Reducing HP 4720s power consumption under Ubuntu Linux 11.10

Mainly annoyed by the loud fan I looked into ways of reducing power consumption of the HP Probook 4720s and came up with this script:
#!/bin/sh -e
# Increase filesystem write cache timeoutecho 1500 > /proc/sys/vm/dirty_writeback_centisecs
# Enable power management on all PCI devices
find /sys/devices/pci* -path “*power/control” -exec bash -c “echo auto > ‘{}'” \;

# Enable power aware CPU scheduler
echo 1 > /sys/devices/system/cpu/sched_mc_power_savings
# Enable WLAN power management
iwconfig wlan0 power on
# Enable Intel audio power management
echo 1 > /sys/module/snd_hda_intel/parameters/power_save
# Enable SATA power management
for i in /sys/class/scsi_host/host*/link_power_management_policy; do echo min_power > $i; done
# Enable laptop mode tools
echo 5 > /proc/sys/vm/laptop_mode
# Override PCIE power management
echo powersave > /sys/module/pcie_aspm/parameters/policy
# Disable wake on lan for LAN
ethtool -s eth1 wol d
In order for the PCIE_ASPM hack to work, the kernel needs to be started with some extra parameters in grub. Thus:
1. edit /etc/default/grub and add this setting:

to his entry:
2. save
3. run update-grub
4. reboot 
The 4720s uses an ATI graphics adapter. The following setting in /etc/X11/xorg.conf device section reduced the overall event count reported by powertop by 50 events/second:

        Option      “NoDRI”
        Option       “no_dri” “no”

 A word of warning though: the UI is afterwards notably slower and fullscreen video is choppy.

[2012.05.06] Also check out the follow-up for Ubuntu 12.04

3 thoughts on “Reducing HP 4720s power consumption under Ubuntu Linux 11.10

  1. Just wanted to report that my 4720s with 4GB RAM uses 10 Watts running Ubuntu 12.04 with an empty desktop and minimal backlight after implementing your power tuning advice. That's sensational! Thanks.


  2. BTW: I additionally disabled bluetooth (via rfkill / stop bluetooth) and I didn't find it necessary to disable DRI as the fglrx driver causes around 50 events/s only with DRI enabled.


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