old-www/LDP/Mobile-Guide/html/mobile-guide-p6a5s7-power-s...

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML
><HEAD
><TITLE
>Power Saving Techniques</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
REL="HOME"
TITLE="Linux on the Road"
HREF="index.html"><LINK
REL="UP"
TITLE="Dealing with Limited Resources or Tuning the System"
HREF="mobile-guide-a5-limited-resources.html"><LINK
REL="PREVIOUS"
TITLE="Low CPU Speed"
HREF="mobile-guide-p6a5s6-low-cpu-speed.html"><LINK
REL="NEXT"
TITLE="Kernel"
HREF="mobile-guide-p6a5s8-kernel.html"></HEAD
><BODY
CLASS="sect1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>Linux on the Road: </TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="mobile-guide-p6a5s6-low-cpu-speed.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Appendix E. Dealing with Limited Resources or Tuning the System</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="mobile-guide-p6a5s8-kernel.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="mobile-guide-p6a5s7-power-saving-techniques"
></A
>E.7. Power Saving Techniques</H1
><P
>&#13;
<P
></P
><OL
TYPE="1"
><LI
><P
>&#13;   If you don't need infrared support, disable it in the
   <SPAN
CLASS="acronym"
>BIOS</SPAN
> or shutdown the <SPAN
CLASS="trademark"
>IrDA</SPAN
>&reg; device driver. There are also some
   <SPAN
CLASS="trademark"
>IrDA</SPAN
>&reg; features of the kernel
   which are useful for saving power.
</P
></LI
><LI
><P
>&#13;   <SPAN
CLASS="acronym"
>PCMCIA</SPAN
> services consume much power, so shut them down if you don't need them.
</P
></LI
><LI
><P
>&#13;   I'm not sure to which extend the <EM
>backlight</EM
> consumes power.
</P
><DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="../images/warning.gif"
HSPACE="5"
ALT="Warning"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>&#13;


   As far as I know this device can only bear a limited
   number of uptime circles. So avoid using screensavers,
   which turn off the backlight.
</P
></TD
></TR
></TABLE
></DIV
><P
>&#13;   If you want do it anyhow, you may use <B
CLASS="command"
>xset +dpms</B
>
   and <B
CLASS="command"
>xset dpms 0 0 300</B
> This turns the screen off
   after 5 minutes of inactivity. Works only if the display is DPMS
   capable.
</P
></LI
><LI
><P
>&#13;   For some examples to build batteries with increased uptime up to
   8 hours look at
   <A
HREF="http://repair4laptop.org/notebook_battery.html"
TARGET="_top"
>Repair4Laptop: Battery</A
>
   .
</P
></LI
><LI
><P
>&#13;   For information about <SPAN
CLASS="acronym"
>APM</SPAN
> look at the chapter
   <SPAN
CLASS="acronym"
>APM</SPAN
> above.
</P
></LI
><LI
><P
>&#13;   The "noatime" option when mouting filesystems tells the kernel to
   <EM
>not</EM
> update the <EM
>access time</EM
>
   information of the file. This information, although sometimes useful, is
   not used by most people. Therefore, you can safely disable it, then
   preventing disk access each time you <B
CLASS="command"
>cat</B
> a file. Here
   is an example of a <TT
CLASS="filename"
>/etc/fstab</TT
> with this
   power-saving option: <B
CLASS="command"
> /dev/hda7 /var ext2 defaults,noatime 0 2
   </B
>

</P
></LI
><LI
><P
>&#13;<A
HREF="http://sourceforge.net/projects/hdparm/"
TARGET="_top"
>hdparm</A
>
<EM
>hdparm</EM
> is a Linux disk utility that lets you
set spin-down timeouts and other disk parameters.
</P
></LI
><LI
><P
>&#13;   <A
HREF="http://www.complang.tuwien.ac.at/ulrich/linux/tips.html"
TARGET="_top"
>Mobile Update Daemon</A
>
   This is a drop-in replacement for the standard <B
CLASS="command"
>update</B
>
   daemon, <B
CLASS="command"
>mobile-update</B
> minimizes disk spin ups and
   reduces disk uptime. It flushes buffers only when other disk activity is
   present. To ensure a consistent file system call <B
CLASS="command"
>sync</B
>
   manually. Otherwise files may be lost on power failure.
   <B
CLASS="command"
>mobile-update</B
> does not use APM. So it works also on
   older systems.
</P
></LI
><LI
><P
>&#13;   <A
HREF="http://noflushd.sourceforge.net/"
TARGET="_top"
>noflushd</A
>
   : <B
CLASS="command"
>noflushd</B
> monitors disk activity and spins down
   disks that have been idle for more than &#60;timeout&#62; seconds. It
   requires a kernel &#62;=2.2.11 . Useful in combination with
   <B
CLASS="command"
>hdparm</B
> and <B
CLASS="command"
>mount</B
> with
   <EM
>noatime</EM
> option to bring down disk activity.


