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?

  • 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 Dec 18, 2017 at 21:22

3 Answers 3


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.


Restarting SMC chipset helped fixing it.

  • Shut down Mac
  • Hold. CTRL+OPTION+SHIFT+POWER button for 10 seconds
  • Start mac
  • 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

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.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .