Bugzilla

> intel_gpu_top reports roughly twice as high GPU load with WR compositor enabled vs. disabled and higher GPU power consumption accordingly.

To me that sounds like missing optimizations regarding opaque regions and subsurfaces in Kwin. Things *should* look quite different on Gnome and, more importantly, in theory (on a perfect compositor).
Regarding low end devices: I also test this on an old Thinkpad T400 and get quite good results. It was also reported that this improves performance on e.g. the Pinephone. That was on Gnome (which has dynamic latency reduction based on measurements) and Weston (which like Gnome should have proper optimizations for subsurfaces in place) though.

Anyway, please let's continue any performance related conversation either in bug 1717902 or open a new bug for compositor specific issues (such as "Higher GPU utilization on Kwin" / "Performance on Kwin"). From your report the later sounds like a good idea.

> intel_gpu_top reports roughly twice as high GPU load with WR compositor enabled vs. disabled and higher GPU power consumption accordingly.

To me that sounds like missing optimizations regarding opaque regions and subsurfaces in Kwin. Things *should* look quite different on Gnome and, more importantly, in theory (on a perfect compositor).
Regarding low end devices: I also test this on an old Thinkpad T400 and get quite good results. It was also reported that this improves performance on e.g. the Pinephone. That was on Gnome (which has dynamic latency reduction based on measurements) and Weston (which like Gnome should have proper optimizations for subsurfaces in place) though. Kwin and Sway are the compositors I know least about.

Anyway, please let's continue any performance related conversation either in bug 1717902 or open a new bug for compositor specific issues (such as "Higher GPU utilization on Kwin" / "Performance on Kwin"). From your report the later sounds like a good idea.