SUMMARY *** scrolling a lot of text incurs large performance overhead. konsole is consuming up to 65% of a single core if I'm doing, f.e. , `tail` -f of a quickly updating log file *** STEPS TO REPRODUCE 1. induce scrolling . easiest way is to run 'while [ 1 ] ; do echo 'testtesttesttesttest' ; done 2. open `top` or run another performance monitor OBSERVED RESULT high cpu usage, over 50% of a single core EXPECTED RESULT negligible cpu usage, as with other terminal emulation software SOFTWARE/OS VERSIONS Linux/KDE Plasma: KDE Plasma Version: kde-frameworks/plasma-5.104.0:5/5.104 KDE Frameworks Version: 5.104 Qt Version: 5.15.8 ADDITIONAL INFORMATION I have tested this with both Gentoo packages built from source by myself , and precompiled Arch linux packages. During investigation I've compiled konsole and QtGui with debugging symbols, and ran `perf record` + `perf report` dwhile reproducing the issue. The culprit seems to be incorrect or excessive usage of alphargbblend_argb32 37.13% 0.00% konsole libQt5Gui.so.5.15.8 [.] QtSharedPointer::ExternalRefCountWithCustomDeleter<QColorTrcLut, QtSharedPointer::NormalDeleter>::deleter | ---QtSharedPointer::ExternalRefCountWithCustomDeleter<QColorTrcLut, QtSharedPointer::NormalDeleter>::deleter 0x5645ea71a9c0 | |--31.87%--alphargbblend_argb32 | --5.26%--qt_alphargbblit_argb32
I can repro the same issue with qterminal , but with smaller performance hit (CPU usage hovers in 20% to 50%, which is still too much compared with VTE-based terminals). Highest CPU consumer is the same (alphargbblend_argb32 )
Please re-try that with 24.08 or later. Thanks!
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24.12.0 does not exhibit this issue any more. I did the same test, and , while I was able to make konsole consume 100% cpu on scrolling, both scroll speed and konsole responsiveness were much higher, and alternative terminal emulation software produced similar results (100% CPU usage, due to internal issues not related to QT ). I think this bug could be marked as resolved.