How to conserve battery power using laptop-mode

-----------------------------------------------

Document Author: Bart Samwel (bart@samwel.tk)

Date created: January 2, 2004

Introduction

------------

Laptopmode is used to minimize the time that the hard disk needs to be spun up,

to conserve battery power on laptops. It has been reported to cause significant

power savings.

Contents

--------

* Introduction

* The short story

* Caveats

* The details

* Tips & Tricks

* Control script

* ACPI integration

* Monitoring tool

The short story

---------------

If you just want to use it, run the laptop_mode control script (which is included

at the end of this document) as follows:

# laptop_mode start

Then set your harddisk spindown time to a relatively low value with hdparm:

hdparm -S 4 /dev/hda

The value -S 4 means 20 seconds idle time before spindown. Your harddisk will

now only spin up when a disk cache miss occurs, or at least once every 10

minutes to write back any pending changes.

To stop laptop_mode, remount your filesystems with regular commit intervals

(e.g., 5 seconds), and run "laptop_mode stop".

Caveats

-------

* The downside of laptop mode is that you have a chance of losing up

  to 10 minutes of work. If you cannot afford this, don't use it!

* Most desktop hard drives have a very limited lifetime measured in spindown

  cycles, typically about 50.000 times (it's usually listed on the spec sheet).

  Check your drive's rating, and don't wear down your drive's lifetime if you

  don't need to.

* If you mount some of your ext3/reiserfs filesystems with the -n option, then

  the control script will not be able to remount them correctly. You must set

  DO_REMOUNTS=0 in the control script, otherwise it will remount them with the

  wrong options -- or it will fail because it cannot write to /etc/mtab.

* If you have your filesystems listed as type "auto" in fstab, like I did, then

  the control script will not recognize them as filesystems that need remounting.

The details

-----------

Laptop-mode is controlled by the flag /proc/sys/vm/laptop_mode. When this

flag is set, any physical disk read operation (that might have caused the

hard disk to spin up) causes Linux to flush all dirty blocks. The result

of this is that after a disk has spun down, it will not be spun up anymore

to write dirty blocks, because those blocks had already been written

immediately after the most recent read operation

To increase the effectiveness of the laptop_mode strategy, the laptop_mode

control script increases dirty_expire_centisecs and dirty_writeback_centisecs in

/proc/sys/vm to about 10 minutes (by default), which means that pages that are

dirtied are not forced to be written to disk as often. The control script also

changes the dirty background ratio, so that background writeback of dirty pages

is not done anymore. Combined with a higher commit value (also 10 minutes) for

ext3 or ReiserFS filesystems (also done automatically by the control script),

this results in concentration of disk activity in a small time interval which

occurs only once every 10 minutes, or whenever the disk is forced to spin up by

a cache miss. The disk can then be spun down in the periods of inactivity.

If you want to find out which process caused the disk to spin up, you can

gather information by setting the flag /proc/sys/vm/block_dump. When this flag

is set, Linux reports all disk read and write operations that take place, and

all block dirtyings done to files. This makes it possible to debug why a disk

needs to spin up, and to increase battery life even more.

If 10 minutes is too much or too little downtime for you, you can configure

this downtime as follows. In the control script, set the MAX_AGE value to the

maximum number of seconds of disk downtime that you would like. You should

then set your filesystem's commit interval to the same value. The dirty ratio

is also configurable from the control script.

If you don't like the idea of the control script remounting your filesystems

for you, you can change DO_REMOUNTS to 0 in the script.

Thanks to Kiko Piris, the control script can be used to enable laptop mode on

both the Linux 2.4 and 2.6 series.

Tips & Tricks

-------------

* Bartek Kania reports getting up to 50 minutes of extra battery life (on top

  of his regular 3 to 3.5 hours) using very aggressive power management (hdparm

  -B1) and a spindown time of 5 seconds (hdparm -S1).

* You can spin down the disk while playing MP3, by setting the disk readahead

  to 8MB (hdparm -a 16384). Effectively, the disk will read a complete MP3 at

  once, and will then spin down while the MP3 is playing. (Thanks to Bartek

  Kania.)

* Drew Scott Daniels observed: "I don't know why, but when I decrease the number

  of colours that my display uses it consumes less battery power. I've seen

  this on powerbooks too. I hope that this is a piece of information that

  might be useful to the Laptop Mode patch or it's users."

Control script

--------------

Please note that this control script works for the Linux 2.4 and 2.6 series.

