641 lines
15 KiB
HTML
641 lines
15 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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>Power Management</TITLE
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="POWERMGM"
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></A
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>1. Power Management</H1
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><P
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>If you have a relatively recent x86 laptop, odds are it supports either
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Advanced Power Management (APM) or Advanced Configuration and Power Interface
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(ACPI). ACPI is the newer of the two technologies and puts power management in
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the hands of the operating system, allowing for more intelligent power
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management than is possible with BIOS controlled APM. This is most useful for
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battery-powered laptops.
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You can only have one
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power management interface in control of your machine at a time, so it's
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important you decide which method best suits your situation.</P
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="APM"
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></A
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>1.1. Advanced Power Management (APM)</H2
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><P
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><EM
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>Advanced Power Management (APM)</EM
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>
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allows your computer's BIOS to control your system's power management
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without the knowledge of the operating system.
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The advantages to APM under Linux are that it's stable, well supported by
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Linux vendors and has a solid history behind it.
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However, not much development has been done with it over the past few
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years.</P
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><P
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>To use it, you'll need to enable APM in the kernel:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> [*] Power Management support
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<*> Advanced Power Management BIOS support
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[ ] Ignore USER SUSPEND (NEW)
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[ ] Enable PM at boot time (NEW)
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[ ] Make CPU Idle calls when idle (NEW)
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[ ] Enable console blanking using APM (NEW)
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[ ] RTC stores time in GMT (NEW)
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[ ] Allow interrupts during APM BIOS calls (NEW)
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[ ] Use real mode APM BIOS call to power off (NEW)</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>Most of the other APM
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options exist as work-arounds for known problems with specific hardware
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devices,
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so you'll probably only want to enable the first one (CONFIG_APM).</P
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><P
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></P
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><UL
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><LI
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><P
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>Advanced Power Management BIOS support (CONFIG_APM):
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You'll need to enable this in order to do anything
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useful
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with APM. User-space programs will receive
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notification of
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APM events (e.g., battery status change) and a
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/proc/apm
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device will provide you with battery status
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information.</P
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></LI
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><LI
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><P
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>Ignore USER SUSPEND (CONFIG_APM_IGNORE_USER_SUSPEND):
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This is a workaround for NEC Versa M
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notebooks.</P
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></LI
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><LI
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><P
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>Enable PM at boot time (CONFIG_APM_DO_ENABLE):
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Although it sounds nifty, most machines do
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not require this feature to be enabled and in fact can
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hang
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some systems at boot time.</P
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></LI
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><LI
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><P
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>Make CPU Idle calls when idle (CONFIG_APM_CPU_IDLE):
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On some machines,
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this option provides increased power savings. On
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others, it will
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hang the system at boot time. Use with
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caution.</P
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></LI
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><LI
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><P
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>Enable console blanking using APM
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(CONFIG_APM_DISPLAY_BLANK):
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Instead of blanking the virtual console actually turn
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off the
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screen. This won't work with X-Windows and actually
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can cause more
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problems that it solves.</P
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></LI
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><LI
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><P
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>RTC stores time in GMT (CONFIG_APM_RTC_IS_GMT): If you
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want to
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store GMT (Greenwich Mean Time) in your RTC (Real Time
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Clock),
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say yes here.</P
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></LI
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><LI
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><P
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>Allow interrupts during APM BIOS calls
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(CONFIG_APM_ALLOW_INTS):
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This is a workaround for some IBM Thinkpads that hang
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while
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suspending.</P
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></LI
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><LI
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><P
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>Use real mode APM BIOS call to power off
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(CONFIG_APM_REAL_MODE_POWER_OFF):
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This is a workaround for a number of broken BIOSes.
