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Occasionally my machine will have a kernel_task instance max out the CPU:
This can last from minutes to sometimes hours. The machine is effectively unusable in this state. Restarting doesn't help; a new kernel_task pops up again until it finishes whatever it's doing.
How can I find out what this process is doing?
High kernel_task CPU Usage is due to high chassis temperature caused by charging. In particular Left Thunderbolt port usage.
Solutions include:
Proof:
Actual CPU temperature or application CPU usage is uncorrelated with kernel_task. A hot CPU is throttled by reducing its clock speed, not by scheduling fake no-op load.
The graphs below are from iStatMenus. The machine had been used on battery then plugged in.
State A a USB-C hub (a mouse and keyboard, plus power) and a USB-C HDMI 2.0 adapter, both on the left side. You can see the Thunderbolt Left Proximity temperature sensor rise quickly. About 3-4 minutes later the dreaded kernel_task high CPU usage starts.
State B cures the kernel_task problem by moving power from the left ports to the right. The left side temperature drops and the kernel_task goes away within about 15 seconds.
This is causal. Moving power back to the left side, restoring State A, quickly restores the temperatures and kernel_task again comes back after 3-4 minutes. Again moving power back to the right side, restoring State B, resolves the problem immediately.
State C shows that simply having stuff plugged in to TB ports raises their temperature significantly. Both the hub (mouse and keyboard ONLY) and HDMI adapter individually raise the temperature about 10 degrees, and 15 degrees together.
(all other temperatures were both low and flat. Under 55 degrees.)
Note that high temperature on the right side appears to be ignored by the OS. Plugging everything into the two right ports instead of the left raised the Right temperatures to over 100 degrees, without the fans coming on. No kernel_task either, but the machine becomes unusable from something throttling.
Ergo, high CPU usage by kernel_task is caused by high Thunderbolt Left Proximity temperature, which is caused by charging and having normal peripherals plugged in at the same time.
2017 15" Macbook Pro, MacOS 10.14.5
To actually answer the question:
How can I find out what this process is doing?
The only way to actually ask the kernel what it's doing is to attach a kernel debugger. That means getting a debug kernel from Apple, rebooting, then using a second Mac to attach to the debugged machine. You can then examine stack traces and guess what they mean.
Otherwise guessing and testing is the only way. Of course that leads to false conclusions more often than not.
Today I had this problem.
Interestingly, after changing the port I'd been using for charging the laptop and using a different port of the laptop, the CPU usage dropped:
If you're encountering this on Macbook Pro 16" (2019), this seems to be a well-known problem regarding the laptop body not being able to handle the heat from both the CPU and GPU when external monitors are connected. The ultimate solution seems to be to use an eGPU... which would probably not be practical for most people.
An AMD Community thread further pointed out that the culprit is that the dGPU goes on full drive and draws ~20W of power whenever the laptop outputs to multiple monitors, seemingly because the driver lets the dGPU memory run on full clock speed "to avoid tearing". This quickly leads to the chassis overheating. Outputting to only one monitor (the count includes the built-in monitor), with no scaling or integer scaling of the resolution, seems to reduce the power usage to ~9W and thus mostly solve the issue.
From the sensor data, it seems that the trigger for the throttling were most likely the Thunderbolt Left/Right Proximity temperatures.
Update: Now I still connect my MBP to multiple monitors (the dGPU draws ~20W), but I followed the advice from one comment and bought a small desktop fan to point at the MBP... The temperature seems to be mostly under control now and I don't get kernel_task kicking in most of the time. You'd think that you wouldn't need such a hack on the supposedly best laptop you can buy out there, though I guess there are no perfect laptops and I'd still rather stick with Macbook for now.
Update 2: I finally had my eGPU set up and as expected, the MBP 16" hasn't suffered from throttling yet since then. I guess you could still consider this as an option if all other alternatives fail. You don't need a fancy/expensive graphics card. I am driving one 4K display and 2 additional displays with an RX 580 without any issue.
