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1 swift 1.1 <?xml version='1.0' encoding="UTF-8"?>
2     <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
3 swift 1.48 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/power-management-guide.xml,v 1.47 2011/08/17 07:10:12 swift Exp $ -->
4 nightmorph 1.42
5     <guide>
6 swift 1.1 <title>Power Management Guide</title>
7    
8 swift 1.4 <author title="Author">
9 nightmorph 1.17 <mail link="earthwings@gentoo.org">Dennis Nienhüser</mail>
10 swift 1.1 </author>
11 rane 1.19 <author title="Editor">
12     <mail link="chriswhite@gentoo.org">Chris White</mail>
13     </author>
14 nightmorph 1.26 <author title="Editor">
15 nightmorph 1.42 <mail link="nightmorph"/>
16 nightmorph 1.26 </author>
17 swift 1.1
18     <abstract>
19     Power Management is the key to extend battery run time on mobile systems like
20     laptops. This guide assists you setting it up on your laptop.
21     </abstract>
22    
23     <!-- The content of this document is licensed under the CC-BY-SA license -->
24 so 1.15 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
25 swift 1.1 <license/>
26    
27 swift 1.48 <version>4</version>
28 swift 1.47 <date>2011-08-17</date>
29 swift 1.1
30     <chapter>
31     <title>Introduction</title>
32     <section>
33     <body>
34    
35 swift 1.48 <!--
36     Remove this note after 6 months - ETA 01/02/2012
37     By then, we can assume that OpenRC migrations are not that frequent
38     anymore and this note can be dropped.
39     ~ Sven Vermeulen
40     -->
41     <impo>
42     Since the introduction of OpenRC, the <c>pmg_switch_runlevel.sh</c> script
43     needs to be updated. If you have issues after the OpenRC upgrade, please update
44     this script according to this guide.
45     </impo>
46    
47 swift 1.1 <p>
48 so 1.15 Capacity and lifetime of laptop batteries have improved much in the last years.
49 swift 1.1 Nevertheless modern processors consume much more energy than older ones and
50     each laptop generation introduces more devices hungry for energy. That's why
51     Power Management is more important than ever. Increasing battery run time
52     doesn't necessarily mean buying another battery. Much can be achieved applying
53     intelligent Power Management policies.
54     </p>
55    
56     </body>
57     </section>
58     <section>
59 rane 1.19 <title>A Quick Overview</title>
60 swift 1.1 <body>
61    
62     <p>
63     Please notice that this guide describes Power Management for <e>laptops</e>.
64     While some sections might also suite for <e>servers</e>, others do not and may
65     even cause harm. Please do not apply anything from this guide to a server
66     unless you really know what you are doing.
67     </p>
68    
69     <p>
70     As this guide has become rather long, here's a short overview helping you to
71     find your way through it.
72     </p>
73    
74     <p>
75 rane 1.19 The <uri link="#doc_chap2">Prerequisites</uri> chapter talks about some
76     requirements that should be met before any of the following device individual
77     sections will work. This includes BIOS settings, kernel configuration and some
78     simplifications in user land. The following three chapters focus on devices
79     that typically consume most energy - processor, display and hard drive. Each
80 nightmorph 1.46 can be configured separately. <uri link="#doc_chap3">CPU Power Management</uri>
81 rane 1.19 shows how to adjust the processor's frequency to save a maximum of energy
82 rane 1.21 without losing too much performance. A few different tricks prevent your hard
83 rane 1.19 drive from working unnecessarily often in <uri link="#doc_chap5">Disk Power
84     Management</uri> (decreasing noise level as a nice side effect). Some notes on
85 rane 1.20 graphics cards, Wireless LAN and USB finish the device section in <uri
86     link="#doc_chap6">Power Management For Other Devices</uri> while another
87 rane 1.19 chapter is dedicated to the (rather experimental) <uri link="#doc_chap7">sleep
88 rane 1.20 states</uri>. Last not least <uri link="#doc_chap8">Troubleshooting</uri> lists
89     common pitfalls.
90 swift 1.1 </p>
91    
92     </body>
93     </section>
94     <section>
95 rane 1.19 <title>Power Budget For Each Component</title>
96 swift 1.1 <body>
97    
98 swift 1.2 <figure link="/images/energy-budget.png" short="Which component consumes how
99 swift 1.1 much energy?" caption="Power budget for each component"/>
100    
101     <p>
102     Nearly every component can operate in different states - off, sleep, idle,
103     active to name a few - consuming a different amount of energy. Major parts are
104     consumed by the LCD display, CPU, chipset and hard drives. Often one is able to
105     activate OS-independent Power Management in the BIOS, but an intelligent setup
106     in the operating system adapting to different situations can achieve much more.
107     </p>
108    
109     </body>
110     </section>
111     </chapter>
112    
113     <chapter>
114     <title>Prerequisites</title>
115     <section>
116     <body>
117    
118     <p>
119 nightmorph 1.17 Before discussing the details of making individual devices Power Management
120 rane 1.20 aware, make sure certain requirements are met. After controlling BIOS settings,
121     some kernel options want to be enabled - these are in short ACPI, sleep states
122     and CPU frequency scaling. As power saving most of the time comes along with
123     performance loss or increased latency, it should only be enabled when running
124     on batteries. That's where a new runlevel <e>battery</e> comes in handy.
125 swift 1.1 </p>
126    
127     </body>
128     </section>
129     <section>
130 rane 1.19 <title>The BIOS Part</title>
131 swift 1.1 <body>
132    
133     <p>
134     First have a look into your BIOS Power Management settings. The best way is to
135     combine BIOS and operating system policies, but for the moment it's better to
136     disable most of the BIOS part. This makes sure it doesn't interfere with your
137     policies. Don't forget to re-check BIOS settings after you configured
138     everything else.
139     </p>
140    
141     </body>
142     </section>
143     <section>
144 rane 1.19 <title>Setting USE Flags</title>
145 nightmorph 1.17 <body>
146    
147     <p>
148     Please check that the <c>acpi</c> USE flag is set in
149     <path>/etc/make.conf</path>. Other USE flags that might be interesting for your
150     system are <c>apm</c>, <c>lm_sensors</c>, <c>nforce2</c>, <c>nvidia</c>,
151     <c>pmu</c>. See <path>/usr/portage/profiles/use*.desc</path> for details. If
152     you forgot to set one of these flags, you can recompile affected packages using
153 rane 1.19 the <c>--newuse</c> flag in <c>emerge</c>, see <c>man emerge</c>.
154 nightmorph 1.17 </p>
155    
156     </body>
157     </section>
158     <section>
159 rane 1.19 <title>Configuring The Kernel</title>
160 swift 1.1 <body>
161    
162     <p>
163     ACPI (Advanced Configuration and Power Interface) support in the kernel is
164     still work in progress. Using a recent kernel will make sure you'll get the
165     most out of it.
166     </p>
167    
168     <p>
169 rane 1.20 There are different kernel sources in Portage. I'd recommend using
170 jkt 1.33 <c>gentoo-sources</c> or <c>tuxonice-sources</c>. The latter contains patches
171 jkt 1.34 for TuxOnIce, see the chapter about <uri link="#doc_chap7">sleep states</uri>
172     for more details. When configuring the kernel, activate at least these options:
173 swift 1.1 </p>
174    
175     <pre caption="Minimum kernel setup for Power Management (Kernel 2.6)">
176 nightmorph 1.39 Power management and ACPI options ---&gt;
177 nightmorph 1.40 [*] Power Management support
178 swift 1.1 [ ] Software Suspend
179    
180     ACPI( Advanced Configuration and Power Interface ) Support ---&gt;
181 nightmorph 1.39 [ ] Deprecated /proc/acpi/ files
182 neysx 1.12 [*] AC Adapter
183     [*] Battery
184 swift 1.1 &lt;M&gt; Button
185 so 1.15 &lt;M&gt; Video
186     [ ] Generic Hotkey
187 swift 1.1 &lt;M&gt; Fan
188     &lt;M&gt; Processor
189     &lt;M&gt; Thermal Zone
190     &lt; &gt; ASUS/Medion Laptop Extras
191 so 1.15 &lt; &gt; IBM ThinkPad Laptop Extras
192 swift 1.1 &lt; &gt; Toshiba Laptop Extras
193 so 1.15 (0) Disable ACPI for systems before Jan 1st this year
194 swift 1.1 [ ] Debug Statements
195 so 1.15 [*] Power Management Timer Support
196     &lt; &gt; ACPI0004,PNP0A05 and PNP0A06 Container Driver (EXPERIMENTAL)
197 rane 1.20
198 swift 1.1 CPU Frequency Scaling ---&gt;
199     [*] CPU Frequency scaling
200 so 1.15 [ ] Enable CPUfreq debugging
201     &lt; &gt; CPU frequency translation statistics
202     [ ] CPU frequency translation statistics details
203 swift 1.1 Default CPUFreq governor (userspace)
204     &lt;*&gt; 'performance' governor
205     &lt;*&gt; 'powersave' governor
206 swift 1.8 &lt;*&gt; 'ondemand' cpufreq policy governor
207 so 1.15 &lt;*&gt; 'conservative' cpufreq governor
208 swift 1.1 &lt;*&gt; CPU frequency table helpers
209     &lt;M&gt; ACPI Processor P-States driver
210     &lt;*&gt; <i>CPUFreq driver for your processor</i>
211     </pre>
212    
213     <p>
214 so 1.15 Decide yourself whether you want to enable Software Suspend, and Sleep States
215     (see below). If you own an ASUS, Medion, IBM Thinkpad or Toshiba laptop, enable
216 neysx 1.12 the appropriate section.
