GNU bug report logs - #74813
31.0.50; scroll-down is 10x slower and laggy than scroll-up

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From: Eli Zaretskii <eliz <at> gnu.org>
To: execvy <at> gmail.com
Cc: 74813 <at> debbugs.gnu.org
Subject: bug#74813: 31.0.50; scroll-down is 10x slower and laggy than scroll-up
Date: Fri, 10 Jan 2025 10:20:55 +0200

> Date: Fri, 10 Jan 2025 16:04:47 +0800
> From: execvy <at> gmail.com
> 
> My auto-repeat rate is 100 times/second

Mine is 30/sec.  Maybe this is the reason for what you see.
Programmatically, M-v needs to do more than C-v does, so if your CPU
is not powerful enough, maybe Emacs cannot keep up with 100 keys per
second moving back.

If this is the reason, then it's expected.

> It's hard to notice performance difference by eyes and hands.
> You can do profiler-start (cpu) and profiler-report, then you will notice
> the profiler result is totally different.

The profiler result is expected to be different, because M-v invokes
different functions than C-v does.

What I measured is the total time of scrolling through the entire
file, and I didn't see any difference, as reported: 35 sec both down
and up.  I measured the time with a stopper, not by eyes.

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