Created attachment 117748 [details] Screenshot of KSysGuard with montor plugged in via HDMI SUMMARY A laptop running Plasma slows down significantly when a secondary monitor is plugged in via HDMI. Doesn't seem to slow down when plugged in via VGA. STEPS TO REPRODUCE 1. Plug the the monitor to the laptop via HDMI 2. You'll notice the sluggish performance immediately 3. OBSERVED RESULT Clock frequency stays at <1GHz most of the time. EXPECTED RESULT Performance shouldn't degrade SOFTWARE/OS VERSIONS Linux/KDE Plasma: (available in About System) KDE Plasma Version: 5.14.5 KDE Frameworks Version: 5.52.0 Qt Version: 5.11.1 ADDITIONAL INFORMATION Intel Core i7-4510U 16GB RAM
Just confirmed that VGA doesn't suffer from that same problem
Which process/processes are using a higher CPU when in this configuration?
Turns out that a change I made to Firefox months ago made the performance suffer (disabled recommended settings). However, is it normal for the CPU to dip below the minimum frequency (1.0GHz) I set on TLP?
Just in case you misunderstand, I meant I re-enabled recommended settings for it to turbo clock again.
I can't help with CPU governor settings, sorry. Thanks for investigating.
Is it possible to reopen this report? Turns out that it wasn't solved. This was the frequencies on my laptop when I plugged a second monitor: $ cpufreq-info | grep -i "current CPU freq" current CPU frequency is 1.54 GHz. current CPU frequency is 1.58 GHz. current CPU frequency is 1.73 GHz. current CPU frequency is 1.83 GHz. Sometimes performance comes back after unplugging it, other times, reboot is required. After reboot: $ cpufreq-info | grep -i "current CPU freq" current CPU frequency is 2.95 GHz. current CPU frequency is 2.79 GHz. current CPU frequency is 2.85 GHz. current CPU frequency is 2.78 GHz.
My current system info: Operating System: Kubuntu 18.10 KDE Plasma Version: 5.15.2 KDE Frameworks Version: 5.54.0 Qt Version: 5.11.1 Kernel Version: 4.18.0-15-generic OS Type: 64-bit Processors: 4 × Intel® Core™ i7-4510U CPU @ 2.00GHz Memory: 15.6 GiB of RAM
Plasma itself does not change the CPU speed. Please ask in a forum of your distribution which component of your system could be responsible. Comment #5 suggests that it is related to kernel CPU governor settings. It is possible that kernel is configured to change the frequency to prevent overheating on-chip GPU when driving multiple monitors.