Performance hackfest

Last evening I came back from the GNOME performance hackfest happening in Cambridge. There was plenty of activity, clear skies, and pub evenings. Here’s some incomplete and unordered items, just the ones I could do/remember/witness/talk/overhear:

  • Xwayland 1.20 seems to be a big battery saver. Christian Kellner noticed that X11 Firefox playing Youtube could take his laptop to >20W consumption, traced to fairly intensive GPU activity. One of the first things we did was trying master, which dropped power draw to 8-9W. We presumed this was due to the implementation of the Present extension.
  • I was looking into dropping the gnome-shell usage of AtspiEventListener for the OSK, It is really taxing on CPU usage (even if the events we want are a minuscule subset, gnome-shell will forever get all that D-Bus traffic, and a11y is massively verbose), plus it slowly but steadily leaks memory.

    For the other remaining path I started looking into at least being able to deinitialize it. The leak deserves investigation, but I thought my time could be better invested on other things than learning yet another codebase.

  • Jonas Ã…dahl and Christian Hergert worked towards having Mutter dump detailed per-frame information, and Sysprof able to visualize it. This is quite exciting as all classic options just let us know where do we spend time overall, but doesn’t let us know whether we missed the frame mark, nor why precisely would that be. Update: I’ve been pointed out that Eric Anholt also worked on GPU perf events in mesa/vc4, so this info could also be visualized through sysprof
  • Peter Robinson and Marco Trevisan run into some unexpected trouble when booting GNOME in an ARM board with no input devices whatsoever. I helped a bit with debugging and ideas, Marco did some patches to neatly handle this situation.
  • Hans de Goede did some nice progress towards having the GDM session consume as little as possible while switched away from it.
  • Some patch review went on, Jonas/Marco/me spent some time looking at a screen very close and discussing the mipmapping optimizations from Daniel Van Vugt.
  • I worked towards fixing the reported artifact from my patches to aggressively cache paint volumes. These are basically one-off cases where individual ClutterActors break the invariants that would make caching possible.
  • Christian Kellner picked up my idea of performing pointer picking purely on the CPU side when the stage purely consists of 2D actors, instead of using the usual GL approach of “repaint in distinctive colors, read pixel to perform hit detection” which is certainly necessary for 3D, but quite a big roundtrip for 2D.
  • Alberto Ruiz and Richard Hughes talked about how to improve gnome-software memory usage in the background.
  • Alberto and me briefly dabbled with the idea of having specific search provider API that were more tied to Tracker, in order to ease the many context switches triggered by overview search.
  • On the train ride back, I unstashed and continued work on a WIP tracker-miners patch to have tracker-extract able to shutdown on inactivity. One less daemon to have usually running.

Overall, it was a nice and productive event. IMO having people with good knowledge both deep in the stack and wide in GNOME was determining, I hope we can repeat this feat again soon!

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