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Re: emacs rendering comparisson between emacs23 and emacs26.3


From: Dmitry Gutov
Subject: Re: emacs rendering comparisson between emacs23 and emacs26.3
Date: Sun, 5 Apr 2020 21:05:00 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 05.04.2020 19:15, Eli Zaretskii wrote:
Do you at least see CPU activity significantly go up when you do such
mouse wheel scrolling?
With what build?  With the -O0 build with --enable-checking, I don't
need the mouse: it's enough to lean on C-v and let the keyboard
auto-repeat do its job -- one execution unit of the CPU maxes out
after 5 to 10 C-v's.

But with a -O2 optimized production build, Emacs keeps up both when I
lean on C-v and when I turn the mouse wheel constantly.

Same here. And much as I like to see certain modes improved, I'm not sure this is only a performance problem. Because no matter how fast syntax highlighting is, you can lean on C-v faster.

IIRC, redisplay-dont-pause was supposed to help with things like this. But it doesn't (and it's obsolete), and apparently jit-lock does its thing anyway. This looks like the interesting part of the profile:

    - scroll-up                                              5657  73%
     - jit-lock-function                                     5444  70%
      - jit-lock-fontify-now                                 5439  70%
       + jit-lock--run-functions                             5431  70%
       + run-with-timer                                         5   0%

Do you guys want to try (setq jit-lock-defer-time 0)? It comes with a certain visual downside, though.

Or, alternatively, (setq fast-but-imprecise-scrolling t). This var seems like a good idea in general, so we might consider going further with it.



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