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Power management guide updated for bug 122017

1 <?xml version='1.0' encoding="UTF-8"?>
2 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
3 <!-- $Header: $ -->
4 <guide link="/doc/en/power-management-guide.xml">
5 <title>Power Management Guide</title>
6
7 <author title="Author">
8 <mail link="earthwings@gentoo.org">Dennis Nienhüser</mail>
9 </author>
10
11 <abstract>
12 Power Management is the key to extend battery run time on mobile systems like
13 laptops. This guide assists you setting it up on your laptop.
14 </abstract>
15
16 <!-- The content of this document is licensed under the CC-BY-SA license -->
17 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
18 <license/>
19
20 <version>1.26</version>
21 <date>2006-02-12</date>
22
23 <chapter>
24 <title>Introduction</title>
25 <section>
26 <body>
27
28 <p>
29 Capacity and lifetime of laptop batteries have improved much in the last years.
30 Nevertheless modern processors consume much more energy than older ones and
31 each laptop generation introduces more devices hungry for energy. That's why
32 Power Management is more important than ever. Increasing battery run time
33 doesn't necessarily mean buying another battery. Much can be achieved applying
34 intelligent Power Management policies.
35 </p>
36
37 </body>
38 </section>
39
40 <section>
41 <title>A quick overview</title>
42 <body>
43
44 <p>
45 Please notice that this guide describes Power Management for <e>laptops</e>.
46 While some sections might also suite for <e>servers</e>, others do not and may
47 even cause harm. Please do not apply anything from this guide to a server
48 unless you really know what you are doing.
49 </p>
50
51 <p>
52 As this guide has become rather long, here's a short overview helping you to
53 find your way through it.
54 </p>
55
56 <p>
57 The <e>Prerequisites</e> chapter talks about some requirements that should be
58 met before any of the following device individual sections will work. This
59 includes BIOS settings, kernel configuration and some simplifications in user
60 land. The following three chapters focus on devices that typically consume
61 most energy - processor, display and hard drive. Each can be configured
62 seperately. <e>CPU Power Management</e> shows how to adjust the processor's
63 frequency to save a maximum of energy whithout losing too much performance. A
64 few different tricks prevent your hard drive from working unnecessarily often
65 in <e>Disk Power Management</e> (decreasing noise level as a nice side
66 effect). Some notes on graphics cards, Wireless LAN and USB finish the device
67 section in <e>Power Management for other devices</e> while another chapter is
68 dedicated to the (rather experimental) <e>sleep states</e>. Last not least
69 <e>Troubleshooting</e> lists common pitfalls.
70 </p>
71
72 </body>
73 </section>
74
75 <section>
76 <title>Power Budget for each component</title>
77 <body>
78
79 <figure link="/images/energy-budget.png" short="Which component consumes how
80 much energy?" caption="Power budget for each component"/>
81
82 <p>
83 Nearly every component can operate in different states - off, sleep, idle,
84 active to name a few - consuming a different amount of energy. Major parts are
85 consumed by the LCD display, CPU, chipset and hard drives. Often one is able to
86 activate OS-independent Power Management in the BIOS, but an intelligent setup
87 in the operating system adapting to different situations can achieve much more.
88 </p>
89
90 </body>
91 </section>
92 </chapter>
93
94 <chapter>
95 <title>Prerequisites</title>
96 <section>
97 <body>
98
99 <p>
100 Before discussing the details of making individual devices Power Management
101 aware, make sure certain requirements are met. After controlling BIOS
102 settings, some kernel options want to be enabled - these are in short ACPI,
103 sleep states and CPU frequency scaling. As power saving most of the time comes
104 along with performance loss or increased latency, it should only be enabled
105 when running on batteries. That's where a new runlevel <e>battery</e> comes in
106 handy.
107 </p>
108
109 </body>
110 </section>
111 <section>
112 <title>The BIOS part</title>
113 <body>
114
115 <p>
116 First have a look into your BIOS Power Management settings. The best way is to
117 combine BIOS and operating system policies, but for the moment it's better to
118 disable most of the BIOS part. This makes sure it doesn't interfere with your
119 policies. Don't forget to re-check BIOS settings after you configured
120 everything else.
121 </p>
122
123 </body>
124 </section>
125 <section>
126 <title>Setting USE flags</title>
127 <body>
128
129 <p>
130 Please check that the <c>acpi</c> USE flag is set in
131 <path>/etc/make.conf</path>. Other USE flags that might be interesting for your
132 system are <c>apm</c>, <c>lm_sensors</c>, <c>nforce2</c>, <c>nvidia</c>,
133 <c>pmu</c>. See <path>/usr/portage/profiles/use*.desc</path> for details. If
134 you forgot to set one of these flags, you can recompile affected packages using
135 the <c>--newuse</c> flag in <c>emerge</c>, see <c>man 1 emerge</c>.
136 </p>
137
138 </body>
139 </section>
140 <section>
141 <title>Configuring the kernel</title>
142 <body>
143
144 <p>
145 ACPI (Advanced Configuration and Power Interface) support in the kernel is
146 still work in progress. Using a recent kernel will make sure you'll get the
147 most out of it.
148 </p>
149
150 <p>
151 There are different kernel sources in Portage. I'd recommend using
152 <c>gentoo-sources</c> or <c>suspend2-sources</c>. The latter contains patches
153 for Software Suspend 2, see the chapter about sleep states for details. When
154 configuring the kernel, activate at least these options:
155 </p>
156
157 <pre caption="Minimum kernel setup for Power Management (Kernel 2.6)">
158 Power Management Options ---&gt;
159 [*] Power Management Support
160 [ ] Software Suspend
161
162 ACPI( Advanced Configuration and Power Interface ) Support ---&gt;
163 [*] ACPI Support
164 [ ] Sleep States
165 [ ] /proc/acpi/sleep (deprecated)
166 [*] AC Adapter
167 [*] Battery
168 &lt;M&gt; Button
169 &lt;M&gt; Video
170 [ ] Generic Hotkey
171 &lt;M&gt; Fan
172 &lt;M&gt; Processor
173 &lt;M&gt; Thermal Zone
174 &lt; &gt; ASUS/Medion Laptop Extras
175 &lt; &gt; IBM ThinkPad Laptop Extras
176 &lt; &gt; Toshiba Laptop Extras
177 (0) Disable ACPI for systems before Jan 1st this year
178 [ ] Debug Statements
179 [*] Power Management Timer Support
180 &lt; &gt; ACPI0004,PNP0A05 and PNP0A06 Container Driver (EXPERIMENTAL)
181
182 CPU Frequency Scaling ---&gt;
183 [*] CPU Frequency scaling
184 [ ] Enable CPUfreq debugging
185 &lt; &gt; CPU frequency translation statistics
186 [ ] CPU frequency translation statistics details
187 Default CPUFreq governor (userspace)
188 &lt;*&gt; 'performance' governor
189 &lt;*&gt; 'powersave' governor
190 &lt;*&gt; 'ondemand' cpufreq policy governor
191 &lt;*&gt; 'conservative' cpufreq governor
192 &lt;*&gt; CPU frequency table helpers
193 &lt;M&gt; ACPI Processor P-States driver
194 &lt;*&gt; <i>CPUFreq driver for your processor</i>
195 </pre>
196
197 <p>
198 Decide yourself whether you want to enable Software Suspend, and Sleep States
199 (see below). If you own an ASUS, Medion, IBM Thinkpad or Toshiba laptop, enable
200 the appropriate section.
201 </p>
202
203 <p>
204 The kernel has to know how to enable CPU frequency scaling on your processor. As
205 each type of CPU has a different interface, you've got to choose the right
206 driver for your processor. Be careful here - enabling <e>Intel Pentium 4 clock
207 modulation</e> on a Pentium M system will lead to strange results for example.