217 swift 1.8 </p>
218    
219     <p>
220 rane 1.20 The kernel has to know how to enable CPU frequency scaling on your processor.
221     As each type of CPU has a different interface, you've got to choose the right
222 rane 1.19 driver for your processor. Be careful here - enabling <c>Intel Pentium 4 clock
223     modulation</c> on a Pentium M system will lead to strange results for example.
224 swift 1.8 Consult the kernel documentation if you're unsure which one to take.
225 swift 1.1 </p>
226    
227     <p>
228     Compile your kernel, make sure the right modules get loaded at startup and boot
229 rane 1.20 into your new ACPI-enabled kernel. Next run <c>emerge sys-power/acpid</c> to
230     get the acpi daemon. This one informs you about events like switching from AC
231     to battery or closing the lid. Make sure the modules are loaded if you didn't
232     compile them into the kernel and start acpid by executing <c>/etc/init.d/acpid
233     start</c>. Run <c>rc-update add acpid default</c> to load it on startup. You'll
234     soon see how to use it.
235 swift 1.1 </p>
236    
237     <pre caption="Installing acpid">
238 yoswink 1.10 # <i>emerge sys-power/acpid</i>
239 swift 1.1 # <i>/etc/init.d/acpid start</i>
240     # <i>rc-update add acpid default</i>
241     </pre>
242    
243     </body>
244     </section>
245     <section>
246 rane 1.19 <title>Creating A "battery" Runlevel</title>
247 swift 1.1 <body>
248    
249     <p>
250     The default policy will be to enable Power Management only when needed -
251     running on batteries. To make the switch between AC and battery convenient,
252 rane 1.19 create a runlevel <c>battery</c> that holds all the scripts starting and
253 swift 1.1 stopping Power Management.
254     </p>
255    
256     <note>
257     You can safely skip this section if you don't like the idea of having another
258     runlevel. However, skipping this step will make the rest a bit trickier to set
259 rane 1.19 up. The next sections assume a runlevel <c>battery</c> exists.
260 swift 1.1 </note>
261    
262     <pre caption="Creating a battery runlevel">
263     # <i>cd /etc/runlevels</i>
264     # <i>cp -a default battery</i>
265     </pre>
266    
267     <p>
268 rane 1.19 Finished. Your new runlevel <c>battery</c> contains everything like
269     <c>default</c>, but there is no automatic switch between both yet. Time to
270 swift 1.1 change it.
271     </p>
272    
273     </body>
274     </section>
275     <section>
276 rane 1.19 <title>Reacting On ACPI Events</title>
277 swift 1.1 <body>
278    
279     <p>
280     Typical ACPI events are closing the lid, changing the power source or pressing
281 swift 1.8 the sleep button. An important event is changing the power source, which should
282 so 1.15 cause a runlevel switch. A small script will take care of it.
283     </p>
284    
285     <p>
286     First you need a script which changes the runlevel to <c>default</c>
287     respectively <c>battery</c> depending on the power source. The script uses the
288 nightmorph 1.43 <c>on_ac_power</c> command from <c>sys-power/pm-utils</c> - make sure the
289 so 1.15 package is installed on your system.
290     </p>
291    
292 nightmorph 1.43 <pre caption="Installing pm-utils">
293     # <i>emerge pm-utils</i>
294 so 1.15 </pre>
295    
296     <p>
297 rane 1.20 You are now able to determine the power source by executing <c>on_ac_power
298     &amp;&amp; echo AC available || echo Running on batteries</c> in a shell. The
299     script below is responsible for changing runlevels. Save it as
300 so 1.15 <path>/etc/acpi/actions/pmg_switch_runlevel.sh</path>.
301 swift 1.8 </p>
302    
303 neysx 1.12 <pre caption="/etc/acpi/actions/pmg_switch_runlevel.sh">
304 swift 1.8 #!/bin/bash
305    
306 swift 1.48 # BEGIN configuration
307 swift 1.8 RUNLEVEL_AC="default"
308     RUNLEVEL_BATTERY="battery"
309 swift 1.48
310     if [ -x /usr/bin/logger ]; then
311     LOGGER="/usr/bin/logger -s -p daemon.info -t /etc/acpi/actions/pmg_switch_runlevel.sh"
312     else
313     LOGGER="/bin/echo"
314     fi
315    
316     ON_AC_POWER=/usr/bin/on_ac_power
317     # END configuration
318 swift 1.8
319 swift 1.1
320 neysx 1.12 if [ ! -d "/etc/runlevels/${RUNLEVEL_AC}" ]
321     then
322 swift 1.48 ${LOGGER} "${0}: Runlevel ${RUNLEVEL_AC} does not exist. Aborting."
323 nightmorph 1.17 exit 1
324 neysx 1.12 fi
325 swift 1.8
326 neysx 1.12 if [ ! -d "/etc/runlevels/${RUNLEVEL_BATTERY}" ]
327     then
328 swift 1.48 ${LOGGER} "${0}: Runlevel ${RUNLEVEL_BATTERY} does not exist. Aborting."
329 nightmorph 1.17 exit 1
330 neysx 1.12 fi
331 swift 1.1
332 swift 1.48 if ${on_ac_power}
333 neysx 1.12 then
334 swift 1.48 if [[ "$(rc-status --runlevel)" != "${RUNLEVEL_AC}" ]]
335 nightmorph 1.17 then
336 swift 1.48 ${LOGGER} "Switching to ${RUNLEVEL_AC} runlevel"
337     /sbin/rc ${RUNLEVEL_AC}
338 nightmorph 1.17 fi
339 swift 1.48 elif [[ "$(rc-status --runlevel)" != "${RUNLEVEL_BATTERY}" ]]
340 neysx 1.12 then
341 swift 1.48 ${LOGGER} "Switching to ${RUNLEVEL_BATTERY} runlevel"
342 nightmorph 1.17 /sbin/rc ${RUNLEVEL_BATTERY}
343 neysx 1.12 fi
344 swift 1.8 </pre>
345    
346 so 1.15 <p>
347     Dont forget to run <c>chmod +x /etc/acpi/actions/pmg_switch_runlevel.sh</c> to
348     make the script executable. The last thing that needs to be done is calling the
349     script whenever the power source changes. That's done by catching ACPI events
350     with the help of <c>acpid</c>. First you need to know which events are
351     generated when the power source changes. The events are called
352 rane 1.19 <c>ac_adapter</c> and <c>battery</c> on most laptops, but it might be different
353 so 1.15 on yours.
354     </p>
355    
356     <pre caption="Determining ACPI events for changing the power source">
357 nightmorph 1.42 # <i>tail -f /var/log/messages | grep "ACPI event"</i>
358 so 1.15 </pre>
359    
360     <p>
361 rane 1.20 Run the command above and pull the power cable. You should see something like
362     this:
363 so 1.15 </p>
364    
365     <pre caption="Sample output for power source changes">
366 nightmorph 1.42 [Tue Sep 20 17:39:06 2005] ACPI event "ac_adapter AC 00000080 00000000"
367     [Tue Sep 20 17:39:06 2005] ACPI event "battery BAT0 00000080 00000001"
368 so 1.15 </pre>
369    
370     <p>
371 jkt 1.44 The interesting part is the quoted string after <c>ACPI event</c>. It will
372 so 1.15 be matched by the event line in the files you are going to create below. Don't
373     worry if your system generates multiple events or always the same. As long as
374     any event is generated, runlevel changing will work.
375     </p>
376    
377 swift 1.8 <pre caption="/etc/acpi/events/pmg_ac_adapter">
378 neysx 1.12 <comment># replace "ac_adapter" below with the event generated on your laptop</comment>
379 so 1.15 <comment># For example, ac_adapter.* will match ac_adapter AC 00000080 00000000</comment>
380 swift 1.8 event=ac_adapter.*
381 neysx 1.12 action=/etc/acpi/actions/pmg_switch_runlevel.sh %e
382 swift 1.8 </pre>
383    
384     <pre caption="/etc/acpi/events/pmg_battery">
385 neysx 1.12 <comment># replace "battery" below with the event generated on your laptop</comment>
386 so 1.15 <comment># For example, battery.* will match battery BAT0 00000080 00000001</comment>
387 swift 1.8 event=battery.*
388 neysx 1.12 action=/etc/acpi/actions/pmg_switch_runlevel.sh %e
389 swift 1.8 </pre>
390 swift 1.1
391 swift 1.8 <p>
392 so 1.15 Finally acpid has to be restarted to recognize the changes.
393 swift 1.8 </p>
394 swift 1.1
395 swift 1.8 <pre caption="Finishing runlevel switching with acpid">
396 rane 1.19 # <i>/etc/init.d/acpid restart</i>
397 swift 1.1 </pre>
398    
399     <p>
400     Give it a try: Plug AC in and out and watch syslog for the "Switching to AC
401 rane 1.20 mode" or "Switching to battery mode" messages. See the <uri
402     link="#doc_chap8">Troubleshooting section</uri> if the script is not able to
403     detect the power source correctly.
