The Cost Of ATI Kernel Mode-Setting On Fedora 12
Written by Michael Larabel in Display Drivers on 25 November 2009. Page 3 of 3. 34 Comments

Next up we have results for World of Padman when run at 800 x 600, 1024 x 768, and 1280 x 1024. When running Fedora 12 with its Mesa stack, World of Padman would end up freezing halfway through the testing process at resolutions greater than 1280 x 1024 in our configuration. Anyways, Fedora 12 (UMS) and Fedora 10 were neck-and-neck in terms of frame-rate performance at 800 x 600 and 1024 x 768 resolutions, while at 1280 x 1024 the Fedora 12 configuration with nomodeset had a higher frame-rate. Fedora 12 with kernel mode-setting continued to suffer. At 1280 x 1024, when running Fedora 12 with the default kernel mode-setting for the ATI R520 GPU its frame-rate was 44 FPS, but when simply switching to using the older mode-setting paths it resulted in a frame-rate of 101 FPS.

Lastly, we have results from the Unreal Tournament 2004 Demo. This game had not run on Fedora 10 with the Mesa stack there, so these results are limited to Fedora 12 between user and kernel mode-setting. At 800 x 600, 1024 x 768, and 1280 x 1024, the results were rather close for this OpenGL game between UMS and KMS, but when upping the resolution the older code paths prevailed with it ending out at 43 vs. 29 FPS in favor of user-space mode-setting.

Running Fedora 12 with ATI kernel mode-setting may cost you a great deal in terms of quantitative performance, unless your system configuration happens to be exempt from these problems. However, anyone can switch to using the traditional DDX mode-setting by simply adding nomodeset to their /etc/grub/grub.conf configuration in Fedora -- unless you really love seeing Plymouth and using a virtual terminal at the monitor's native resolution, etc. While the performance differences right now are large between the UMS and KMS paths, these performance regressions should be addressed shortly as the new ATI Linux driver stack matures, and hopefully this will all be worked out by Fedora 13 and when other distributions begin using ATI kernel mode-setting next year once it exits the staging driver area.

These initial performance drops though are not exactly surprising though since the ATI Linux code is going through the same overhaul that the Intel driver was going through earlier this year when its performance was a disaster earlier this year when tackling the fallout from the kernel mode-setting, memory management, and other underlying work. As always, if you have problems with your ATI Linux setup stop by the Phoronix Forums and at Phoronix-Test-Suite.com is our open-source testing software if you wish to quantify any problems you have been encountering.

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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.


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