GNU bug report logs - #77961
31.0.50; Rendering HTML email is very slow since commit #eab14d68b2e72b9a6b8b0cc67c9667c2bfbed4f5

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From: martin rudalics <rudalics <at> gmx.at>
To: Eli Zaretskii <eliz <at> gnu.org>, Gerd Möllmann <gerd.moellmann <at> gmail.com>
Cc: yantar92 <at> posteo.net, inigoserna <at> gmx.com, 77961 <at> debbugs.gnu.org
Subject: bug#77961: 31.0.50; Rendering HTML email is very slow since commit #eab14d68b2e72b9a6b8b0cc67c9667c2bfbed4f5
Date: Wed, 23 Apr 2025 08:17:29 +0200

>>> Looking into reverse call tree (B), I see that
>>>
>>>          1874  33% + set-window-configuration
>>>
>>> takes 1/3 of CPU cycles. Looking into its source, it does deal with
>>> glyph matrices. So, it is the suspect, judging from the submitted
>>> profiler report.
>>
>> Thanks, indeed.
>>
>> Which I also find weird. Why is that done in the first place?
>
> If the comment in set-window-configuration before it messes with glyph
> matrices doesn't answer this question, maybe Martin (CC'ed) can help us
> understand the reason?

Do you mean the adjust_frame_glyphs call?  It's called whenever we may
have changed window sizes.  We could have 'set-window-configuration' use
checks similar to those from run_window_change_functions.  But such a
change would have to be done with considerable care: After all, an
accidentally missing call of 'window-size-change-functions' would be
hardly noticed.  The missing update of a glyph matrix would be much more
harmful.

'save-window-excursion' should be banned.  Its reminder

  BEWARE: Most uses of this macro introduce bugs.

is much too mild in my opinion.  AFAICT the first two calls in shr.el
could be avoided by using 'buffer-text-pixel-size'.  The one in
'shr-render-td-1' looks worse - since it calls 'shr-pixel-buffer-width'
it nests one 'save-window-excursion' call into another which is simply
evil.

martin

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