Someone asked Why did moving the mouse cursor cause Windows 95 to run more quickly? over on Retrocomputing.
Raffzahn's answer mentions that it's also possible to observe the effect of things running faster when the user moves the mouse whilst scrolling through a large text file. Nowadays I don't scroll through text files anymore (because I flip through pages or search for a string that's close to the location I'm looking for), so over the years this knowledge got lost on me. But I remember always doing this when working on a Windows XP computer.
However, when I subsequently tried it on my 2019 computer running Linux 4.15, I still found the effect to exist. This is despite only one core going up to 50%, none going above that, and all of the others just idling away. I can get one core go over 90% and sometimes reach 100% by wiggling with my mouse.
Why is it still like that, even if many cores are available and even the one that's serving the text editor is only busy half of the time?