The Real Need For Nouveau Power Management
Next up we looked at the video playback performance between Nouveau and the proprietary NVIDIA driver. We used the video-cpu-usage test profile within the Phoronix Test Suite, which uses MPlayer for full-screen 1080p H.264 playback. We tested out the Nouveau driver when using X-Video, the proprietary NVIDIA driver when using X-Video, and the NVIDIA driver when we were using VDPAU. VPAU is only available via NVIDIA's binary driver right now and this is the premiere video decoding API for Linux at this point. It is wonderful and can even allow HD video playback on a $20 CPU and $30 GPU as much of the video work is successfully moved over to the graphics processor.
Again, Nouveau really goes through the power. When comparing both drivers using X-Video, the Nouveau driver went through approximately 10% more power than the binary driver. However, when NVIDIA was using VDPAU, the notebook's power consumption dropped by 7%, or a 16% difference to the free software NVIDIA driver. In fact, the peak power consumption with the NVIDIA driver when using the Video Decode and Presentation API for Unix was even less than the Nouveau driver's average power consumption rate.
As the GPU is more taxed when using VDPAU than X-Video, PowerMizer does not down-clock the GPU core as you can see from the chart above. However, the power savings with VDPAU mostly come as the Intel Core 2 Duo is able to clock itself down to a lower frequency stepping via Enhanced Intel SpeedStep Technology.
As you can see from the chart above, the CPU usage is about the same when playing back the video file on the ThinkPad T61 between Nouveau and NVIDIA with X-Video, but with the NVIDIA driver you get greater power savings. When switching over to VDPAU though, the CPU usage zeros out and is of huge benefit over X-Video. There have been plans to bring VDPAU support to the Gallium3D driver architecture, but so far, it has not materialized.
The results in this article speak for themselves. It is rather unfortunate, but due to the lack of power management work within the Nouveau driver at this time, if you plan to use this free software driver on a mobile NVIDIA device, be prepared to have a much shorter battery life. This is unfortunate with more NVIDIA GPUs appearing in more notebooks and also NVIDIA's ION and forthcoming ION2 chipsets appearing in netbooks.
The Quadro NVS 140M is not even one of NVIDIA's most high-performance, power hungry mobile GPUs. Even still, compared to NVIDIA's official driver, the Nouveau driver burned through 28% more power when idling, 7% more power when gaming, and 10% more power with video playback (or 17% compared to VDPAU). This is all while the NVIDIA driver ran five and a half times faster with the OpenArena game and with VDPAU proved to be a superior solution for video playback. For those with NVIDIA graphics cards in desktops, the lack of proper power management support means greater power consumption, greater energy costs, and the GPU's fan running faster and more loudly. Hopefully in the coming months we will be able to report better news for power management in the Nouveau driver.
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