Mobile

Configuration: a 2 GHz Intel® Core™ 2 Duo processor laptop with Intel 965 Express GM integrated graphics, 1 Gb RAM

Kernel Power Performance Trend
This graph shows the power performance trend of the latest mainline kernel.

Power Saving Features
The following graph shows the saving in power by employing various power saving features in the Linux development kernel.

Here is a description of the power saving features, the cumulative power reduction effect is shown in the graph below.

1. Tickless: The tickless feature allows the CPU to stay in low power mode for longer period of time without waking up.
2. ondemand-gov-fix-patch: The Ondemand CPUFREQ governor has a bug in the interaction between tickless idle and multicore. This bug can make the CPU run at the maximum frequency, needlessly and for a significant amount of time. The patch can be found in the latest ACPI patch set.
3. cpuidle-patch: The CPUIDLE infrastructure is a replacement for the C-state selection algorithm in the kernel. The previous C-state selection algorithm was fundamentally designed around having a regular clock tick, and does not work well in a tickless kernel. The effect was that the CPU would spend a significant amount of time in the more shallow C-states, using more power than needed. The CPUIDLE infrastructure allows the CPU to enter deeper C-states for longer periods of time. The patch can be found in the latest ACPI patch set
4. alpm-patch: Many AHCI SATA controller chips have a feature that allows the controller to power down the SATA link to the disk when idle. This feature can save up to 1 Watt of power per SATA link. The patch can be found here.
5. backlight-fix: The standard GNOME screen-brightness application (gnome-power-manager) does not actually change the brightness of the backlight on the T61, but changes only the color of the pixels on the screen. Using the xbacklight application to change the screen to the reference brightness changes the backlight power and saves almost 1 Watt.
6. turn on C4 on C3 En bit: By remapping of the ACPI C3 state in the kernel to the deeper power saving C4 state for the CPU hardware, we can save extra power.
7. framebuffer-compression: By using the frame buffer compression capability in the Intel graphics chipset, access to the frame buffer memory and the related busses can be avoided to keep the CPU in the deepest possible low power C-state. The X11 config to enable this feature can be found here.