ATI Radeon KMS vs. UMS Performance With Ubuntu 10.04

Earlier this week we published comparative benchmarks of Mandriva, PCLinuxOS, Ubuntu, and openSUSE. In the discussion that followed, a number of people requested a set of tests that compare the performance of the ATI Radeon Linux graphics driver stack with kernel mode-setting (KMS) vs. user-space mode-setting (UMS), so today we have such results to deliver.

The kernel mode-setting support for ATI Radeon graphics processors left the staging area of the Linux kernel with Linux 2.6.33 and it's been adopted by Fedora, Ubuntu, and various other Linux distributions. Kernel mode-setting allows for a cleaner boot experience, better VT switching, the ability for the X Server to run without root privileges, and other advantages. Kernel mode-setting is the way forward and it is following the work done by Intel on their driver and it is the only method of mode-setting that is supported by the Nouveau graphics driver.

With the Radeon driver, kernel mode-setting is even more important as the DRI2 (Direct Rendering Infrastructure 2) support is only implemented along the KMS code path and is not active when using user-space mode-setting. ATI kernel mode-setting is supported for the R700 series (Radeon HD 4000 series) and all earlier graphics card generations, while the R800 (Radeon HD 5000 series) support is still emerging but will be present in the Linux 2.6.34 kernel but without any 2D/3D/video acceleration.

In the case of Ubuntu 10.04, they have back-ported all of the Linux 2.6.33 DRM onto the Linux 2.6.32 kernel so the DRM is in relatively good condition (albeit lacking in-kernel GPU power management and the very other latest additions) and its X.Org driver is following an xf86-video-ati 6.13 snapshot. On the 3D side there is Mesa 7.7, but the soon to be released Mesa 7.8 will not be pulled in for the Lucid Lynx release.

For this Ubuntu ATI KMS testing we compared the 3D graphics (OpenGL) performance using an Ubuntu 10.04 daily development snapshot from 2010-03-17 and ran our battery of tests when using the default kernel mode-setting and then again when we disabled KMS so that the older user-space mode-setting was used. The graphics card under test was an ATI Radeon HD 4870 512MB graphics card that was residing within a AMD Opteron 2384 Quad-Core workstation with a Tyan S2927 motherboard, and an OCZ 64GB Agility EX SSD. On the software side with our 2010-03-17 snapshot of Ubuntu 10.04 was the 2.6.32-16-generic (x86_64) kernel, GNOME 2.29.92, X Server 1.7.5, xf86-video-radeon 6.12.191, and an EXT4 file-system. The screen resolution was 1920 x 1080 for the Dell S2409W LCD display.

Through the Phoronix Test Suite we ran the World of Padman, OpenArena, Tremulous, Urban Terror, and VDrift tests. On the next two pages are the results.