Bug 133849 - Automatic spell check in calc with many misspelled words causes high CPU load scrolling and text movement
Summary: Automatic spell check in calc with many misspelled words causes high CPU load...
Alias: None
Product: LibreOffice
Classification: Unclassified
Component: Calc (show other bugs)
(earliest affected) release
Hardware: All All
: medium normal
Assignee: Not Assigned
Depends on:
Blocks: Spell-Checking Scrolling-Performance
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Reported: 2020-06-10 09:02 UTC by Telesto
Modified: 2022-01-02 03:56 UTC (History)
3 users (show)

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Crash report or crash signature:


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Description Telesto 2020-06-10 09:02:25 UTC
The spell checker in Calc only checks the on screen part of wrong spelled words. In principle no issue with that. However if you start scrolling, the spell checker 'restarts' checking everything on screen. So also the already checked part. Nothing is cached..

So spell checker is doing same stuff multiple times.. At the same time causes the restart the spell checker repaints of the red underlining.. which means shaping text over and over. And shaping text isn't cheap anymore (since Harfbuzz). 

Which - both together - creates an massive CPU load while scrolling moving text 

Steps to Reproduce:
1. Open the attached file
2. Automatic spell check enabled. Scroll up down & monitor CPU usage

Actual Results:
15-25% depending on scroll speed etc

Expected Results:
Can be improved

Reproducible: Always

User Profile Reset: No

Additional Info:
Version: (x64)
Build ID: 59939d2490726336546c7ad05082d23031074e12
CPU threads: 4; OS: Windows 6.3 Build 9600; UI render: default; VCL: win
Locale: nl-NL (nl_NL); UI: en-US
Calc: CL
Comment 1 Buovjaga 2021-05-07 15:34:35 UTC
(In reply to Telesto from comment #0)
> Steps to Reproduce:
> 1. Open the attached file

Please attach an example document.
Change back to UNCONFIRMED after you have provided the document.
Comment 2 QA Administrators 2021-11-04 04:10:14 UTC Comment hidden (obsolete)
Comment 3 QA Administrators 2022-01-02 03:56:05 UTC
Dear Telesto,

Please read this message in its entirety before proceeding.

Your bug report is being closed as INSUFFICIENTDATA due to inactivity and
a lack of information which is needed in order to accurately
reproduce and confirm the problem. We encourage you to retest
your bug against the latest release. If the issue is still
present in the latest stable release, we need the following
information (please ignore any that you've already provided):

a) Provide details of your system including your operating
   system and the latest version of LibreOffice that you have
   confirmed the bug to be present

b) Provide easy to reproduce steps – the simpler the better

c) Provide any test case(s) which will help us confirm the problem

d) Provide screenshots of the problem if you think it might help

e) Read all comments and provide any requested information

Once all of this is done, please set the bug back to UNCONFIRMED
and we will attempt to reproduce the issue. Please do not:

a) respond via email 

b) update the version field in the bug or any of the other details
   on the top section of our bug tracker

Warm Regards,
QA Team