bug#46350: 28.0.50; touchpad-scrolling-eats-lots-of-cpu-samples

[Eli Zaretskii <eliz@gnu.org>]

> From: Andrey Orst <andreyorst@gmail.com>
> Date: Sun, 7 Feb 2021 21:33:25 +0300
> Cc: 46350@debbugs.gnu.org
> 
> On Sun, Feb 7, 2021 at 8:49 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > 1350 calls during what time, approximately? less than a second?
> 
> If you've watched the video I've linked

I cannot watch that video, sorry.  But I don't think it matters, see
below.

> you can get a sense of what
> time it takes -- about 15 seconds. Or more if I continue swyping
> rapidly, since Emacs just sits at the bottom eating all input until I
> stop.

I didn't ask how much time it takes Emacs to process the inputs.  I
asked how much time did it take you to generate them by moving your
finger on the touchpad.  I very much doubt the answer to that is 15
sec.

> Touchpad generates about 20-30 inputs per swipe, so I think ~90 inputs
> is maximum human can produce in 1 second

~100 1-line scrolls per second is also a lot, for what Emacs must do
to scroll.

> Can Emacs poll mouse events less frequently?

Emacs doesn't poll the mouse.  The mouse events are received from the
X event queue, together with all the other events: keyboard input,
expose events, etc.  We read the events from X and then process them
one by one.

> > So, once we've established that the touchpad injects 1-line scroll
> > requests at such a high rate, what else needs to be investigated here?
> 
> There I was talking about progressive speed turned on, as it builds up
> almost instantly with my touchpad producing 30 inputs per swipe.

Sorry, I don't understand: what builds up?