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Why CPU goes mad while connected to external displays ?

S

soamz

macrumors 6502a
Original poster
Jun 20, 2010
704
8
Orissa, India
I have a LG UC98 huge display connected to MacBook Pro Retina Late 2013 on thunderbolt port.
It works fine.
But almost like 50 times in a day, the CPU becomes 100% usage and the MacBook pro is dead.

I unplug the thunderbolt for 5 minutes and then it becomes normal.

Then again, it becomes 100% after sometime and I just do again unplug.

Its happening almost 50 times in a day and Im really frustrated.

Why would an external display take CPU power from the MacBook ?
 
soamz said:
I have a LG UC98 huge display connected to MacBook Pro Retina Late 2013 on thunderbolt port.
It works fine.
But almost like 50 times in a day, the CPU becomes 100% usage and the MacBook pro is dead.

I unplug the thunderbolt for 5 minutes and then it becomes normal.

Then again, it becomes 100% after sometime and I just do again unplug.

Its happening almost 50 times in a day and Im really frustrated.

Why would an external display take CPU power from the MacBook ?
Click to expand...

It would help if you can identify which process is taking up your cpu time.
Pumping pixels out on external display, especially the high resolution display you have is a very processor intensive task, but it should not go dead. If your usage is taken up by "kernel_task" then it is likely that your laptop is at critical temperature levels and the operating system is trying to cool it down by occupying capacity. You can read about it here.

https://support.apple.com/en-us/HT207359

If that is the case, make sure that your laptop is on the flat surface and your fan is spinning. If it is not spinning then it might be faulty and if it is then you might need to clean it by taking to a good repair shop. In either case it should handle one display well, even if it goes really loud.
 
More pixels require more power. If you system has a dGPU it can offload some of this to the GPU, if not, the CPU must handle the scaling and other work itself. Since the CPU only has so many cycles, this limits the other work it can do.

If you need more help. Please let us know the exact configuration of your Mac from "About this mac". How you have monitor connected (direct to Thunderbolt, HDMI, etc). And whether you are using the macbook with the screen closed or open. All of these effect performance.
 
rutrack said:
It would help if you can identify which process is taking up your cpu time.
Pumping pixels out on external display, especially the high resolution display you have is a very processor intensive task, but it should not go dead. If your usage is taken up by "kernel_task" then it is likely that your laptop is at critical temperature levels and the operating system is trying to cool it down by occupying capacity. You can read about it here.

https://support.apple.com/en-us/HT207359

If that is the case, make sure that your laptop is on the flat surface and your fan is spinning. If it is not spinning then it might be faulty and if it is then you might need to clean it by taking to a good repair shop. In either case it should handle one display well, even if it goes really loud.
Click to expand...


Here are the screenshots I took, when it dies :(
[doublepost=1493738536][/doublepost]
jerryk said:
More pixels require more power. If you system has a dGPU it can offload some of this to the GPU, if not, the CPU must handle the scaling and other work itself. Since the CPU only has so many cycles, this limits the other work it can do.

If you need more help. Please let us know the exact configuration of your Mac from "About this mac". How you have monitor connected (direct to Thunderbolt, HDMI, etc). And whether you are using the macbook with the screen closed or open. All of these effect performance.
Click to expand...

Here it is bro.
Please let me know.
 

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soamz said:
Here are the screenshots I took, when it dies :(
[doublepost=1493738536][/doublepost]

Here it is bro.
Please let me know.
Click to expand...


It looks like your system overheats. This happens due to high load on the system running external display in combination with inadequate cooling. If your laptop sounds like it's about to take off, then your fans are running normal and you just need to clean the system inside to remove any dust that makes cooling inefficient. If you don't hear any sounds, then you likely need to replace your fans.

In the mean time here is a quick hack you can do.

- Make sure your laptop is set up on flat surface with nothing around it, so that cool air is easily accessible

- Download any fan control app, I like Macs fan control (https://www.crystalidea.com/macs-fan-control) , but there are others and make sure you run your fans at constant high speeds. Your laptop will be loud, but it will get to higher temperatures much slower. It will also let you check temperature from all the core sensors.
 
soamz said:
I have a LG UC98 huge display connected to MacBook Pro Retina Late 2013 on thunderbolt port.
Click to expand...

http://www.lg.com/us/monitors/lg-34UC98-W-ultrawide-monitor

That's a monstrosity of a monitor. Heck, I bet an RX480, or a 1060 would have some problems running that beast at 4k with all it's features turned on. You're using a 4 year old laptop with a mobile core i7 and outdated nVidia, no wonder the little laptop is choking.
 
Last edited:
That's strange that it is running with such high cpu usage. I have a similar 15" late 2013 model mbp (2.6/16GB/1TB/750M) and I have no problems running my 4k tv through the thunderbolt 2/miniDP port (via club3D miniDP to HDMI 2.0 adapter for 4k 60hz) and running a 1080P connected at the same time via the HDMI plug. My kernel task percentage usually stays very low (well under 10%) depending on what I have open.

My fans do turn on when running something on the 4k screen, but the temps aren't super high. I have Macs Fan Control installed to check. It's very handy app to have installed.

Have you tried any of the suggestions in this thread?
https://forums.macrumors.com/threads/how-to-solve-kernel_task-high-cpu-usage.1706948/
 
My 2014 15" MBP [high end stock], struggles a little with the LG 5k monitor, and the fans go on nearly the instant it is connected. Not maxing it out or anything but there is a notable increase in fan noise when it is attached and a noticeable slow down in general use.
 
soamz said:
yes fans spinning fine.

Do you want me to install Fan control or something ?
Click to expand...

You should check what the cpu temperature is when the kernel_task is occupying your processor time. If it is getting too hot, then you should just take your laptop for cleaning the internals. You can just install the iStats, open the terminal app and type:

sudo gem install iStats

then in the terminal type

iStats

See what your CPU temp is, when your laptop "dies", it is likely going to be too hot and the system slows down all the processes so that it can cool down.
 
Unless there's scaling problem software wise, I don't see how his monitor is too much for his laptop. That monitor is only physically big, but resolution wise, it's less than 4k monitor.
 
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I'm running into these symptoms myself where kernel_task is taking up over 200% CPU time. I'm using a LG 24" 4K display over HDMI and I've had to put a desk fan on the laptop in addition to opening all the windows to bring the CPU load down.

Maybe it's time to crack open the laptop (2015 model 15MBP) and see if the fans and vents need some love.
 
blackcypher said:
I'm running into these symptoms myself where kernel_task is taking up over 200% CPU time. I'm using a LG 24" 4K display over HDMI and I've had to put a desk fan on the laptop in addition to opening all the windows to bring the CPU load down.

Maybe it's time to crack open the laptop (2015 model 15MBP) and see if the fans and vents need some love.
Click to expand...

It is time, I'm running the same laptop with three external monitors, it gets loud, but the system does not overload, although I'm not running anything hard on graphics, just terminals and editors.
 
I agree with the previous posts... that monitor should not be causing the system to overheat. My mid-2014 rMBP with the same GT 750M run my Dell 4k monitor without any issue over Thunderbolt (miniDP). I run it in clamshell mode with this setup and it idles around 5-10C warmer than if the monitor is not connected, but it does not cause the fans to go above idle unless I push it with other tasks.

I would definitely try cleaning out the dust to see if that helps the situation. What temps is iStat reporting when this issue happens?
 
here is the CPU and sensors details when it dies.
 

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soamz said:
here is the CPU and sensors details when it dies.
Click to expand...

Based on those numbers it is not a heat problem. My machine idles with higher CPU and GPU temperatures when plugged into my 4K monitor. The fans are going full speed on your machine and there doesn't appear to be a reason based on the temps. Maybe make a Genius Bar appointment (if you have an Apple Store close by); even if out of warrantee, they can perhaps make a diagnosis.
 
soamz said:
Its 2013 retina, no warranty left
Click to expand...

The Genius Bar will still provide diagnosis free of charge assuming they can replicate the problem. May be worth a shot to see what they say. Someone else here my be able to give better advice, but I really don't think the problem is heat-related given the temps in the image you posted.

Good luck!
 
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