Comment 32 for bug 1058040

@John Winterton - You are half right. CPU overhead is higher with the open-source radeon driver than with the closed-source Catalyst (fglrx) driver. However the ATI/AMD GPU is used as much more than just a presentation device - most of the 3D calculations and rendering (including parts of Ubuntu's Unity desktop) are done on the GPU. Most of the excess heat produced by the radeon driver compared to the fglrx driver is produced by the GPU. Although there is some basic power management in the radeon driver - see http://www.x.org/wiki/radeonBuildHowTo#radeon-KMS_power-management - not only does the dynpm method not work on some hardware, when it does both it and the profile method only reduce heat and increase battery life partially when compared to the fglrx driver.

That said, there is some work going on to reduce the CPU overhead of the radeon driver. Some improvements were made in Mesa 7.11 (used in Ubuntu 11.10) for both the r300g driver for old hardware up to and including the Radeon X1000 series GPUs and the r600g driver for newer hardware from Radeon HD2000 series and later. There was at least one improvement to the r600g driver in Mesa 9.0 (used in Ubuntu 12.10 "Quantal Quetzal") - see http://cgit.freedesktop.org/mesa/mesa/commit/?id=c76462b45f1e3a0aa2ee7971191e30e8a5f52015 - and already another in the development tree for the future Mesa 9.1 - see http://cgit.freedesktop.org/mesa/mesa/commit/?id=e73bf3b805de78299f1a652668ba4e6eab9bac94