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If your computer
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crashes instead of powering off properly, turn this
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on.</P
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></LI
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></UL
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><P
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>You'll want to install the APM daemon from
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<A
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HREF="http://www.worldvisions.ca/~apenwarr/apmd/"
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TARGET="_top"
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>http://www.worldvisions.ca/~apenwarr/apmd/</A
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>
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and configure your system startup scripts to activate it on boot:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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># Start the APM daemon if it exists and if APM is enabled in the kernel
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if [ -x /usr/sbin/apmd -a -d /proc/apm ]; then
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if cat /proc/apm 1> /dev/null 2> /dev/null ; then
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echo "Starting APM daemon: /usr/sbin/apmd"
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/usr/sbin/apmd
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fi
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fi</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>The APM daemon is actually made up of three primary programs:</P
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><P
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></P
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><UL
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><LI
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><P
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><B
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CLASS="COMMAND"
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>apmd</B
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> - handles power management
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tasks</P
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></LI
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><LI
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><P
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><B
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CLASS="COMMAND"
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>apm</B
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> - a command-line tool to print
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the current battery status or suspend the computer</P
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></LI
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><LI
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><P
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><B
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CLASS="COMMAND"
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>xapm</B
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> - a simple battery meter for
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X</P
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></LI
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></UL
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><P
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>If you're looking for a simple, "works out of the box" approach to power
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management for your Laptop, APM is definitely the way to go.</P
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><P
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>A simple script to notify you how much battery time is remaining can be
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added to your <TT
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CLASS="FILENAME"
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>~/.profile</TT
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> file:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>if [ -f /proc/apm ]; then
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DUMMY=`cat /proc/apm | cut -d" " -f 7`
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# Don't display when fully charged
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if [ "$DUMMY" != "99%" ]; then
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LEVEL=`cat /proc/apm | sed -e "s/^.*% //"`
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echo "Battery at $DUMMY ($LEVEL)"
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fi
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fi</PRE
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></FONT
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></TD
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></TR
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></TABLE
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
|
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><A
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NAME="ACPI"
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></A
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>1.2. Advanced Configuration and Power Interface (ACPI)</H2
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><P
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><EM
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>Advanced Configuration and Power Interface (ACPI)</EM
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>
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is the successor to APM, which places the responsibility of power management
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away from the BIOS and into the hands of the operating system.
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ACPI Linux is newer than APM Linux, more flexible in responding to power
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management events, has seen
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much more development as of late, and as a result of all this is prone to its
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own share of bugs from
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time to time.</P
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><P
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>If you're into cutting-edge development and are not intimidated with
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kernel
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builds and applying patches against source code, ACPI is worth
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consideration.</P
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><P
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>There are two parts to ACPI under Linux: The ACPI driver built into the
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kernel itself, and the ACPI daemon (ACPID). ACPID in its current incarnation
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is
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pretty simple: monitor /proc/acpi/event and do things in response. Even if
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you don't load the daemon, you'll still get the benefit of ACPI features built
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into the kernel such as processor thermal support.</P
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><P
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>You can determine which version
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of the ACPI driver you are using, along with supported suspend states, by
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using:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>bash $ cat /proc/acpi/info
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version: 20030619
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states: S0 S1 S3 S4 S4 S5</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>ACPI development is progressing at a steady rate, so you might want to
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consider
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<A
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HREF="http://sourceforge.net/project/showfiles.php?group_id=36832"
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TARGET="_top"
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>patching</A
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>
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your kernel against any recent updates to the kernel-level ACPI code. Once
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you have downloaded the
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patch for your specific kernel, you can patch it with something like:</P
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><TABLE
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BORDER="1"
|
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>bash$ gunzip acpi-[version-kernel].diff.gz
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bash# cd /usr/src/linux-[version]
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bash# patch -Np1 -i ../acpi-[version-kernel].diff</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>You'll want to recompile your kernel after this, of course:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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> [*] ACPI Support
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[ ] CPU Enumeration Only
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<*> AC Adapter
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<*> Battery
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<*> Button
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<*> Fan
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<*> Processor
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<*> Thermal Zone
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< > ASUS Laptop Extras
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< > Toshiba Laptop Extras
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[*] Debug Statements</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>You'll also want to install the ACPID daemon from
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<A
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HREF="http://sourceforge.net/project/showfiles.php?group_id=33140"
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TARGET="_top"
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>http://sourceforge.net/project/showfiles.php?group_id=33140</A
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>
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and configure your system startup scripts to activate it on boot:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>if [ -x /usr/sbin/acpid -a -d /proc/acpi ]; then
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echo "Starting ACPID Daemon: /usr/sbin/acpid"
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/usr/sbin/acpid
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fi</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>A bit of history... Microsoft was the first vendor to implement ACPI.
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This is both good and
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bad. It is good because when you buy a system, you can pretty much guarantee
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that it has passed Microsoft's hardware compliance tests, including the test
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of its ACPI implementation. However, these tests come up short in that they
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do not indicate compliance with the ACPI specification, but rather with
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Microsoft's implementation of ACPI. When that same machine is used with
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Linux, some classes of errors that did not manifest themselves under Windows
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may become apparent. To protect against this problem, the Linux ACPI driver
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maintains a "bad BIOS" blacklist of known BIOS's that are known to not be ACPI
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compliant, and as a result will refuse to enable ACPI if your system is
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listed.</P
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><P
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>Many manufacturers are now validating that their systems run on Linux.
