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1 <?xml version='1.0' encoding="UTF-8"?>
2 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
3 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/power-management-guide.xml,v 1.29 2007/07/08 17:51:23 nightmorph Exp $ -->
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 <author title="Editor">
11 <mail link="chriswhite@gentoo.org">Chris White</mail>
12 </author>
13 <author title="Editor">
14 <mail link="nightmorph@gentoo.org">Joshua Saddler</mail>
15 </author>
16
17 <abstract>
18 Power Management is the key to extend battery run time on mobile systems like
19 laptops. This guide assists you setting it up on your laptop.
20 </abstract>
21
22 <!-- The content of this document is licensed under the CC-BY-SA license -->
23 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
24 <license/>
25
26 <version>1.35</version>
27 <date>2007-07-24</date>
28
29 <chapter>
30 <title>Introduction</title>
31 <section>
32 <body>
33
34 <p>
35 Capacity and lifetime of laptop batteries have improved much in the last years.
36 Nevertheless modern processors consume much more energy than older ones and
37 each laptop generation introduces more devices hungry for energy. That's why
38 Power Management is more important than ever. Increasing battery run time
39 doesn't necessarily mean buying another battery. Much can be achieved applying
40 intelligent Power Management policies.
41 </p>
42
43 </body>
44 </section>
45 <section>
46 <title>A Quick Overview</title>
47 <body>
48
49 <p>
50 Please notice that this guide describes Power Management for <e>laptops</e>.
51 While some sections might also suite for <e>servers</e>, others do not and may
52 even cause harm. Please do not apply anything from this guide to a server
53 unless you really know what you are doing.
54 </p>
55
56 <p>
57 As this guide has become rather long, here's a short overview helping you to
58 find your way through it.
59 </p>
60
61 <p>
62 The <uri link="#doc_chap2">Prerequisites</uri> chapter talks about some
63 requirements that should be met before any of the following device individual
64 sections will work. This includes BIOS settings, kernel configuration and some
65 simplifications in user land. The following three chapters focus on devices
66 that typically consume most energy - processor, display and hard drive. Each
67 can be configured seperately. <uri link="#doc_chap3">CPU Power Management</uri>
68 shows how to adjust the processor's frequency to save a maximum of energy
69 without losing too much performance. A few different tricks prevent your hard
70 drive from working unnecessarily often in <uri link="#doc_chap5">Disk Power
71 Management</uri> (decreasing noise level as a nice side effect). Some notes on
72 graphics cards, Wireless LAN and USB finish the device section in <uri
73 link="#doc_chap6">Power Management For Other Devices</uri> while another
74 chapter is dedicated to the (rather experimental) <uri link="#doc_chap7">sleep
75 states</uri>. Last not least <uri link="#doc_chap8">Troubleshooting</uri> lists
76 common pitfalls.
77 </p>
78
79 </body>
80 </section>
81 <section>
82 <title>Power Budget For Each Component</title>
83 <body>
84
85 <figure link="/images/energy-budget.png" short="Which component consumes how
86 much energy?" caption="Power budget for each component"/>
87
88 <p>
89 Nearly every component can operate in different states - off, sleep, idle,
90 active to name a few - consuming a different amount of energy. Major parts are
91 consumed by the LCD display, CPU, chipset and hard drives. Often one is able to
92 activate OS-independent Power Management in the BIOS, but an intelligent setup
93 in the operating system adapting to different situations can achieve much more.
94 </p>
95
96 </body>
97 </section>
98 </chapter>
99
100 <chapter>
101 <title>Prerequisites</title>
102 <section>
103 <body>
104
105 <p>
106 Before discussing the details of making individual devices Power Management
107 aware, make sure certain requirements are met. After controlling BIOS settings,
108 some kernel options want to be enabled - these are in short ACPI, sleep states
109 and CPU frequency scaling. As power saving most of the time comes along with
110 performance loss or increased latency, it should only be enabled when running
111 on batteries. That's where a new runlevel <e>battery</e> comes in handy.
112 </p>
113
114 </body>
115 </section>
116 <section>
117 <title>The BIOS Part</title>
118 <body>
119
120 <p>
121 First have a look into your BIOS Power Management settings. The best way is to
122 combine BIOS and operating system policies, but for the moment it's better to
123 disable most of the BIOS part. This makes sure it doesn't interfere with your
124 policies. Don't forget to re-check BIOS settings after you configured
125 everything else.
126 </p>
127
128 </body>
129 </section>
130 <section>
131 <title>Setting USE Flags</title>
132 <body>
133
134 <p>
135 Please check that the <c>acpi</c> USE flag is set in
136 <path>/etc/make.conf</path>. Other USE flags that might be interesting for your
137 system are <c>apm</c>, <c>lm_sensors</c>, <c>nforce2</c>, <c>nvidia</c>,
138 <c>pmu</c>. See <path>/usr/portage/profiles/use*.desc</path> for details. If
139 you forgot to set one of these flags, you can recompile affected packages using
140 the <c>--newuse</c> flag in <c>emerge</c>, see <c>man emerge</c>.
141 </p>
142
143 </body>
144 </section>
145 <section>
146 <title>Configuring The Kernel</title>
147 <body>
148
149 <p>
150 ACPI (Advanced Configuration and Power Interface) support in the kernel is
151 still work in progress. Using a recent kernel will make sure you'll get the
152 most out of it.
153 </p>
154
155 <p>
156 There are different kernel sources in Portage. I'd recommend using
157 <c>gentoo-sources</c> or <c>suspend2-sources</c>. The latter contains patches
158 for Software Suspend 2, see the chapter about <uri link="#doc_chap7">sleep
159 states</uri> for more details. When configuring the kernel, activate at least
160 these options:
161 </p>
162
163 <pre caption="Minimum kernel setup for Power Management (Kernel 2.6)">
164 Power Management Options ---&gt;
165 [*] Power Management Support
166 [ ] Software Suspend
167
168 ACPI( Advanced Configuration and Power Interface ) Support ---&gt;
169 [*] ACPI Support
170 [ ] Sleep States
171 [ ] /proc/acpi/sleep (deprecated)
172 [*] AC Adapter
173 [*] Battery
174 &lt;M&gt; Button
175 &lt;M&gt; Video
176 [ ] Generic Hotkey
177 &lt;M&gt; Fan
178 &lt;M&gt; Processor
179 &lt;M&gt; Thermal Zone
180 &lt; &gt; ASUS/Medion Laptop Extras
181 &lt; &gt; IBM ThinkPad Laptop Extras
182 &lt; &gt; Toshiba Laptop Extras
183 (0) Disable ACPI for systems before Jan 1st this year
184 [ ] Debug Statements
185 [*] Power Management Timer Support
186 &lt; &gt; ACPI0004,PNP0A05 and PNP0A06 Container Driver (EXPERIMENTAL)
187
188 CPU Frequency Scaling ---&gt;
189 [*] CPU Frequency scaling
190 [ ] Enable CPUfreq debugging
191 &lt; &gt; CPU frequency translation statistics
192 [ ] CPU frequency translation statistics details
193 Default CPUFreq governor (userspace)
194 &lt;*&gt; 'performance' governor
195 &lt;*&gt; 'powersave' governor
196 &lt;*&gt; 'ondemand' cpufreq policy governor
197 &lt;*&gt; 'conservative' cpufreq governor
198 &lt;*&gt; CPU frequency table helpers
199 &lt;M&gt; ACPI Processor P-States driver
200 &lt;*&gt; <i>CPUFreq driver for your processor</i>
201 </pre>
202
203 <p>
204 Decide yourself whether you want to enable Software Suspend, and Sleep States
205 (see below). If you own an ASUS, Medion, IBM Thinkpad or Toshiba laptop, enable
206 the appropriate section.
207 </p>
208
209 <p>
210 The kernel has to know how to enable CPU frequency scaling on your processor.
211 As each type of CPU has a different interface, you've got to choose the right
212 driver for your processor. Be careful here - enabling <c>Intel Pentium 4 clock
213 modulation</c> on a Pentium M system will lead to strange results for example.
