KWin Can Cause A Performance Hit Too, But It's Different From Compiz

Last week we published Arch Linux vs. Ubuntu benchmarks to finally lay to rest that for the overall system performance the speed of the rolling Arch Linux distribution is not too different from that of Ubuntu when running with similar package versions. One of the areas, however, where the performance was different with the "out of the box" experience was the OpenGL gaming where Ubuntu was using Compiz by default where as Arch had Metacity. This surprised many so we published another article entitled The Cost Of Running Compiz where we showed the performance penalties of a compositing window manager with different hardware and drivers. This led some to ask whether the performance of KWin also causes the OpenGL frame-rate to drop, so here are those KDE benchmarks.

Our KWin testing was done with the same hardware and software as last week's tests. This included an Intel Core i3 530 processor clocked at 3.32GHz, an ECS H55H-M motherboard, 2GB of system memory, and a 65GB OCZ Vertex SSD. When testing the Intel graphics we used the integrated Clarkdale graphics, for the ATI graphics we used a Radeon HD 4830 graphics card, and for the NVIDIA graphics was a GeForce 9800GT. The testing was done on a stock Kubuntu 10.04 installation with the Linux 2.6.32-21-generic x86_64 kernel, KDE 4.4.2, X.Org Server 1.7.6, Mesa 7.7, xf86-video-intel 2.9.1, xf86-video-ati 6.13.0, Catalyst 10.4, and NVIDIA 195.36.15 drivers.

The games we ran for this Compiz testing included Warsow, OpenArena, World of Padman, Tremulous, Urban Terror, Nexuiz, VDrift, Unigine Sanctuary, Unigine Tropics, Unigine Heaven, and Lightsmark. Testing was done with the Phoronix Test Suite. The results from the Radeon UMS-DRI1 testing were left out from publishing in this article to give more room for the extra KWin results and that the ATI Radeon driver performance when using user-space mode-setting with the older DRI1 support had not changed much between Compiz/KWin/Metacity.

Starting with Warsow, the results were immediately interesting for KWin. With the Intel Clarkdale graphics configuration, KWin caused no performance penalty compared to Metacity without compositing where as with Compiz there was the Intel performance drop to note. With the ATI Catalyst driver there was also no performance drop under KWin (but it was actually slightly faster), but last week's results already show that the Catalyst driver handles compositing support quite well. With the proprietary NVIDIA driver there continued to be a performance drop with KWin that was similar to Compiz.

With OpenArena, there again was no performance drop to note with the Intel Clarkdale graphics when running the KDE 4.4 desktop with Kwin where as with Compiz on GNOME the frame-rate dropped from 37 to 32 FPS. With the open-source Radeon driver bearing KMS/DRI2 support there was a performance hit when running OpenArena with KWin and the hit was even more significant than when Compiz was running. Again, with the Catalyst driver there was no significant performance difference between the Compiz, KWin, and Metacity window managers while the proprietary NVIDIA driver had encountered another performance hit.