Chris Tyler - Fedora Linux

Shows the history of the calculated time to charge the battery, when you're on AC power, or to discharge the battery, when you're running only on the battery. Power events are also shown on this log.

Event Log

Displays a more verbose listing of the same power events shown on the graphs.

On an AC-only system, the graphs will all be flat lines, but power events will still be displayed.

If CMOS semiconductors were perfect, they would consume power only when they changed state. They're not perfect, so they leak energy and consume power when idle, but that's a tiny fraction of the power they consume when changing state.

The system clock is a pulse generator that controls the speed at which the CPU changes state, and therefore controls the amount of energy used by the CPU and related system components. Therefore, there is a trade-off between performance and power consumption.

Fedora can balance power usage against performance automatically according to system workload. This feature is provided by the cpuspeed service and is enabled by default.

The default parameters used by this service work well in most cases, but can be adjusted by editing the file /etc/cpuspeed.conf , which looks like this:

VMAJOR=1

VMINOR=1

# uncomment this and set to the name of your CPUFreq module

#DRIVER="powernow-k7"

# Let background (nice) processes speed up the cpu

OPTS="$OPTS -n"

# Add your favorite options here

#OPTS="$OPTS -s 0 -i 10 -r"

# uncomment and modify this to check the state of the AC adapter

#OPTS="$OPTS -a /proc/acpi/ac_adapter/*/state"

# uncomment and modify this to check the system temperature

#OPTS="$OPTS -t /proc/acpi/thermal_zone/*/temperature 75"

Usually the DRIVER, VMAJOR, and VMINOR lines should not be changed.

Uncomment the OPTS lines that contain additional options you wish to use. The pre-configured lines have these meanings:

-n

Allow processes that have been marked as low priority using the nice command to run at full speed. The default is to slow down the processor when only low-priority processes are running.

-s 0 -i 10 -r

Manages only CPU 0 ( -s 0 ), making speed change decisions once a second instead of the default of once every two seconds ( -i 10 ), and restore the original speed when cpuspeed exits ( -r ).

-a /proc/acpi/ac_adapter/*/state

Monitors the AC adapter and switches to minimum speed when AC power is removed. Adding -C will force the system to operate at maximum speed when AC power is connected.

-t /proc/acpi/thermal_zone/*/temperature 75

Watches the system temperature and slows down the CPU when the temperature exceeds 75 degrees Celsius (167 degrees Fahrenheit).

To see a list of all available options, run this command:

$ /usr/sbin/cpuspeed --help 2>&1|less

After editing /etc/cpuspeed , restart the cpuspeed service:

# service cpuspeed restart

Stopping cpuspeed: [ OK ]

Starting cpuspeed: [ OK ]

You can monitor the CPU speed by installing a monitor on your panel. Right-click on your GNOME panel, then select "Add to Panel." Choose the CPU Frequency Scaling Monitor and click Add. The icon shown in Figure 3-5 will appear; the bar graph will rise and fall as the CPU clock speed is adjusted, and hovering your mouse cursor over the display will show the current frequency setting (the box that appears below the icon in Figure 3-5).

Figure 3-5. CPU Frequency Scaling Monitor

If you are using your system through a text-mode console, you can still access the important power-management tools.

To suspend the system, execute the pm-suspend script:

$ pm-suspend

To hibernate, use the pm-hibernate script:

$ pm-hibernate

To view the battery status, access ACPI through the /proc filesystem:

$ cat /proc/acpi/battery/*/state

present: yes

capacity state: ok

charging state: charging

present rate: 3079 mA

remaining capacity: 2912 mAh

present voltage: 16273 mV

Battery details are also available from ACPI:

$ cat /proc/acpi/battery/*/info

present: yes

design capacity: 6450 mAh

last full capacity: 5154 mAh

battery technology: rechargeable

design voltage: 14800 mV

design capacity warning: 515 mAh

design capacity low: 156 mAh

capacity granularity 1: 5 mAh

capacity granularity 2: 5 mAh

model number: DELL 0017F

serial number: 14639

battery type: LION

OEM info: Sony

By dividing the last full capacity by the design capacity, you can determine the condition of the battery. In this case, the battery can presently store 5154/6450 mAh, or about 80 percent of its design capacity, indicating that it's in reasonably good condition.

To further reduce power consumption:

 Dim your screen as much as the ambient lighting conditions will allow. The backlight for the screen draws a huge amount of power; one of my systems draws 31 percent more power in total when the screen is at maximum brightness than when it is set to minimum brightness.

 Turn off all unneeded services, reducing CPU and disk activity.

 Use a lightweight desktop environment such as Xfce instead of GNOME or KDE.

Xfce can be easily installed (see Lab 5.3, "Using Repositories"). To select your desktop environment, use the Session menu on the graphical login screen.

 Unplug any unneeded external devices, including USB devices, headphones, mice, and keyboards. Each USB device can consume up to 2.5 watts of power, increasing your power consumption by as much as 20 percent.

 Turn off your wireless network radio when it is not in use. Most laptops have a wireless kill switch (sometimes labeled airplane or flight mode ) that turns off the radio portion of the wireless card. This can cut your power consumption by up to 5 percent.

The ACPI specification enables a system's BIOS to supply data and program code to the operating system. The code is written in a unique, processor-independent pseudo-machine language called ACPI Machine Langauge (AML). The Linux kernel interpretively executes the AML code to access certain features of the host hardware system. You can think of the AML code as a type of device driver that is downloaded from the BIOS to the operating system.

The Linux kernel uses the ACPI data and code to collect data that is then exposed through the /proc/acpi directory. Information received through the /proc/acpi directorysuch as instructions to change the CPU frequencyis passed to the ACPI code.

Applications such as cpuspeed and gnome-power-manager monitor the ACPI information and combine it with other information (such as current process load) and then make power management decisions. These decisions cause actions to be taken by various subsystems such as the ACPI, the X Window server, storage, and loadable modules.