214 Consult the kernel documentation if you're unsure which one to take.
215 </p>
216
217 <p>
218 Compile your kernel, make sure the right modules get loaded at startup and boot
219 into your new ACPI-enabled kernel. Next run <c>emerge sys-power/acpid</c> to
220 get the acpi daemon. This one informs you about events like switching from AC
221 to battery or closing the lid. Make sure the modules are loaded if you didn't
222 compile them into the kernel and start acpid by executing <c>/etc/init.d/acpid
223 start</c>. Run <c>rc-update add acpid default</c> to load it on startup. You'll
224 soon see how to use it.
225 </p>
226
227 <pre caption="Installing acpid">
228 # <i>emerge sys-power/acpid</i>
229 # <i>/etc/init.d/acpid start</i>
230 # <i>rc-update add acpid default</i>
231 </pre>
232
233 </body>
234 </section>
235 <section>
236 <title>Creating A "battery" Runlevel</title>
237 <body>
238
239 <p>
240 The default policy will be to enable Power Management only when needed -
241 running on batteries. To make the switch between AC and battery convenient,
242 create a runlevel <c>battery</c> that holds all the scripts starting and
243 stopping Power Management.
244 </p>
245
246 <note>
247 You can safely skip this section if you don't like the idea of having another
248 runlevel. However, skipping this step will make the rest a bit trickier to set
249 up. The next sections assume a runlevel <c>battery</c> exists.
250 </note>
251
252 <pre caption="Creating a battery runlevel">
253 # <i>cd /etc/runlevels</i>
254 # <i>cp -a default battery</i>
255 </pre>
256
257 <p>
258 Finished. Your new runlevel <c>battery</c> contains everything like
259 <c>default</c>, but there is no automatic switch between both yet. Time to
260 change it.
261 </p>
262
263 </body>
264 </section>
265 <section>
266 <title>Reacting On ACPI Events</title>
267 <body>
268
269 <p>
270 Typical ACPI events are closing the lid, changing the power source or pressing
271 the sleep button. An important event is changing the power source, which should
272 cause a runlevel switch. A small script will take care of it.
273 </p>
274
275 <p>
276 First you need a script which changes the runlevel to <c>default</c>
277 respectively <c>battery</c> depending on the power source. The script uses the
278 <c>on_ac_power</c> command from <c>sys-power/powermgmt-base</c> - make sure the
279 package is installed on your system.
280 </p>
281
282 <pre caption="Installing powermgt-base">
283 # <i>emerge powermgmt-base</i>
284 </pre>
285
286 <p>
287 You are now able to determine the power source by executing <c>on_ac_power
288 &amp;&amp; echo AC available || echo Running on batteries</c> in a shell. The
289 script below is responsible for changing runlevels. Save it as
290 <path>/etc/acpi/actions/pmg_switch_runlevel.sh</path>.
291 </p>
292
293 <pre caption="/etc/acpi/actions/pmg_switch_runlevel.sh">
294 #!/bin/bash
295
296 <comment># BEGIN configuration</comment>
297 RUNLEVEL_AC="default"
298 RUNLEVEL_BATTERY="battery"
299 <comment># END configuration</comment>
300
301
302 if [ ! -d "/etc/runlevels/${RUNLEVEL_AC}" ]
303 then
304 logger "${0}: Runlevel ${RUNLEVEL_AC} does not exist. Aborting."
305 exit 1
306 fi
307
308 if [ ! -d "/etc/runlevels/${RUNLEVEL_BATTERY}" ]
309 then
310 logger "${0}: Runlevel ${RUNLEVEL_BATTERY} does not exist. Aborting."
311 exit 1
312 fi
313
314 if on_ac_power
315 then
316 if [[ "$(&lt;/var/lib/init.d/softlevel)" != "${RUNLEVEL_AC}" ]]
317 then
318 logger "Switching to ${RUNLEVEL_AC} runlevel"
319 /sbin/rc ${RUNLEVEL_AC}
320 fi
321 elif [[ "$(&lt;/var/lib/init.d/softlevel)" != "${RUNLEVEL_BATTERY}" ]]
322 then
323 logger "Switching to ${RUNLEVEL_BATTERY} runlevel"
324 /sbin/rc ${RUNLEVEL_BATTERY}
325 fi
326 </pre>
327
328 <p>
329 Dont forget to run <c>chmod +x /etc/acpi/actions/pmg_switch_runlevel.sh</c> to
330 make the script executable. The last thing that needs to be done is calling the
331 script whenever the power source changes. That's done by catching ACPI events
332 with the help of <c>acpid</c>. First you need to know which events are
333 generated when the power source changes. The events are called
334 <c>ac_adapter</c> and <c>battery</c> on most laptops, but it might be different
335 on yours.
336 </p>
337
338 <pre caption="Determining ACPI events for changing the power source">
339 # <i>tail -f /var/log/acpid | grep "received event"</i>
340 </pre>
341
342 <p>
343 Run the command above and pull the power cable. You should see something like
344 this:
345 </p>
346
347 <pre caption="Sample output for power source changes">
348 [Tue Sep 20 17:39:06 2005] received event "ac_adapter AC 00000080 00000000"
349 [Tue Sep 20 17:39:06 2005] received event "battery BAT0 00000080 00000001"
350 </pre>
351
352 <p>
353 The interesting part is the quoted string after <c>received event</c>. It will
354 be matched by the event line in the files you are going to create below. Don't
355 worry if your system generates multiple events or always the same. As long as
356 any event is generated, runlevel changing will work.
357 </p>
358
359 <pre caption="/etc/acpi/events/pmg_ac_adapter">
360 <comment># replace "ac_adapter" below with the event generated on your laptop</comment>
361 <comment># For example, ac_adapter.* will match ac_adapter AC 00000080 00000000</comment>
362 event=ac_adapter.*
363 action=/etc/acpi/actions/pmg_switch_runlevel.sh %e
364 </pre>
365
366 <pre caption="/etc/acpi/events/pmg_battery">
367 <comment># replace "battery" below with the event generated on your laptop</comment>
368 <comment># For example, battery.* will match battery BAT0 00000080 00000001</comment>
369 event=battery.*
370 action=/etc/acpi/actions/pmg_switch_runlevel.sh %e
371 </pre>
372
373 <p>
374 Finally acpid has to be restarted to recognize the changes.
375 </p>
376
377 <pre caption="Finishing runlevel switching with acpid">
378 # <i>/etc/init.d/acpid restart</i>
379 </pre>
380
381 <p>
382 Give it a try: Plug AC in and out and watch syslog for the "Switching to AC
383 mode" or "Switching to battery mode" messages. See the <uri
384 link="#doc_chap8">Troubleshooting section</uri> if the script is not able to
385 detect the power source correctly.
386 </p>
387
388 <p>
389 Due to the nature of the event mechanism, your laptop will boot into runlevel
390 <c>default</c> regardless of the AC/battery state. This is fine when running
391 from AC, but we'd like to boot into the battery runlevel otherwise. One
392 solution would be to add another entry to the boot loader with the parameter
393 <c>softlevel=battery</c>, but it's likely to forget choosing it. A better way
394 is faking an ACPI event in the end of the boot process and letting
395 <path>pmg_switch_runlevel.sh</path> script decide whether a runlevel change is
396 necessary. Open <path>/etc/conf.d/local.start</path> in your favourite editor
397 and add these lines:
398 </p>
399
400 <pre caption="Runlevel adjustment at boot time by editing local.start">
401 <comment># Fake acpi event to switch runlevel if running on batteries</comment>
402 /etc/acpi/actions/pmg_switch_runlevel.sh "battery/battery"
403 </pre>
404
405 <p>
406 Prepared like this you can activate Power Management policies for individual
407 devices.
408 </p>
409
410 </body>
411 </section>
412 </chapter>
413
414 <chapter>
415 <title>CPU Power Management</title>
416 <section>
417 <body>
418
419 <p>
420 Mobile processors can operate at different frequencies. Some allow changing
421 voltage as well. Most of the time your CPU doesn't need to run at full speed
422 and scaling it down will save much energy - often without any performance
423 decrease.