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However, they use major Linux distributions with the default kernel. This
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means that it is somewhat difficult to get OEMs to ensure that their systems
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work with ACPI-enabled Linux until a major Linux distribution ships an ACPI
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kernel. This presents a slight dilemma in that Linux distributions want to
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ship kernels that run on as many systems as possible, but there have been some
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positive moves in this area lately.</P
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><P
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|
>To conserve energy while remaining quickly available, ACPI-compatible
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PCs may enter system sleep states. The ACPI specification defines five of
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these states, known as S-states. Unlike processor sleep states, no work is
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done by the system under S-states. Each state introduces greater power savings
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but requires commensurately more time to awaken and begin performing work.
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These are patterned on system states from the APM standard, a predecessor of
|
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ACPI.</P
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><P
|
|
>Full details on ACPI sleep states are available at
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<A
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HREF="http://acpi.sourceforge.net/documentation/sleep.html"
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TARGET="_top"
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>http://acpi.sourceforge.net/documentation/sleep.html</A
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>.
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Processor states are described at
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<A
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HREF="http://acpi.sourceforge.net/documentation/processor.html"
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TARGET="_top"
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>http://acpi.sourceforge.net/documentation/processor.html</A
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>.</P
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><P
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>For more specific background information on ACPI itself, you can visit
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the ACPI website at
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<A
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HREF="http://www.acpi.info"
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TARGET="_top"
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>http://www.acpi.info</A
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></P
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></DIV
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><DIV
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CLASS="SECT2"
|
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><H2
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CLASS="SECT2"
|
|
><A
|
|
NAME="WHICHONE"
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></A
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|
>1.3. APM vs. ACPI: Which one?</H2
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><P
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>There are currently two competing standards for providing power
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management: APM and ACPI. Both cannot be used at the same time, so which one
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is best for your situation? If you have a relatively recent (>2.4.20) kernel
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and are not intimidated by kernel builds and patching source code, you'll find
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many benefits with the flexibility of ACPI. If you just want to enable
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generic power management, or are using an older machine, choose APM. Neither
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method spins down idle hard drives; use hdparm for that instead. Either way,
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your system's BIOS must correctly support the power management scheme you'd
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like to use as well; if your system does not fully support either standard,
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some of the power management options might crash your system and/or cause data
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loss. You have been warned!</P
|
|
><P
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|
>Even if you don't enable power management on your x86-laptop, Linux will
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always issue the HLT instruction to your
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processor whenever nothing needs to be done
|
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|
|
<A
|
|
NAME="AEN101"
|
|
HREF="#FTN.AEN101"
|
|
><SPAN
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|
CLASS="footnote"
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|
>[1]</SPAN
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|
></A
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>.
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Many Microsoft Windows CPU cooling program use this technique. This results
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in lowering the power consumption of your CPU. Note that the system doesn't
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power down when it receives the HLT instruction; it just stops executing
|
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instructions until there is an interrupt.</P
|
|
><P
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|
>There is generally no advantage to
|
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enabling either type of power management on servers or workstations that do
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not fall into
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these categories.</P
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></DIV
|
|
><DIV
|
|
CLASS="SECT2"
|
|
><H2
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|
CLASS="SECT2"
|
|
><A
|
|
NAME="HYPERTHREAD"
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></A
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|
>1.4. SMP, Hyper-Threading, IA64 & NUMA</H2
|
|
><P
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|
>Some SMP system manufacturers may have omitted the pre-ACPI tables used
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for SMP configurations. In this case, ACPI is required.</P
|
|
><P
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|
>If you have a newer system that supports
|
|
<A
|
|
HREF="http://www.intel.com/technology/hyperthread/"
|
|
TARGET="_top"
|
|
>Hyper-Threading</A
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|
>,
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you will need to enable ACPI (and, of course, SMP). Without it, your Linux system
|
|
may be unable to discover and initialize all of the virtual processors.</P
|
|
><P
|
|
>IA64 machines require ACPI as well. Additionally, NUMA servers are
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|
starting to require it for proper initialization.</P
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|
></DIV
|
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></DIV
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>[1]</SPAN
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>source/arch/i386/kernel/process.c</P
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