404 swift 1.1 </p>
405    
406     <p>
407     Due to the nature of the event mechanism, your laptop will boot into runlevel
408 rane 1.19 <c>default</c> regardless of the AC/battery state. This is fine when running
409 rane 1.20 from AC, but we'd like to boot into the battery runlevel otherwise. One
410     solution would be to add another entry to the boot loader with the parameter
411 so 1.15 <c>softlevel=battery</c>, but it's likely to forget choosing it. A better way
412 rane 1.20 is faking an ACPI event in the end of the boot process and letting
413     <path>pmg_switch_runlevel.sh</path> script decide whether a runlevel change is
414 swift 1.47 necessary. Create a <path>/etc/local.d/battery.start</path> file with the
415     following contents:
416 swift 1.1 </p>
417    
418 swift 1.47 <pre caption="Runlevel adjustment at boot time through local.d/battery.start">
419     #!/bin/sh
420 swift 1.1 <comment># Fake acpi event to switch runlevel if running on batteries</comment>
421 neysx 1.12 /etc/acpi/actions/pmg_switch_runlevel.sh "battery/battery"
422 swift 1.1 </pre>
423    
424     <p>
425 swift 1.47 Don't forget to mark the file as executable (<c>chmod +x
426     /etc/local.d/battery.start</c>). Prepared like this you can activate Power
427     Management policies for individual devices.
428 swift 1.1 </p>
429    
430     </body>
431     </section>
432     </chapter>
433    
434     <chapter>
435     <title>CPU Power Management</title>
436     <section>
437 nightmorph 1.17 <body>
438    
439     <p>
440     Mobile processors can operate at different frequencies. Some allow changing
441     voltage as well. Most of the time your CPU doesn't need to run at full speed
442     and scaling it down will save much energy - often without any performance
443     decrease.
444     </p>
445    
446     </body>
447     </section>
448     <section>
449 rane 1.19 <title>Some Technical Terms</title>
450 swift 1.8 <body>
451    
452     <p>
453     CPU frequency scaling brings up some technical terms that might be unknown to
454     you. Here's a quick introduction.
455     </p>
456    
457     <p>
458 so 1.15 First of all, the kernel has to be able to change the processor's frequency.
459 rane 1.19 The <b>CPUfreq processor driver</b> knows the commands to do it on your CPU.
460 rane 1.20 Thus it's important to choose the right one in your kernel. You should already
461     have done it above. Once the kernel knows how to change frequencies, it has to
462     know which frequency it should set. This is done according to the <b>policy</b>
463     which consists of a <b>CPUfreq policy</b> and a <b>governor</b>. A CPUfreq
464     policy are just two numbers which define a range the frequency has to stay
465     between - minimal and maximal frequency. The governor now decides which of the
466     available frequencies in between minimal and maximal frequency to choose. For
467     example, the <b>powersave governor</b> always chooses the lowest frequency
468     available, the <b>performance governor</b> the highest one. The <b>userspace
469     governor</b> makes no decision but chooses whatever the user (or a program in
470     userspace) wants - which means it reads the frequency from
471 swift 1.8 <path>/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed</path>.
472     </p>
473    
474     <p>
475     This doesn't sound like dynamic frequency changes yet and in fact it isn't.
476 rane 1.20 Dynamics however can be accomplished with various approaches. For example, the
477     <b>ondemand governor</b> makes its decisions depending on the current CPU load.
478     The same is done by various userland tools like <c>cpudyn</c>, <c>cpufreqd</c>,
479     <c>powernowd</c> and many more. ACPI events can be used to enable or disable
480     dynamic frequency changes depending on power source.
481 swift 1.8 </p>
482    
483     </body>
484     </section>
485     <section>
486 nightmorph 1.41 <title>Setting The Frequency</title>
487 swift 1.1 <body>
488    
489     <p>
490     Decreasing CPU speed and voltage has two advantages: On the one hand less
491     energy is consumed, on the other hand there is thermal improvement as your
492     system doesn't get as hot as running on full speed. The main disadvantage is
493     obviously the loss of performance. Decreasing processor speed is a trade off
494     between performance loss and energy saving.
495     </p>
496    
497     <note>
498     Not every laptop supports frequency scaling. If unsure, have a look at the list
499 rane 1.19 of supported processors in the <uri link="#doc_chap8">Troubleshooting</uri>
500     section to verify yours is supported.
501 swift 1.1 </note>
502    
503     <p>
504 neysx 1.12 It's time to test whether CPU frequency changing works. Let's install another
505 nightmorph 1.41 tool: <c>sys-power/cpufrequtils</c>.
506 swift 1.1 </p>
507    
508 neysx 1.12 <pre caption="Checking CPU frequency">
509     # <i>emerge cpufrequtils</i>
510     # <i>cpufreq-info</i>
511 swift 1.1 </pre>
512    
513     <p>
514 neysx 1.12 Here is an example output:
515 swift 1.1 </p>
516    
517 neysx 1.12 <pre caption="Sample output from cpufreq-info">
518 so 1.15 cpufrequtils 0.3: cpufreq-info (C) Dominik Brodowski 2004
519 neysx 1.12 Report errors and bugs to linux@brodo.de, please.
520     analyzing CPU 0:
521     driver: centrino
522     CPUs which need to switch frequency at the same time: 0
523     hardware limits: 600 MHz - 1.40 GHz
524     available frequency steps: 600 MHz, 800 MHz, 1000 MHz, 1.20 GHz, 1.40 GHz
525 so 1.15 available cpufreq governors: conservative, ondemand, powersave, userspace, performance
526 neysx 1.12 current policy: frequency should be within 924 MHz and 1.40 GHz.
527     The governor "performance" may decide which speed to use
528     within this range.
529 so 1.15 current CPU frequency is 1.40 GHz.
530 neysx 1.12 </pre>
531    
532 swift 1.1 <p>
533 neysx 1.12 Now play around with <c>cpufreq-set</c> to make sure frequency switching works.
534     Run <c>cpufreq-set -g ondemand</c> for example to activate the ondemand
535     governor and verify the change with <c>cpufreq-info</c>. If it doesn't work as
536 rane 1.20 expected, you might find help in the <uri link="#doc_chap8">Troubleshooting
537     section</uri> in the end of this guide.
538 swift 1.1 </p>
539    
540 nightmorph 1.41 <p>
541     <c>cpufrequtils</c> can operate in an automatic mode (when you use the
542     <b>ondemand</b> governor), you can also switch to the <b>userspace</b> governor
543     if you want to manually set a specific speed. You can also statically set your
544     CPU to its highest or lowest frequency by using the <b>performance</b>
545     and <b>powersave</b> governors, respectively.
546     </p>
547    
548     <pre caption="Changing CPU speeds">
549     <comment>(Set the highest available frequency)</comment>
550     # <i>cpufreq-set -g performance</i>
551     <comment>(Set the lowest available frequency)</comment>
552     # <i>cpufreq-set -g powersave</i>
553     <comment>(Set a specific frequency)</comment>
554     # <i>cpufreq-set -g userspace</i>
555     # <i>cpufreq-set -f 2.00ghz</i>
556     </pre>
557    
558 swift 1.1 </body>
559     </section>
560     <section>
561 nightmorph 1.41 <title>Other CPU Speed Utilities</title>
562 swift 1.1 <body>
563    
564     <p>
565 nightmorph 1.41 While <c>cpufrequtils</c> may be the best all-around program, there are some
566     other choices available in Portage. The following table gives a quick overview
567     of available CPU speed utilities. It's roughly separated in three categories
568     <b>kernel</b> for approaches that only need kernel support, <b>daemon</b> for
569     programs that run in the background and <b>graphical</b> for programs that
570     provide a GUI for easy configuration and changes.
571 swift 1.1 </p>
572    
573     <table>
574     <tr>
575     <th>Name</th>
576 swift 1.8 <th>Category</th>
577     <th>Switch decision</th>
578     <th>Kernel governors</th>
579     <th>Further governors</th>
580     <th>Comments</th>
581     </tr>
582     <tr>
583     <ti>'ondemand' governor</ti>
584     <ti>Kernel</ti>
585     <ti>CPU load</ti>
586     <ti>N.A.</ti>
587     <ti>N.A.</ti>
588     <ti>
589 so 1.15 Chooses maximal frequency on CPU load and slowly steps down when the CPU is
590     idle. Further tuning through files in
591 swift 1.8 <path>/sys/devices/system/cpu/cpu0/cpufreq/ondemand/</path>. Still requires
592     userland tools (programs, scripts) if governor switching or similar is
593     desired.
594     </ti>
595 swift 1.1 </tr>
596     <tr>
597 so 1.15 <ti>'conservative' governor</ti>
598     <ti>Kernel</ti>
599     <ti>CPU load</ti>
600     <ti>N.A.</ti>
601     <ti>N.A.</ti>
602     <ti>
603 neysx 1.16 Unlike the ondemand governor, conversative doesn't jump to maximum
604     frequency when CPU load is high, but increases the frequency step by step.
605     Further tuning through files in
606     <path>/sys/devices/system/cpu/cpu0/cpufreq/ondemand/</path>. Still requires
607     userland tools (programs, scripts) if governor switching or similar is
608     desired.
609 so 1.15 </ti>
610     </tr>
611     <tr>
612 swift 1.1 <ti><uri link="http://mnm.uib.es/~gallir/cpudyn/">cpudyn</uri></ti>
613 swift 1.8 <ti>Daemon</ti>
614     <ti>CPU load</ti>
615 neysx 1.12 <ti>Performance, powersave</ti>
616 swift 1.8 <ti>Dynamic</ti>
617     <ti>
618     Also supports disk standby - notice however that <e>laptop mode</e> in most
619     cases will do a better job.
620     </ti>
621 swift 1.1 </tr>
622     <tr>
623 swift 1.8 <ti><uri link="http://sourceforge.net/projects/cpufreqd/">cpufreqd</uri></ti>
624     <ti>Daemon</ti>
625 nightmorph 1.17 <ti>Battery state, CPU load, temperature, running programs and more</ti>
626 swift 1.8 <ti>All available</ti>
627     <ti>None</ti>
628     <ti>
629 nightmorph 1.17 Sophisticated (but somewhat complicated) setup. Extendible through plugins
630     like sensor monitoring (lm_sensors) or coordinating some NVidia based
631     graphics card memory and core. Cpufreqd is SMP aware and can optionally be
632     controlled manually at runtime.