424 </p>
425
426 </body>
427 </section>
428 <section>
429 <title>Some Technical Terms</title>
430 <body>
431
432 <p>
433 CPU frequency scaling brings up some technical terms that might be unknown to
434 you. Here's a quick introduction.
435 </p>
436
437 <p>
438 First of all, the kernel has to be able to change the processor's frequency.
439 The <b>CPUfreq processor driver</b> knows the commands to do it on your CPU.
440 Thus it's important to choose the right one in your kernel. You should already
441 have done it above. Once the kernel knows how to change frequencies, it has to
442 know which frequency it should set. This is done according to the <b>policy</b>
443 which consists of a <b>CPUfreq policy</b> and a <b>governor</b>. A CPUfreq
444 policy are just two numbers which define a range the frequency has to stay
445 between - minimal and maximal frequency. The governor now decides which of the
446 available frequencies in between minimal and maximal frequency to choose. For
447 example, the <b>powersave governor</b> always chooses the lowest frequency
448 available, the <b>performance governor</b> the highest one. The <b>userspace
449 governor</b> makes no decision but chooses whatever the user (or a program in
450 userspace) wants - which means it reads the frequency from
451 <path>/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed</path>.
452 </p>
453
454 <p>
455 This doesn't sound like dynamic frequency changes yet and in fact it isn't.
456 Dynamics however can be accomplished with various approaches. For example, the
457 <b>ondemand governor</b> makes its decisions depending on the current CPU load.
458 The same is done by various userland tools like <c>cpudyn</c>, <c>cpufreqd</c>,
459 <c>powernowd</c> and many more. ACPI events can be used to enable or disable
460 dynamic frequency changes depending on power source.
461 </p>
462
463 </body>
464 </section>
465 <section>
466 <title>Setting The Frequency Manually</title>
467 <body>
468
469 <p>
470 Decreasing CPU speed and voltage has two advantages: On the one hand less
471 energy is consumed, on the other hand there is thermal improvement as your
472 system doesn't get as hot as running on full speed. The main disadvantage is
473 obviously the loss of performance. Decreasing processor speed is a trade off
474 between performance loss and energy saving.
475 </p>
476
477 <note>
478 Not every laptop supports frequency scaling. If unsure, have a look at the list
479 of supported processors in the <uri link="#doc_chap8">Troubleshooting</uri>
480 section to verify yours is supported.
481 </note>
482
483 <p>
484 It's time to test whether CPU frequency changing works. Let's install another
485 tool which is very handy for debugging purposes: <c>sys-power/cpufrequtils</c>
486 </p>
487
488 <pre caption="Checking CPU frequency">
489 # <i>emerge cpufrequtils</i>
490 # <i>cpufreq-info</i>
491 </pre>
492
493 <p>
494 Here is an example output:
495 </p>
496
497 <pre caption="Sample output from cpufreq-info">
498 cpufrequtils 0.3: cpufreq-info (C) Dominik Brodowski 2004
499 Report errors and bugs to linux@brodo.de, please.
500 analyzing CPU 0:
501 driver: centrino
502 CPUs which need to switch frequency at the same time: 0
503 hardware limits: 600 MHz - 1.40 GHz
504 available frequency steps: 600 MHz, 800 MHz, 1000 MHz, 1.20 GHz, 1.40 GHz
505 available cpufreq governors: conservative, ondemand, powersave, userspace, performance
506 current policy: frequency should be within 924 MHz and 1.40 GHz.
507 The governor "performance" may decide which speed to use
508 within this range.
509 current CPU frequency is 1.40 GHz.
510 </pre>
511
512 <p>
513 Now play around with <c>cpufreq-set</c> to make sure frequency switching works.
514 Run <c>cpufreq-set -g ondemand</c> for example to activate the ondemand
515 governor and verify the change with <c>cpufreq-info</c>. If it doesn't work as
516 expected, you might find help in the <uri link="#doc_chap8">Troubleshooting
517 section</uri> in the end of this guide.
518 </p>
519
520 </body>
521 </section>
522 <section>
523 <title>Automated frequency adaption</title>
524 <body>
525
526 <p>
527 The above is quite nice, but not doable in daily life. Better let your system
528 set the appropriate frequency automatically. There are many different
529 approaches to do this. The following table gives a quick overview to help you
530 decide on one of them. It's roughly separated in three categories <b>kernel</b>
531 for approaches that only need kernel support, <b>daemon</b> for programs that
532 run in the background and <b>graphical</b> for programs that provide a GUI for
533 easy configuration and changes.
534 </p>
535
536 <table>
537 <tr>
538 <th>Name</th>
539 <th>Category</th>
540 <th>Switch decision</th>
541 <th>Kernel governors</th>
542 <th>Further governors</th>
543 <th>Comments</th>
544 </tr>
545 <tr>
546 <ti>'ondemand' governor</ti>
547 <ti>Kernel</ti>
548 <ti>CPU load</ti>
549 <ti>N.A.</ti>
550 <ti>N.A.</ti>
551 <ti>
552 Chooses maximal frequency on CPU load and slowly steps down when the CPU is
553 idle. Further tuning through files in
554 <path>/sys/devices/system/cpu/cpu0/cpufreq/ondemand/</path>. Still requires
555 userland tools (programs, scripts) if governor switching or similar is
556 desired.
557 </ti>
558 </tr>
559 <tr>
560 <ti>'conservative' governor</ti>
561 <ti>Kernel</ti>
562 <ti>CPU load</ti>
563 <ti>N.A.</ti>
564 <ti>N.A.</ti>
565 <ti>
566 Unlike the ondemand governor, conversative doesn't jump to maximum
567 frequency when CPU load is high, but increases the frequency step by step.
568 Further tuning through files in
569 <path>/sys/devices/system/cpu/cpu0/cpufreq/ondemand/</path>. Still requires
570 userland tools (programs, scripts) if governor switching or similar is
571 desired.
572 </ti>
573 </tr>
574 <tr>
575 <ti><uri link="http://mnm.uib.es/~gallir/cpudyn/">cpudyn</uri></ti>
576 <ti>Daemon</ti>
577 <ti>CPU load</ti>
578 <ti>Performance, powersave</ti>
579 <ti>Dynamic</ti>
580 <ti>
581 Also supports disk standby - notice however that <e>laptop mode</e> in most
582 cases will do a better job.
583 </ti>
584 </tr>
585 <tr>
586 <ti><uri link="http://sourceforge.net/projects/cpufreqd/">cpufreqd</uri></ti>
587 <ti>Daemon</ti>
588 <ti>Battery state, CPU load, temperature, running programs and more</ti>
589 <ti>All available</ti>
590 <ti>None</ti>
591 <ti>
592 Sophisticated (but somewhat complicated) setup. Extendible through plugins
593 like sensor monitoring (lm_sensors) or coordinating some NVidia based
594 graphics card memory and core. Cpufreqd is SMP aware and can optionally be
595 controlled manually at runtime.
596 </ti>
597 </tr>
598 <tr>
599 <ti>
600 <uri link="http://www.deater.net/john/powernowd.html">powernowd</uri>
601 </ti>
602 <ti>Daemon</ti>
603 <ti>CPU load</ti>
604 <ti>None</ti>
605 <ti>Passive, sine, aggressive</ti>
606 <ti>
607 Supports SMP.
608 </ti>
609 </tr>
610 <tr>
611 <ti>ncpufreqd</ti>
612 <ti>Daemon</ti>
613 <ti>Temperature</ti>
614 <ti>None</ti>
615 <ti>Powersave, performance</ti>
616 <ti>
617 Toggles the used governor between performance and powersave depending on
618 system temperature. Very useful on laptops with notorious heat problems.
