Tip for significantly increasing battery life / reducing power consumption (Thinkpad X220)

The biggest win was setting i915.i915_enable_rc6=1 on the kernel command 
line, although I've read that this can cause some instability, depending 
on you kernel and usage -- had a couple of crashes/freezes a 6 months 
ago, but it seems pretty stable now.  The benefits for a laptop 
definitely out-weigh the inconvenience or a few rare freezes, but it 
would be different for a server.

Might try out the other kernel line options and see if I can do better :-)

Here's my /etc/rc.d/rc.local file in case you are interested:
-------------------------------------
#!/bin/bash

echo 5 > /proc/sys/vm/laptop_mode
echo 0 > /proc/sys/kernel/nmi_watchdog
echo 1 > /sys/devices/system/cpu/sched_mc_power_savings
echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo 1500 > /proc/sys/vm/dirty_writeback_centisecs
for i in /sys/bus/usb/devices/*/power/autosuspend; do echo 1 > $i; done
for i in /sys/bus/usb/devices/*/power/level; do echo auto > $i; done
echo min_power > /sys/class/scsi_host/host0/link_power_management_policy
echo min_power > /sys/class/scsi_host/host1/link_power_management_policy
echo Y > /sys/module/snd_hda_intel/parameters/power_save_controller
echo 1 > /sys/module/snd_hda_intel/parameters/power_save
for i in /sys/bus/{pci,i2c}/devices/*/power/control; do echo auto > $i; done

iwconfig wlan0 power on

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