633 swift 1.8 </ti>
634     </tr>
635     <tr>
636     <ti>
637     <uri link="http://www.deater.net/john/powernowd.html">powernowd</uri>
638     </ti>
639     <ti>Daemon</ti>
640     <ti>CPU load</ti>
641     <ti>None</ti>
642     <ti>Passive, sine, aggressive</ti>
643     <ti>
644     Supports SMP.
645     </ti>
646 swift 1.1 </tr>
647     <tr>
648 nightmorph 1.31 <ti>
649     <uri
650     link="http://projects.simpledesigns.com.pl/project/ncpufreqd/">ncpufreqd</uri>
651     </ti>
652 so 1.15 <ti>Daemon</ti>
653     <ti>Temperature</ti>
654     <ti>None</ti>
655     <ti>Powersave, performance</ti>
656     <ti>
657     Toggles the used governor between performance and powersave depending on
658     system temperature. Very useful on laptops with notorious heat problems.
659     </ti>
660     </tr>
661     <tr>
662 swift 1.1 <ti><uri link="http://www.goop.org/~jeremy/speedfreq/">speedfreq</uri></ti>
663 swift 1.8 <ti>Daemon</ti>
664     <ti>CPU load</ti>
665     <ti>None</ti>
666     <ti>Dynamic, powersave, performance, fixed speed</ti>
667     <ti>
668 so 1.15 Easy to configure with a nice client/server interface. Requires a 2.6
669     kernel. Unmaintained, broken and thus removed from Portage. Please switch
670     to cpufreqd if you're still using it.
671 swift 1.8 </ti>
672     </tr>
673     <tr>
674     <ti><uri link="http://cpuspeedy.sourceforge.net/">gtk-cpuspeedy</uri></ti>
675     <ti>Graphical</ti>
676     <ti>None</ti>
677     <ti>None</ti>
678     <ti>None</ti>
679 swift 1.1 <ti>
680 swift 1.8 Gnome application, a graphical tool to set CPU frequency manually. It does
681 neysx 1.12 not offer any automation.
682 swift 1.1 </ti>
683     </tr>
684     <tr>
685 swift 1.8 <ti>klaptopdaemon</ti>
686     <ti>Graphical</ti>
687     <ti>Battery state</ti>
688     <ti>All available</ti>
689     <ti>None</ti>
690     <ti>
691     KDE only, 'ondemand' governor required for dynamic frequency scaling.
692     </ti>
693 swift 1.1 </tr>
694     </table>
695    
696     <p>
697 so 1.15 While adjusting the frequency to the current load looks simple at a first
698     glance, it's not such a trivial task. A bad algorithm can cause switching
699     between two frequencies all the time or wasting energy when setting frequency
700 rane 1.20 to an unnecessary high level.
701 swift 1.1 </p>
702    
703     <p>
704 neysx 1.12 Which one to choose? If you have no idea about it, try <c>cpufreqd</c>:
705 swift 1.1 </p>
706    
707     <pre caption="Installing cpufreqd">
708     # <i>emerge cpufreqd</i>
709     </pre>
710    
711     <p>
712 neysx 1.12 <c>cpufreqd</c> can be configured by editing <path>/etc/cpufreqd.conf</path>.
713     The default one that ships with cpufreqd may look a bit confusing. I recommend
714 nightmorph 1.22 replacing it with the one from former Gentoo developer Henrik Brix Andersen
715     (see below). Please notice that you need cpufreqd-2.0.0 or later. Earlier
716     versions have a different syntax for the config file.
717 swift 1.1 </p>
718    
719 nightmorph 1.17 <pre caption="/etc/cpufreqd.conf (cpufreqd-2.0.0 and later)">
720 swift 1.1 [General]
721     pidfile=/var/run/cpufreqd.pid
722 nightmorph 1.17 poll_interval=3
723     enable_plugins=acpi_ac, acpi_battery
724 nightmorph 1.18 enable_remote=1
725     remote_group=wheel
726 neysx 1.12 verbosity=5
727 nightmorph 1.17 [/General]
728 swift 1.1
729     [Profile]
730 neysx 1.12 name=ondemand
731     minfreq=0%
732     maxfreq=100%
733     policy=ondemand
734 nightmorph 1.17 [/Profile]
735 swift 1.1
736     [Profile]
737 so 1.15 name=conservative
738     minfreq=0%
739     maxfreq=100%
740     policy=conservative
741 nightmorph 1.17 [/Profile]
742 so 1.15
743     [Profile]
744 neysx 1.12 name=powersave
745     minfreq=0%
746     maxfreq=100%
747 swift 1.1 policy=powersave
748 nightmorph 1.17 [/Profile]
749 swift 1.1
750     [Profile]
751 neysx 1.12 name=performance
752     minfreq=0%
753     maxfreq=100%
754     policy=performance
755 nightmorph 1.17 [/Profile]
756 swift 1.1
757     [Rule]
758 neysx 1.12 name=battery
759     ac=off
760 so 1.15 profile=conservative
761 nightmorph 1.17 [/Rule]
762 swift 1.1
763     [Rule]
764 neysx 1.12 name=battery_low
765 swift 1.1 ac=off
766 neysx 1.12 battery_interval=0-10
767     profile=powersave
768 nightmorph 1.17 [/Rule]
769 swift 1.1
770     [Rule]
771 neysx 1.12 name=ac
772     ac=on
773 so 1.15 profile=ondemand
774 nightmorph 1.17 [/Rule]
775 neysx 1.12 </pre>
776    
777     <p>
778 rane 1.19 Now you can start the cpufreqd daemon. Add it to the <c>default</c> and
779     <c>battery</c> runlevel as well.
780 swift 1.1 </p>
781    
782 neysx 1.12 <pre caption="Starting cpufreqd">
783     # <i>rc-update add cpufreqd default battery</i>
784 nightmorph 1.41 # <i>/etc/init.d/cpufreqd start</i>
785 neysx 1.12 </pre>
786    
787 nightmorph 1.17 <p>
788     Sometimes it can be desirable to select another policy than the daemon chooses,
789     for example when battery power is low, but you know that AC will be available
790 rane 1.20 soon. In that case you can turn on cpufreqd's manual mode with <c>cpufreqd-set
791     manual</c> and select one of your configured policies (as listed by
792     <c>cpufreqd-get</c>). You can leave manual mode by executing <c>cpufreqd-set
793     dynamic</c>.
794 nightmorph 1.17 </p>
795    
796 neysx 1.12 <warn>
797     Do not run more than one of the above programs at the same time. It may cause
798     confusion like switching between two frequencies all the time.
799     </warn>
800    
801 swift 1.8 </body>
802     </section>
803     <section>
804     <title>Verifying the result</title>
805     <body>
806    
807 swift 1.1 <p>
808     The last thing to check is that your new policies do a good job. An easy way to
809 swift 1.8 do so is monitoring CPU speed while working with your laptop:
810 swift 1.1 </p>
811    
812     <pre caption="Monitoring CPU speed">
813 yoswink 1.13 # <i>watch grep \"cpu MHz\" /proc/cpuinfo</i>
814 swift 1.1 </pre>
815    
816     <p>
817 rane 1.20 If <path>/proc/cpuinfo</path> doesn't get updated (see <uri
818 swift 1.32 link="#doc_chap8">Troubleshooting</uri>), monitor the CPU frequency with
819     <c>sys-apps/x86info</c>:
820 swift 1.1 </p>
821    
822     <pre caption="Alternative CPU speed monitoring">
823 neysx 1.12 # <i>watch x86info -mhz</i>
824 swift 1.1 </pre>
825    
826     <p>
827     Depending on your setup, CPU speed should increase on heavy load, decrease on
828 rane 1.19 no activity or just stay at the same level. When using <c>cpufreqd</c> and
829 rane 1.20 verbosity set to 5 or higher in <path>cpufreqd.conf</path> you'll get
830     additional information about what's happening reported to <c>syslog</c>.
831 swift 1.1 </p>
832    
833     </body>
834     </section>
835     </chapter>
836    
837     <chapter>
838     <title>LCD Power Management</title>
839     <section>
840     <body>
841    
842     <p>
843 rane 1.20 As you can see in <uri link="#doc_chap1_fig1">figure 1.1</uri>, the LCD
844     display consumes the biggest part of energy (might not be the case for
845     non-mobile CPU's). Thus it's quite important not only to shut the display off
846     when not needed, but also to reduce it's backlight if possible. Most laptops
847     offer the possibility to control the backlight dimming.
848 swift 1.1 </p>
849    
850 nightmorph 1.17 </body>
851     </section>
852     <section>
853     <title>Standby settings</title>
854     <body>
855    
856 swift 1.1 <p>
857 nightmorph 1.17 The first thing to check is the standby/suspend/off timings of the display. As
858     this depends heavily on your windowmanager, I'll let you figure it out
859 rane 1.20 yourself. Just two common places: Blanking the terminal can be done with
860 nightmorph 1.17 <c>setterm -blank &lt;number-of-minutesM&gt;</c>, <c>setterm -powersave on</c>
861     and <c>setterm -powerdown &lt;number-of-minutesM&gt;</c>. For X.org, modify
862     <path>/etc/X11/xorg.conf</path> similar to this:
863 swift 1.1 </p>
864    
865 nightmorph 1.35 <pre caption="LCD suspend settings in X.org">
866     Section "ServerFlags"
867     Option "blank time" "5" <comment># Blank the screen after 5 minutes (Fake)</comment>
868     Option "standby time" "10" <comment># Turn off screen after 10 minutes (DPMS)</comment>
869     Option "suspend time" "20" <comment># Full suspend after 20 minutes</comment>
870     Option "off time" "30" <comment># Turn off after half an hour</comment>
871 swift 1.1 [...]
