You do realize it's the thing compositing your desktop, right? it's not 1995

londons_explore · on July 5, 2023

For which, no CPU time is needed - all it's doing is pointing the GPU towards the right buffers to render in the right places.

pengaru · on July 5, 2023

It's a long-running process that's waking up constantly for IPC+compositing duties alone.

If you're still on X I'd expect more of the compositing cost reflected in the Xorg process than gnome-shell.

But on a "modern" Wayland-based gnome session, the gnome-shell process encompasses what used to occur in Xorg. So all that time is now attributed to gnome-shell.

It's not like you just arrange the GPU with some buffers and never wake up to send it commands on what to draw when. The compositor is a rather busy process, esp. if you have many clients/windows active.

This stuff was easier to reason about in the Xorg days with WM "policy" running in a clearly separate process from the X "mechanism" side. Wayland tends to conflate everything, unless the compositor developers choose to use separate well-labeled threads for things like input/compositing/policy...

I don't personally use gnome so it's inconvenient for me to check despite mild curiosity. It may be interesting to look at a threaded view of `top` if you're on Wayland, and see if gnome-shell has clearly separated threads.

Interestingly, modern Xorg uses separate threads now, from this machine:

  524 anon    20   0  637516  92996  53592 S   5.3   0.6  82:54.35 Xorg
  525 anon    39  19  637516  92996  53592 S   0.0   0.6   0:00.00 Xorg:disk$0
  526 anon    20   0  637516  92996  53592 S   1.0   0.6  36:32.18 Xorg:gdrv0
  527 anon    39  19  637516  92996  53592 S   0.0   0.6   0:00.00 Xorg:disk$0
  529 anon    20   0  637516  92996  53592 S   1.0   0.6   1:10.52 InputThread

So gdrv0 alone has consumed 36.5 hours during my ~1.5 day uptime.

If this were a Wayland situation, that time would be reflected in my compositor process instead.

~83 hours for the main Xorg thread, which I presume is largely IPC but X also does heaps of crap from its huge protocol on-CPU so I think it's best to just ignore that.

londons_explore · on July 5, 2023

I debugged it, and found: https://news.ycombinator.com/item?id=36608714