--------------------CONTROL SCRIPT BEGIN------------------------------------------

#!/bin/sh

# start or stop laptop_mode, best run by a power management daemon when

# ac gets connected/disconnected from a laptop

#

# install as /sbin/laptop_mode

#

# Contributors to this script:   Kiko Piris

#				 Bart Samwel

#				 Dax Kelson

# Original Linux 2.4 version by: Jens Axboe

parse_mount_opts () {

	echo "$*"			| \

	sed 's/commit=[0-9]*//g'	| \

	sed 's/,,*/,/g'			| \

	sed 's/^,//'			| \

	sed 's/,$//'			| \

	cat -

}

KLEVEL="$(uname -r | cut -c1-3)"

case "$KLEVEL" in

	"2.4")

		true

		;;

	"2.6")

		true

		;;

	*)

		echo "Unhandled kernel level: $KLEVEL ('uname -r' = '$(uname -r)')"

		exit 1

		;;

esac

# Shall we remount journaled fs. with appropiate commit interval? (1=yes)

DO_REMOUNTS=1

# age time, in seconds. should be put into a sysconfig file

MAX_AGE=600

# Allowed dirty ratio, in pct. should be put into a sysconfig file as well.

DIRTY_RATIO=40

# kernel default dirty buffer age

DEF_AGE=30

DEF_UPDATE=5

DEF_DIRTY_BACKGROUND_RATIO=10

DEF_DIRTY_RATIO=40

if [ ! -e /proc/sys/vm/laptop_mode ]; then

	echo "Kernel is not patched with laptop_mode patch."

	exit 1

fi

if [ ! -w /proc/sys/vm/laptop_mode ]; then

	echo "You do not have enough privileges to enable laptop_mode."

	exit 1

fi

case "$1" in

	start)

		AGE=$((100*$MAX_AGE))

		echo -n "Starting laptop_mode"

		case "$KLEVEL" in

			"2.4")

				echo "1"				> /proc/sys/vm/laptop_mode

				echo "30 500 0 0 $AGE $AGE 60 20 0"	> /proc/sys/vm/bdflush

				;;

			"2.6")

				echo "1"				> /proc/sys/vm/laptop_mode

				echo "$AGE"				> /proc/sys/vm/dirty_writeback_centisecs

				echo "$AGE"				> /proc/sys/vm/dirty_expire_centisecs

				echo "$DIRTY_RATIO"			> /proc/sys/vm/dirty_ratio

				echo "$DIRTY_RATIO"			> /proc/sys/vm/dirty_background_ratio

				;;

		esac

		if [ $DO_REMOUNTS -eq 1 ]; then

			cat /etc/mtab | while read DEV MP FST OPTS DUMP PASS ; do

				PARSEDOPTS="$(parse_mount_opts "$OPTS")"

				case "$FST" in

					"ext3")		mount $DEV -t $FST $MP -o remount,$PARSEDOPTS,commit=$MAX_AGE ;;

					"reiserfs")	mount $DEV -t $FST $MP -o remount,$PARSEDOPTS,commit=$MAX_AGE ;;

					"xfs")		mount $DEV -t $FST $MP -o remount,$PARSEDOPTS,commit=$MAX_AGE ;;

				esac

			done

		fi

		echo "."

		;;

	stop)

		U_AGE=$((100*$DEF_UPDATE))

		B_AGE=$((100*$DEF_AGE))

		echo -n "Stopping laptop_mode"

		case "$KLEVEL" in

			"2.4")

				echo "0"				> /proc/sys/vm/laptop_mode

				echo "30 500 0 0 $U_AGE $B_AGE 60 20 0"	> /proc/sys/vm/bdflush

				;;

			"2.6")

				echo "0"				> /proc/sys/vm/laptop_mode

				echo "$U_AGE"				> /proc/sys/vm/dirty_writeback_centisecs

				echo "$B_AGE"				> /proc/sys/vm/dirty_expire_centisecs

				echo "$DEF_DIRTY_RATIO"			> /proc/sys/vm/dirty_ratio

				echo "$DEF_DIRTY_BACKGROUND_RATIO"	> /proc/sys/vm/dirty_background_ratio

				;;

		esac

		if [ $DO_REMOUNTS -eq 1 ]; then

			cat /etc/mtab | while read DEV MP FST OPTS DUMP PASS ; do

				PARSEDOPTS="$(parse_mount_opts "$OPTS")"

				case "$FST" in

					"ext3")		mount $DEV -t $FST $MP -o remount,$PARSEDOPTS ;;

					"reiserfs")	mount $DEV -t $FST $MP -o remount,$PARSEDOPTS ;;

					"xfs")		mount $DEV -t $FST $MP -o remount,$PARSEDOPTS ;;

				esac

			done

		fi

		echo "."

		;;

	*)

		echo "$0 {start|stop}"

		;;

esac

exit 0

--------------------CONTROL SCRIPT END--------------------------------------------

ACPI integration

----------------

Dax Kelson submitted this so that the ACPI acpid daemon will

kick off the laptop_mode script and run hdparm.