872     EndSection
873    
874     [...]
875    
876     Section "Monitor"
877     Identifier [...]
878 nightmorph 1.35 Option "DPMS"
879 swift 1.1 [...]
880     EndSection
881     </pre>
882    
883 nightmorph 1.17 </body>
884     </section>
885     <section>
886     <title>Backlight dimming</title>
887     <body>
888    
889 swift 1.1 <p>
890     Probably more important is the backlight dimming. If you have access to the
891     dimming settings via a tool, write a small script that dims the backlight in
892 rane 1.19 battery mode and place it in your <c>battery</c> runlevel. The following script
893 nightmorph 1.17 should work on most IBM Thinkpads and Toshiba laptops. You've got to enable the
894 rane 1.20 appropriate option in your kernel (IBM Thinkpads only). For Toshiba laptops,
895 nightmorph 1.35 install <c>sys-power/acpitool</c> and skip configuration of <c>thinkpad_acpi</c>
896     (formerly called <c>ibm_acpi</c>) as described below.
897 neysx 1.12 </p>
898    
899     <warn>
900 swift 1.36 Support for setting brightness is marked experimental in thinkpad_acpi. It
901     accesses hardware directly and may cause severe harm to your system. Please
902     read the <uri link="http://ibm-acpi.sourceforge.net/">thinkpad_acpi
903     website</uri>
904 neysx 1.12 </warn>
905    
906     <p>
907 swift 1.36 To be able to set the brightness level, the thinkpad_acpi module has to be
908     loaded with the experimental parameter.
909 neysx 1.12 </p>
910    
911 swift 1.47 <pre caption="Automatically loading the thinkpad_acpi module">
912 neysx 1.12 <comment>(Please read the warnings above before doing this!)</comment>
913 swift 1.47
914 nightmorph 1.37 # <i>echo "options thinkpad_acpi experimental=1" >> /etc/modprobe.d/thinkpad_acpi</i>
915     # <i>update-modules</i>
916 swift 1.47 # <i>nano /etc/conf.d/modules</i>
917     <comment># Autoload the thinkpad_acpi module</comment>
918     modules_2_6="thinkpad_acpi"
919     <comment># Parameters for the thinkpad_acpi module</comment>
920     modules_thinkpad_acpi_args_2_6="experimental=1"
921    
922 nightmorph 1.35 # <i>modprobe thinkpad_acpi</i>
923 neysx 1.12 </pre>
924    
925     <p>
926     This should work without error messages and a file
927     <path>/proc/acpi/ibm/brightness</path> should be created after loading the
928 rane 1.20 module. An init script will take care of choosing the brightness according to
929     the power source.
930 neysx 1.12 </p>
931    
932     <pre caption="/etc/conf.d/lcd-brightness">
933     <comment># See /proc/acpi/ibm/brightness for available values</comment>
934 nightmorph 1.35 <comment># Please read /usr/src/linux/Documentation/thinkpad-acpi.txt</comment>
935 neysx 1.12
936 nightmorph 1.23 <comment># brightness level in ac mode. Default is 7.</comment>
937 neysx 1.12 BRIGHTNESS_AC=7
938    
939     <comment># brightness level in battery mode. Default is 4.</comment>
940     BRIGHTNESS_BATTERY=4
941     </pre>
942    
943     <pre caption="/etc/init.d/lcd-brightness">
944     #!/sbin/runscript
945    
946     set_brightness() {
947     if on_ac_power
948     then
949     LEVEL=${BRIGHTNESS_AC:-7}
950     else
951     LEVEL=${BRIGHTNESS_BATTERY:-4}
952     fi
953    
954     if [ -f /proc/acpi/ibm/brightness ]
955     then
956     ebegin "Setting LCD brightness"
957     echo "level ${LEVEL}" > /proc/acpi/ibm/brightness
958     eend $?
959 nightmorph 1.17 elif [[ -e /usr/bin/acpitool &amp;&amp; -n $(acpitool -T | grep "LCD brightness") ]]
960     then
961     ebegin "Setting LCD brightness"
962     acpitool -l $LEVEL >/dev/null || ewarn "Unable to set lcd brightness"
963     eend $?
964 neysx 1.12 else
965     ewarn "Setting LCD brightness is not supported."
966 nightmorph 1.35 ewarn "For IBM Thinkpads, check that thinkpad_acpi is loaded into the kernel"
967 nightmorph 1.23 ewarn "For Toshiba laptops, you've got to install sys-power/acpitool"
968 neysx 1.12 fi
969     }
970    
971     start() {
972     set_brightness
973     }
974    
975     stop () {
976     set_brightness
977     }
978     </pre>
979    
980     <p>
981     When done, make sure brightness is adjusted automatically by adding it to the
982     battery runlevel.
983 swift 1.1 </p>
984    
985 neysx 1.12 <pre caption="Enabling automatic brightness adjustment">
986 rane 1.19 # <i>chmod +x /etc/init.d/lcd-brightness</i>
987     # <i>rc-update add lcd-brightness battery</i>
988     # <i>rc</i>
989 neysx 1.12 </pre>
990    
991 swift 1.1 </body>
992     </section>
993     </chapter>
994    
995     <chapter>
996     <title>Disk Power Management</title>
997     <section>
998 nightmorph 1.17 <body>
999 rane 1.19
1000 nightmorph 1.17 <p>
1001     Hard disks consume less energy in sleep mode. Therefore it makes sense to
1002     activate power saving features whenever the hard disk is not used for a certain
1003     amount of time. I'll show you two alternative possibilities to do it. First,
1004     laptop-mode will save most energy due to several measures which prevent or at
1005     least delay write accesses. The drawback is that due to the delayed write
1006     accesses a power outage or kernel crash will be more dangerous for data loss.
1007     If you don't like this, you have to make sure that there are no processes which
1008     write to your hard disk frequently. Afterwards you can enable power saving
1009 rane 1.19 features of your hard disk with <c>hdparm</c> as the second alternative.
1010 nightmorph 1.17 </p>
1011    
1012     </body>
1013     </section>
1014     <section>
1015     <title>Increasing idle time - laptop-mode</title>
1016 swift 1.1 <body>
1017    
1018     <p>
1019 nightmorph 1.27 Recent 2.6 kernels include the so-called <c>laptop-mode</c>. When activated,
1020     dirty buffers are written to disk on read calls or after 10 minutes (instead of
1021     30 seconds). This minimizes the time the hard disk needs to be spun up.
1022 swift 1.1 </p>
1023    
1024 nightmorph 1.17 <pre caption="Automated start of laptop-mode">
1025     # <i>emerge laptop-mode-tools</i>
1026     </pre>
1027 swift 1.1
1028 nightmorph 1.17 <p>
1029     <c>laptop-mode-tools</c> has its configuration file in
1030     <path>/etc/laptop-mode/laptop-mode.conf</path>. Adjust it the way you like it,
1031     it's well commented. Run <c>rc-update add laptop_mode battery</c> to start it
1032     automatically.
1033     </p>
1034    
1035     <p>
1036     Recent versions (1.11 and later) of laptop-mode-tools include a new tool
1037     <c>lm-profiler</c>. It will monitor your system's disk usage and running
1038     network services and suggests to disable unneeded ones. You can either disable
1039     them through laptop-mode-tools builtin runlevel support (which will be reverted
1040 rane 1.19 by Gentoo's <c>/sbin/rc</c>) or use your <c>default</c>/<c>battery</c>
1041 nightmorph 1.17 runlevels (recommended).
1042     </p>
1043    
1044     <pre caption="Sample output from running lm-profiler">
1045 rane 1.19 # <i>lm-profiler</i>
1046 nightmorph 1.17 Profiling session started.
1047     Time remaining: 600 seconds
1048     [4296896.602000] amarokapp
1049     Time remaining: 599 seconds
1050     [4296897.714000] sort
1051     [4296897.970000] mv
1052     Time remaining: 598 seconds
1053     Time remaining: 597 seconds
1054     [4296900.482000] reiserfs/0
1055     </pre>
1056    
1057     <p>
1058     After profiling your system for ten minutes, lm-profiler will present a list of
1059     services which might have caused disk accesses during that time.
1060     </p>
1061    
1062     <pre caption="lm-profiler suggests to disable some services">
1063     Program: "atd"
1064     Reason: standard recommendation (program may not be running)
1065     Init script: /etc/init.d/atd (GUESSED)
1066    
1067 rane 1.19 Do you want to disable this service in battery mode? [y/N]: <i>n</i>
1068 swift 1.1 </pre>
1069    
1070     <p>
1071 nightmorph 1.17 To disable atd as suggested in the example above, you would run <c>rc-update
1072     del atd battery</c>. Be careful not to disable services that are needed for
1073 rane 1.20 your system to run properly - <c>lm-profiler</c> is likely to generate some
1074     false positives. Do not disable a service if you are unsure whether it's
1075     needed.
1076 nightmorph 1.17 </p>
1077    
1078     </body>
1079     </section>
1080     <section>
1081 rane 1.19 <title>Limiting Write Accesses</title>
1082 nightmorph 1.17 <body>
1083    
1084     <p>
1085     If you don't want to use laptop-mode, you must take special care to disable
1086     services that write to your disk frequently - <c>syslogd</c> is a good
1087     candidate, for example. You probably don't want to shut it down completely, but
1088     it's possible to modify the config file so that "unnecessary" things don't get
1089 rane 1.20 logged and thus don't create disk traffic. <c>Cups</c> writes to disk
1090     periodically, so consider shutting it down and only enable it manually when
1091     needed.