619 </ti>
620 </tr>
621 <tr>
622 <ti><uri link="http://www.goop.org/~jeremy/speedfreq/">speedfreq</uri></ti>
623 <ti>Daemon</ti>
624 <ti>CPU load</ti>
625 <ti>None</ti>
626 <ti>Dynamic, powersave, performance, fixed speed</ti>
627 <ti>
628 Easy to configure with a nice client/server interface. Requires a 2.6
629 kernel. Unmaintained, broken and thus removed from Portage. Please switch
630 to cpufreqd if you're still using it.
631 </ti>
632 </tr>
633 <tr>
634 <ti><uri link="http://cpuspeedy.sourceforge.net/">gtk-cpuspeedy</uri></ti>
635 <ti>Graphical</ti>
636 <ti>None</ti>
637 <ti>None</ti>
638 <ti>None</ti>
639 <ti>
640 Gnome application, a graphical tool to set CPU frequency manually. It does
641 not offer any automation.
642 </ti>
643 </tr>
644 <tr>
645 <ti>klaptopdaemon</ti>
646 <ti>Graphical</ti>
647 <ti>Battery state</ti>
648 <ti>All available</ti>
649 <ti>None</ti>
650 <ti>
651 KDE only, 'ondemand' governor required for dynamic frequency scaling.
652 </ti>
653 </tr>
654 </table>
655
656 <p>
657 While adjusting the frequency to the current load looks simple at a first
658 glance, it's not such a trivial task. A bad algorithm can cause switching
659 between two frequencies all the time or wasting energy when setting frequency
660 to an unnecessary high level.
661 </p>
662
663 <p>
664 Which one to choose? If you have no idea about it, try <c>cpufreqd</c>:
665 </p>
666
667 <pre caption="Installing cpufreqd">
668 # <i>emerge cpufreqd</i>
669 </pre>
670
671 <p>
672 <c>cpufreqd</c> can be configured by editing <path>/etc/cpufreqd.conf</path>.
673 The default one that ships with cpufreqd may look a bit confusing. I recommend
674 replacing it with the one from former Gentoo developer Henrik Brix Andersen
675 (see below). Please notice that you need cpufreqd-2.0.0 or later. Earlier
676 versions have a different syntax for the config file.
677 </p>
678
679 <pre caption="/etc/cpufreqd.conf (cpufreqd-2.0.0 and later)">
680 [General]
681 pidfile=/var/run/cpufreqd.pid
682 poll_interval=3
683 enable_plugins=acpi_ac, acpi_battery
684 enable_remote=1
685 remote_group=wheel
686 verbosity=5
687 [/General]
688
689 [Profile]
690 name=ondemand
691 minfreq=0%
692 maxfreq=100%
693 policy=ondemand
694 [/Profile]
695
696 [Profile]
697 name=conservative
698 minfreq=0%
699 maxfreq=100%
700 policy=conservative
701 [/Profile]
702
703 [Profile]
704 name=powersave
705 minfreq=0%
706 maxfreq=100%
707 policy=powersave
708 [/Profile]
709
710 [Profile]
711 name=performance
712 minfreq=0%
713 maxfreq=100%
714 policy=performance
715 [/Profile]
716
717 [Rule]
718 name=battery
719 ac=off
720 profile=conservative
721 [/Rule]
722
723 [Rule]
724 name=battery_low
725 ac=off
726 battery_interval=0-10
727 profile=powersave
728 [/Rule]
729
730 [Rule]
731 name=ac
732 ac=on
733 profile=ondemand
734 [/Rule]
735 </pre>
736
737 <p>
738 Now you can start the cpufreqd daemon. Add it to the <c>default</c> and
739 <c>battery</c> runlevel as well.
740 </p>
741
742 <pre caption="Starting cpufreqd">
743 # <i>rc-update add cpufreqd default battery</i>
744 # <i>rc</i>
745 </pre>
746
747 <p>
748 Sometimes it can be desirable to select another policy than the daemon chooses,
749 for example when battery power is low, but you know that AC will be available
750 soon. In that case you can turn on cpufreqd's manual mode with <c>cpufreqd-set
751 manual</c> and select one of your configured policies (as listed by
752 <c>cpufreqd-get</c>). You can leave manual mode by executing <c>cpufreqd-set
753 dynamic</c>.
754 </p>
755
756 <warn>
757 Do not run more than one of the above programs at the same time. It may cause
758 confusion like switching between two frequencies all the time.
759 </warn>
760
761 </body>
762 </section>
763 <section>
764 <title>Verifying the result</title>
765 <body>
766
767 <p>
768 The last thing to check is that your new policies do a good job. An easy way to
769 do so is monitoring CPU speed while working with your laptop:
770 </p>
771
772 <pre caption="Monitoring CPU speed">
773 # <i>watch grep \"cpu MHz\" /proc/cpuinfo</i>
774 </pre>
775
776 <p>
777 If <path>/proc/cpuinfo</path> doesn't get updated (see <uri
778 link="#doc_chap8">Troubleshooting</uri>), monitor the CPU frequency with:
779 </p>
780
781 <pre caption="Alternative CPU speed monitoring">
782 # <i>watch x86info -mhz</i>
783 </pre>
784
785 <p>
786 Depending on your setup, CPU speed should increase on heavy load, decrease on
787 no activity or just stay at the same level. When using <c>cpufreqd</c> and
788 verbosity set to 5 or higher in <path>cpufreqd.conf</path> you'll get
789 additional information about what's happening reported to <c>syslog</c>.
790 </p>
791
792 </body>
793 </section>
794 </chapter>
795
796 <chapter>
797 <title>LCD Power Management</title>
798 <section>
799 <body>
800
801 <p>
802 As you can see in <uri link="#doc_chap1_fig1">figure 1.1</uri>, the LCD
803 display consumes the biggest part of energy (might not be the case for
804 non-mobile CPU's). Thus it's quite important not only to shut the display off
805 when not needed, but also to reduce it's backlight if possible. Most laptops
806 offer the possibility to control the backlight dimming.
807 </p>
808
809 </body>
810 </section>
811 <section>
812 <title>Standby settings</title>
813 <body>
814
815 <p>
816 The first thing to check is the standby/suspend/off timings of the display. As
817 this depends heavily on your windowmanager, I'll let you figure it out
818 yourself. Just two common places: Blanking the terminal can be done with
819 <c>setterm -blank &lt;number-of-minutesM&gt;</c>, <c>setterm -powersave on</c>
820 and <c>setterm -powerdown &lt;number-of-minutesM&gt;</c>. For X.org, modify
821 <path>/etc/X11/xorg.conf</path> similar to this:
822 </p>
823
824 <pre caption="LCD suspend settings in X.org and XFree86">
825 Section "ServerLayout"
826 Identifier [...]
827 [...]
828 Option "BlankTime" "5" <comment># Blank the screen after 5 minutes (Fake)</comment>
829 Option "StandbyTime" "10" <comment># Turn off screen after 10 minutes (DPMS)</comment>
830 Option "SuspendTime" "20" <comment># Full suspend after 20 minutes</comment>
831 Option "OffTime" "30" <comment># Turn off after half an hour</comment>
832 [...]
833 EndSection
834
835 [...]
836
837 Section "Monitor"
838 Identifier [...]
839 Option "DPMS" "true"
840 [...]
841 EndSection
842 </pre>
843
844 <p>
845 This is the same for XFree86 and <path>/etc/X11/XF86Config</path>.
846 </p>
847
848 </body>
849 </section>
850 <section>
851 <title>Backlight dimming</title>
852 <body>
853
854 <p>
855 Probably more important is the backlight dimming. If you have access to the
856 dimming settings via a tool, write a small script that dims the backlight in
857 battery mode and place it in your <c>battery</c> runlevel. The following script
858 should work on most IBM Thinkpads and Toshiba laptops. You've got to enable the
859 appropriate option in your kernel (IBM Thinkpads only). For Toshiba laptops,
860 install <c>sys-power/acpitool</c> and skip configuration of <c>ibm_acpi</c> as
861 described below.
862 </p>
863
864 <warn>
865 Support for setting brightness is marked experimental in ibm-acpi. It accesses
866 hardware directly and may cause severe harm to your system. Please read the
867 <uri link="http://ibm-acpi.sourceforge.net/">ibm-acpi website</uri>
868 </warn>
869
870 <p>
871 To be able to set the brightness level, the ibm_acpi module has to be loaded
872 with the experimental parameter.
873 </p>
874
875 <pre caption="automatically loading the ibm_acpi module">
876 <comment>(Please read the warnings above before doing this!)</comment>
877 # <i>echo "options ibm_acpi experimental=1" >> /etc/modules.d/ibm_acpi</i>
878 # <i>/sbin/update-modules</i>
879 # <i>echo ibm_acpi >> /etc/modules.autoload.d/kernel-2.6</i>
880 # <i>modprobe ibm_acpi</i>
881 </pre>
882
883 <p>
884 This should work without error messages and a file
885 <path>/proc/acpi/ibm/brightness</path> should be created after loading the
886 module. An init script will take care of choosing the brightness according to
887 the power source.
888 </p>
889
890 <pre caption="/etc/conf.d/lcd-brightness">
891 <comment># See /proc/acpi/ibm/brightness for available values</comment>
892 <comment># Please read /usr/src/linux/Documentation/ibm-acpi.txt</comment>
893
894 <comment># brightness level in ac mode. Default is 7.</comment>
895 BRIGHTNESS_AC=7
896
897 <comment># brightness level in battery mode. Default is 4.</comment>
898 BRIGHTNESS_BATTERY=4
899 </pre>
900
901 <pre caption="/etc/init.d/lcd-brightness">
902 #!/sbin/runscript
903
904 set_brightness() {
905 if on_ac_power
906 then
907 LEVEL=${BRIGHTNESS_AC:-7}
908 else
909 LEVEL=${BRIGHTNESS_BATTERY:-4}
910 fi
911
912 if [ -f /proc/acpi/ibm/brightness ]
913 then
914 ebegin "Setting LCD brightness"
915 echo "level ${LEVEL}" > /proc/acpi/ibm/brightness
916 eend $?
917 elif [[ -e /usr/bin/acpitool &amp;&amp; -n $(acpitool -T | grep "LCD brightness") ]]
918 then
919 ebegin "Setting LCD brightness"
920 acpitool -l $LEVEL >/dev/null || ewarn "Unable to set lcd brightness"
921 eend $?
922 else
923 ewarn "Setting LCD brightness is not supported."
924 ewarn "For IBM Thinkpads, check that ibm_acpi is loaded into the kernel"
925 ewarn "For Toshiba laptops, you've got to install sys-power/acpitool"
926 fi
927 }
928
929 start() {
930 set_brightness
931 }
932
933 stop () {
934 set_brightness
935 }
936 </pre>
937
938 <p>
939 When done, make sure brightness is adjusted automatically by adding it to the
940 battery runlevel.
941 </p>
942
943 <pre caption="Enabling automatic brightness adjustment">
944 # <i>chmod +x /etc/init.d/lcd-brightness</i>
945 # <i>rc-update add lcd-brightness battery</i>
946 # <i>rc</i>
947 </pre>
948
949 </body>
950 </section>
951 </chapter>
952
953 <chapter>
954 <title>Disk Power Management</title>
955 <section>
956 <body>
957
958 <p>
959 Hard disks consume less energy in sleep mode. Therefore it makes sense to
960 activate power saving features whenever the hard disk is not used for a certain
961 amount of time. I'll show you two alternative possibilities to do it. First,
962 laptop-mode will save most energy due to several measures which prevent or at
963 least delay write accesses. The drawback is that due to the delayed write
964 accesses a power outage or kernel crash will be more dangerous for data loss.
965 If you don't like this, you have to make sure that there are no processes which
966 write to your hard disk frequently. Afterwards you can enable power saving
967 features of your hard disk with <c>hdparm</c> as the second alternative.
968 </p>
969
970 </body>
971 </section>
972 <section>
973 <title>Increasing idle time - laptop-mode</title>
974 <body>
975
976 <p>
977 Recent 2.6 kernels include the so-called <c>laptop-mode</c>. When activated,
978 dirty buffers are written to disk on read calls or after 10 minutes (instead of
979 30 seconds). This minimizes the time the hard disk needs to be spun up.
980 </p>
981
982 <pre caption="Automated start of laptop-mode">
983 # <i>emerge laptop-mode-tools</i>
984 </pre>
985
986 <p>
987 <c>laptop-mode-tools</c> has its configuration file in
988 <path>/etc/laptop-mode/laptop-mode.conf</path>. Adjust it the way you like it,
989 it's well commented. Run <c>rc-update add laptop_mode battery</c> to start it
990 automatically.
991 </p>
992
993 <p>
994 Recent versions (1.11 and later) of laptop-mode-tools include a new tool
995 <c>lm-profiler</c>. It will monitor your system's disk usage and running
996 network services and suggests to disable unneeded ones. You can either disable
997 them through laptop-mode-tools builtin runlevel support (which will be reverted
998 by Gentoo's <c>/sbin/rc</c>) or use your <c>default</c>/<c>battery</c>
999 runlevels (recommended).
1000 </p>
1001
1002 <pre caption="Sample output from running lm-profiler">
1003 # <i>lm-profiler</i>
1004 Profiling session started.
1005 Time remaining: 600 seconds
1006 [4296896.602000] amarokapp
1007 Time remaining: 599 seconds
1008 [4296897.714000] sort
1009 [4296897.970000] mv
1010 Time remaining: 598 seconds
1011 Time remaining: 597 seconds
1012 [4296900.482000] reiserfs/0
1013 </pre>
1014
1015 <p>
1016 After profiling your system for ten minutes, lm-profiler will present a list of
1017 services which might have caused disk accesses during that time.
1018 </p>
1019
1020 <pre caption="lm-profiler suggests to disable some services">
1021 Program: "atd"
1022 Reason: standard recommendation (program may not be running)
1023 Init script: /etc/init.d/atd (GUESSED)
1024
1025 Do you want to disable this service in battery mode? [y/N]: <i>n</i>
1026 </pre>
1027
1028 <p>
1029 To disable atd as suggested in the example above, you would run <c>rc-update
1030 del atd battery</c>. Be careful not to disable services that are needed for
1031 your system to run properly - <c>lm-profiler</c> is likely to generate some
1032 false positives. Do not disable a service if you are unsure whether it's
1033 needed.
1034 </p>
1035
1036 </body>
1037 </section>
1038 <section>
1039 <title>Limiting Write Accesses</title>
1040 <body>
1041
1042 <p>
1043 If you don't want to use laptop-mode, you must take special care to disable
1044 services that write to your disk frequently - <c>syslogd</c> is a good
1045 candidate, for example. You probably don't want to shut it down completely, but
1046 it's possible to modify the config file so that "unnecessary" things don't get
1047 logged and thus don't create disk traffic. <c>Cups</c> writes to disk
1048 periodically, so consider shutting it down and only enable it manually when
1049 needed.
1050 </p>
1051
1052 <pre caption="Disabling cups in battery mode">
1053 # <i>rc-update del cupsd battery</i>
1054 </pre>
1055
1056 <p>
1057 You can also use <c>lm-profiler</c> from laptop-mode-tools (see above) to find
1058 services to disable. Once you eliminated all of them, go on with configuring
1059 hdparm.
1060 </p>
1061
1062 </body>
1063 </section>
1064 <section>
1065 <title>hdparm</title>
1066 <body>
1067
1068 <p>
1069 The second possibility is using <c>hdparm</c>. Skip this if
1070 you are using laptop-mode. Otherwise, edit <path>/etc/conf.d/hdparm</path> and
1071 add the following values to your drive entries. This example assumes your hard
1072 drive is called <b>hda</b>:
1073 </p>
1074
1075 <pre caption="Using /etc/conf.d/hdparm for disk standby">
1076 hda_args="-q -S12"
1077 </pre>
1078
1079 <p>
1080 This will activate power management for your hard drive. If you ever want to
1081 deactivate power management, you can edit <path>/etc/conf.d/hdparm</path> and
1082 change the values to <c>-q -S0</c>, or just run <c>hdparm -q -S0 /dev/hda</c>.
1083 </p>
1084
1085 <p>
1086 See <c>man hdparm</c> for the options. Though you can always start <c>hdparm</c>
1087 manually when you are on battery power by running <c>/etc/init.d/hdparm
1088 start</c>, it's much easier to automate its startup and shutdown. To do so, add
1089 <c>hdparm</c> to the battery runlevel so that it will automatically enable power
1090 management.
1091 </p>
1092
1093 <pre caption="Automate disk standby settings">
1094 # <i>rc-update add hdparm battery</i>
1095 </pre>
1096
1097 <impo>
1098 Be careful with sleep/spin down settings of your hard drive. Setting it to
1099 small values might wear out your drive and lose warranty.
1100 </impo>
1101
1102 </body>
1103 </section>
1104 <section>
1105 <title>Other tricks</title>
1106 <body>
1107
1108 <p>
1109 Another possibility is to deactivate swap in battery mode. Before writing a
1110 swapon/swapoff switcher, make sure there is enough RAM and swap isn't used
1111 heavily, otherwise you'll be in big problems.
1112 </p>
1113
1114 <p>
1115 If you don't want to use laptop-mode, it's still possible to minimize disk
1116 access by mounting certain directories as <c>tmpfs</c> - write accesses are not
1117 stored on a disk, but in main memory and get lost with unmounting. Often it's
1118 useful to mount <path>/tmp</path> like this - you don't have to pay special
1119 attention as it gets cleared on every reboot regardless whether it was mounted
1120 on disk or in RAM. Just make sure you have enough RAM and no program (like a
1121 download client or compress utility) needs extraordinary much space in
1122 <path>/tmp</path>. To activate this, enable tmpfs support in your kernel and
1123 add a line to <path>/etc/fstab</path> like this:
1124 </p>
1125
1126 <pre caption="Editing /etc/fstab to make /tmp even more volatile">
1127 none /tmp tmpfs size=32m 0 0
1128 </pre>
1129
1130 <warn>
1131 Pay attention to the size parameter and modify it for your system. If you're
1132 unsure, don't try this at all, it can become a performance bottleneck easily. In
1133 case you want to mount <path>/var/log</path> like this, make sure to merge the
1134 log files to disk before unmounting. They are essential. Don't attempt to mount
1135 <path>/var/tmp</path> like this. Portage uses it for compiling...
1136 </warn>
1137
1138 </body>
1139 </section>
1140 </chapter>
1141
1142 <chapter>
1143 <title>Power Management For Other Devices</title>
1144 <section>
1145 <title>Graphics Cards</title>
1146 <body>
1147
1148 <p>
1149 In case you own an ATI graphics card supporting PowerPlay (dynamic clock
1150 scaling for the graphics processing unit GPU), you can activate this
1151 feature in X.org. Open <path>/etc/X11/xorg.conf</path> and add (or enable) the
1152 <c>DynamicClocks</c> option in the Device section. Please notice that this
1153 feature will lead to crashes on some systems.
1154 </p>
1155
1156 <pre caption="Enabling ATI PowerPlay support in X.org">
1157 Section "Device"
1158 [...]
1159 Option "DynamicClocks" "on"
1160 EndSection
1161 </pre>
1162
1163 </body>
1164 </section>
1165 <section>
1166 <title>Wireless Power Management</title>
1167 <body>
1168
1169 <p>
1170 Wireless LAN cards consume quite a bit of energy. Put them in Power Management
1171 mode just like your hard drives.
1172 </p>
1173
1174 <note>
1175 This script assumes your wireless interface is called <c>wlan0</c>; replace
1176 this with the actual name of your interface.
1177 </note>
1178
1179 <p>
1180 Add the following option to <path>/etc/conf.d/net</path> to automatically enable
1181 power management for your wireless card:
1182 </p>
1183
1184 <pre caption="Automated WLAN Power Management">
1185 iwconfig_wlan0="power on"
1186 </pre>
1187
1188 <p>
1189 See <c>man iwconfig</c> for details and more options like the period between
1190 wakeups or timeout settings. If your driver and access point support changing
1191 the beacon time, this is a good starting point to save even more energy.
1192 </p>
1193
1194 </body>
1195 </section>
1196 <section>
1197 <title>USB Power Management</title>
1198 <body>
1199
1200 <p>
1201 There are two problems with USB devices regarding energy consumption: First,
1202 devices like USB mice, digital cameras or USB sticks consume energy while
1203 plugged in. You cannot avoid this (nevertheless remove them in case they're not
1204 needed). Second, when there are USB devices plugged in, the USB host controller
1205 periodically accesses the bus which in turn prevents the CPU from going into
1206 sleep mode. The kernel offers an experimental option to enable suspension of
1207 USB devices through driver calls or one of the <path>power/state</path> files
1208 in <path>/sys</path>.
1209 </p>
1210
1211 <pre caption="Enabling USB suspend support in the kernel">
1212 Device Drivers
1213 USB support
1214 [*] Support for Host-side USB
1215 [*] USB suspend/resume (EXPERIMENTAL)
1216 </pre>
1217
1218 </body>
1219 </section>
1220 </chapter>
1221
1222 <chapter>
1223 <title>Sleep States: sleep, standby, and suspend to disk</title>
1224 <section>
1225 <body>
1226
1227 <p>
1228 ACPI defines different sleep states. The more important ones are
1229 </p>
1230
1231 <ul>
1232 <li>S1 aka Standby</li>
1233 <li>S3 aka Suspend to RAM aka Sleep</li>
1234 <li>S4 aka Suspend to Disk aka Hibernate</li>
1235 </ul>
1236
1237 <p>
1238 They can be called whenever the system is not in use, but a shutdown is not
1239 wanted due to the long boot time.
1240 </p>
1241
1242 </body>
1243 </section>
1244 <section>
1245 <title>Sleep (S3)</title>
1246 <body>
1247
1248 <p>
1249 The ACPI support for these sleep states is marked experimental for good reason.
1250 APM sleep states seem to be more stable, however you can't use APM and ACPI
1251 together.
1252 </p>
1253
1254 <pre caption="Kernel configuration for the various suspend types">
1255 Power Management Options ---&gt;
1256 [*] Power Management support
1257 ACPI (Advanced Configuration and Power Interface) Support ---&gt;
1258 [*] ACPI Support
1259 [*] Sleep States
1260 </pre>
1261
1262 <p>
1263 Once your kernel is properly configured, you can use the
1264 <c>hibernate-script</c> to activate suspend or sleep mode. Let's install that
1265 first.
1266 </p>
1267
1268 <pre caption="Installing the hibernate-script">
1269 # <i>emerge hibernate-script</i>
1270 </pre>
1271
1272 <p>
1273 Some configuration has to be done in <path>/etc/hibernate</path>. The default
1274 package introduces a few configuration files for each sleep state. Options that
1275 are common to all suspend methods are placed in <path>common.conf</path>; make
1276 sure this file is properly set up for your system.
1277 </p>
1278
1279 <p>
1280 To configure sleep, edit <path>sysfs-ram.conf</path> in
1281 <path>/etc/hibernate</path>. <c>UseSysfsPowerState mem</c> is already setup
1282 correctly, but if you need to make further changes to this particular sleep
1283 state (or any other sleep state) you should add them to
1284 <path>/etc/hibernate/hibernate.conf</path>. The comments and option names will
1285 guide you. If you use nfs or samba shares over the network, make sure to
1286 shutdown the appropriate init scripts to avoid timeouts.
1287 </p>
1288
1289 <note>
1290 For more information on setting up sleep states, read <c>man
1291 hibernate.conf</c>.
1292 </note>
1293
1294 <p>
1295 Ready? Now is the last chance to backup any data you want to keep after
1296 executing the next command. Notice that you probably have to hit a special key
1297 like <c>Fn</c> to resume from sleep.