Update 3: Now I see some folks recommending limiting the CPU frequency with Turbo Boost Switcher. I didn't try it while I was using my MBP 16" since I already had the eGPU (BTW I'm now using ARM Macs where this problem is completely gone), but it might be worth checking out.
kernel_task problem. After turning off Turbo Boost, CPU usage went down from 80-100% to 10-20% in less than 10 seconds.
May 24 at 13:18
As it persists for a very long time, and it persists across restarts, it seems likely that your problem is caused by a hardware problem - namely lack of cooling. You do not describe which type of computer you have, but try looking at its cooling to see if it's working as intended. You might have a broken fan, lots of dust or similar.
The kernel_task virtual process does, amongst other things, throttle CPU usage in order to keep the CPU below its maximum operating temperature. The purpose is to keep the CPU from shutting down unexpectedly. kernel_task does this by ensuring that the CPU is doing nothing for long periods of time - essentially making sure the CPU uses as little power as possible, which means that it gives off less heat. This makes it seem like kernel_task is using a lot of CPU, but in reality it is not.
kernel_task went away when the left thunderbolt temperature dropped below 70 degrees. I also noticed that plugging in a charger raises the temperature on the charging side by about 20-30 degrees. This means the effect is testable, and I'll confirm next time this problem happens.
This is most often due to thermal throttling.
A common issue is the voltage regulator modules (VRM) overheating which have no publicly accessible sensors to view.
Run: sudo watch -d -t -n1 thermal levels
When CPU > 100, you are being thermally throttled. You should keep an eye on this as you try to solve your issues.
Run: sudo powermetrics --samplers smc |grep -i "CPU die temperature"
This shows your CPU temperature. If it is < 100C, its your VRM causing it.
What is your ambient room temperature? >24C and you will start struggling to cool it adequately using any means.
You can observe throttling visually by installing the Intel Power Gadget.
Non-invasive
thermal levels to confirm.Invasive
Also, don't place ice bricks under the laptop - this can cause condensation and break things.
/System/Library/kernels/kernel and is an interface between the hardware and software and conducts communication. - But how can a software component communicate more when a hardware module is usually hot and doesn't even have sensors. The only thing that would seem logical to me if the fans were turning faster. Any ideas? Thanks for the answer
brew install watch. Or just omit it. Run sudo thermal levels.
For me this happens almost everytime I connect to an external monitor. The graphics switches to dedicated ones and the system starts to overheat in just under 5 min. Took me quite a while to figure this out. Room temperature is 27C so I don't think it's related to hot weather as well.
Funny thing is my 7 year old laptop still works fine under same conditions (even outperforms the MBP 2019).
It’s usually temperature. Buy a small desk fan and point it at your MacBook rear. I used to have this problem and since using a fan it never happens.
EDIT: See my other answer
I'll just leave this here in case it helps someone else:
For me, the issue went away when I switched to a charger with higher watt capacity. I accidentally had been running with a 15W charger instead of 87W. This caused the charging to be prolonged, heating up the whole computer.
First measure the temperature around the Mac and then see if cooler air reduces this.
In your case, Skype and Firefox are getting all the cycles left over due to running hot. Windowserver and kernel just do the bidding of the other programs. Also, for a longer term view of what the CPU is doing, watch the energy tab in activity monitor.
By closing the apps that take CPU, you can “let the system run cool”. Running like this won’t hurt things, just there are thermal limits so more efficient apps or less demanding tabs / video / content lets you get more work done before the system protects itself.
Also on Catalina, you can see actual GPU usage in Activity Monitor and test changes to browser settings if you think GPU is putting the machine into thermal throttling states.
Macbook pro 15" 2018, I have a usb c adapter (7 in 1) 2 monitors, and 2 external usb hdd, the adapter on right side and on the left only charging, I have a few months that I can't work in multitask only a few apps and the macbook just starts burning out extremely, I discover this kernel_task service going to thousands!! on percent column on the activity monitor, after play around connecting on different ports (hdmi, usbc and the dock) the kernel_task just go back to normally!!! my working configuration was move the charger to the right side and one of the monitor cables to the left, so on the left I just have a usbc-hdmi cable and on the right side I have the dock with 2 usb ports used along with the hdmi for the second monitor and the charger, great testing Adam!!