1092 nightmorph 1.17 </p>
1093    
1094     <pre caption="Disabling cups in battery mode">
1095     # <i>rc-update del cupsd battery</i>
1096     </pre>
1097    
1098     <p>
1099     You can also use <c>lm-profiler</c> from laptop-mode-tools (see above) to find
1100     services to disable. Once you eliminated all of them, go on with configuring
1101     hdparm.
1102     </p>
1103    
1104     </body>
1105     </section>
1106     <section>
1107     <title>hdparm</title>
1108     <body>
1109    
1110     <p>
1111 nightmorph 1.28 The second possibility is using <c>hdparm</c>. Skip this if
1112     you are using laptop-mode. Otherwise, edit <path>/etc/conf.d/hdparm</path> and
1113     add the following values to your drive entries. This example assumes your hard
1114     drive is called <b>hda</b>:
1115 swift 1.1 </p>
1116    
1117 nightmorph 1.28 <pre caption="Using /etc/conf.d/hdparm for disk standby">
1118     hda_args="-q -S12"
1119     </pre>
1120 neysx 1.12
1121 nightmorph 1.28 <p>
1122     This will activate power management for your hard drive. If you ever want to
1123     deactivate power management, you can edit <path>/etc/conf.d/hdparm</path> and
1124     change the values to <c>-q -S0</c>, or just run <c>hdparm -q -S0 /dev/hda</c>.
1125     </p>
1126 swift 1.1
1127     <p>
1128 nightmorph 1.28 See <c>man hdparm</c> for the options. Though you can always start <c>hdparm</c>
1129     manually when you are on battery power by running <c>/etc/init.d/hdparm
1130     start</c>, it's much easier to automate its startup and shutdown. To do so, add
1131     <c>hdparm</c> to the battery runlevel so that it will automatically enable power
1132     management.
1133 swift 1.1 </p>
1134    
1135     <pre caption="Automate disk standby settings">
1136 nightmorph 1.28 # <i>rc-update add hdparm battery</i>
1137 swift 1.1 </pre>
1138    
1139     <impo>
1140     Be careful with sleep/spin down settings of your hard drive. Setting it to
1141     small values might wear out your drive and lose warranty.
1142     </impo>
1143    
1144     </body>
1145     </section>
1146     <section>
1147     <title>Other tricks</title>
1148     <body>
1149    
1150     <p>
1151     Another possibility is to deactivate swap in battery mode. Before writing a
1152     swapon/swapoff switcher, make sure there is enough RAM and swap isn't used
1153     heavily, otherwise you'll be in big problems.
1154     </p>
1155    
1156     <p>
1157     If you don't want to use laptop-mode, it's still possible to minimize disk
1158 rane 1.19 access by mounting certain directories as <c>tmpfs</c> - write accesses are not
1159 swift 1.1 stored on a disk, but in main memory and get lost with unmounting. Often it's
1160     useful to mount <path>/tmp</path> like this - you don't have to pay special
1161     attention as it gets cleared on every reboot regardless whether it was mounted
1162     on disk or in RAM. Just make sure you have enough RAM and no program (like a
1163     download client or compress utility) needs extraordinary much space in
1164     <path>/tmp</path>. To activate this, enable tmpfs support in your kernel and
1165     add a line to <path>/etc/fstab</path> like this:
1166     </p>
1167    
1168     <pre caption="Editing /etc/fstab to make /tmp even more volatile">
1169     none /tmp tmpfs size=32m 0 0
1170     </pre>
1171    
1172     <warn>
1173     Pay attention to the size parameter and modify it for your system. If you're
1174 rane 1.21 unsure, don't try this at all, it can become a performance bottleneck easily. In
1175 swift 1.1 case you want to mount <path>/var/log</path> like this, make sure to merge the
1176     log files to disk before unmounting. They are essential. Don't attempt to mount
1177 rane 1.19 <path>/var/tmp</path> like this. Portage uses it for compiling...
1178 swift 1.1 </warn>
1179    
1180     </body>
1181     </section>
1182     </chapter>
1183    
1184     <chapter>
1185 rane 1.19 <title>Power Management For Other Devices</title>
1186 swift 1.1 <section>
1187 rane 1.19 <title>Graphics Cards</title>
1188 so 1.15 <body>
1189    
1190     <p>
1191     In case you own an ATI graphics card supporting PowerPlay (dynamic clock
1192 nightmorph 1.25 scaling for the graphics processing unit GPU), you can activate this
1193 rane 1.20 feature in X.org. Open <path>/etc/X11/xorg.conf</path> and add (or enable) the
1194     <c>DynamicClocks</c> option in the Device section. Please notice that this
1195     feature will lead to crashes on some systems.
1196 so 1.15 </p>
1197    
1198     <pre caption="Enabling ATI PowerPlay support in X.org">
1199     Section "Device"
1200     [...]
1201     Option "DynamicClocks" "on"
1202     EndSection
1203     </pre>
1204    
1205     </body>
1206     </section>
1207     <section>
1208 swift 1.1 <title>Wireless Power Management</title>
1209     <body>
1210    
1211     <p>
1212 nightmorph 1.17 Wireless LAN cards consume quite a bit of energy. Put them in Power Management
1213 nightmorph 1.28 mode just like your hard drives.
1214 swift 1.1 </p>
1215    
1216 nightmorph 1.17 <note>
1217     This script assumes your wireless interface is called <c>wlan0</c>; replace
1218     this with the actual name of your interface.
1219     </note>
1220    
1221 nightmorph 1.28 <p>
1222 nightmorph 1.29 Add the following option to <path>/etc/conf.d/net</path> to automatically enable
1223 nightmorph 1.28 power management for your wireless card:
1224     </p>
1225 swift 1.1
1226 nightmorph 1.28 <pre caption="Automated WLAN Power Management">
1227     iwconfig_wlan0="power on"
1228 swift 1.1 </pre>
1229    
1230     <p>
1231 nightmorph 1.28 See <c>man iwconfig</c> for details and more options like the period between
1232     wakeups or timeout settings. If your driver and access point support changing
1233     the beacon time, this is a good starting point to save even more energy.
1234 swift 1.1 </p>
1235    
1236     </body>
1237     </section>
1238     <section>
1239     <title>USB Power Management</title>
1240     <body>
1241    
1242     <p>
1243     There are two problems with USB devices regarding energy consumption: First,
1244     devices like USB mice, digital cameras or USB sticks consume energy while
1245     plugged in. You cannot avoid this (nevertheless remove them in case they're not
1246     needed). Second, when there are USB devices plugged in, the USB host controller
1247     periodically accesses the bus which in turn prevents the CPU from going into
1248 rane 1.20 sleep mode. The kernel offers an experimental option to enable suspension of
1249 so 1.15 USB devices through driver calls or one of the <path>power/state</path> files
1250     in <path>/sys</path>.
1251 swift 1.1 </p>
1252    
1253 so 1.15 <pre caption="Enabling USB suspend support in the kernel">
1254     Device Drivers
1255     USB support
1256     [*] Support for Host-side USB
1257     [*] USB suspend/resume (EXPERIMENTAL)
1258     </pre>
1259    
1260 swift 1.1 </body>
1261     </section>
1262     </chapter>
1263    
1264     <chapter>
1265 rane 1.19 <title>Sleep States: sleep, standby, and suspend to disk</title>
1266 swift 1.1 <section>
1267     <body>
1268    
1269     <p>
1270     ACPI defines different sleep states. The more important ones are
1271     </p>
1272    
1273 rane 1.20 <ul>
1274 swift 1.1 <li>S1 aka Standby</li>
1275     <li>S3 aka Suspend to RAM aka Sleep</li>
1276     <li>S4 aka Suspend to Disk aka Hibernate</li>
1277     </ul>
1278    
1279     <p>
1280     They can be called whenever the system is not in use, but a shutdown is not
1281     wanted due to the long boot time.
1282     </p>
1283    
1284     </body>
1285     </section>
1286     <section>
1287 so 1.15 <title>Sleep (S3)</title>
1288 swift 1.1 <body>
1289    
1290     <p>
1291 so 1.15 The ACPI support for these sleep states is marked experimental for good reason.
1292     APM sleep states seem to be more stable, however you can't use APM and ACPI
1293     together.
1294     </p>
1295    
1296     <pre caption="Kernel configuration for the various suspend types">
1297     Power Management Options ---&gt;
1298     [*] Power Management support
1299 nightmorph 1.40 [*] Suspend to RAM and standby
1300 so 1.15 </pre>
1301    
1302     <p>
1303 nightmorph 1.17 Once your kernel is properly configured, you can use the
1304 so 1.15 <c>hibernate-script</c> to activate suspend or sleep mode. Let's install that
1305     first.
1306     </p>
1307    
1308     <pre caption="Installing the hibernate-script">
1309 rane 1.19 # <i>emerge hibernate-script</i>
1310 so 1.15 </pre>
1311    
1312     <p>
1313 nightmorph 1.25 Some configuration has to be done in <path>/etc/hibernate</path>. The default
1314 nightmorph 1.24 package introduces a few configuration files for each sleep state. Options that
1315     are common to all suspend methods are placed in <path>common.conf</path>; make
1316     sure this file is properly set up for your system.
1317 so 1.15 </p>
1318    
1319     <p>
1320 nightmorph 1.24 To configure sleep, edit <path>sysfs-ram.conf</path> in
1321     <path>/etc/hibernate</path>. <c>UseSysfsPowerState mem</c> is already setup
1322 nightmorph 1.25 correctly, but if you need to make further changes to this particular sleep
1323     state (or any other sleep state) you should add them to
1324 nightmorph 1.24 <path>/etc/hibernate/hibernate.conf</path>. The comments and option names will
1325     guide you. If you use nfs or samba shares over the network, make sure to
1326     shutdown the appropriate init scripts to avoid timeouts.
1327 so 1.15 </p>
1328    
1329 nightmorph 1.24 <note>
1330     For more information on setting up sleep states, read <c>man
1331     hibernate.conf</c>.
1332     </note>
1333    
1334 so 1.15 <p>
1335     Ready? Now is the last chance to backup any data you want to keep after
1336     executing the next command. Notice that you probably have to hit a special key
1337 rane 1.19 like <c>Fn</c> to resume from sleep.
1338 so 1.15 </p>
1339    
1340     <pre caption="Calling sleep">
1341 rane 1.19 # <i>hibernate-ram</i>
1342 so 1.15 </pre>
1343    
1344     <p>
1345 rane 1.20 If you're still reading, it seems to work. You can also setup standby (S1) in a
1346 nightmorph 1.24 similar way by editing <path>sysfs-ram.conf</path> and changing
1347     "UseSysfsPowerState mem" to "UseSysfsPowerState standby". S3 and S4 are the more
1348     interesting sleep states due to greater energy savings however.
1349 so 1.15 </p>
1350    
1351     </body>
1352     </section>
1353     <section>
1354     <title>Hibernate (S4)</title>
1355     <body>
1356    
1357     <p>
1358     This section introduces hibernation, where a snapshot of the running system is
1359     written to disk before powering off. On resume, the snapshot is loaded and you
1360     can go on working at exactly the point you called hibernate before.
1361 swift 1.1 </p>
1362    
1363     <warn>
1364 so 1.15 Don't exchange non hot-pluggable hardware when suspended. Don't attempt to load
1365     a snapshot with a different kernel image than the one it was created with.
1366     Shutdown any NFS or samba server/client before hibernating.
1367 swift 1.1 </warn>
1368    
1369     <p>
1370 so 1.15 There are two different implementations for S4. The original one is swsusp,
1371 nightmorph 1.39 then there is the newer tuxonice (formerly suspend2) with a nicer interface
1372 swift 1.36 (including fbsplash support). A <uri
1373 nightmorph 1.39 link="http://tuxonice.net/features.html#compare">feature comparison</uri> is
1374     available at the <uri link="http://www.tuxonice.net">tuxonice homepage</uri>.
1375 swift 1.36 There used to be Suspend-to-Disk (pmdisk), a fork of swsusp, but it has been
1376     merged back.
1377 swift 1.1 </p>
1378    
1379     <p>
1380 jkt 1.33 TuxOnIce is not included in the mainline kernel yet, therefore you either have
1381 rane 1.20 to patch your kernel sources with the patches provided by <uri
1382 nightmorph 1.39 link="http://www.tuxonice.net">tuxonice.net</uri> or use
1383 jkt 1.33 <c>sys-kernel/tuxonice-sources</c>.
1384 swift 1.1 </p>
1385    
1386     <p>
1387 jkt 1.33 The kernel part for both swusp and TuxOnIce is as follows:
1388 swift 1.1 </p>
1389    
1390     <pre caption="Kernel configuration for the various suspend types">
1391 nightmorph 1.40 Power Management support ---&gt;
1392 swift 1.1 <comment>(hibernate with swsusp)</comment>
1393 nightmorph 1.39 [*] Hibernation (aka 'suspend to disk')
1394 so 1.15 <comment>(replace /dev/SWAP with your swap partition)</comment>
1395     (/dev/SWAP) Default resume partition
1396 rane 1.20
1397 jkt 1.33 <comment>(hibernate with TuxOnIce)</comment>
1398     Enhanced Hibernation (TuxOnIce)
1399 nightmorph 1.39 --- Image Storage (you need at least one allocator)
1400     [*] File Allocator
1401     [*] Swap Allocator
1402 so 1.15 --- General Options
1403 nightmorph 1.39 [*] Compression support
1404 so 1.15 [ ] Allow Keep Image Mode
1405 nightmorph 1.39 [*] Replace swsusp by default
1406 swift 1.1 </pre>
1407    
1408     <p>
1409 so 1.15 The configuration for swsusp is rather easy. If you didn't store the location
1410     of your swap partition in the kernel config, you can also pass it as a
1411     parameter with the <c>resume=/dev/SWAP</c> directive. If booting is not
1412     possible due to a broken image, use the <c>noresume</c> kernel parameter. The
1413 rane 1.20 <c>hibernate-cleanup</c> init script invalidates swsusp images during the boot
1414     process.
1415 swift 1.1 </p>
1416    
1417 so 1.15 <pre caption="Invalidating swsusp images during the boot process">
1418 rane 1.19 # <i>rc-update add hibernate-cleanup boot</i>
1419 so 1.15 </pre>
1420    
1421 swift 1.1 <p>
1422 so 1.15 To activate hibernate with swsusp, use the hibernate script and set
1423 nightmorph 1.24 <c>UseSysfsPowerState disk</c> in <path>/etc/hibernate/sysfs-disk</path>.
1424 swift 1.1 </p>
1425    
1426     <warn>
1427     Backup your data before doing this. Run <c>sync</c> before executing one of the
1428     commands to have cached data written to disk. First try it outside of X, then
1429     with X running, but not logged in.
1430     </warn>
1431 rane 1.20
1432 swift 1.1 <p>
1433     If you experience kernel panics due to uhci or similar, try to compile USB
1434     support as module and unload the modules before sending your laptop to sleep
1435 nightmorph 1.24 mode. There are configuration options for this in <path>common.conf</path>
1436 swift 1.1 </p>
1437    
1438 so 1.15 <pre caption="Hibernating with swsusp">
1439 nightmorph 1.24 # <i>nano -w /etc/hibernate/common.conf</i>
1440 so 1.15 <comment>(Make sure you have a backup of your data)</comment>
1441 rane 1.19 # <i>hibernate</i>
1442 so 1.15 </pre>
1443    
1444 swift 1.1 <p>
1445 jkt 1.34 The following section discusses the setup of TuxOnIce including fbsplash support
1446     for a nice graphical progress bar during suspend and resume.
1447 so 1.15 </p>
1448    
1449     <p>
1450 rane 1.20 The first part of the configuration is similar to the configuration of swsusp.
1451     In case you didn't store the location of your swap partition in the kernel
1452     config, you have to pass it as a kernel parameter with the
1453 jkt 1.33 <c>resume=swap:/dev/SWAP</c> directive. If booting is not possible due to a
1454     broken image, append the <c>noresume</c> parameter. Additionally, the
1455 jkt 1.34 <c>hibernate-cleanup</c> init script invalidates TuxOnIce images during the boot
1456     process.
1457 so 1.15 </p>
1458    
1459 jkt 1.33 <pre caption="Invalidating TuxOnIce images during the boot process">
1460 rane 1.19 # <i>rc-update add hibernate-cleanup boot</i>
1461 so 1.15 </pre>
1462    
1463 rane 1.20 <p>
1464 nightmorph 1.39 Now edit <path>/etc/hibernate/tuxonice.conf</path>, enable the <c>TuxOnIce</c>
1465 nightmorph 1.24 options you need. Do not enable the <c>fbsplash</c> options in
1466     <c>common.conf</c> just yet.
1467 swift 1.1 </p>
1468    
1469 jkt 1.33 <pre caption="Hibernating with TuxOnIce">
1470 nightmorph 1.39 # <i>nano -w /etc/hibernate/tuxonice.conf</i>
1471 so 1.15 <comment>(Make sure you have a backup of your data)</comment>
1472 rane 1.19 # <i>hibernate</i>
1473 swift 1.8 </pre>
1474    
1475 so 1.15 <p>
1476 rane 1.20 Please configure <c>fbsplash</c> now if you didn't do already. To enable
1477 jkt 1.34 fbsplash support during hibernation, the <c>sys-apps/tuxonice-userui</c> package
1478     is needed. Additionally, you've got to enable the <c>fbsplash</c> USE flag.
1479 so 1.15 </p>
1480    
1481 jkt 1.33 <pre caption="Installing tuxonice-userui">
1482     # <i>echo "sys-apps/tuxonice-userui fbsplash" >> /etc/portage/package.use</i>
1483     # <i>emerge tuxonice-userui</i>
1484 so 1.15 </pre>
1485    
1486     <p>
1487     The ebuild tells you to make a symlink to the theme you want to use. For
1488     example, to use the <c>livecd-2005.1</c> theme, run the following command:
1489     </p>
1490    
1491     <pre caption="Using the livecd-2005.1 theme during hibernation">
1492 nightmorph 1.39 # <i>ln -sfn /etc/splash/livecd-2005.1 /etc/splash/tuxonice</i>
1493 so 1.15 </pre>
1494    
1495     <p>
1496     If you don't want a black screen in the first part of the resume process, you
1497 jkt 1.33 have to add the <c>tuxoniceui_fbsplash</c> tool to your initrd image. Assuming
1498 so 1.15 you created the initrd image with <c>splash_geninitramfs</c> and saved it as
1499 rane 1.20 <path>/boot/fbsplash-emergence-1024x768</path>, here's how to do that.
