Chosen Solution
I am working on a MacBook Pro that has dual GPUS (Intel Iris & AMD Radeon) The user uses 2 external monitors. His computer starts slowing down, the kernel usage gets to 87% and oddly bounces as high as 240 %. The laptop is a bit warmer than usual but no thermal problems. The user reports that when this problem started that it was about 1 hour or so before the computer slows down; it is now starting to slow down in about 5 minutes. The user has reset the PRAM and also SMC reset but no change. Is this a hardware failure? Thanks
Seems like the gpu just cant handle the extra horsepower needed to run the monitors. Try it with no monitors and see how long it lasts without them.
The problem seems to go away if you decide to turn off “Displays have separate Spaces” from System Preferences —-> Mission Control. Of course, this means you don’t really have two separate split screens. However, it seems this is the reason why the WindowServer goes nuts in terms of CPU utilization. Seems like an OS-level issue, not really a hardware problem.
I would start off by opening the system and cleaning the dust out of the fans. Make sure both working. I would also download this app: TG Pro even using the free version might clue you in on whats happening with the heat transfer from the CPU and/or GPU. The full version offers more for less than $20 US its worth it! Look to see if the heatsink temp is following the GPU/CPU’s temp. If not the heatsink has likely lost its coolant so the CPU or GPU is not able to shed its heat so the system is throttling down. If the values are the same then you’ll need to look deeper into the system as well as see if the drive is too full. SSD’s need a bit of wiggle room for wear-evening. In addition, if the system is only a 8 GB model the system maybe using the SSD for virtual RAM and depending on the app cache or paging.
Have you checked if the display settings are using the external monitors? If it is thats probably it. I changed it back to display and it stopped lagging
I have had a very similar problem with MacBook Pro and Samsung external display. So after an hour on support to Apple and Samsung doing PRAM resets etc and both blaming each other, Apple mentioned that third party software could be causing it. I was running Flux (which is a colour temperature app. Like nightshift). Removed that and it worked instantly. Check any third party apps that might be running in the background and then reintroduce them. Good luck everyone!
Can you adjust screen resolution se if that helps?
For me the problem disappeared when I connected my MBP to my monitors HDMI ports instead of the TB ports. I have MBP 15” 2017, Lenovo ThinkVision 4K monitor and an old Samsung HD monitor.
Hi. I have similar problem. I connected an external monitor (4k) with DisplayPort to MBP 15’’ mid 15 (m370x). And I see that CPU speed is slow down. I use Intel Power Gadget for monitoring. The Cpu temperature never gets higher than 60 degrees, but Cpu speed easily can be stuck on 0.8Ghz for 20minutes or more. For the short period, it can work in the 1.5-2.5 range, but after that stuck again on 0.8Ghz. I thought I paid for 2.5Ghz + turbobust. Now It gives me «1500 Multi-Core score» in geekbench and it’s impossible to work on this machine. Without external monitor 14000 scores. It looks like the real bug. What is going on? How to fix it? PS: I also tried HDMI port and low resolution. It gives the same result.
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.
Setting my fan control back to automatic worked for me. Ty
For me up until now this was the solution for 500+% kernel CPU !!!kernel_task takes up 500% of my CPU when plugging in external monitorI have also disabled Seperate Spaces for both monitors but not sure if this is doing anything…