208 Consult the kernel documentation if you're unsure which one to take.
209 </p>
210
211 <p>
212 Compile your kernel, make sure the right modules get loaded at startup and boot
213 into your new ACPI-enabled kernel. Next run <c>emerge sys-power/acpid</c> to get
214 the acpi daemon. This one informs you about events like switching from AC to
215 battery or closing the lid. Make sure the modules are loaded if you didn't
216 compile them into the kernel and start acpid by executing
217 <c>/etc/init.d/acpid start</c>. Run <c>rc-update add acpid default</c> to load
218 it on startup. You'll soon see how to use it.
219 </p>
220
221 <pre caption="Installing acpid">
222 # <i>emerge sys-power/acpid</i>
223 # <i>/etc/init.d/acpid start</i>
224 # <i>rc-update add acpid default</i>
225 </pre>
226
227 </body>
228 </section>
229 <section>
230 <title>Creating a "battery" runlevel</title>
231 <body>
232
233 <p>
234 The default policy will be to enable Power Management only when needed -
235 running on batteries. To make the switch between AC and battery convenient,
236 create a runlevel <e>battery</e> that holds all the scripts starting and
237 stopping Power Management.
238 </p>
239
240 <note>
241 You can safely skip this section if you don't like the idea of having another
242 runlevel. However, skipping this step will make the rest a bit trickier to set
243 up. The next sections assume a runlevel <e>battery</e> exists.
244 </note>
245
246 <pre caption="Creating a battery runlevel">
247 # <i>cd /etc/runlevels</i>
248 # <i>cp -a default battery</i>
249 </pre>
250
251 <p>
252 Finished. Your new runlevel <e>battery</e> contains everything like
253 <e>default</e>, but there is no automatic switch between both yet. Time to
254 change it.
255 </p>
256
257 </body>
258 </section>
259 <section>
260 <title>Reacting on ACPI events</title>
261 <body>
262
263 <p>
264 Typical ACPI events are closing the lid, changing the power source or pressing
265 the sleep button. An important event is changing the power source, which should
266 cause a runlevel switch. A small script will take care of it.
267 </p>
268
269 <p>
270 First you need a script which changes the runlevel to <c>default</c>
271 respectively <c>battery</c> depending on the power source. The script uses the
272 <c>on_ac_power</c> command from <c>sys-power/powermgmt-base</c> - make sure the
273 package is installed on your system.
274 </p>
275
276 <pre caption="Installing powermgt-base">
277 <i># emerge powermgmt-base</i>
278 </pre>
279
280 <p>
281 You are now able to determine the power source by executing
282 <c>on_ac_power &amp;&amp; echo AC available || echo Running on batteries</c> in
283 a shell. The script below is responsible for changing runlevels. Save it as
284 <path>/etc/acpi/actions/pmg_switch_runlevel.sh</path>.
285 </p>
286
287 <pre caption="/etc/acpi/actions/pmg_switch_runlevel.sh">
288 #!/bin/bash
289
290 <comment># BEGIN configuration</comment>
291 RUNLEVEL_AC="default"
292 RUNLEVEL_BATTERY="battery"
293 <comment># END configuration</comment>
294
295
296 if [ ! -d "/etc/runlevels/${RUNLEVEL_AC}" ]
297 then
298 logger "${0}: Runlevel ${RUNLEVEL_AC} does not exist. Aborting."
299 exit 1
300 fi
301
302 if [ ! -d "/etc/runlevels/${RUNLEVEL_BATTERY}" ]
303 then
304 logger "${0}: Runlevel ${RUNLEVEL_BATTERY} does not exist. Aborting."
305 exit 1
306 fi
307
308 if on_ac_power
309 then
310 if [[ "$(cat /var/lib/init.d/softlevel)" != "${RUNLEVEL_AC}" ]]
311 then
312 logger "Switching to ${RUNLEVEL_AC} runlevel"
313 /sbin/rc ${RUNLEVEL_AC}
314 fi
315 elif [[ "$(cat /var/lib/init.d/softlevel)" != "${RUNLEVEL_BATTERY}" ]]
316 then
317 logger "Switching to ${RUNLEVEL_BATTERY} runlevel"
318 /sbin/rc ${RUNLEVEL_BATTERY}
319 fi
320 </pre>
321
322 <p>
323 Dont forget to run <c>chmod +x /etc/acpi/actions/pmg_switch_runlevel.sh</c> to
324 make the script executable. The last thing that needs to be done is calling the
325 script whenever the power source changes. That's done by catching ACPI events
326 with the help of <c>acpid</c>. First you need to know which events are
327 generated when the power source changes. The events are called
328 <e>ac_adapter</e> and <e>battery</e> on most laptops, but it might be different
329 on yours.
330 </p>
331
332 <pre caption="Determining ACPI events for changing the power source">
333 <i># tail -f /var/log/acpid | grep "received event"</i>
334 </pre>
335
336 <p>
337 Run the command above and pull the power cable. You should see something
338 like this:
339 </p>
340
341 <pre caption="Sample output for power source changes">
342 [Tue Sep 20 17:39:06 2005] received event "ac_adapter AC 00000080 00000000"
343 [Tue Sep 20 17:39:06 2005] received event "battery BAT0 00000080 00000001"
344 </pre>
345
346 <p>
347 The interesting part is the quoted string after <e>received event</e>. It will
348 be matched by the event line in the files you are going to create below. Don't
349 worry if your system generates multiple events or always the same. As long as
350 any event is generated, runlevel changing will work.
351 </p>
352
353 <pre caption="/etc/acpi/events/pmg_ac_adapter">
354 <comment># replace "ac_adapter" below with the event generated on your laptop</comment>
355 <comment># For example, ac_adapter.* will match ac_adapter AC 00000080 00000000</comment>
356 event=ac_adapter.*
357 action=/etc/acpi/actions/pmg_switch_runlevel.sh %e
358 </pre>
359
360 <pre caption="/etc/acpi/events/pmg_battery">
361 <comment># replace "battery" below with the event generated on your laptop</comment>
362 <comment># For example, battery.* will match battery BAT0 00000080 00000001</comment>
363 event=battery.*
364 action=/etc/acpi/actions/pmg_switch_runlevel.sh %e
365 </pre>
366
367 <p>
368 Finally acpid has to be restarted to recognize the changes.
369 </p>
370
371 <pre caption="Finishing runlevel switching with acpid">
372 <i># /etc/init.d/acpid restart</i>
373 </pre>
374
375 <p>
376 Give it a try: Plug AC in and out and watch syslog for the "Switching to AC
377 mode" or "Switching to battery mode" messages. See the Troubleshooting
378 section if the script is not able to detect the power source correctly.
379 </p>
380
381 <p>
382 Due to the nature of the event mechanism, your laptop will boot into runlevel
383 <e>default</e> regardless of the AC/battery state. This is fine when running
384 from AC, but we'd like to boot into the battery runlevel otherwise. One
385 solution would be to add another entry to the boot loader with the parameter
386 <c>softlevel=battery</c>, but it's likely to forget choosing it. A better way
387 is faking an ACPI event in the end of the boot process and letting
388 <path>pmg_switch_runlevel.sh</path> script decide whether a
389 runlevel change is necessary. Open <path>/etc/conf.d/local.start</path> in your
390 favourite editor and add these lines:
391 </p>
392
393 <pre caption="Runlevel adjustment at boot time by editing local.start">
394 <comment># Fake acpi event to switch runlevel if running on batteries</comment>
395 /etc/acpi/actions/pmg_switch_runlevel.sh "battery/battery"
396 </pre>
397
398 <p>
399 Prepared like this you can activate Power Management policies for individual
400 devices.
401 </p>
402
403 </body>
404 </section>
405 </chapter>
406
407 <chapter>
408 <title>CPU Power Management</title>
409 <section>
410 <body>
411
412 <p>
413 Mobile processors can operate at different frequencies. Some allow changing
414 voltage as well. Most of the time your CPU doesn't need to run at full speed
415 and scaling it down will save much energy - often without any performance
416 decrease.
