Wednesday, 11 November 2009

Improving battery life on the HP Mini

A few weeks ago I wrote about my experience using an HP Mini netbook - well in this follow up article describes how I reduced the power consumption on this device with some fairly basic steps.

I started from a fresh clean install of Ubuntu Karmic 9.10 (32 bit) and pulled in all the latest updates. I then installed powertop using:

apt-get install powertop

Then I unplugged the power and let powertop run for 10 minutes to settle in and then noted that ACPI power estimate was ~13.0W.

My first saving was to totally disable Bluetooth - wireless power savings are a good way of saving power. I don't use Bluetooth at all and to save memory from the driver being loaded I blacklisted the btusb module by adding btusb to /etc/modprobe.d/blacklist.conf (this is rather a heavy handed approach!). I then rebooted and re-measured the power consumption - down to 9.7W.

My next tweak was to enable laptop mode. To do this, edit /etc/default/acpi-support and set ENABLE_LAPTOP_MODE=true. Not sure if this is a big win for devices with SSD like my netbook, I believe one will see a bigger power saving with HDD based devices using this setting.

I noted that powertop was informing me to use usbcore.autosuspend=1 and disable hal polling, so I'd thought I'd follow it's wisdom and make these tweaks.

I edited /etc/default/grub and changed the GRUB_CMDLINE_LINUX_DEFAULT setting by adding usbcore.autosuspend=1, and then ran sudo update-grub to update /boot/grub/grub.cfg.

Next I ran:

sudo hal-disable-polling --device /dev/sdb

..for some reason /dev/sdb was being polled and I don't require this overhead for some auto sensing functionality.

I rebooted and remeasured the power consumption - down to 8.7W. Not bad.

Next I totally disabled compiz and turned my display brightness down - this saved 0.3W, bringing the the system down to a reasonable 8.4W. I'm not sure if the compiz savings were much, but if I can save the GPU work by turning off compositing then that must save some power.

My final tweak was to disable the Gnome terminal cursor from flashing - this saves 2 wakeups a second (not much!). To disable the cursor blink for the Default profile I ran gconf-editor and set /apps/gnome-terminal/profiles/Default/cursor_blink_mode to off. This saving is negligible, but makes me feel good to know I've saved two wakeups a second :-)

So now my machine was in a usable state, and down to 8.4W. I could tweak my access point to reduce the number of beacon intervals to save Wifi wakeups, but that's going a little too far, even for me! I then wondered much power Wifi was using, so I disabled it and after 15 minutes my system dropped down to 7.3W. This is good to know but a little pointless for my normal work pattern when I need net access - it is a netbook after all!

I'm sure I can save a little more power, but for now it's a good win for a little amount of work. I'm open to any suggestions on how to save more power. Please let me know!

1 comment:

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