Kubuntu 15.10 Gaming Impact With KDE Plasma 5 Compositing For R600 Gallium3D
Written by Michael Larabel in KDE on 26 October 2015 at 11:19 AM EDT. 42 Comments
KDE --
With yesterday's Fedora 23: KDE vs. Xfce vs. GNOME vs. LXDE vs. MATE article that looked at the OpenGL graphics impact of different desktop environments on the new Fedora Linux release, what most people were talking about were the KDE results.

As mentioned in yesterday's article with KDE Plasma 5 generally leading to a slower gaming experience than GNOME, Xfce, LXDE, and MATE, the issue comes down to KDE continuing to composite full-screen windows by default. This leads to a performance penalty as has been explained and tested in many articles before on Phoronix. For making things fair, it was a performance comparison of these Fedora 23 desktop environments out-of-the-box as representative what a new user would encounter and making the assumption the software vendor makes the best decisions regarding defaults. However, in the comments to yesterday's article were several requests for running some fresh tests to show the impact of the full-screen window compositing versus when the compositing is suspended.

By the time those requests came in, that particular system with its Fedora 23 installation had been wiped and was running Ubuntu 15.10. So I switched over to Kubuntu 15.10 for running this quick comparison. Kubuntu 15.10 ships with the latest KDE Plasma + KDE Frameworks experience, Linux 4.2 kernel, and Mesa 11.0.2. The FirePro V7900 has a Cayman GPU that's supported by the R600g driver.

This follow-up testing was almost foiled though due to Plasma 5 issues. On the first boot, the bottom panel was mis-rendered with the clock appearing in the wrong location and the other icons being rendered entirely tiny.

Shortly after that, Plasma had a segmentation fault...

When rebooting the system, the bottom panel was still acting up, albeit differently... Yes, this is with the latest KDE Plasma 5 + KDE Frameworks 5 stack on Kubuntu 15.10.

After another reboot, things started working! So I ran tests of this KDE Plasma experience on Kubuntu 15.10 out-of-the-box and then after the compositing tweak (suspend compositing via Alt + Shift + F12).

To no surprise and in line with past results when specifically comparing the functionality, once changing the compositing rule, the Linux gaming performance was noticeably faster...

KDE Plasma 5 could now probably compete with the other desktop environments, but this isn't the default behavior. Full-screen windows continue to have this overhead since reportedly otherwise on alt-tab'ing out of full-screen games there can be tearing and previously this functionality was needed for full-screen color correction. There's plenty more commentary in this forum thread.

Fortunately this FirePro V7900 with Cayman GPU is fast enough that the averages either way are greater than 60 FPS... However, with lower-end Radeon GPUs or especially NVIDIA hardware on Nouveau where re-clocking may only partially work, this could mean the difference of a playable experience or not.

Anyhow, if you care to see more of these benchmark results, you can find this performance data via this OpenBenchmarking.org result file. It seems unlikely that the default behavior will change though as Martin of KWin wrote in the forums this weekend that they assume Linux gamers to turn off desktop effects before gaming or start their game in its own dedicated X Server.
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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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