417 </p>
418
419 </body>
420 </section>
421
422 <section>
423 <title>Some technical terms</title>
424 <body>
425
426 <p>
427 CPU frequency scaling brings up some technical terms that might be unknown to
428 you. Here's a quick introduction.
429 </p>
430
431 <p>
432 First of all, the kernel has to be able to change the processor's frequency.
433 The <e>CPUfreq processor driver</e> knows the commands to do it on your CPU.
434 Thus it's important to choose the right one in your kernel. You should
435 already have done it above. Once the kernel knows how to change frequencies,
436 it has to know which frequency it should set. This is done according to the
437 <e>policy</e> which consists of a <e>CPUfreq policy</e> and a
438 <e>governor</e>. A CPUfreq policy are just two numbers which define a range
439 the frequency has to stay between - minimal and maximal frequency. The
440 governor now decides which of the available frequencies in between minimal
441 and maximal frequency to choose. For example, the <e>powersave governor</e>
442 always chooses the lowest frequency available, the <e>performance
443 governor</e> the highest one. The <e>userspace governor</e> makes no decision
444 but chooses whatever the user (or a program in userspace) wants - which means
445 it reads the frequency from
446 <path>/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed</path>.
447 </p>
448
449 <p>
450 This doesn't sound like dynamic frequency changes yet and in fact it isn't.
451 Dynamics however can be accomplished with various approaches. For example,
452 the <e>ondemand governor</e> makes its decisions depending on the current CPU
453 load. The same is done by various userland tools like <c>cpudyn</c>,
454 <c>cpufreqd</c>, <c>powernowd</c> and many more. ACPI events can be used to
455 enable or disable dynamic frequency changes depending on power source.
456 </p>
457
458 </body>
459 </section>
460 <section>
461 <title>Setting the frequency manually</title>
462 <body>
463
464 <p>
465 Decreasing CPU speed and voltage has two advantages: On the one hand less
466 energy is consumed, on the other hand there is thermal improvement as your
467 system doesn't get as hot as running on full speed. The main disadvantage is
468 obviously the loss of performance. Decreasing processor speed is a trade off
469 between performance loss and energy saving.
470 </p>
471
472 <note>
473 Not every laptop supports frequency scaling. If unsure, have a look at the list
474 of supported processors in the <e>Troubleshooting</e> section to verify your's
475 is supported.
476 </note>
477
478 <p>
479 It's time to test whether CPU frequency changing works. Let's install another
480 tool which is very handy for debugging purposes: <c>sys-power/cpufrequtils</c>
481 </p>
482
483 <pre caption="Checking CPU frequency">
484 # <i>emerge cpufrequtils</i>
485 # <i>cpufreq-info</i>
486 </pre>
487
488 <p>
489 Here is an example output:
490 </p>
491
492 <pre caption="Sample output from cpufreq-info">
493 cpufrequtils 0.3: cpufreq-info (C) Dominik Brodowski 2004
494 Report errors and bugs to linux@brodo.de, please.
495 analyzing CPU 0:
496 driver: centrino
497 CPUs which need to switch frequency at the same time: 0
498 hardware limits: 600 MHz - 1.40 GHz
499 available frequency steps: 600 MHz, 800 MHz, 1000 MHz, 1.20 GHz, 1.40 GHz
500 available cpufreq governors: conservative, ondemand, powersave, userspace, performance
501 current policy: frequency should be within 924 MHz and 1.40 GHz.
502 The governor "performance" may decide which speed to use
503 within this range.
504 current CPU frequency is 1.40 GHz.
505 </pre>
506
507 <p>
508 Now play around with <c>cpufreq-set</c> to make sure frequency switching works.
509 Run <c>cpufreq-set -g ondemand</c> for example to activate the ondemand
510 governor and verify the change with <c>cpufreq-info</c>. If it doesn't work as
511 expected, you might find help in the Troubleshooting section in the end of this
512 guide.
513 </p>
514
515 </body>
516 </section>
517 <section>
518 <title>Automated frequency adaption</title>
519 <body>
520
521 <p>
522 The above is quite nice, but not doable in daily life. Better let your system
523 set the appropriate frequency automatically. There are many different
524 approaches to do this. The following table gives a quick overview to help you
525 decide on one of them. It's roughly seperated in three categories
526 <e>kernel</e> for approaches that only need kernel support, <e>daemon</e> for
527 programs that run in the background and <e>graphical</e> for programs that
528 provide a GUI for easy configuration and changes.
529 </p>
530
531 <table>
532 <tr>
533 <th>Name</th>
534 <th>Category</th>
535 <th>Switch decision</th>
536 <th>Kernel governors</th>
537 <th>Further governors</th>
538 <th>Comments</th>
539 </tr>
540 <tr>
541 <ti>'ondemand' governor</ti>
542 <ti>Kernel</ti>
543 <ti>CPU load</ti>
544 <ti>N.A.</ti>
545 <ti>N.A.</ti>
546 <ti>
547 Chooses maximal frequency on CPU load and slowly steps down when the CPU is
548 idle. Further tuning through files in
549 <path>/sys/devices/system/cpu/cpu0/cpufreq/ondemand/</path>. Still requires
550 userland tools (programs, scripts) if governor switching or similar is
551 desired.
552 </ti>
553 </tr>
554 <tr>
555 <ti>'conservative' governor</ti>
556 <ti>Kernel</ti>
557 <ti>CPU load</ti>
558 <ti>N.A.</ti>
559 <ti>N.A.</ti>
560 <ti>
561 Unlike the ondemand governor, conversative doesn't jump to maximum
562 frequency when CPU load is high, but increases the frequency step by step.
563 Further tuning through files in
564 <path>/sys/devices/system/cpu/cpu0/cpufreq/ondemand/</path>. Still requires
565 userland tools (programs, scripts) if governor switching or similar is
566 desired.
567 </ti>
568 </tr>
569 <tr>
570 <ti><uri link="http://mnm.uib.es/~gallir/cpudyn/">cpudyn</uri></ti>
571 <ti>Daemon</ti>
572 <ti>CPU load</ti>
573 <ti>Performance, powersave</ti>
574 <ti>Dynamic</ti>
575 <ti>
576 Also supports disk standby - notice however that <e>laptop mode</e> in most
577 cases will do a better job.
578 </ti>
579 </tr>
580 <tr>
581 <ti><uri link="http://sourceforge.net/projects/cpufreqd/">cpufreqd</uri></ti>
582 <ti>Daemon</ti>
583 <ti>Battery state, CPU load, temperature, running programs and more</ti>
584 <ti>All available</ti>
585 <ti>None</ti>
586 <ti>
587 Sophisticated (but somewhat complicated) setup. Extendible through plugins
588 like sensor monitoring (lm_sensors) or coordinating some NVidia based
589 graphics card memory and core. Cpufreqd is SMP aware and can optionally be
590 controlled manually at runtime.
591 </ti>
592 </tr>
593 <tr>
594 <ti>
595 <uri link="http://www.deater.net/john/powernowd.html">powernowd</uri>
596 </ti>
597 <ti>Daemon</ti>
598 <ti>CPU load</ti>
599 <ti>None</ti>
600 <ti>Passive, sine, aggressive</ti>
601 <ti>
602 Supports SMP.
603 </ti>
604 </tr>
605 <tr>
606 <ti>
607 <uri link="http://fatcat.ftj.agh.edu.pl/~nelchael/index.php?cat=projs&amp;subcat=ncpufreqd&amp;language=en">ncpufreqd</uri>
608 </ti>
609 <ti>Daemon</ti>
610 <ti>Temperature</ti>
611 <ti>None</ti>
612 <ti>Powersave, performance</ti>
613 <ti>
614 Toggles the used governor between performance and powersave depending on
615 system temperature. Very useful on laptops with notorious heat problems.
616 </ti>
617 </tr>
618 <tr>
619 <ti><uri link="http://www.goop.org/~jeremy/speedfreq/">speedfreq</uri></ti>
620 <ti>Daemon</ti>
621 <ti>CPU load</ti>
622 <ti>None</ti>
623 <ti>Dynamic, powersave, performance, fixed speed</ti>
624 <ti>
625 Easy to configure with a nice client/server interface. Requires a 2.6
626 kernel. Unmaintained, broken and thus removed from Portage. Please switch
627 to cpufreqd if you're still using it.
