Cinnamon causes generally a much hotter CPU than e.g. GNOME classic

"Recently" I've stumbled over the temperature issues described in #953 (closed) (which is likely a duplicate of #614 (closed)) and made in addition the observation that (even under kernel 5.2, where, AFAIU, the issue of #614 (closed) shouldn't be present) the Cinnamon desktop environment causes generally a much hotter CPU/GPU than e.g. GNOME classic does. @ickle suggested to file a separate bug for this.

I've made some more extensive test series (see #953 (comment 380857)) from which I conclude that in 5.2 (in 5.4 it's much much worse) an idle Cinnamon runs ~2°C hotter than an idle GNOME Classic (which is just GNOME Shell with some extra extensions).

This isn't much, but things look far worse, if playing videos (or when moving around windows in circles): For a low res video in full screen, Cinnamon yields in 75°C with VAAPI - GNOME only 56°C ... 20°C difference.

For details of my testing methods, versions, etc. please have a look at #953 (comment 380857) .

Now of course Cinnamon and GNOME Shell aren't exactly the same (though I though Cinnamon is a fork of the later an thus maybe they aren't that different either), but I'd only expect that it runs generally maybe 2°C hotter (because having more background services or so),... but just playing a video shouldn't cause that huge difference.

So I guess there must be some issue here, either Cinnamon doing something inefficiently or in a way not expected/intended by the kernel graphics stack. I've also filed https://github.com/linuxmint/cinnamon/issues/9085

If anyone could help or tell me what to try/debug... it would be great.

Thanks, Chris.