I was experiencing extremely HIGH Kernel_task CPU usage whenever I was trying to stream on Youtube. I have a 2017 MBP 15 inch hooked up to 2 monitors via USB. One is connected directly to the MBP and the other one is connected as a pass-through a CalDigit TS3+ dock and with Airplay on the Apple TV. And what caused the problem for my system is simply Apple’s HiDPI scaling. If I set any type of scaling within system preferences Kernel_task cpu usage will shoot up to 500% within minutes. And any type of streaming especially Youtube will stutter having trouble loading videos smoothly. Took a lot of time digging around the internet until ironically I stumble upon a Youtube video showing similar issues referring that the culprit is HiDPI scaling. When I reset the main display’s resolution to default the MPB is back to normal and works just fine. But that’s not an ideal resolution to work with (1650x1050). So I use SwitchResX to adjust the resolution. But there’s a catch… Again, cannot select any settings that is HiDPI otherwise the CPU will start to throttle again. It seems like Apple did not make HiDPI mode to work coherently when connected to any external monitors. Results may differ if it is connected to an Apple Display.