Comment 3 for bug 1744515

The 'Show Repaint' plugin in compiz showed that most of the screen was not getting repainted. Disabling 'Framebuffer object' under OpenGL, in ccsm (CompizConfig Settings Manager), caused the whole screen to be repainted but CPU usage of compiz stayed the same. If Workarounds > 'Force full screen redraws (buffer swap) on repaint' was enabled, CPU usage without Framebuffer object was the same, but with both on, CPU usage of compiz was ~3% higher (from 13% to 16% with CPUs at lowest frequency).

Kworker CPU usage doesn't seem to change when I switch CPUs from 1/3 frequency, to maximum frequency. Compiz drops about 1/3 when I do so (instead of 2/3). On highest frequency, the problem kworker thread uses three times the CPU of compiz.

kworker CPU usage seems proportional to the frames-per-second recorded in the Benchmark plugin. When the ffplay window is reduced to 1 pixel height, so it shows only a constant blue line for audio frequencies, the Benchmark still shows ~55 fps. Toggling on or off the benchmark makes it fade with high fps (from 60 fps), which shows same high kworker usage.

(Metacity has screen tearing.)