---------------------------/etc/acpi/events/ac_adapter BEGIN-------------------------------------------

event=ac_adapter

action=/etc/acpi/actions/battery.sh

---------------------------/etc/acpi/events/ac_adapter END-------------------------------------------

---------------------------/etc/acpi/actions/battery.sh BEGIN-------------------------------------------

#!/bin/sh

# cpu throttling

# cat /proc/acpi/processor/CPU0/throttling for more info

ACAD_THR=0

BATT_THR=2

# spindown time for HD (man hdparm for valid values)

# I prefer 2 hours for acad and 20 seconds for batt

ACAD_HD=244

BATT_HD=4

# ac/battery event handler

status=`awk '/^state: / { print $2 }' /proc/acpi/ac_adapter/AC/state`

case $status in

        "on-line")

                echo "Setting HD spindown to 2 hours"

                /sbin/laptop-mode stop

                /sbin/hdparm -S $ACAD_HD /dev/hda > /dev/null 2>&1

                /sbin/hdparm -B 255 /dev/hda > /dev/null 2>&1

                #echo -n $ACAD_CPU:$ACAD_THR > /proc/acpi/processor/CPU0/limit

                exit 0

        ;;

        "off-line")

                echo "Setting HD spindown to 20 seconds"

                /sbin/laptop-mode start

                /sbin/hdparm -S $BATT_HD /dev/hda > /dev/null 2>&1

                /sbin/hdparm -B 1 /dev/hda > /dev/null 2>&1

                #echo -n $BATT_CPU:$BATT_THR > /proc/acpi/processor/CPU0/limit

                exit 0

        ;;

esac

---------------------------/etc/acpi/actions/battery.sh END-------------------------------------------

Monitoring tool

---------------

Bartek Kania submitted this, it can be used to measure how much time your disk

spends spun up/down.

---------------------------dslm.c BEGIN-------------------------------------------

/*

 * Simple Disk SLeep Monitor

 *  by Bartek Kania

 * Licenced under the GPL

 */

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <fcntl.h>

#include <errno.h>

#include <time.h>

#include <string.h>

#include <signal.h>

#include <sys/ioctl.h>

#include <linux/hdreg.h>

#ifdef DEBUG

#define D(x) x

#else

#define D(x)

#endif

int endit = 0;

/* Check if the disk is in powersave-mode

 * Most of the code is stolen from hdparm.

 * 1 = active, 0 = standby/sleep, -1 = unknown */

int check_powermode(int fd)

{

    unsigned char args[4] = {WIN_CHECKPOWERMODE1,0,0,0};

    int state;

    if (ioctl(fd, HDIO_DRIVE_CMD, &args)

	&& (args[0] = WIN_CHECKPOWERMODE2) /* try again with 0x98 */

	&& ioctl(fd, HDIO_DRIVE_CMD, &args)) {

	if (errno != EIO || args[0] != 0 || args[1] != 0) {

	    state = -1; /* "unknown"; */

	} else

	    state = 0; /* "sleeping"; */

    } else {

	state = (args[2] == 255) ? 1 : 0;

    }

    D(printf(" drive state is:  %s\n", state));

    return state;

}

char *state_name(int i)

{

    if (i == -1) return "unknown";

    if (i == 0) return "sleeping";

    if (i == 1) return "active";

    return "internal error";

}

char *myctime(time_t time)

{

    char *ts = ctime(&time);

    ts[strlen(ts) - 1] = 0;

    return ts;

}

void measure(int fd)

{

    time_t start_time;

    int last_state;

    time_t last_time;

    int curr_state;

    time_t curr_time = 0;

    time_t time_diff;

    time_t active_time = 0;

    time_t sleep_time = 0;

    time_t unknown_time = 0;

    time_t total_time = 0;

    int changes = 0;

    float tmp;

    printf("Starting measurements\n");

    last_state = check_powermode(fd);

    start_time = last_time = time(0);

    printf("  System is in state %s\n\n", state_name(last_state));

    while(!endit) {

	sleep(1);

	curr_state = check_powermode(fd);

	if (curr_state != last_state || endit) {

	    changes++;

	    curr_time = time(0);

	    time_diff = curr_time - last_time;

	    if (last_state == 1) active_time += time_diff;

	    else if (last_state == 0) sleep_time += time_diff;

	    else unknown_time += time_diff;

	    last_state = curr_state;

	    last_time = curr_time;

	    printf("%s: State-change to %s\n", myctime(curr_time),

		   state_name(curr_state));

