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Kernel_task eating up CPU with external 4K Monitor ?

S

soamz

macrumors 6502a
Original poster
Jun 20, 2010
705
8
Orissa, India
Hi, I have a 32 inch LG 4K HDR Monitor connected to MacBook pro.
Most of the time, the kernel_task is running at 500% halting the whole computer and Im not able to do anything.
Once I unplug the external display, then it gets back to normal.
Whats the issue ?
How to fix ?

I have connected the 4K monitor to MacBook Pro using a display cable to usb-C cable.

Im on top config MacBook Pro Late 2017 model.
 
Short answer:
- it’s a know issue due to throttling. Your mbp cannot handle this scenario due to combined cpu and gpu heat
- a limited temp fix is to disable turbo boost, but with intensive tasks it only delays the inevitable by a few minutes.
- only proper fix is to get an egpu

or of course the mbp 16.

Sorry for the bad news. This was the reason why I switched from mbp 2019 15inch to 16inch. But even the 16” works much better with egpu
 
The latest i9 MacBook Pro also goes mad with external 4K displays ?
Why is apple then saying, it supports 2 x 4K displays, where as it cannot even handle one single 4K display, shame.
 
The reports of high CPU usage and excessive heat when using external monitors are baffling. I run two LG UltraFine 4K displays with my 2019 13" MacBook Pro, and the fans rarely turn on. The CPU sits at about 92% idle when browsing the web or composing emails - almost identical to the load when using the laptop screen only. My thought is that it must be a software issue.
 
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Nathan King said:
The reports of high CPU usage and excessive heat when using external monitors are baffling. I run two LG UltraFine 4K displays with my 2019 13" MacBook Pro, and the fans rarely turn on. The CPU sits at about 92% idle when browsing the web or composing emails - almost identical to the load when using the laptop screen only. My thought is that it must be a software issue.
Click to expand...
Are you in clamshell mode or do you have the laptop lid open?
 
impulse462 said:
Are you in clamshell mode or do you have the laptop lid open?
Click to expand...

I run clamshell mode 90% of the time but occasionally open the lid for a third screen. I do not notice a performance difference either way. The big difference is the dGPU, or rather something with its implementation, that is likely causing issues. It's certainly not an actual system resource issue though.
 
Connecting my 1440p monitor to my 16" MBP automatically adds 10-15 degrees Celsius to the CPU, which unfortunately means I can always hear the fans when connected to a monitor.
 
Having the same issue with a 2019 MBP16" and LG4k UltraFine Display. (running with MBP open on a raised stand) The problem was getting worse over time, never happened in the first 6-7 months since I first got it in late December last year. I finally realized that disconnecting the display stopped the 1000%+ kernel_task. Also noticed the sensor for Left Thunderbolt Proximity was one of the hotter ones. (using iStat Menus to monitor that one and GPU Proximity)

Once I realized it was basically a heat issue, I took off my leather case and blasted all 4 vent slots with air and saw a ridiculous amount of dust come out which I suspect is the reason it's gotten worse over time. I also reset SMC. Fans seem to have gone from always around 98% to 25% for the first time all day. If it does come back I plan to switch to the right side TB instead of left. I'll set a reminder to update this thread either way.
 
Last edited:
Quick update… Since the blow out and SMC reset, I've tried maxing out the processors to trigger the problem again, but the kernel_task hasn't come back. Fans are still under 50%. Temps seem about the same. Since I tried two fixes at the same time it's hard to know which helped most, but due to the similar temps before and after, I suspect the SMC reset did the trick, but I would still recommend blowing out any dust that's built up. I'll update again next week after I get some solid work time on it.
 
Still no problems, no CPU spikes, no kernel_task. Blowing out the vents AND/OR the SMC reset appears to have stopped the issue. Screenshot below of iStat Menus, you can see the spikes getting progressively worse, red ones are the kernel_taks. The huge one at the beginning of Sept was when I gave up and started working on my other Mac, then the gap around the 5th was the labor day weekend, followed again by progressively worse spikes. The last spike on the 10th was when I reset SMC and blew out the vents.

So my question after all of this… From what I've read, the kernel_task is a response to a heat issue, but how exactly is maxing out all 8 processors supposed to help a heat issue? Or is the heat issue caused by the kernel_task? And why cant the system recognize this problem and suggest this solution? Why did I have to deal with these progressively worse and worse spikes until I eventually found the right search terms to lead me to this ridiculously simple fix?

Screen Shot 2020-09-14 at 1.41.27 PM.png
 
Last edited:
Nathan King said:
The reports of high CPU usage and excessive heat when using external monitors are baffling. I run two LG UltraFine 4K displays with my 2019 13" MacBook Pro, and the fans rarely turn on. The CPU sits at about 92% idle when browsing the web or composing emails - almost identical to the load when using the laptop screen only. My thought is that it must be a software issue.
Click to expand...
But do you have 5 stat monitoring apps running along with a fan control app and screen resolution app and fifty other things in your menu bar? :)
 
Hazyface said:
Still no problems, no CPU spikes, no kernel_task. Blowing out the vents AND/OR the SMC reset appears to have stopped the issue. Screenshot below of iStat Menus, you can see the spikes getting progressively worse, red ones are the kernel_taks. The huge one at the beginning of Sept was when I gave up and started working on my other Mac, then the gap around the 5th was the labor day weekend, followed again by progressively worse spikes. The last spike on the 10th was when I reset SMC and blew out the vents.
Click to expand...

Thank you so much for taking valuable time and updating here. I bought Dell ultrasharp 27" 4K (u2720q) and my MacBook Pro (2019) is extremely struggling to handle it causing kernel_task to come over again and again.

I did Reset SMC, but that didn't solve the problem. One noticeable thing is that when I choose any Scaled resolution, even the smallest (other than default), my GPU gets maxed on load. As soon as I use it on default resolution, it works fine.

This gives one more sense, if my Macbook can't handle a single 4K resolution is it worth going for M1 Mac Mini?
 
Immediately go ahead and order the M1 16GB.
Its the best setup I have now.
Now MacBook will ever come close to this.
I hate MacBooks for this, as they cannot even handle one 4K display.

M1 Mac Mini is crazy crazy good. You will never ever feel a single second of slowness.

The attached 4K monitor will feel like a default display only.
 
soamz said:
Immediately go ahead and order the M1 16GB.
Its the best setup I have now.
Now MacBook will ever come close to this.
I hate MacBooks for this, as they cannot even handle one 4K display.

M1 Mac Mini is crazy crazy good. You will never ever feel a single second of slowness.

The attached 4K monitor will feel like a default display only.
Click to expand...

Congratulations on M1 Mac Mini. What kind of workload you have? Do you use a 4K monitor in Full Resolution or unscaled resolution? Which 4k Monitor you are using and inches?

Your response will make me buy an M1 Mac mini so be careful :D :D Hoping to get a sincere response from you.
 
Of course, full resolution 4K.
I use this - https://amzn.to/3pT2Erm

And I use this for 100% FCPX video editing only - 10 bit files of Sony a7s3 full day of editing and rendering for my Youtube channels.

This is a GOD-SENT DEVICE!
Never had such a perfect apple product. M1 is a magic!
 
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Same thing happens to my 2018 i9 MPB but not with a monitor attached, but always with the charging cable plugged in. It happens randomly, but not that often, and I notice it when the system becomes unresponsive or laggy. Full CPU utilisation by the kernel_task and the fans are spinning. What I do to fix it, I just unplug the charging cable and the kernel_task goes away, system becomes responsive but battery is drained. I dont know why or how but at least i found the remedy.
 
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