An Optimized Open-Source Driver Tries To Compete With AMD Catalyst
There's been a number of recent open-source driver improvements that have come about for modern ATI/AMD Radeon graphics cards under Linux, but not all of these features have yet to be merged or enabled by default (e.g. 2D color tiling, PCI Express 2.0, and HyperZ). With some basic tweaks, can the open-source Radeon Gallium3D driver now compete with AMD's proprietary Catalyst Linux driver when it comes to OpenGL performance? Let's see.
For a number of different graphics cards spanning several generations of Radeon GPUs, this article provides a comparison of the recent Catalyst driver (as found in Ubuntu 12.04) to the default open-source driver experience on Ubuntu 12.04 LTS (using Linux 3.2 + Mesa 8.0.2) and then lastly in the "Tweaked Git" state that basically puts each graphics card in the best state for being most performance-enhanced to compete with AMD's binary blob.
The "Tweaked Git" state included updating to the latest Linux kernel (Linux 3.5), libdrm, xf86-video-ati, and Mesa (8.1-devel) from their Git master repositories as of 8 June 2012. The tweaks included:
- Patching Mesa 8.1-devel git-306c9f0 with the latest R600g HyperZ/HierarchicalZ patch. This ended up being the 0001-r600g-add-htile-support-v6 patch from Jerome Glisse and then setting R600_HYPERZ=1 as an environment variable when testing the R600+ class hardware. However, for not all graphics cards did this HyperZ support work out well so for some GPUs it had to be disabled where it caused adverse effects or other issues.
- Enabling PCI Express 2.0 support via passing radeon.pcie_gen2=1 to the kernel at boot time. Due to bugs for a small minority of Linux users on the open-source Radeon driver, PCI Express 2.0 bandwidth is not even used when running a PCI-E 2.0 graphics card on a PCI-E 2.0 motherboard. PCI Express 2.0 support for the Radeon driver has been around for many months and PCI-E 2.0 can really boost the graphics performance, but it has been hidden behind the kernel parameter that is not widely known to Linux desktop users aside from graphics enthusiasts. It is silly that the Radeon PCI-E 2.0 issues have not yet been worked out so that the common feature can be enabled by default.
- The Linux 3.5 kernel by default provides some mighty performance improvements due to an important bug-fix affecting some "Evergreen" graphics processors.
- For both the Ubuntu 12.04 stock and tweaked configuration, swap buffers wait was disabled to avoid syncing to vblanks via SwapbuffersWait in the xorg.conf. (The Phoronix Test Suite also does vblank_mode=0 by default for all open-source drivers.)
- 2D color tiling can provide performance improvements and was manually enabled. Setting true for ColorTiling and ColorTiling2D in the xorg.conf can enable 2D color tiling for R600+ hardware. However, for some GPUs the 2D color tiling can still cause problems.
- KDE 4.8.3 was used as the desktop environment rather than the default Unity desktop with Compiz, since Unity/Compiz can cause OpenGL performance problems (though some OpenGL problems are fixed now with Unity 5.12). KDE's KWin was also set to suspend desktop effects on full-screen applications (see Tweaking KDE's KWin For Linux Gaming Performance). KDE was the default just not for the tweaked driver state but for all of the benchmarking in this article.
The graphics cards being compared in this article under the three configurations (stock Ubuntu 12.04, stock Catalyst, Tweaked Git) included the Radeon HD 6950, HD 6870, HD 6770, HD 6450, HD 5830, HD 5750, HD 4890, HD 3850, HD 3650, X1950PRO, and X1800XL. No Radeon HD 7000 series graphics card was tested since there still is not yet any usable open-source support. The Radeon X1950PRO and X1800XL graphics cards are from the R500 generation and use the R300 Gallium3D driver that is now mature and feature-complete, but the results were done for reference in this article to compare to the R600g-enabled graphics cards.
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