When I copy a large file over our local, gigabit Ethernet network, my 2016 MacBook Pro is unusable as kernal_task consumes all of the CPU resources.

Here's my Mac specs:

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Here's an snapshot of the utilization. It peaks over 400% at times:

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It is normal for the CPU utilization to be this high on an network file transfer?

If not, what steps can I take to reduce CPU utilization so that I can use my MacBook while transferring lark files?

  • 1
    so whats your question?
    – Natsfan
    Nov 5, 2017 at 13:32
  • 2
    What brand of Thunderbolt 3 <> Ethernet adaptor are you using? Is the adaptor warm/hot to the touch? Does it appear to get hotter when in use transferring data? To echo @jmh, what is your question?
    – IconDaemon
    Nov 5, 2017 at 15:54
  • 1
    I/O that's not getting routed via DMA will eat up the CPU and cause temperatures to rise. Saturating a 10 GbE link is impossible without hardware/software that's able to use DMA.
    – Nick T
    Nov 5, 2017 at 20:16
  • You wouldn't happen to have any antivirus installed, would you?
    – Siguza
    Nov 5, 2017 at 21:13
  • Are you using an official Apple Ethernet adapter? Nov 5, 2017 at 22:44

1 Answer 1


That's mainly the unfortunate tale of thermally inept design. The kernel_task uses up so much because the temperature has risen too high. Install a sensor app and confirm, install Intel CPU PowerGadget to confirm again. Widespread and common problem.

Thunderbolt chips get hot and are inadequately connected to the cooling system and so the system tries to slow things down by occupying the CPU with meaningless cycle sucking to prevent a halt and catch fire situation.

To mitigate this, you might try to disconnect other peripherals, install a fan control software that is set to max rpm, use external cooling solutions (stands, pads, fans, AC), stop all other processes causing calculations that translate into heat. If you are daring and think you know better than Apple's 'designers' on how much heat your machine should be able to stand, you may also override this with some hacking. (This is not recommended.)

  • 2
    It's a bit premature given what we know about the user's environments to default to "bad thermal design." How do you know he's not working in a sauna? We also don't know what other processes the user is running and what activities (disk I/O, memory, etc.) they are generating
    – Allan
    Nov 5, 2017 at 14:30
  • 3
    A sauna would stress the operational temp limits of the machine and the sanity of the user. In my understanding high kernel_task is answered by Apple with the reasoning above in HT207359. Your additional factors are not unimportant and addressed in my answer ("stop all other…") but they also just pile on top of that thermal issue ethernet and TB generate on their own. Nov 5, 2017 at 16:32
  • Oh man this explains why my macbook stopped transmitting at full speed over wifi. I was running the tests always when trying to play games which obviously heated up the whole thing. This is horrible and nasty. Thanks for the heads up! Nov 5, 2017 at 23:00
  • "tries to slow things down by occupying the CPU with meaningless cycle sucking to prevent a halt and catch fire situation" That's hilarious. Surely they could have come up with a better solution.
    – Rob
    Nov 6, 2017 at 3:02
  • Of course they could: Proper cooling would have been nice. But that would alter the thinness of the case, imply the use of better fans, thermal paste etc. In short, things only professional users would want. And Apple doesn't cater to this group anymore. Dec 7, 2017 at 14:58

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