</P
><P
>&#13;   Here are some comments and thoughts by Nat Makarevitch

   about a possible approach which may
   reduce the disk activity under Linux (sparing energy, especially with
   noflushd) the file Documentation/filesystems/proc.txt of the Linux sourcetree
   documents some useful features, esp. in the
   <TT
CLASS="filename"
>/proc/sys/vm</TT
> section.

   Under Linux 2.2 I used:

<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
>&#13;echo "100 5000 8 256 500 60000 60000 1884 2" &#62; /proc/sys/vm/bdflush
</PRE
></FONT
></TD
></TR
></TABLE
>

   especially under Linux 2.4 which uses its spare time to 'pre-save' the
   less-used memory pages into the swap, increasing the disk activity

   I tried to figure the more adequate parameters (Linux 2.4.9, 192 MB RAM,
   Toshiba 3480 laptop)

   beware: some of those parameters may be dangerous or useless (I have not
   gathered serious data about the practical efficiency).  moreover do not
   forget that delaying disk writes of data is intrinsically dangerous

<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
>&#13;echo 99 512 32 512 0 300000 60 0 0 &#62; /proc/sys/vm/bdflush
# is '60' the max value for age_super?
echo 1 1 96 &#62; /proc/sys/vm/buffermem
echo 512 128 32 &#62; /proc/sys/vm/kswapd
echo 1 10 96 &#62; /proc/sys/vm/pagecache
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
></LI
><LI
><P
>&#13;   The
   <A
HREF="http://www.buzzard.me.uk/toshiba/index.html"
TARGET="_top"
>Toshiba Linux Utilities</A
>
   are a set of Linux utilities for controlling the fan, supervisor passwords,
   and hot key functions of Toshiba Pentium notebooks.
   There is a KDE package <EM
>Klibreta</EM
>, too.
</P
></LI
><LI
><P
>&#13;   At Kenneth E. Harker's page there is a recommendation for LCDproc
   <A
HREF="http://lcdproc.omnipotent.net/"
TARGET="_top"
>LCDProc</A
>
   . "LCDproc is a small piece of software that will enable your Linux
   box to display live system information on a 20x4 line backlit
   <SPAN
CLASS="acronym"
>LCD</SPAN
> display. This program shows, among other
   things, battery status on notebooks." I tried this package and
   found that it connects only to the external
   <A
HREF="http://www.matrixorbital.com/"
TARGET="_top"
>Matrix-Orbital</A
>
   <SPAN
CLASS="acronym"
>LCD</SPAN
> 20x4 display
   , which is a <SPAN
CLASS="acronym"
>LCD</SPAN
> display connected to a serial
   port. I can't see any use for a laptop yet, but you might use it to
   build a wearable.
</P
></LI
><LI
><P
>&#13;   The
   <A
HREF="http://sourceforge.net/projects/diald/"
TARGET="_top"
>Diald Dial Daemon</A
>
   provides on demand Internet connectivity
   using the SLIP or PPP protocols. Diald can automatically dial
   in to a remote host when needed or bring down dial-up
   connections that are inactive.

</P
></LI
><LI
><P
>&#13;   <A
HREF="http://www.kde.org"
TARGET="_top"
>KDE</A
>
   provides <EM
>KAPM</EM
>,
   <EM
>Kbatmon</EM
> and
   <EM
>Kcmlaptop</EM
>. Written by Paul Campbell
   <EM
>kcmlaptop</EM
> is a set of KDE control panels
   that implements laptop computer support functions, it includes
   a dockable battery status monitor for laptops - in short a
   little icon in the KDE status bar that shows how much battery
   time you have left. It also will warn you when power is
   getting low and allows you to configure power saving options.
   Similar packages you may find at the GNOME project
   <A
HREF="http://www.gnome.org/"
TARGET="_top"
>GNOME</A
>
   . See the software maps at both
   sites.

