With the Fermi acceleration code having been merged into the Linux 2.6.38 kernel, the user-space DDX code for the X.Org Server was merged to xf86-video-nouveau as well. The other piece of the equation then is to be using a Git snapshot of xf86-video-nouveau (they're still not doing releases) after 2011-01-16. For 3D acceleration, the support has also been pushed into Git for Mesa 7.11 with Nouveau Gallium3D via the "NVC0" driver.
By the time of Ubuntu 11.10, Fedora 16, etc there will hopefully be pleasant "out of the box" GeForce 400/500 GPU support. For now though just ensure you are using Linux 2.6.38 or newer, Mesa 7.11-devel, xf86-video-nouveau Git, and the custom "fuc" firmware. It is also best using the Linux 2.6.39 kernel or newer due to page-flipping support that leads to faster performance. For today's testing, Git of all major components (including the pre-2.6.39-rc1 kernel) were used as of 2011-03-28.
There has already been some Nouveau Fermi benchmarks on OpenBenchmarking.org by independent users, but in this article a NVIDIA GeForce GTX 460 is being used. The performance is being compared to the proprietary NVIDIA driver 270.30 beta release.
To see how well the Nouveau NVC0 performance compares to the previous-generation Nouveau NV50 driver, there's benchmarks too from a GeForce GT 220 and GeForce 9800GT under the same Nouveau driver stack and then with the binary driver. Results from a GeForce GTX 485M mobile Fermi GPU will be published in the coming days from a System76 Serval Professional.
These open-source Linux tests were carried out on the Intel Sandy Bridge system as of late; Intel Core i5 2500K, Sapphire Pure Black P67 Hydra motherboard, 4GB of system memory, and 250GB Seagate SATA HDD. Ubuntu 10.10 x86_64 was the base operating system aside from the graphics stack changes.
With this initial Nouveau NVC0 testing, some games at some resolutions also experienced rendering problems, as shown by the screenshots. Over the course of a day's testing, the Nouveau DRM on the GeForce GTX 460 caused a lock-up a few times (both issues also found on the GeForce GTX 485M).
Hopefully by the time the NVC0 firmware is sorted out, these initial problems will be addressed, but regardless it's quite impressive how far the open-source Fermi support has come in less than a year with clean-room reverse-engineering by a few developers and few GeForce 400 owners testing out the code. Now let's see where the performance is at with Nexuiz, OpenArena, World of Padman, Urban Terror, and VDrift.