https://bugs.documentfoundation.org/show_bug.cgi?id=157830
Bug ID: 157830
Summary: When scrolling a document at a resolution of 4k, CPU
usage jumps to 50% or more and performance is
laggy/choppy.
Product: LibreOffice
Version: 7.6.2.1 release
Hardware: x86-64 (AMD64)
OS: Linux (All)
Status: UNCONFIRMED
Severity: normal
Priority: medium
Component: Writer
Assignee: libreoffice-bugs@lists.freedesktop.org
Reporter: jake.m.knep...@gmail.com
This is pretty easy to replicate.
LibreOffice version: 7.4, 7.5, 7.6 (exits in Flatpak versions and native
versions, such as .deb and .rpm)
Hardware I've tested this on (different distros listed and tested on each one):
Machine #1: 2700x, RX 580, DDR4 16GB 3200mhz RAM (Debian 12/Linux Mint
21/Fedora 38/KDE Neon)
Machine #2: 13700k, RX 7900 XT, DDR5 32GB 7200mhz RAM (Ubuntu 23.10/Fedora
38/Fedora 39 Beta/Most recent version of MX Linux)
I used a 40 page document, both in .odt and .docx. Results were the same.
To replicate (it is CRITICAL to test for this bug at 4k - 1920x1080 is too low
of a resolution and won't reproduce the result!):
1. Make sure display resolution is set to 3840x2160 (4k).
2. Open LibreOffice Writer.
3. Open any multi-page document, the bigger the better.
4. Scroll.
5. Observe that CPU usage of a core or two will spike well beyond 50% or more.
6. Observe choppy, laggy performance - your fans might even spin up on the CPU
to compensate for the high usage.
Increasing resolution definitely makes it worse.
Setting scaling to 200% or 150% also makes it worse, but not by a lot. The
problem seems to exist independent of scaling. As noted, the higher the
resolution, the more LibreOffice hits the CPU when scrolling and the laggier it
gets.
Not sure why this is happening. Microsoft Word only uses about 3% CPU when
scrolling through a large document and isn't laggy at all. Very smooth.
I thought maybe it was a GTK thing, but it's not since it still happens on KDE
Neon.
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