Necro-bumping here, but this issue has seen an important development with kernel 3.11 (used in Saucy/13.10).
radeon/ATI libre driver is indeed concerned by OP's question (and I believe it is, based on the accepted answer), then it should be mentionned that 3.11 introduces the
dpm (Dynamic Power Management) method, which "should greatly help power consumption, especially when idle". (source: RadeonDriver Ubuntu Community Wiki)
More specifically, "dpm" mode
uses hardware on the GPU to dynamically change the clocks and voltage based on GPU load. It also enables clock and power gating.
Note however that it is only supported on R6xx and newer asics (what includes OP's HD 3650 card). Sources : X.org RadeonFeature/KMS Power Management Options, and RadeonDriver Ubuntu Community Wiki for a matrix of cards commercial/development names.
How to use it
To enable it, you just have to edit
/etc/default/grub and add
radeon.dpm=1 to the
GRUB_CMDLINE_LINUX_DEFAULT line, so it would look something like:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash radeon.dpm=1"
After you save/quit the text editor, update grub:
There are 3 operation modes to choose from:
- battery: lowest power consumption
- balanced: sane default
- performance: highest performance
They can be changed via sysfs:
echo battery > /sys/class/drm/card0/device/power_dpm_state
(source : Archlinux wiki)
Tips if you use GNOME Shell
There is a GNOME Shell extension (forked from the previously mentioned one by StuntsPT) that implements support for
dpm modes management : you can find it here. To use it, simply download the master
zip file (direct link) and use
Tweak Tool to install AND enable it. Alternatively, extract the extension folder and put it in
~/.local/share/gnome-shell/extensions. The extension will then show up in
Tweak tool which you can use to enable the extension. If it doesn't appear in the top panel, try to restart the shell with
Alt+F2 r (enter).