I'm trying to solve the mystery of a crazy high cpu usage on kernel_task.

MacBook Pro (Retina, Mid 2012), 2.7 GHz Intel Core i7, Yosemite 10.10.2

I saw some advice to download the Intel Power Gadget. That showed me that the my CPU is slowing way down. How do I fix this? When this happens, I can sometimes cycle the power on the MBP. But this is driving me crazy.

enter image description here

enter image description here

  • 1
    what does the temperature graph show for the same period, as it slows down?
    – Tetsujin
    Commented Apr 1, 2015 at 9:02
  • 1
    Mine (Late 2013 MBP) seems stuck permanently at that same 0.80 GHz level. CPU utilization is 60-100%. Temps are reasonable – 50-60C... 🤷
    – Nolan Amy
    Commented Aug 16, 2018 at 19:15

3 Answers 3


Apple documents this.

Activity Monitor may show that a process named kernel_task is using a large percentage of your CPU, and during this time you may notice a lot of fan activity. This process helps manage temperature by making the CPU less available to processes that are using the CPU intensely. In other words, kernel_task responds to conditions that cause your CPU to become too hot. When the temperature decreases, kernel_task automatically reduces its activity.


You might want to reset the SMC one time to be sure it's not stuck and providing incorrect temperature readings to the processor.

If the SMC or high temperatures is the root cause, you should be able to correlate the various internal temperature sensors and physical measurement of the case and exhaust air temperature with the design throttling of the kernel scheduling and the clock rate adjustments the chipset is designed to make in response to thermal measurements.

Worst case, you have a hardware issue with faulty temperature sensors or an out-of-spec CPU that generates more heat than it should for a given GHz clock rate.

  • Hi @bmike, I also got the problem. Whenever I use external monitor, it will make the kernel_task that high. Or to be more precise, whenever I use GPU. Is it normal? I use MacBook Pro Retina 2016. Commented Sep 20, 2016 at 10:03
  • What proof is there that heat is the actual cause in this case?
    – ash
    Commented Apr 28, 2018 at 5:07
  • @ash In this thread apple.stackexchange.com/a/363933/297783 one of the comments points to the code in MacOS, in kern/thread_info.h and kern/thread.h there are values TH_FLAGS_GLOBAL_FORCED_IDLE and TH_OPT_GLOBAL_FORCED_IDLE which is described as "Thread performs forced idle for thermal control"
    – drkvogel
    Commented Jul 26, 2020 at 18:25
  • In fact here's the source: opensource.apple.com/source/xnu/xnu-4570.71.2/osfmk/kern/…
    – drkvogel
    Commented Jul 26, 2020 at 18:27
  • 1
    BTW, to give a little more context - for anyone researching this issue - in my case, the problem happened in all the following states: charging (i.e. on power), discharging (i.e. disconnected from power), clamshell, open screen. And it often triggered on changing between these states.
    – ash
    Commented Jul 27, 2020 at 21:48

In my case, I had a MBP used continuously for 3 years. The local Mac store opened the case and cleared out the dust. That FIXED the problem!!!!

Basically the extra dust caused the CPU to overheat.


My current MB Pro Retina(late 2013) suffers from this. I installed Ubuntu on my laptop just so that I can barely run the browser and terminal.

The reason behind my laptops throttling seems to be faulty temperature sensors. Some of the sensors are reporting a reading of -127C which starts the throttling. I have compiled temperature readings from sensors in this github gist.

So far, there's no solution in sight. I have tried cleaning, modifying kernel extensions and resetting SMC.

  • 1
    Welcome to Ask Different! Please refrain from adding comments in the Answer section, this is for answers to the questions. Once you have sufficient reputation you’ll be able to add comments and ask follow-up questions. To gain reputation, answer questions that are clear and concise. - From Review -
    – fsb
    Commented Aug 8, 2016 at 13:39

You must log in to answer this question.

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