628 </ti>
629 </tr>
630 <tr>
631 <ti><uri link="http://cpuspeedy.sourceforge.net/">gtk-cpuspeedy</uri></ti>
632 <ti>Graphical</ti>
633 <ti>None</ti>
634 <ti>None</ti>
635 <ti>None</ti>
636 <ti>
637 Gnome application, a graphical tool to set CPU frequency manually. It does
638 not offer any automation.
639 </ti>
640 </tr>
641 <tr>
642 <ti>klaptopdaemon</ti>
643 <ti>Graphical</ti>
644 <ti>Battery state</ti>
645 <ti>All available</ti>
646 <ti>None</ti>
647 <ti>
648 KDE only, 'ondemand' governor required for dynamic frequency scaling.
649 </ti>
650 </tr>
651 </table>
652
653 <p>
654 While adjusting the frequency to the current load looks simple at a first
655 glance, it's not such a trivial task. A bad algorithm can cause switching
656 between two frequencies all the time or wasting energy when setting frequency
657 to an unnecessary high level.
658 </p>
659
660 <p>
661 Which one to choose? If you have no idea about it, try <c>cpufreqd</c>:
662 </p>
663
664 <pre caption="Installing cpufreqd">
665 # <i>emerge cpufreqd</i>
666 </pre>
667
668 <p>
669 <c>cpufreqd</c> can be configured by editing <path>/etc/cpufreqd.conf</path>.
670 The default one that ships with cpufreqd may look a bit confusing. I recommend
671 replacing it with the one from Gentoo developer Henrik Brix Andersen (see
672 below). Please notice that you need cpufreqd-2.0.0 or later. Earlier versions
673 have a different syntax for the config file.
674 </p>
675
676 <pre caption="/etc/cpufreqd.conf (cpufreqd-2.0.0 and later)">
677 [General]
678 pidfile=/var/run/cpufreqd.pid
679 poll_interval=3
680 enable_plugins=acpi_ac, acpi_battery
681 verbosity=5
682 [/General]
683
684 [Profile]
685 name=ondemand
686 minfreq=0%
687 maxfreq=100%
688 policy=ondemand
689 [/Profile]
690
691 [Profile]
692 name=conservative
693 minfreq=0%
694 maxfreq=100%
695 policy=conservative
696 [/Profile]
697
698 [Profile]
699 name=powersave
700 minfreq=0%
701 maxfreq=100%
702 policy=powersave
703 [/Profile]
704
705 [Profile]
706 name=performance
707 minfreq=0%
708 maxfreq=100%
709 policy=performance
710 [/Profile]
711
712 [Rule]
713 name=battery
714 ac=off
715 profile=conservative
716 [/Rule]
717
718 [Rule]
719 name=battery_low
720 ac=off
721 battery_interval=0-10
722 profile=powersave
723 [/Rule]
724
725 [Rule]
726 name=ac
727 ac=on
728 profile=ondemand
729 [/Rule]
730 </pre>
731
732 <p>
733 Now you can start the cpufreqd daemon. Add it to the <e>default</e> and
734 <e>battery</e> runlevel as well.
735 </p>
736
737 <pre caption="Starting cpufreqd">
738 # <i>rc-update add cpufreqd default battery</i>
739 # <i>rc</i>
740 </pre>
741
742 <p>
743 Sometimes it can be desirable to select another policy than the daemon chooses,
744 for example when battery power is low, but you know that AC will be available
745 soon. In that case you can turn on cpufreqd's manual mode with
746 <c>cpufreqd-set manual</c> and select one of your configured policies (as
747 listed by <c>cpufreqd-get</c>). You can leave manual mode by executing
748 <c>cpufreqd-set dynamic</c>.
749 </p>
750
751 <warn>
752 Do not run more than one of the above programs at the same time. It may cause
753 confusion like switching between two frequencies all the time.
754 </warn>
755
756 </body>
757 </section>
758
759 <section>
760 <title>Verifying the result</title>
761
762 <body>
763
764 <p>
765 The last thing to check is that your new policies do a good job. An easy way to
766 do so is monitoring CPU speed while working with your laptop:
767 </p>
768
769 <pre caption="Monitoring CPU speed">
770 # <i>watch grep \"cpu MHz\" /proc/cpuinfo</i>
771 </pre>
772
773 <p>
774 If <path>/proc/cpuinfo</path> doesn't get updated (see Troubleshooting),
775 monitor the CPU frequency with:
776 </p>
777
778 <pre caption="Alternative CPU speed monitoring">
779 # <i>watch x86info -mhz</i>
780 </pre>
781
782 <p>
783 Depending on your setup, CPU speed should increase on heavy load, decrease on
784 no activity or just stay at the same level. When using cpufreqd and verbosity
785 set to 5 or higher in <path>cpufreqd.conf</path> you'll get additional
786 information about what's happening reported to syslog.
787 </p>
788
789 </body>
790 </section>
791 </chapter>
792
793 <chapter>
794 <title>LCD Power Management</title>
795 <section>
796 <body>
797
798 <p>
799 As you can see in <uri link="#doc_chap1_fig1">figure 1.1</uri>, the LCD display
800 consumes the biggest part of energy (might not be the case for non-mobile
801 CPU's). Thus it's quite important not only to shut the display off when not
802 needed, but also to reduce it's backlight if possible. Most laptops offer the
803 possibility to control the backlight dimming.
804 </p>
805
806 </body>
807 </section>
808 <section>
809 <title>Standby settings</title>
810 <body>
811
812 <p>
813 The first thing to check is the standby/suspend/off timings of the display. As
814 this depends heavily on your windowmanager, I'll let you figure it out
815 yourself. Just two common places: Blanking the terminal can be done with
816 <c>setterm -blank &lt;number-of-minutesM&gt;</c>, <c>setterm -powersave on</c>
817 and <c>setterm -powerdown &lt;number-of-minutesM&gt;</c>. For X.org, modify
818 <path>/etc/X11/xorg.conf</path> similar to this:
819 </p>
820
821 <pre caption="LCD suspend settings in X.org and XFree86">
822 Section "ServerLayout"
823 Identifier [...]
824 [...]
825 Option "BlankTime" "5" <comment># Blank the screen after 5 minutes (Fake)</comment>
826 Option "StandbyTime" "10" <comment># Turn off screen after 10 minutes (DPMS)</comment>
827 Option "SuspendTime" "20" <comment># Full suspend after 20 minutes</comment>
828 Option "OffTime" "30" <comment># Turn off after half an hour</comment>
829 [...]
830 EndSection
831
832 [...]
833
834 Section "Monitor"
835 Identifier [...]
836 Option "DPMS" "true"
837 [...]
838 EndSection
839 </pre>
840
841 <p>
842 This is the same for XFree86 and <path>/etc/X11/XF86Config</path>.
843 </p>
844
845 </body>
846 </section>
847 <section>
848 <title>Backlight dimming</title>
849 <body>
850
851 <p>
852 Probably more important is the backlight dimming. If you have access to the
853 dimming settings via a tool, write a small script that dims the backlight in
854 battery mode and place it in your <e>battery</e> runlevel. The following script
855 should work on most IBM Thinkpads and Toshiba laptops. You've got to enable the
856 appropriate option in your kernel (IBM Thinkpads only). For Toshiba laptops, install
857 <c>app-laptop/acpitool</c> and skip configuration of ibm_acpi as described below.
858 </p>
859
860 <warn>
861 Support for setting brightness is marked experimental in ibm-acpi. It accesses
862 hardware directly and may cause severe harm to your system. Please read the
863 <uri link="http://ibm-acpi.sourceforge.net/">ibm-acpi website</uri>
864 </warn>
865
866 <p>
867 To be able to set the brightness level, the ibm_acpi module has to be loaded
868 with the experimental parameter.
869 </p>
870
871 <pre caption="automatically loading the ibm_acpi module">
872 <comment>(Please read the warnings above before doing this!)</comment>
873 <i># echo "options ibm_acpi experimental=1" >> /etc/modules.d/ibm_acpi</i>
874 <i># /sbin/modules-update</i>
875 <i># echo ibm_acpi >> /etc/modules.autoload.d/kernel-2.6</i>
876 <i># modprobe ibm_acpi</i>
877 </pre>
878
879 <p>
880 This should work without error messages and a file
881 <path>/proc/acpi/ibm/brightness</path> should be created after loading the
882 module. An init script will take care of choosing the brightness according
883 to the power source.
884 </p>
885
886 <pre caption="/etc/conf.d/lcd-brightness">
887 <comment># See /proc/acpi/ibm/brightness for available values</comment>
888 <comment># Please read /usr/src/linux/Documentation/ibm-acpi.txt</comment>
889
890 <comment># brigthness level in ac mode. Default is 7.</comment>
891 BRIGHTNESS_AC=7
892
893 <comment># brightness level in battery mode. Default is 4.</comment>
894 BRIGHTNESS_BATTERY=4
895 </pre>
896
897 <pre caption="/etc/init.d/lcd-brightness">
898 #!/sbin/runscript
899
900 set_brightness() {
901 if on_ac_power
902 then
903 LEVEL=${BRIGHTNESS_AC:-7}
904 else
905 LEVEL=${BRIGHTNESS_BATTERY:-4}
906 fi
907
908 if [ -f /proc/acpi/ibm/brightness ]
909 then
910 ebegin "Setting LCD brightness"
911 echo "level ${LEVEL}" > /proc/acpi/ibm/brightness
912 eend $?
913 elif [[ -e /usr/bin/acpitool &amp;&amp; -n $(acpitool -T | grep "LCD brightness") ]]
914 then
915 ebegin "Setting LCD brightness"
916 acpitool -l $LEVEL >/dev/null || ewarn "Unable to set lcd brightness"
917 eend $?
918 else
919 ewarn "Setting LCD brightness is not supported."
920 ewarn "For IBM Thinkpads, check that ibm_acpi is loaded into the kernel"
921 ewarn "For Toshiba laptops, you've got to install app-laptop/acpitool"
922 fi
923 }
924
925 start() {
926 set_brightness
927 }
928
929 stop () {
930 set_brightness
931 }
932 </pre>
933
934 <p>
935 When done, make sure brightness is adjusted automatically by adding it to the
936 battery runlevel.
937 </p>
938
939 <pre caption="Enabling automatic brightness adjustment">
940 <i># chmod +x /etc/init.d/lcd-brightness</i>
941 <i># rc-update add lcd-brightness battery</i>
942 <i># rc</i>
943 </pre>
944
945 </body>
946 </section>
947 </chapter>
948
949 <chapter>
950 <title>Disk Power Management</title>
951 <section>
952 <body>
953 <p>
954 Hard disks consume less energy in sleep mode. Therefore it makes sense to
955 activate power saving features whenever the hard disk is not used for a certain
956 amount of time. I'll show you two alternative possibilities to do it. First,
957 laptop-mode will save most energy due to several measures which prevent or at
958 least delay write accesses. The drawback is that due to the delayed write
959 accesses a power outage or kernel crash will be more dangerous for data loss.
960 If you don't like this, you have to make sure that there are no processes which
961 write to your hard disk frequently. Afterwards you can enable power saving
962 features of your hard disk with hdparm as the second alternative.
963 </p>
964
965 </body>
966 </section>
967
968 <section>
969 <title>Increasing idle time - laptop-mode</title>
970 <body>
971
972 <p>
973 Recent kernels (2.6.6 and greater, recent 2.4 ones and others with patches)
974 include the so-called <e>laptop-mode</e>. When activated, dirty buffers are
975 written to disk on read calls or after 10 minutes (instead of 30 seconds). This
976 minimizes the time the hard disk needs to be spun up.
977 </p>
978
979 <pre caption="Automated start of laptop-mode">
980 # <i>emerge laptop-mode-tools</i>
981 </pre>
982
983 <p>
984 <c>laptop-mode-tools</c> has its configuration file in
985 <path>/etc/laptop-mode/laptop-mode.conf</path>. Adjust it the way you like it,
986 it's well commented. Run <c>rc-update add laptop_mode battery</c> to start it
987 automatically.
988 </p>
989
990 <p>
991 Recent versions (1.11 and later) of laptop-mode-tools include a new tool
992 <c>lm-profiler</c>. It will monitor your system's disk usage and running
993 network services and suggests to disable unneeded ones. You can either disable
994 them through laptop-mode-tools builtin runlevel support (which will be reverted
995 by Gentoo's <c>/sbin/rc</c>) or use your <e>default</e>/<e>battery</e>
996 runlevels (recommended).
997 </p>
998
999 <pre caption="Sample output from running lm-profiler">
1000 # lm-profiler
1001 Profiling session started.
1002 Time remaining: 600 seconds
1003 [4296896.602000] amarokapp
1004 Time remaining: 599 seconds
1005 [4296897.714000] sort
1006 [4296897.970000] mv
1007 Time remaining: 598 seconds
1008 Time remaining: 597 seconds
1009 [4296900.482000] reiserfs/0
1010 </pre>
1011
1012 <p>
1013 After profiling your system for ten minutes, lm-profiler will present a list of
1014 services which might have caused disk accesses during that time.
1015 </p>
1016
1017 <pre caption="lm-profiler suggests to disable some services">
1018 Program: "atd"
1019 Reason: standard recommendation (program may not be running)
1020 Init script: /etc/init.d/atd (GUESSED)
1021
1022 Do you want to disable this service in battery mode? [y/N]: n
1023 </pre>
1024
1025 <p>
1026 To disable atd as suggested in the example above, you would run <c>rc-update
1027 del atd battery</c>. Be careful not to disable services that are needed for
1028 your system to run properly - lm-profiler is likely to generate some false
1029 positives. Do not disable a service if you are unsure whether it's needed.
1030 </p>
1031
1032 </body>
1033 </section>
1034
1035 <section>
1036 <title>Limiting write accesses</title>
1037 <body>
1038
1039 <p>
1040 If you don't want to use laptop-mode, you must take special care to disable
1041 services that write to your disk frequently - <c>syslogd</c> is a good
1042 candidate, for example. You probably don't want to shut it down completely, but
1043 it's possible to modify the config file so that "unnecessary" things don't get
1044 logged and thus don't create disk traffic. Cups writes to disk periodically, so
1045 consider shutting it down and only enable it manually when needed.
1046 </p>
1047
1048 <pre caption="Disabling cups in battery mode">
1049 # <i>rc-update del cupsd battery</i>
1050 </pre>
1051
1052 <p>
1053 You can also use <c>lm-profiler</c> from laptop-mode-tools (see above) to find
1054 services to disable. Once you eliminated all of them, go on with configuring
1055 hdparm.
1056 </p>
1057
1058 </body>
1059 </section>
1060
1061 <section>
1062 <title>hdparm</title>
1063 <body>
1064
1065 <p>
1066 The second possibility is using a small script and hdparm. Skip this if you
1067 are using laptop-mode. Otherwise, create <path>/etc/init.d/pmg_hda</path>:
1068 </p>
1069
1070 <pre caption="Using hdparm for disk standby">
1071 #!/sbin/runscript
1072
1073 depend() {
1074 after hdparm
1075 }
1076
1077 start() {
1078 ebegin "Activating Power Management for Hard Drives"
1079 hdparm -q -S12 /dev/hda
1080 eend $?
1081 }
1082
1083 stop () {
1084 ebegin "Deactivating Power Management for Hard Drives"
1085 hdparm -q -S253 /dev/hda
1086 eend $?
1087 }
1088 </pre>
1089
1090 <p>
1091 See <c>man hdparm</c> for the options. If your script is ready, add it to the
1092 battery runlevel.
