bug#51886: 29.0.50; pixel-scroll-mode garbage collects like crazy

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Tue, 16 Nov 2021 15:21:31 +0800
>> From:  Po Lu via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> Starting from `emacs -Q', do M-x pixel-scroll-mode RET, then configure
>> it as follows:
>> 
>>     (setq pixel-dead-time 0)
>>     (setq pixel-resolution-fine-flag 1)
>>     (setq garbage-collection-messages t)
>> 
>> Then scroll the display with the mouse wheel.  It will garbage collect
>> like crazy, leading to a great deal of stuttering (in emacs-28 as well).
>> 
>> I want to reuse most of the code in pixel-scroll.el for XInput2 pixel
>> scrolling, but this is holding me back, as the excessive garbage
>> collection makes it completely unusable.
>
> Did you try to figure out which part of the code produces most of the
> garbage?

Here's the report from the memory profiler scrolling down (emacs)Top
with those settings applied in Info:

    347,738,992  30% + beginning-of-visual-line
    203,047,297  17% + end-of-visual-line
    170,995,572  14% + pixel-posn-y-at-point
    143,277,076  12% + pixel-visual-line-height
    113,156,817   9% + pixel-visible-pos-in-window
     99,928,040   8% + if
     11,567,121   1% + pixel-line-height
      9,885,201   0% + pixel--whistlestop-pixel-up
      9,471,180   0% + pixel--whistlestop-line-up
      7,420,310   0% + redisplay
      5,325,728   0% + window-current-scroll-bars
      4,814,936   0% + pixel-scroll-up
      4,092,960   0% + pixel-eob-at-top-p
      3,597,328   0% + profiler-stop
      2,783,202   0% + unless
      2,146,848   0% + window-edges
      1,586,384   0% + sit-for
      1,448,085   0% + window-inside-pixel-edges
      1,297,072   0% + pixel-point-at-top-p
      1,196,572   0% + pixel-scroll-pixel-up
        978,872   0% + mouse-wheel--get-scroll-window
        268,778   0% + apply
        220,291   0% + eval
        166,360   0% + c-type-finder-timer-func
        155,896   0% + timer--time-less-p
        144,822   0% + read-from-minibuffer
        117,312   0% + execute-extended-command
        105,840   0% + timer--time-setter
        102,392   0% + timer-relative-time
         95,312   0% + timer-create
         94,648   0% + pixel-scroll-in-rush-p
         83,304   0% + Info-check-pointer
         66,944   0% + mwheel-scroll
         65,968   0% + Info-extract-pointer
         38,435   0% + completing-read-default
         38,008   0% + frame-focus-state
         32,736   0% + funcall-interactively
         29,768   0% + posn-at-point
         22,176   0% + timer-activate
         17,952   0% + window-pixel-edges
         17,136   0% + call-interactively
         15,840   0% + redisplay_internal (C function)
         12,664   0% + command-execute
         12,432   0% + jit-lock--run-functions
         11,248   0% + menu-bar-update-buffers-1
          8,288   0% + #<compiled 0x19a292a7afa00b7d>
          8,184   0% + x-gtk-map-stock
          7,494   0% + window-frame
          7,432   0% + pos-visible-in-window-p
          7,312   0% + jit-lock-fontify-now
          6,336   0% + #<compiled 0xa2ad9af8e9ade27>
          6,336   0% + user-error
          6,336   0% + undo-auto--boundaries
          3,810   0% + line-number-at-pos
          2,120   0% + scroll-up
          1,959   0%   timer-event-handler
          1,921   0% + fboundp
          1,905   0% + window-scroll-bars
          1,905   0% + constrain-to-field
          1,905   0%   clear-minibuffer-message
          1,905   0% + frame-live-p
          1,863   0% + window-margins
          1,863   0% + line-pixel-height
          1,863   0% + mwheel-event-button
          1,863   0% + profiler-memory-running-p
          1,056   0% + handle-focus-in
          1,056   0% + minibuffer-mode
          1,056   0% + #<compiled 0x1d710e244bc5248e>
          1,056   0% + menu-bar-update-buffers
          1,056   0% + keymap-canonicalize
          1,056   0% + run-hooks
          1,024   0%   mouse-fixup-help-message
            912   0% + count-lines
            631   0% + profiler-start
             21   0% + generate-new-buffer

And here's the entire profile:

profile
Description: Binary data

I hope this helps, thanks.