1298 </p>
1299
1300 <pre caption="Calling sleep">
1301 # <i>hibernate-ram</i>
1302 </pre>
1303
1304 <p>
1305 If you're still reading, it seems to work. You can also setup standby (S1) in a
1306 similar way by editing <path>sysfs-ram.conf</path> and changing
1307 "UseSysfsPowerState mem" to "UseSysfsPowerState standby". S3 and S4 are the more
1308 interesting sleep states due to greater energy savings however.
1309 </p>
1310
1311 </body>
1312 </section>
1313 <section>
1314 <title>Hibernate (S4)</title>
1315 <body>
1316
1317 <p>
1318 This section introduces hibernation, where a snapshot of the running system is
1319 written to disk before powering off. On resume, the snapshot is loaded and you
1320 can go on working at exactly the point you called hibernate before.
1321 </p>
1322
1323 <warn>
1324 Don't exchange non hot-pluggable hardware when suspended. Don't attempt to load
1325 a snapshot with a different kernel image than the one it was created with.
1326 Shutdown any NFS or samba server/client before hibernating.
1327 </warn>
1328
1329 <p>
1330 There are two different implementations for S4. The original one is swsusp,
1331 then there is the newer suspend2 with a nicer interface (including fbsplash
1332 support). A <uri link="http://suspend2.net/features.html#compare"> feature
1333 comparison</uri> is available at the <uri link="http://suspend2.net"> suspend2
1334 Homepage</uri>. There used to be Suspend-to-Disk (pmdisk), a fork of swsusp,
1335 but it has been merged back.
1336 </p>
1337
1338 <p>
1339 Suspend2 is not included in the mainline kernel yet, therefore you either have
1340 to patch your kernel sources with the patches provided by <uri
1341 link="http://suspend2.net">suspend2.net</uri> or use
1342 <c>sys-kernel/suspend2-sources</c>.
1343 </p>
1344
1345 <p>
1346 The kernel part for both swusp and suspend2 is as follows:
1347 </p>
1348
1349 <pre caption="Kernel configuration for the various suspend types">
1350 Power Management Options ---&gt;
1351 <comment>(hibernate with swsusp)</comment>
1352 [*] Software Suspend
1353 <comment>(replace /dev/SWAP with your swap partition)</comment>
1354 (/dev/SWAP) Default resume partition
1355
1356 <comment>(hibernate with suspend2)</comment>
1357 Software Suspend 2
1358 --- Image Storage (you need at least one writer)
1359 [*] File Writer
1360 [*] Swap Writer
1361 --- General Options
1362 [*] LZF image compression
1363 <comment>(replace /dev/SWAP with your swap partition)</comment>
1364 (swap:/dev/SWAP) Default resume device name
1365 [ ] Allow Keep Image Mode
1366 </pre>
1367
1368 <p>
1369 The configuration for swsusp is rather easy. If you didn't store the location
1370 of your swap partition in the kernel config, you can also pass it as a
1371 parameter with the <c>resume=/dev/SWAP</c> directive. If booting is not
1372 possible due to a broken image, use the <c>noresume</c> kernel parameter. The
1373 <c>hibernate-cleanup</c> init script invalidates swsusp images during the boot
1374 process.
1375 </p>
1376
1377 <pre caption="Invalidating swsusp images during the boot process">
1378 # <i>rc-update add hibernate-cleanup boot</i>
1379 </pre>
1380
1381 <p>
1382 To activate hibernate with swsusp, use the hibernate script and set
1383 <c>UseSysfsPowerState disk</c> in <path>/etc/hibernate/sysfs-disk</path>.
1384 </p>
1385
1386 <warn>
1387 Backup your data before doing this. Run <c>sync</c> before executing one of the
1388 commands to have cached data written to disk. First try it outside of X, then
1389 with X running, but not logged in.
1390 </warn>
1391
1392 <p>
1393 If you experience kernel panics due to uhci or similar, try to compile USB
1394 support as module and unload the modules before sending your laptop to sleep
1395 mode. There are configuration options for this in <path>common.conf</path>
1396 </p>
1397
1398 <pre caption="Hibernating with swsusp">
1399 # <i>nano -w /etc/hibernate/common.conf</i>
1400 <comment>(Make sure you have a backup of your data)</comment>
1401 # <i>hibernate</i>
1402 </pre>
1403
1404 <p>
1405 The following section discusses the setup of suspend2 including fbsplash
1406 support for a nice graphical progress bar during suspend and resume.
1407 </p>
1408
1409 <p>
1410 The first part of the configuration is similar to the configuration of swsusp.
1411 In case you didn't store the location of your swap partition in the kernel
1412 config, you have to pass it as a kernel parameter with the
1413 <c>resume2=swap:/dev/SWAP</c> directive. If booting is not possible due to a
1414 broken image, append the <c>noresume2</c> parameter. Additionally, the
1415 <c>hibernate-cleanup</c> init script invalidates suspend2 images during the
1416 boot process.
1417 </p>
1418
1419 <pre caption="Invalidating suspend2 images during the boot process">
1420 # <i>rc-update add hibernate-cleanup boot</i>
1421 </pre>
1422
1423 <p>
1424 Now edit <path>/etc/hibernate/suspend2.conf</path>, enable the <c>suspend2</c>
1425 options you need. Do not enable the <c>fbsplash</c> options in
1426 <c>common.conf</c> just yet.
1427 </p>
1428
1429 <pre caption="Hibernating with suspend2">
1430 # <i>nano -w /etc/hibernate/suspend2.conf</i>
1431 <comment>(Make sure you have a backup of your data)</comment>
1432 # <i>hibernate</i>
1433 </pre>
1434
1435 <p>
1436 Please configure <c>fbsplash</c> now if you didn't do already. To enable
1437 fbsplash support during hibernation, the <c>sys-apps/suspend2-userui</c>
1438 package is needed. Additionally, you've got to enable the <c>fbsplash</c> USE
1439 flag.
1440 </p>
1441
1442 <pre caption="Installing suspend2-userui">
1443 # <i>echo "sys-apps/suspend2-userui fbsplash" >> /etc/portage/package.use</i>
1444 <comment>(It may be marked ~arch, so first it must be keyworded)</comment>
1445 # <i>echo "sys-apps/suspend2-userui" >> /etc/portage/package.keywords</i>
1446 # <i>emerge suspend2-userui</i>
1447 </pre>
1448
1449 <p>
1450 The ebuild tells you to make a symlink to the theme you want to use. For
1451 example, to use the <c>livecd-2005.1</c> theme, run the following command:
1452 </p>
1453
1454 <pre caption="Using the livecd-2005.1 theme during hibernation">
1455 # <i>ln -sfn /etc/splash/livecd-2005.1 /etc/splash/suspend2</i>
1456 </pre>
1457
1458 <p>
1459 If you don't want a black screen in the first part of the resume process, you
1460 have to add the <c>suspend2ui_fbsplash</c> tool to your initrd image. Assuming
1461 you created the initrd image with <c>splash_geninitramfs</c> and saved it as
1462 <path>/boot/fbsplash-emergence-1024x768</path>, here's how to do that.
1463 </p>
1464
1465 <pre caption="Adding suspend2ui_fbsplash to an initrd image">
1466 # <i>mount /boot</i>
1467 # <i>mkdir ~/initrd.d</i>
1468 # <i>cp /boot/fbsplash-emergence-1024x768 ~/initrd.d/</i>
1469 # <i>cd ~/initrd.d</i>
1470 # <i>gunzip -c fbsplash-emergence-1024x768 | cpio -idm --quiet -H newc</i>
1471 # <i>rm fbsplash-emergence-1024x768</i>
1472 # <i>cp /usr/sbin/suspend2ui_fbsplash sbin/</i>
1473 # <i>find . | cpio --quiet --dereference -o -H newc | gzip -9 > /boot/fbsplash-suspend2-emergence-1024x768</i>
1474 </pre>
1475
1476 <p>
1477 Afterwards adjust <path>grub.conf</path> (or <path>lilo.conf</path>) so that
1478 your suspend2 kernel uses
1479 <path>/boot/fbsplash-suspend2-emergence-1024x768</path> as initrd image. You can
1480 now test a dry run to see if everything is setup correctly.