1093 </p>
1094
1095 <pre caption="Automate disk standby settings">
1096 # <i>chmod +x /etc/init.d/pmg_hda</i>
1097 # <i>/sbin/depscan.sh</i>
1098 # <i>rc-update add pmg_hda battery</i>
1099 </pre>
1100
1101 <impo>
1102 Be careful with sleep/spin down settings of your hard drive. Setting it to
1103 small values might wear out your drive and lose warranty.
1104 </impo>
1105
1106 </body>
1107 </section>
1108
1109 <section>
1110 <title>Other tricks</title>
1111 <body>
1112
1113 <p>
1114 Another possibility is to deactivate swap in battery mode. Before writing a
1115 swapon/swapoff switcher, make sure there is enough RAM and swap isn't used
1116 heavily, otherwise you'll be in big problems.
1117 </p>
1118
1119 <p>
1120 If you don't want to use laptop-mode, it's still possible to minimize disk
1121 access by mounting certain directories as <e>tmpfs</e> - write accesses are not
1122 stored on a disk, but in main memory and get lost with unmounting. Often it's
1123 useful to mount <path>/tmp</path> like this - you don't have to pay special
1124 attention as it gets cleared on every reboot regardless whether it was mounted
1125 on disk or in RAM. Just make sure you have enough RAM and no program (like a
1126 download client or compress utility) needs extraordinary much space in
1127 <path>/tmp</path>. To activate this, enable tmpfs support in your kernel and
1128 add a line to <path>/etc/fstab</path> like this:
1129 </p>
1130
1131 <pre caption="Editing /etc/fstab to make /tmp even more volatile">
1132 none /tmp tmpfs size=32m 0 0
1133 </pre>
1134
1135 <warn>
1136 Pay attention to the size parameter and modify it for your system. If you're
1137 unsure, don't try this at all, it can become a perfomance bottleneck easily. In
1138 case you want to mount <path>/var/log</path> like this, make sure to merge the
1139 log files to disk before unmounting. They are essential. Don't attempt to mount
1140 /var/tmp like this. Portage uses it for compiling...
1141 </warn>
1142
1143 </body>
1144 </section>
1145 </chapter>
1146
1147 <chapter>
1148 <title>Power Management for other devices</title>
1149 <section>
1150 <title>Graphics cards</title>
1151 <body>
1152
1153 <p>
1154 In case you own an ATI graphics card supporting PowerPlay (dynamic clock
1155 scaling for the the graphics processing unit GPU), you can activate this
1156 feature in X.org. Open <path>/etc/X11/xorg.conf</path> and add (or enable)
1157 the <c>DynamicClocks</c> option in the Device section. Please notice that
1158 this feature will lead to crashes on some systems.
1159 </p>
1160
1161 <pre caption="Enabling ATI PowerPlay support in X.org">
1162 Section "Device"
1163 [...]
1164 Option "DynamicClocks" "on"
1165 EndSection
1166 </pre>
1167
1168 </body>
1169 </section>
1170 <section>
1171 <title>Wireless Power Management</title>
1172 <body>
1173
1174 <p>
1175 Wireless LAN cards consume quite a bit of energy. Put them in Power Management
1176 mode in analogy to the pmg_hda script.
1177 </p>
1178
1179 <note>
1180 This script assumes your wireless interface is called <c>wlan0</c>; replace
1181 this with the actual name of your interface.
1182 </note>
1183
1184 <pre caption="WLAN Power Management automated">
1185 #!/sbin/runscript
1186 start() {
1187 ebegin "Activating Power Management for Wireless LAN"
1188 iwconfig wlan0 power on
1189 eend $?
1190 }
1191
1192 stop () {
1193 ebegin "Deactivating Power Management for Wireless LAN"
1194 iwconfig wlan0 power off
1195 eend $?
1196 }
1197 </pre>
1198
1199 <p>
1200 Starting this script will activate power saving features for wlan0. Save it as
1201 <path>/etc/init.d/pmg_wlan0</path> and add it to the battery runlevel like the
1202 disk script above. See <c>man iwconfig</c> for details and more options like
1203 the period between wakeups or timeout settings. If your driver and access point
1204 support changing the beacon time, this is a good starting point to save even
1205 more energy.
1206 </p>
1207
1208 <pre caption="Power Management for WLAN">
1209 # <i>chmod +x /etc/init.d/pmg_wlan0</i>
1210 # <i>/sbin/depscan.sh</i>
1211 # <i>rc-update add pmg_wlan0 battery</i>
1212 </pre>
1213
1214 </body>
1215 </section>
1216 <section>
1217 <title>USB Power Management</title>
1218 <body>
1219
1220 <p>
1221 There are two problems with USB devices regarding energy consumption: First,
1222 devices like USB mice, digital cameras or USB sticks consume energy while
1223 plugged in. You cannot avoid this (nevertheless remove them in case they're not
1224 needed). Second, when there are USB devices plugged in, the USB host controller
1225 periodically accesses the bus which in turn prevents the CPU from going into
1226 sleep mode. The kernel offers an experimental option to enable suspension of
1227 USB devices through driver calls or one of the <path>power/state</path> files
1228 in <path>/sys</path>.
1229 </p>
1230
1231 <pre caption="Enabling USB suspend support in the kernel">
1232 Device Drivers
1233 USB support
1234 [*] Support for Host-side USB
1235 [*] USB suspend/resume (EXPERIMENTAL)
1236 </pre>
1237
1238 </body>
1239 </section>
1240 </chapter>
1241
1242 <chapter>
1243 <title>Sleep states: sleep, standby, suspend to disk</title>
1244 <section>
1245 <body>
1246
1247 <p>
1248 ACPI defines different sleep states. The more important ones are
1249 </p>
1250
1251 <ul>
1252 <li>S1 aka Standby</li>
1253 <li>S3 aka Suspend to RAM aka Sleep</li>
1254 <li>S4 aka Suspend to Disk aka Hibernate</li>
1255 </ul>
1256
1257 <p>
1258 They can be called whenever the system is not in use, but a shutdown is not
1259 wanted due to the long boot time.
1260 </p>
1261
1262 </body>
1263 </section>
1264 <section>
1265 <title>Sleep (S3)</title>
1266 <body>
1267
1268 <p>
1269 The ACPI support for these sleep states is marked experimental for good reason.
1270 APM sleep states seem to be more stable, however you can't use APM and ACPI
1271 together.
1272 </p>
1273
1274 <pre caption="Kernel configuration for the various suspend types">
1275 Power Management Options ---&gt;
1276 [*] Power Management support
1277 ACPI (Advanced Configuration and Power Interface) Support ---&gt;
1278 [*] ACPI Support
1279 [*] Sleep States
1280 </pre>
1281
1282 <p>
1283 Once your kernel is properly configured, you can use the
1284 <c>hibernate-script</c> to activate suspend or sleep mode. Let's install that
1285 first.
1286 </p>
1287
1288 <pre caption="Installing the hibernate-script">
1289 <i># emerge hibernate-script</i>
1290 </pre>
1291
1292 <p>
1293 Some configuration has to be done in <path>/etc/hibernate</path> The default
1294 package introduces two configuration files <path>hibernate.conf</path> and
1295 <path>ram.conf</path>.
1296 </p>
1297
1298 <p>
1299 To configure sleep, edit <path>ram.conf</path> in <path>/etc/hibernate</path>.
1300 <c>UseSysfsPowerState mem</c> is already setup correctly, but you have to go
1301 through the rest of the configuration file and set it up for your system. The
1302 comments and option names will guide you. If you use nfs or samba shares over
1303 the network, make sure to shutdown the appropriate init scripts to avoid
1304 timeouts.
1305 </p>
1306
1307 <p>
1308 Ready? Now is the last chance to backup any data you want to keep after
1309 executing the next command. Notice that you probably have to hit a special key
1310 like <e>Fn</e> to resume from sleep.