	}

    }

    changes--; /* Compensate for SIGINT */

    total_time = time(0) - start_time;

    printf("\nTotal running time:  %lus\n", curr_time - start_time);

    printf(" State changed %d times\n", changes);

    tmp = (float)sleep_time / (float)total_time * 100;

    printf(" Time in sleep state:   %lus (%.2f%%)\n", sleep_time, tmp);

    tmp = (float)active_time / (float)total_time * 100;

    printf(" Time in active state:  %lus (%.2f%%)\n", active_time, tmp);

    tmp = (float)unknown_time / (float)total_time * 100;

    printf(" Time in unknown state: %lus (%.2f%%)\n", unknown_time, tmp);

}

void ender(int s)

{

    endit = 1;

}

void usage()

{

    puts("usage: dslm [-w <time>] <disk>");

    exit(0);

}

int main(int ac, char **av)

{

    int fd;

    char *disk = 0;

    int settle_time = 60;

    /* Parse the simple command-line */

    if (ac == 2)

	disk = av[1];

    else if (ac == 4) {

	settle_time = atoi(av[2]);

	disk = av[3];

    } else

	usage();

    if (!(fd = open(disk, O_RDONLY|O_NONBLOCK))) {

	printf("Can't open %s, because: %s\n", disk, strerror(errno));

	exit(-1);

    }

    if (settle_time) {

	printf("Waiting %d seconds for the system to settle down to "

	       "'normal'\n", settle_time);

	sleep(settle_time);

    } else

	puts("Not waiting for system to settle down");

    signal(SIGINT, ender);

    measure(fd);

    close(fd);

    return 0;

}

---------------------------dslm.c END---------------------------------------------

#include <linux/writeback.h>

	if (unlikely(block_dump)) {

		char b[BDEVNAME_SIZE];

		printk("%s(%d): %s block %Lu on %s\n",

			current->comm, current->pid,

			(rw & WRITE) ? "WRITE" : "READ",

			(unsigned long long)bio->bi_sector, bdevname(bio->bi_bdev,b));

	}

			/*

			 * schedule the writeout of pending dirty data when the disk is idle.

			 * (Writeback is not postponed by writes, only by reads.)

			 */

			if (unlikely(laptop_mode))

				disk_is_spun_up(0);

			/*

			 * schedule the writeout of pending dirty data when the disk is idle.

			 * (postpone writeback until system is quiescent again.)

			 */

			if (unlikely(laptop_mode))

				disk_is_spun_up(1);

			}

	VM_LAPTOP_MODE=22,      /* vm laptop mode */

	VM_BLOCK_DUMP=23,       /* block dump mode */

void disk_is_spun_up(int postpone_writeback);

extern int block_dump;

extern int laptop_mode;

	{

		.ctl_name	= VM_LAPTOP_MODE,

		.procname	= "laptop_mode",

		.data		= &laptop_mode,

		.maxlen		= sizeof(laptop_mode),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

		.strategy	= &sysctl_intvec,

		.extra1		= &zero,

	},

	{

		.ctl_name	= VM_BLOCK_DUMP,

		.procname	= "block_dump",

		.data		= &block_dump,

		.maxlen		= sizeof(block_dump),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

		.strategy	= &sysctl_intvec,

		.extra1		= &zero,

	},

#include <linux/quotaops.h>

/*

 * Flag that makes the machine dump writes/reads and block dirtyings.

 */

int block_dump;

/*

 * Flag that puts the machine in "laptop mode".

 */

int laptop_mode;

	if (laptop_mode)

		wbc.older_than_this = NULL;

	del_timer(&laptop_mode_wb_timer); /* May have been set as a result of our writes. */

static struct timer_list laptop_mode_wb_timer;

static void laptop_mode_wb_timer_fn(unsigned long unused)

{

	mod_timer(&wb_timer, jiffies);

}

/*

 * We've spun up the disk and we're in laptop mode: schedule writeback

 * of all dirty data in 5 seconds.

 *

 * Laptop mode writeback will be delayed if it has previously been

 * scheduled to occur within 5 seconds. That way, the writeback will

 * only be triggered if the system is truly quiet again.

 */

void disk_is_spun_up(int postpone_writeback)

{

	if (postpone_writeback || !timer_pending(&laptop_mode_wb_timer))

		mod_timer(&laptop_mode_wb_timer, jiffies + 5 * HZ);

}

/*

 * Handler for wb_timer and laptop_mode_wb_timer.

 */

	init_timer(&laptop_mode_wb_timer);

	laptop_mode_wb_timer.data = 0;

	laptop_mode_wb_timer.function = laptop_mode_wb_timer_fn;

		if (unlikely(block_dump))

			printk("%s(%d): dirtied page\n", current->comm, current->pid);