The Real Need For Nouveau Power Management

We have already published a look at the Fedora 13 Beta, delivered ATI Radeon benchmarks atop Fedora 13 Beta, and have other articles on the way covering this new Fedora release, while in this article we are investigating Nouveau's power performance using this newest Fedora release. If you are a mobile user planning to use the Nouveau stack right now, or you care the least bit about energy savings with your desktop, its power consumption alone may rule this open-source driver out as even a current possibility.

Fedora has always been at the forefront of pulling in the latest Nouveau driver code as it was first to ditch the xf86-video-nv driver in favor of this community-driven effort. Fedora began by shipping user-space mode-setting support with the Nouveau DDX, and then moved over to providing NVIDIA kernel mode-setting support, and now with Fedora 13 there is even the Nouveau Gallium3D driver available. This all while the Nouveau DRM only entered the mainline Linux kernel a few months back and just now with Ubuntu 10.04 LTS and other distributions are they beginning to utilize the Nouveau kernel mode-setting capabilities. It will likely be some months still before the Gallium3D Nouveau driver (and its classic Mesa driver for old NVIDIA ASICs) is picked up by other distributions, but Fedora tends to live on the edge of the open-source Linux graphics stack and Red Hat also happens to employ one of the Nouveau developers (Ben Skeggs) and David Airlie is also involved with the open-source NVIDIA work.

We already benchmarked Nouveau's Gallium3D driver using an earlier Fedora 13 snapshot and found its performance to be well behind the proprietary NVIDIA Linux graphics driver, but at least some games were running and this is at least a superior option to using the xf86-video-nv mess, which has now been discontinued by NVIDIA. The Nouveau Gallium3D driver has improved somewhat with Fedora 13 Beta where there are no longer as many bugs, but still the performance is subpar.

The Nouveau project has made great progress over the years in cleanly reverse engineering NVIDIA's binary blob and then developing this open-source driver stack. The 2D EXA, X Render, X-Video, RandR 1.2, and kernel mode-setting areas have all become quite solid for NVIDIA's graphics processors up through the NV50 (GeForce 9, GeForce GT 200 series). The 3D / OpenGL support, of course, is a work in progress. Unfortunately, not much headway has been made in the area of power management.

Power management though has been an important feature among those considering open-source graphics drivers as they may be able to sacrifice frame-rates in their Linux games -- or the performance isn't even an issue if they are just using desktop applications -- but many are concerned about the free software drivers coming at a cost of their battery life, a warmer notebook or desktop, or just the increased energy consumption they are looking to avoid. We decided to see exactly what the energy cost is of using the Nouveau driver in Fedora 13 compared to NVIDIA's proprietary driver. On the ATI side, it was not until recently that their KMS power management support has been moving along, but since then the open-source users have been ecstatic.

For this round of testing we used a Lenovo ThinkPad T61 with an Intel Core 2 Duo T9300 processor, 4GB of DDR3 system memory, a 100GB Hitachi HTS72201 SATA HDD, and a NVIDIA Quadro NVS 140M 512MB graphics processor. On the software side was Fedora 13 Beta with the 2.6.33.2-41.fc13.x86_64 (x86_64) kernel, GNOME 2.29.92, X.Org Server 1.8.0 RC1, xf86-video-nouveau 0.0.15, and Mesa 7.8-devel. When testing with the proprietary NVIDIA driver we used the most recent NVIDIA 195.36.15 driver. The proprietary NVIDIA Linux driver provides support for PowerMizer and other features to properly down-clock the GPU core and video memory when not being fully utilized along with engaging in other power-saving techniques.