1311 </p>
1312
1313 <pre caption="Calling sleep">
1314 <i># hibernate-ram</i>
1315 </pre>
1316
1317 <p>
1318 If you're still reading, it seems to work. You can also setup standby (S1) in
1319 a similar way by copying <path>ram.conf</path> to <path>standby.conf</path>
1320 and creating a symlink <path>/usr/sbin/hibernate-standby</path> pointing to
1321 <path>/usr/sbin/hibernate</path>. S3 and S4 are the more interesting sleep
1322 states due to greater energy savings however.
1323 </p>
1324
1325 </body>
1326 </section>
1327 <section>
1328 <title>Hibernate (S4)</title>
1329 <body>
1330
1331 <p>
1332 This section introduces hibernation, where a snapshot of the running system is
1333 written to disk before powering off. On resume, the snapshot is loaded and you
1334 can go on working at exactly the point you called hibernate before.
1335 </p>
1336
1337 <warn>
1338 Don't exchange non hot-pluggable hardware when suspended. Don't attempt to load
1339 a snapshot with a different kernel image than the one it was created with.
1340 Shutdown any NFS or samba server/client before hibernating.
1341 </warn>
1342
1343 <p>
1344 There are two different implementations for S4. The original one is swsusp,
1345 then there is the newer suspend2 with a nicer interface (including
1346 fbsplash support). A <uri link="http://suspend2.net/features.html#compare">
1347 feature comparison</uri> is available at the <uri link="http://suspend2.net">
1348 suspend2 Homepage</uri>. There used to be Suspend-to-Disk (pmdisk), a fork of
1349 swsusp, but it has been merged back.
1350 </p>
1351
1352 <p>
1353 Suspend2 is not included in the mainline kernel yet, therefore you either have
1354 to patch your kernel sources with the patches provided by
1355 <uri link="http://suspend2.net">suspend2.net</uri> or use
1356 <c>sys-kernel/suspend2-sources</c>.
1357 </p>
1358
1359 <p>
1360 The kernel part for both swusp and suspend2 is as follows:
1361 </p>
1362
1363 <pre caption="Kernel configuration for the various suspend types">
1364 Power Management Options ---&gt;
1365 <comment>(hibernate with swsusp)</comment>
1366 [*] Software Suspend
1367 <comment>(replace /dev/SWAP with your swap partition)</comment>
1368 (/dev/SWAP) Default resume partition
1369
1370 <comment>(hibernate with suspend2)</comment>
1371 Software Suspend 2
1372 --- Image Storage (you need at least one writer)
1373 [*] File Writer
1374 [*] Swap Writer
1375 --- General Options
1376 [*] LZF image compression
1377 <comment>(replace /dev/SWAP with your swap partition)</comment>
1378 (swap:/dev/SWAP) Default resume device name
1379 [ ] Allow Keep Image Mode
1380 </pre>
1381
1382 <p>
1383 The configuration for swsusp is rather easy. If you didn't store the location
1384 of your swap partition in the kernel config, you can also pass it as a
1385 parameter with the <c>resume=/dev/SWAP</c> directive. If booting is not
1386 possible due to a broken image, use the <c>noresume</c> kernel parameter. The
1387 <c>hibernate-cleanup</c> init script invalidates swsusp images during the
1388 boot process.
1389 </p>
1390
1391 <pre caption="Invalidating swsusp images during the boot process">
1392 <i># rc-update add hibernate-cleanup boot</i>
1393 </pre>
1394
1395 <p>
1396 To activate hibernate with swsusp, use the hibernate script and set
1397 <c>UseSysfsPowerState disk</c> in <path>/etc/hibernate/hibernate.conf</path>.
1398 </p>
1399
1400 <warn>
1401 Backup your data before doing this. Run <c>sync</c> before executing one of the
1402 commands to have cached data written to disk. First try it outside of X, then
1403 with X running, but not logged in.
1404 </warn>
1405
1406 <p>
1407 If you experience kernel panics due to uhci or similar, try to compile USB
1408 support as module and unload the modules before sending your laptop to sleep
1409 mode. There are configuration options for this in <path>hibernate.conf</path>
1410 </p>
1411
1412 <pre caption="Hibernating with swsusp">
1413 <i># nano -w /etc/hibernate.conf</i>
1414 <comment>(Make sure you have a backup of your data)</comment>
1415 <i># hibernate</i>
1416 </pre>
1417
1418 <p>
1419 The following section discusses the setup of suspend2 including fbsplash
1420 support for a nice graphical progress bar during suspend and resume.
1421 </p>
1422
1423 <p>
1424 The first part of the configuration is similar to the configuration of
1425 swsusp. In case you didn't store the location of your swap partition in the
1426 kernel config, you have to pass it as a kernel parameter with the
1427 <c>resume2=swap:/dev/SWAP</c> directive. If booting is not possible due to a
1428 broken image, append the <c>noresume2</c> parameter. Additionally, the
1429 <c>hibernate-cleanup</c> init script invalidates suspend2 images during the
1430 boot process.
1431 </p>
1432
1433 <pre caption="Invalidating suspend2 images during the boot process">
1434 <i># rc-update add hibernate-cleanup boot</i>
1435 </pre>
1436
1437 <p>Now edit <path>/etc/hibernate/hibernate.conf</path>, enable the
1438 <e>suspend2</e> section and comment everything in the <e>sysfs_power_state</e>
1439 and <e>acpi_sleep</e> sections. Do not enable the fbsplash part in global
1440 options yet.
1441 </p>
1442
1443 <pre caption="Hibernating with suspend2">
1444 <i># nano -w /etc/hibernate.conf</i>
1445 <comment>(Make sure you have a backup of your data)</comment>
1446 <i># hibernate</i>
1447 </pre>
1448
1449 <p>
1450 Please configure fbsplash now if you didn't do already. To enable fbsplash
1451 support during hibernation, the <c>sys-apps/suspend2-userui</c> package is
1452 needed. Additionally, you've got to enable the <e>fbsplash</e> USE flag.
1453 </p>
1454
1455 <pre caption="Installing suspend2-userui">
1456 <i># mkdir -p /etc/portage</i>
1457 <i># echo sys-apps/suspend2-userui fbsplash >> /etc/portage/package.use</i>
1458 <i># emerge suspend2-userui</i>
1459 </pre>
1460
1461 <p>
1462 The ebuild tells you to make a symlink to the theme you want to use. For
1463 example, to use the <c>livecd-2005.1</c> theme, run the following command:
1464 </p>
1465
1466 <pre caption="Using the livecd-2005.1 theme during hibernation">
1467 <i># ln -sfn /etc/splash/livecd-2005.1 /etc/splash/suspend2</i>
1468 </pre>
1469
1470 <p>
1471 If you don't want a black screen in the first part of the resume process, you
1472 have to add the <c>suspend2ui_fbsplash</c> tool to your initrd image. Assuming
1473 you created the initrd image with <c>splash_geninitramfs</c> and saved it as
1474 <path>/boot/fbsplash-emergence-1024x768</path>, here's how to do
1475 that.
1476 </p>
1477
1478 <pre caption="Adding suspend2ui_fbsplash to an initrd image">
1479 <i># mount /boot</i>
1480 <i># mkdir ~/initrd.d</i>
1481 <i># cp /boot/fbsplash-emergence-1024x768 ~/initrd.d/</i>
1482 <i># cd ~/initrd.d</i>
1483 <i># gunzip -c fbsplash-emergence-1024x768 | cpio -idm --quiet -H newc</i>
1484 <i># rm fbsplash-emergence-1024x768</i>
1485 <i># cp /usr/sbin/suspend2ui_fbsplash sbin/</i>
1486 <i># find . | cpio --quiet --dereference -o -H newc | gzip -9 > /boot/fbsplash-suspend2-emergence-1024x768</i>
1487 </pre>
1488
1489 <p>
1490 Afterwards adjust <path>grub.conf</path> respectively <path>lilo.conf</path>
1491 so that your suspend2 kernel uses
1492 <path>/boot/fbsplash-suspend2-emergence-1024x768</path> as initrd image. You
1493 can now test a dry run to see if everything is setup correctly.