1500 so 1.15 </p>
1501    
1502 jkt 1.33 <pre caption="Adding tuxoniceui_fbsplash to an initrd image">
1503 rane 1.19 # <i>mount /boot</i>
1504     # <i>mkdir ~/initrd.d</i>
1505     # <i>cp /boot/fbsplash-emergence-1024x768 ~/initrd.d/</i>
1506     # <i>cd ~/initrd.d</i>
1507     # <i>gunzip -c fbsplash-emergence-1024x768 | cpio -idm --quiet -H newc</i>
1508     # <i>rm fbsplash-emergence-1024x768</i>
1509 jkt 1.33 # <i>cp /usr/sbin/tuxoniceui_fbsplash sbin/</i>
1510     # <i>find . | cpio --quiet --dereference -o -H newc | gzip -9 > /boot/fbsplash-tuxonice-emergence-1024x768</i>
1511 so 1.15 </pre>
1512    
1513     <p>
1514 nightmorph 1.24 Afterwards adjust <path>grub.conf</path> (or <path>lilo.conf</path>) so that
1515 jkt 1.33 your TuxOnIce kernel uses
1516     <path>/boot/fbsplash-tuxonice-emergence-1024x768</path> as initrd image. You can
1517 nightmorph 1.24 now test a dry run to see if everything is setup correctly.
1518 so 1.15 </p>
1519    
1520     <pre caption="Test run for fbsplash hibernation">
1521 jkt 1.33 # <i>tuxoniceui_fbsplash -t</i>
1522 so 1.15 </pre>
1523    
1524     <p>
1525 nightmorph 1.24 Afterwards open <path>/etc/hibernate/common.conf</path> and activate the
1526     fbsplash options. Execute <c>hibernate</c> and enjoy.
1527 so 1.15 </p>
1528    
1529 swift 1.1 </body>
1530     </section>
1531     </chapter>
1532    
1533     <chapter>
1534     <title>Troubleshooting</title>
1535     <section>
1536     <body>
1537    
1538     <p>
1539     <e>Q:</e> I'm trying to change the CPU frequency, but
1540     <path>/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor</path> does not
1541     exist.
1542     </p>
1543    
1544     <p>
1545     <e>A:</e> Make sure your processor supports CPU frequency scaling and you chose
1546     the right CPUFreq driver for your processor. Here is a list of processors that
1547 jkt 1.34 are supported by cpufreq (kernel 2.6.7): ARM Integrator, ARM-SA1100, ARM-SA1110,
1548     AMD Elan - SC400, SC410, AMD mobile K6-2+, AMD mobile K6-3+, AMD mobile Duron,
1549     AMD mobile Athlon, AMD Opteron, AMD Athlon 64, Cyrix Media GXm, Intel mobile
1550     PIII and Intel mobile PIII-M on certain chipsets, Intel Pentium 4, Intel Xeon,
1551     Intel Pentium M (Centrino), National Semiconductors Geode GX, Transmeta Crusoe,
1552     VIA Cyrix 3 / C3, UltraSPARC-III, SuperH SH-3, SH-4, several "PowerBook" and
1553     "iBook2" and various processors on some ACPI 2.0-compatible systems (only if
1554     "ACPI Processor Performance States" are available to the ACPI/BIOS interface).
1555 swift 1.1 </p>
1556    
1557     <p>
1558     <e>Q:</e> My laptop supports frequency scaling, but
1559     <path>/sys/devices/system/cpu/cpu0/cpufreq/</path> is empty.
1560     </p>
1561    
1562     <p>
1563     <e>A:</e> Look for ACPI related error messages with <c>dmesg | grep ACPI</c>.
1564     Try to update the BIOS, especially if a broken DSDT is reported. You can also
1565     try to fix it yourself (which is beyond the scope of this guide).
1566     </p>
1567    
1568     <p>
1569 rane 1.19 <e>Q:</e> My laptop supports frequency scaling, but according to
1570     <path>/proc/cpuinfo</path> the speed never changes.
1571 swift 1.1 </p>
1572    
1573     <p>
1574 swift 1.8 <e>A:</e> Probably you have activated symmetric multiprocessing support
1575     (CONFIG_SMP) in your kernel. Deactivate it and it should work. Some older
1576 rane 1.20 kernels had a bug causing this. In that case, run <c>emerge x86info</c>, update
1577 jkt 1.34 your kernel as asked and check the current frequency with <c>x86info -mhz</c>.
1578 swift 1.1 </p>
1579    
1580     <p>
1581     <e>Q:</e> I can change the CPU frequency, but the range is not as wide as in
1582     another OS.
1583     </p>
1584    
1585     <p>
1586     <e>A:</e> You can combine frequency scaling with ACPI throttling to get a lower
1587 jkt 1.34 minimum frequency. Notice that throttling doesn't save much energy and is mainly
1588     used for thermal management (keeping your laptop cool and quiet). You can read
1589     the current throttling state with <c>cat /proc/acpi/processor/CPU/throttling</c>
1590     and change it with <c>echo -n "0:x" > /proc/acpi/processor/CPU/limit</c>, where
1591     x is one of the Tx states listed in
1592 swift 1.1 <path>/proc/acpi/processor/CPU/throttling</path>.
1593     </p>
1594    
1595     <p>
1596 swift 1.8 <e>Q:</e> When configuring the kernel, powersave, performance and userspace
1597     governors show up, but that ondemand thing is missing. Where do I get it?
1598     </p>
1599    
1600     <p>
1601     <e>A:</e> The ondemand governor is only included in recent kernel sources. Try
1602     updating them.
1603     </p>
1604    
1605     <p>
1606 swift 1.1 <e>Q:</e> Battery life time seems to be worse than before.
1607     </p>
1608    
1609     <p>
1610     <e>A:</e> Check your BIOS settings. Maybe you forgot to re-enable some of the
1611     settings.
1612     </p>
1613    
1614     <p>
1615     <e>Q:</e> My battery is charged, but KDE reports there would be 0% left and
1616     immediately shuts down.
1617     </p>
1618    
1619     <p>
1620     <e>A:</e> Check that battery support is compiled into your kernel. If you use
1621     it as a module, make sure the module is loaded.
1622     </p>
1623    
1624     <p>
1625 rane 1.20 <e>Q:</e> My system logger reports things like "logger: ACPI group battery /
1626     action battery is not defined".
1627 nightmorph 1.17 </p>
1628    
1629     <p>
1630 rane 1.20 <e>A:</e> This message is generated by the <path>/etc/acpi/default.sh</path>
1631     script that is shipped with acpid. You can safely ignore it. If you like to get
1632     rid of it, you can comment the appropriate line in
1633     <path>/etc/acpi/default.sh</path> as shown below:
1634 nightmorph 1.17 </p>
1635    
1636     <pre caption="Disabling warnings about unknown acpi events">
1637     *) # logger "ACPI action $action is not defined"
1638     </pre>
1639    
1640     <p>
1641 swift 1.1 <e>Q:</e> I have a Dell Inspiron 51XX and I don't get any ACPI events.
1642     </p>
1643    
1644     <p>
1645     <e>A:</e> This seems to be a kernel bug. Read on <uri
1646     link="http://bugme.osdl.org/show_bug.cgi?id=1752">here</uri>.
1647     </p>
1648    
1649     <p>
1650 rane 1.20 <e>Q:</e> I activated the <c>DynamicClocks</c> option in <path>xorg.conf</path>
1651     and now X.org crashes / the screen stays black / my laptop doesn't shutdown
1652 so 1.15 properly.
1653     </p>
1654    
1655     <p>
1656 rane 1.20 <e>A:</e> This happens on some systems. You have to disable
1657     <c>DynamicClocks</c>.
1658 so 1.15 </p>
1659    
1660     <p>
1661 jkt 1.33 <e>Q:</e> I want to use TuxOnIce, but it tells me my swap partition is too
1662 so 1.15 small. Resizing is not an option.
1663     </p>
1664    
1665     <p>
1666 rane 1.20 <e>A:</e> If there is enough free space on your system, you can use the
1667 jkt 1.34 filewriter instead of the swapwriter. The <c>hibernate-script</c> supports it as
1668     well. More information can be found in
1669 jkt 1.33 <path>/usr/src/linux/Documentation/power/tuxonice.txt</path>.
1670 so 1.15 </p>
1671    
1672     <p>
1673 swift 1.1 <e>Q:</e> I just bought a brand new battery, but it only lasts for some
1674     minutes! What am I doing wrong?
1675     </p>
1676    
1677     <p>
1678     <e>A:</e> First follow your manufacturer's advice on how to charge the battery
1679 rane 1.20 correctly.
1680 swift 1.1 </p>
1681    
1682     <p>
1683     <e>Q:</e> The above didn't help. What should I do then?
1684     </p>
1685    
1686     <p>
1687     <e>A:</e> Some batteries sold as "new" are in fact old ones. Try the following:
1688     </p>
1689    
1690     <pre caption="Querying battery state">
1691     $ <i>grep capacity /proc/acpi/battery/BAT0/info</i>
1692     design capacity: 47520 mWh
1693     last full capacity: 41830 mWh
1694     </pre>
1695    
1696     <p>
1697     If the "last full capacity" differs significantly from the design capacity,
1698     your battery is probably broken. Try to claim your warranty.
1699     </p>
1700    
1701 swift 1.8 <p>
1702     <e>Q:</e> My problem is not listed above. Where should I go next?
1703     </p>
1704    
1705     <p>
1706 nightmorph 1.17 <e>A:</e> Don't fear to contact me, <mail link="earthwings@gentoo.org">Dennis
1707 rane 1.20 Nienhüser</mail>, directly. The <uri link="http://forums.gentoo.org">Gentoo
1708     Forums</uri> are a good place to get help as well. If you prefer IRC, try the
1709 nightmorph 1.38 <c>#gentoo-laptop</c> <uri link="irc://irc.gentoo.org">channel</uri>.
1710 swift 1.8 </p>
1711    
1712 swift 1.1 </body>
1713     </section>
1714     </chapter>
1715     </guide>

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