</P
></LI
><LI
><P
>&#13;   Please see the
   <A
HREF="http://tldp.org/HOWTO/Battery-Powered/"
TARGET="_top"
>Battery-Powered-HOWTO</A
>
   for further information.
</P
></LI
></OL
>

</P
><P
>&#13;   Some more words about
   disks spin down with <B
CLASS="command"
>noflushd</B
> or
   <B
CLASS="command"
>hdparm</B
> utilities. The objective
   is to reduce hard disk usage to minimum, because on most laptops it
   is the primary source of noise and energy consumption. The "noflushd" daemon is a
   replacement of "update" which makes buffer updates on disk only when
   some other data is being read from the disk (the behavior of "update"
   is to flush buffers every 5 seconds, and it usually generates
   constant disk activity, so that the disk never becomes idle).
   "noflushd" also sets the disk spindown time and automatically calls
   "sync" before spindown.  The syntax is something like "noflushd -n 5
   /dev/hda". Using "noflushd" may cause loss of data if some files were
   edited while the disk was parked and not sync'ed, e.g. if the power
   was suddenly lost.
</P
><P
>&#13;   The <B
CLASS="command"
>hdparm</B
> utility can set the sleep time too, and also tune the
   IDE disk parameters for better performance. Make sure that the
   kernel IDE parameter "Use DMA by default when available" (section
   "Block devices") is enabled.
</P
><P
>&#13;   However, it is not enough to enable <B
CLASS="command"
>noflushd</B
>
   or IDE disk sleep time to make the disk
   effectively silent, because the system in most
   default installations is running many cron jobs, writes to log files,
   uses swap and so on. This activity is not always desirable,
   especially if the computer is standalone (not on network) and is used
   mostly by one user.  Here are some recommendations.
</P
><P
>&#13;   First, the cron daemon and friends (anacron, atd, logrotate,
   sendmail / exim / ...) could be removed from the system if the
   services they run (such as, cleaning /tmp directories and logs,
   checking email etc.) are not needed.
</P
><P
>&#13;   Secondly, the syslogd configuration file
   <TT
CLASS="filename"
>/etc/syslog.conf</TT
> should
   be modified to reduce the number of log files and messages
   logged, and also to have "-" signs before every file name (which
   means that the system will not have to sync the disk every time a
   message is logged).
</P
><P
>&#13;   Also, it is advisable to add "mark:none;" to the "syslog" strings,
   so that the "strich strich strich MARK strich strich strich"
   messages do not get written to the log files every half an hour.
   Typical Linux installations today have too many log files for the
   home user.
</P
><P
>&#13;   Finally, the disk may not go to sleep when a lot of swap space is
   in use. Type "free" and see how much swap is being used and how
   much free RAM is available. If you think there is enough free RAM
   to work without swap, or if there is a lot of swap used AND also
   a lot of free RAM, consider freeing the swap space ("su; swapoff
   -a; swapon -a") or switching the swap space off altogether ("su;
   swapoff -a"). Working without swap should be fine on systems with
   64MB or more of RAM.  (Working without swap will reduce the
   available memory, of course, and some software crashes without
   warning when it runs out of memory. But, adding swap will not
   prevent the crash resulting from some runaway memory consumuing
   software, it will only delay it, and it will make the system swap
   a lot before it happens.)
</P
><P
>&#13;   With these changes in the system, one could get the laptop to
   work for extended periods of time with its hard disk switched
   off.
</P
><P
>&#13;   The kernel can be configured with "Yes" to "APM Support" and
   "Enable console blanking using APM" (section "General setup").
   Then the LCD screen lamp will shut off in console mode (so not
   just the screen goes black, but also the lamp). In X mode, the
   same effect can be obtained with "xset +dpms" (enable DPMS
   function) and "xset s blank" (enable screen blanking). One can
   add these commands to the X window session or window manager
   initialization scripts.
</P
><P
>&#13;   The computer's BIOS energy savings options (hard disk sleep
   time, video blanking time and so on) are probably not
   useful and in some cases may even cause crashes.  Therefore
   they could be disabled in the laptop's BIOS.


</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="mobile-guide-p6a5s6-low-cpu-speed.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="mobile-guide-p6a5s8-kernel.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Low CPU Speed</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="mobile-guide-a5-limited-resources.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Kernel</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>