or disable completely power management settings
depending if one is powered by line power or battery. A new
feature in &os; 1.4 is two additional
<application>apmd</application> scripts:
<filename>line</filename> and <filename>battery</filename>.
These scripts are run by <application>apmd</application>
whenever APM detects a power source change. The
<filename>line</filename> script is run upon transition to
line/AC power, and the <filename>battery</filename> script
is run upon transition to battery power. The script
corresponding to the current power source is also run when
<application>apmd</application> is first started.</para>
<para>You can place commands inside of these scripts to change
the power management settings when using battery or line
power. Here are some example scripts:</para>
<itemizedlist>
<listitem>
<filename>/etc/apm/line</filename>
<programlisting>
#!/bin/sh
mount -u /
mount -u /usr
atactl wd0 setidle 0</programlisting>
</listitem>
<listitem>
<filename>/etc/apm/battery</filename>
<programlisting>
#!/bin/sh
mount -u -o async,noatime,nodevmtime /
mount -u -o async,noatime /usr
atactl wd0 setidle 5</programlisting>
</listitem>
</itemizedlist>
<para>See also
<filename>/usr/share/examples/apm/script</filename> for an
example script that can be used to also handles
configuration of network interfaces etc.</para>
<para>Another useful feature is the <option>-a</option> flag
to <command>apmd</command> which will cause
<application>apmd</application> to ignore standby or suspend
events if the machine is currently on line power.</para>
</sect3>
<sect3 id="squid">
<title>Squid is making my laptop disk spin up</title>
<para>Squid probes one of its cache directories every 15
seconds. With 16 first level and 256 second level
directories being used, as default, to construct the cache,
some quick math suggests:</para>
<para><code>16 * 256 * 8k(block size) = ~32mb</code></para>
<para>Squid will slowly work its way through this, each time a
new directory is read that it missed in the buffer cache.
Tweaking <filename>squid.conf</filename> to reduce the
number of directories should fix the problem of a laptop
disk spinning up.</para>
</sect3>
</sect2>
</sect1>
<parentsec url="./" text="&os; Documentation"/>
</webpage>
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