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I've got a late 2013, 15-inch retina MacBook Pro.

Since a couple macOS upgrades ago, my system has become randomly slow, borderline unusable. I've come to realize it spikes when using 3 displays (2 external 1080p and laptop's retina screen). If I close the laptop and only use the 2 external displays, CPU usage instantly drops. And then, if I open it again, rises up and kernel_task can report over 150% CPU usage and transitions, typing, everything becomes laggy. This can happen even on a fresh boot.

I'm clueless, since 3 displays should be effortless on the GPUs task and by no means take over the CPU. I read kernel_task might spike in order to prevent other processes to hog the CPU and overheat. Even then, closing the screen interrupts no CPU consuming processes, so that shouldn't calm kernel_task down. And the laptop should be even hotter while closed than open.

Is there a step that might help resolve the slowdown?

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  • What version of the MacBook Pro do you have? Specifically does it have external or integrated graphics?
    – Agbb
    Dec 18, 2017 at 15:41
  • @ozliftoff It's a 15 Inch RMBP, as stated above. Identifier is MacBookPro11,3. It has both an Intel Iris and Nvidia GT750M
    – Armin Cifuentes
    Dec 18, 2017 at 21:22

3 Answers 3

Reset to default
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I don't know why I didn't try this earlier, but a SMC Reset did it.

So I guess sensors were a little off and that was it? Any additional technical details is still much appreciated.

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Restarting SMC chipset helped fixing it.

  • Shut down Mac
  • Hold. CTRL+OPTION+SHIFT+POWER button for 10 seconds
  • Start mac
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  • 1
    Welcome to Ask Different. How is this different than the main answer here? Perhaps making a suggested edit would be better than posting the same answer on several questions.
    – bmike ♦
    Aug 3, 2020 at 20:44
  • Not only is this not different, you're cutting and pasting the exact same answer for multiple questions: Question 1, Question 2 and Question 3 . Thus far, all of your answers. See How to write a good answer for tips on writing an answer that will get attention and ultimately up voted.
    – Allan
    Aug 3, 2020 at 21:44
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The answer from Kuldip was the correct answer for me, but without explanation, I wouldn't have tried it. Here is another thread that goes into slightly more detail (also answered by Kuldip)

OS slows down when I connect external monitor

Context: My girlfriend's mac pro with 8G was behaving so poorly, as if it was heavily swaping/paging. But I could find no evidence of that using Top. She has two port replicators plugged into the USB C ports with a monitor on each (so 3 monitors total). Restarting the SMC chipset saved the laptop from getting flung out the window.

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