1481 </p>
1482
1483 <pre caption="Test run for fbsplash hibernation">
1484 # <i>suspend2ui_fbsplash -t</i>
1485 </pre>
1486
1487 <p>
1488 Afterwards open <path>/etc/hibernate/common.conf</path> and activate the
1489 fbsplash options. Execute <c>hibernate</c> and enjoy.
1490 </p>
1491
1492 </body>
1493 </section>
1494 </chapter>
1495
1496 <chapter>
1497 <title>Troubleshooting</title>
1498 <section>
1499 <body>
1500
1501 <p>
1502 <e>Q:</e> I'm trying to change the CPU frequency, but
1503 <path>/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor</path> does not
1504 exist.
1505 </p>
1506
1507 <p>
1508 <e>A:</e> Make sure your processor supports CPU frequency scaling and you chose
1509 the right CPUFreq driver for your processor. Here is a list of processors that
1510 are supported by cpufreq (kernel 2.6.7): ARM Integrator, ARM-SA1100,
1511 ARM-SA1110, AMD Elan - SC400, SC410, AMD mobile K6-2+, AMD mobile K6-3+, AMD
1512 mobile Duron, AMD mobile Athlon, AMD Opteron, AMD Athlon 64, Cyrix Media GXm,
1513 Intel mobile PIII and Intel mobile PIII-M on certain chipsets, Intel Pentium 4,
1514 Intel Xeon, Intel Pentium M (Centrino), National Semiconductors Geode GX,
1515 Transmeta Crusoe, VIA Cyrix 3 / C3, UltraSPARC-III, SuperH SH-3, SH-4, several
1516 "PowerBook" and "iBook2" and various processors on some ACPI 2.0-compatible
1517 systems (only if "ACPI Processor Performance States" are available to the
1518 ACPI/BIOS interface).
1519 </p>
1520
1521 <p>
1522 <e>Q:</e> My laptop supports frequency scaling, but
1523 <path>/sys/devices/system/cpu/cpu0/cpufreq/</path> is empty.
1524 </p>
1525
1526 <p>
1527 <e>A:</e> Look for ACPI related error messages with <c>dmesg | grep ACPI</c>.
1528 Try to update the BIOS, especially if a broken DSDT is reported. You can also
1529 try to fix it yourself (which is beyond the scope of this guide).
1530 </p>
1531
1532 <p>
1533 <e>Q:</e> My laptop supports frequency scaling, but according to
1534 <path>/proc/cpuinfo</path> the speed never changes.
1535 </p>
1536
1537 <p>
1538 <e>A:</e> Probably you have activated symmetric multiprocessing support
1539 (CONFIG_SMP) in your kernel. Deactivate it and it should work. Some older
1540 kernels had a bug causing this. In that case, run <c>emerge x86info</c>, update
1541 your kernel as asked and check the current frequency with
1542 <c>x86info -mhz</c>.
1543 </p>
1544
1545 <p>
1546 <e>Q:</e> I can change the CPU frequency, but the range is not as wide as in
1547 another OS.
1548 </p>
1549
1550 <p>
1551 <e>A:</e> You can combine frequency scaling with ACPI throttling to get a lower
1552 minimum frequency. Notice that throttling doesn't save much energy and is
1553 mainly used for thermal management (keeping your laptop cool and quiet). You
1554 can read the current throttling state with <c>cat
1555 /proc/acpi/processor/CPU/throttling</c> and change it with <c>echo -n "0:x" >
1556 /proc/acpi/processor/CPU/limit</c>, where x is one of the Tx states listed in
1557 <path>/proc/acpi/processor/CPU/throttling</path>.
1558 </p>
1559
1560 <p>
1561 <e>Q:</e> When configuring the kernel, powersave, performance and userspace
1562 governors show up, but that ondemand thing is missing. Where do I get it?
1563 </p>
1564
1565 <p>
1566 <e>A:</e> The ondemand governor is only included in recent kernel sources. Try
1567 updating them.
1568 </p>
1569
1570 <p>
1571 <e>Q:</e> Battery life time seems to be worse than before.
1572 </p>
1573
1574 <p>
1575 <e>A:</e> Check your BIOS settings. Maybe you forgot to re-enable some of the
1576 settings.
1577 </p>
1578
1579 <p>
1580 <e>Q:</e> My battery is charged, but KDE reports there would be 0% left and
1581 immediately shuts down.
1582 </p>
1583
1584 <p>
1585 <e>A:</e> Check that battery support is compiled into your kernel. If you use
1586 it as a module, make sure the module is loaded.
1587 </p>
1588
1589 <p>
1590 <e>Q:</e> My system logger reports things like "logger: ACPI group battery /
1591 action battery is not defined".
1592 </p>
1593
1594 <p>
1595 <e>A:</e> This message is generated by the <path>/etc/acpi/default.sh</path>
1596 script that is shipped with acpid. You can safely ignore it. If you like to get
1597 rid of it, you can comment the appropriate line in
1598 <path>/etc/acpi/default.sh</path> as shown below:
1599 </p>
1600
1601 <pre caption="Disabling warnings about unknown acpi events">
1602 *) # logger "ACPI action $action is not defined"
1603 </pre>
1604
1605 <p>
1606 <e>Q:</e> I have a Dell Inspiron 51XX and I don't get any ACPI events.
1607 </p>
1608
1609 <p>
1610 <e>A:</e> This seems to be a kernel bug. Read on <uri
1611 link="http://bugme.osdl.org/show_bug.cgi?id=1752">here</uri>.
1612 </p>
1613
1614 <p>
1615 <e>Q:</e> I activated the <c>DynamicClocks</c> option in <path>xorg.conf</path>
1616 and now X.org crashes / the screen stays black / my laptop doesn't shutdown
1617 properly.
1618 </p>
1619
1620 <p>
1621 <e>A:</e> This happens on some systems. You have to disable
1622 <c>DynamicClocks</c>.
1623 </p>
1624
1625 <p>
1626 <e>Q:</e> I want to use suspend2, but it tells me my swap partition is too
1627 small. Resizing is not an option.
1628 </p>
1629
1630 <p>
1631 <e>A:</e> If there is enough free space on your system, you can use the
1632 filewriter instead of the swapwriter. The <c>hibernate-script</c> supports it
1633 as well. More information can be found in
1634 <path>/usr/src/linux/Documentation/power/suspend2.txt</path>.
1635 </p>
1636
1637 <p>
1638 <e>Q:</e> I just bought a brand new battery, but it only lasts for some
1639 minutes! What am I doing wrong?
1640 </p>
1641
1642 <p>
1643 <e>A:</e> First follow your manufacturer's advice on how to charge the battery
1644 correctly.
1645 </p>
1646
1647 <p>
1648 <e>Q:</e> The above didn't help. What should I do then?
1649 </p>
1650
1651 <p>
1652 <e>A:</e> Some batteries sold as "new" are in fact old ones. Try the following:
1653 </p>
1654
1655 <pre caption="Querying battery state">
1656 $ <i>grep capacity /proc/acpi/battery/BAT0/info</i>
1657 design capacity: 47520 mWh
1658 last full capacity: 41830 mWh
1659 </pre>
1660
1661 <p>
1662 If the "last full capacity" differs significantly from the design capacity,
1663 your battery is probably broken. Try to claim your warranty.
1664 </p>
1665
1666 <p>
1667 <e>Q:</e> My problem is not listed above. Where should I go next?
1668 </p>
1669
1670 <p>
1671 <e>A:</e> Don't fear to contact me, <mail link="earthwings@gentoo.org">Dennis
1672 Nienhüser</mail>, directly. The <uri link="http://forums.gentoo.org">Gentoo
1673 Forums</uri> are a good place to get help as well. If you prefer IRC, try the
1674 <c>#gentoo-laptop</c> channel at <uri
1675 link="irc://irc.freenode.net">irc.freenode.net</uri>.
1676 </p>
1677
1678 </body>
1679 </section>
1680 </chapter>
1681 </guide>

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