1494 </p>
1495
1496 <pre caption="Test run for fbsplash hibernation">
1497 <i># suspend2ui_fbsplash -t</i>
1498 </pre>
1499
1500 <p>
1501 Afterwards open <path>/etc/hibernate/hibernate.conf</path> again and activate
1502 the fbsplash options. Execute <c>hibernate</c> and enjoy.
1503 </p>
1504
1505 </body>
1506 </section>
1507 </chapter>
1508
1509 <chapter>
1510 <title>Troubleshooting</title>
1511 <section>
1512 <body>
1513
1514 <p>
1515 <e>Q:</e> I'm trying to change the CPU frequency, but
1516 <path>/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor</path> does not
1517 exist.
1518 </p>
1519
1520 <p>
1521 <e>A:</e> Make sure your processor supports CPU frequency scaling and you chose
1522 the right CPUFreq driver for your processor. Here is a list of processors that
1523 are supported by cpufreq (kernel 2.6.7): ARM Integrator, ARM-SA1100,
1524 ARM-SA1110, AMD Elan - SC400, SC410, AMD mobile K6-2+, AMD mobile K6-3+, AMD
1525 mobile Duron, AMD mobile Athlon, AMD Opteron, AMD Athlon 64, Cyrix Media GXm,
1526 Intel mobile PIII and Intel mobile PIII-M on certain chipsets, Intel Pentium 4,
1527 Intel Xeon, Intel Pentium M (Centrino), National Semiconductors Geode GX,
1528 Transmeta Crusoe, VIA Cyrix 3 / C3, UltraSPARC-III, SuperH SH-3, SH-4, several
1529 "PowerBook" and "iBook2" and various processors on some ACPI 2.0-compatible
1530 systems (only if "ACPI Processor Performance States" are available to the
1531 ACPI/BIOS interface).
1532 </p>
1533
1534 <p>
1535 <e>Q:</e> My laptop supports frequency scaling, but
1536 <path>/sys/devices/system/cpu/cpu0/cpufreq/</path> is empty.
1537 </p>
1538
1539 <p>
1540 <e>A:</e> Look for ACPI related error messages with <c>dmesg | grep ACPI</c>.
1541 Try to update the BIOS, especially if a broken DSDT is reported. You can also
1542 try to fix it yourself (which is beyond the scope of this guide).
1543 </p>
1544
1545 <p>
1546 <e>Q:</e> My laptop supports frequency scaling, but according to /proc/cpuinfo
1547 the speed never changes.
1548 </p>
1549
1550 <p>
1551 <e>A:</e> Probably you have activated symmetric multiprocessing support
1552 (CONFIG_SMP) in your kernel. Deactivate it and it should work. Some older
1553 kernels had a bug causing this. In that case, run <c>emerge x86info</c>,
1554 update your kernel as asked and check the current frequency with
1555 <c>x86info -mhz</c>.
1556 </p>
1557
1558 <p>
1559 <e>Q:</e> I can change the CPU frequency, but the range is not as wide as in
1560 another OS.
1561 </p>
1562
1563 <p>
1564 <e>A:</e> You can combine frequency scaling with ACPI throttling to get a lower
1565 minimum frequency. Notice that throttling doesn't save much energy and is
1566 mainly used for thermal management (keeping your laptop cool and quiet). You
1567 can read the current throttling state with <c>cat
1568 /proc/acpi/processor/CPU/throttling</c> and change it with <c>echo -n "0:x" >
1569 /proc/acpi/processor/CPU/limit</c>, where x is one of the Tx states listed in
1570 <path>/proc/acpi/processor/CPU/throttling</path>.
1571 </p>
1572
1573 <p>
1574 <e>Q:</e> When configuring the kernel, powersave, performance and userspace
1575 governors show up, but that ondemand thing is missing. Where do I get it?
1576 </p>
1577
1578 <p>
1579 <e>A:</e> The ondemand governor is only included in recent kernel sources. Try
1580 updating them.
1581 </p>
1582
1583 <p>
1584 <e>Q:</e> Battery life time seems to be worse than before.
1585 </p>
1586
1587 <p>
1588 <e>A:</e> Check your BIOS settings. Maybe you forgot to re-enable some of the
1589 settings.
1590 </p>
1591
1592 <p>
1593 <e>Q:</e> My battery is charged, but KDE reports there would be 0% left and
1594 immediately shuts down.
1595 </p>
1596
1597 <p>
1598 <e>A:</e> Check that battery support is compiled into your kernel. If you use
1599 it as a module, make sure the module is loaded.
1600 </p>
1601
1602 <p>
1603 <e>Q:</e> My system logger reports things like "logger: ACPI group battery / action
1604 battery is not defined".
1605 </p>
1606
1607 <p>
1608 <e>A:</e> This message is generated by the /etc/acpi/default.sh script that is
1609 shipped with acpid. You can safely ignore it. If you like to get rid of it, you
1610 can comment the appropriate line in /etc/acpi/default.sh as shown below:
1611 </p>
1612
1613 <pre caption="Disabling warnings about unknown acpi events">
1614 *) # logger "ACPI action $action is not defined"
1615 </pre>
1616
1617 <p>
1618 <e>Q:</e> I have a Dell Inspiron 51XX and I don't get any ACPI events.
1619 </p>
1620
1621 <p>
1622 <e>A:</e> This seems to be a kernel bug. Read on <uri
1623 link="http://bugme.osdl.org/show_bug.cgi?id=1752">here</uri>.
1624 </p>
1625
1626 <p>
1627 <e>Q:</e> I activated the DynamicClocks option in <path>xorg.conf</path> and
1628 now X.org crashes / the screen stays black / my laptop doesn't shutdown
1629 properly.
1630 </p>
1631
1632 <p>
1633 <e>A:</e> This happens on some systems. You have to disable DynamicClocks.
1634 </p>
1635
1636 <p>
1637 <e>Q:</e> I want to use suspend2, but it tells me my swap partition is too
1638 small. Resizing is not an option.
1639 </p>
1640
1641 <p>
1642 <e>A:</e> If there is enough free space on your system, you can use the
1643 filewriter instead of the swapwriter. The <c>hibernate-script</c> supports it
1644 as well. More information can be found in
1645 <path>/usr/src/linux/Documentation/power/suspend2.txt</path>.
1646 </p>
1647
1648 <p>
1649 <e>Q:</e> I just bought a brand new battery, but it only lasts for some
1650 minutes! What am I doing wrong?
1651 </p>
1652
1653 <p>
1654 <e>A:</e> First follow your manufacturer's advice on how to charge the battery
1655 correctly.
1656 </p>
1657
1658 <p>
1659 <e>Q:</e> The above didn't help. What should I do then?
1660 </p>
1661
1662 <p>
1663 <e>A:</e> Some batteries sold as "new" are in fact old ones. Try the following:
1664 </p>
1665
1666 <pre caption="Querying battery state">
1667 $ <i>grep capacity /proc/acpi/battery/BAT0/info</i>
1668 design capacity: 47520 mWh
1669 last full capacity: 41830 mWh
1670 </pre>
1671
1672 <p>
1673 If the "last full capacity" differs significantly from the design capacity,
1674 your battery is probably broken. Try to claim your warranty.
1675 </p>
1676
1677 <p>
1678 <e>Q:</e> My problem is not listed above. Where should I go next?
1679 </p>
1680
1681 <p>
1682 <e>A:</e> Don't fear to contact me, <mail link="earthwings@gentoo.org">Dennis
1683 Nienhüser</mail>, directly. The
1684 <uri link="http://forums.gentoo.org">Gentoo Forums</uri> are a good place to
1685 get help as well. If you prefer IRC, try the <e>#gentoo-laptop</e> channel at
1686 <e>irc.freenode.net</e>.
1687 </p>
1688
1689 </body>
1690 </section>
1691 </chapter>
1692 </guide>

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