Running spindump and or sample process from the activity monitor may help provide you with more information about what’s going on. Try to keep notice of when the CPU usage climbs and then look at the CPU Time on the other items listed in activity Monitor. You may notice a certain process starting up around the same time. Looking into threads in/out can help diagnose too. The issue could be either a bug within the kernel itself or whatever is requesting CPU time. It’s okay to have the CPU jump up every now and then if you don’t notice any system performance or temperature issues. Macs are built with their CPUs to withstand very high temps.
If you download a lot of apps the Launch Daemons, Launch Agents, and startup apps can add up quickly, possibly consuming CPU. It seems your system is having a lot of wake ups. Something could be hung up? You could also run “top” and “lsof” to get an idea of what the kernel is talking to. Also opening console and checking out the logs for any repeating errors helps. Testing a new user account will isolate any user related issues.
Look at you kernel panics and logs to see if there any reoccurring issues.
Make sure your fan starts spinning up when the computer gets warm. If not it could be a SMC issue. You can download software to control the speed of the fans to see if it reduces the CPU %.
The instruments app that comes with Xcode has some debugging and tracking features that also can help.
I own a MacBook Pro (15-inch, 2016). The theory given in accepted answer is correct that the cause of high cpu usage by kernel_task is due to the fact that you are plugging the charger in sockets at left. Using sockets at right immediately fixes the problem and the cpu usage for kernel_task dropped as well. However following are my findings,
The problem did not occur till the MacOS Catalina update. The charging from left as well as right was fine on High Sierra and Catalina in my experience. I hope that Big Sur will acknowledge the problem and possibly fix it. You can try downgrading the OS and see if it fixes the problem.
I recently replaced 3 year old stock thermal paste with Thermal Grizzly's Kyronaut and cleaned the dust accumulated over years with an anti-static brush. The results are amazing. I am no longer facing the over cpu utilisation by kernel_task while charging from either side. The fans are at 2000(ish)RPM on idle whereas it was 2600(ish)RPM.
I would really recommend the second option as it is much easier, cheap and doesn't incorporates any risk of any kind.
powermetrics showed 80C fans at 2900rpm. I'm wondering if the high current through whichever USB-C port it is plugged into impacts the thermal properties.
Edit: Please read through the post as to how I came to the solution, since the underlying factors of how I experienced the slowdown and found the solution are also important, especially to those with similar setups. This is not a lengthy "I have this problem too" comment, since though I do have the same kernel_task issue, the conditions of how I was having it as well as my setup are NOT the same as most here.
I've been having this problem on occasion back then with my previous MBP152011 (yes, the one with the nasty GPU issue) which slowed down while charging. A battery replacement kind of fixed the problem, but, with the GPU issue, it wasn't really long after that I had to replace it. It did serve me well for more than seven years (5 years original Motherboard GPU + 2 year replaced motherboard).
I got a second-hand MBP 15 2014 in 2018, which was in pristine condition. The previous owner is a photographer and he hasn't really used the MBP when he sold it to me.
It had a few issues, specifically, a busted speaker, which I do not really mind, and a USB port that's very choosy when it comes to USB hubs, but I finally found one that works well enough.
Now, after two years of using it, it was scheduled for a battery replacement since the battery started to bloat. I was able to use the Thunderbolt ports with no issue, but I was using the one farther from the charging port ever since I got second external monitor. The first external monitor has always been connected to the HDMI port, which was on the right side.
I started getting the slowdown (kernel_task cpu overload) before the battery replacement, so I thought that that had something to do with it, and replacing the battery, and an SMC reset would fix it.
It didn't. I get a massive CPU slowdown while the MBP was charging, often between 40-80% charge, but sometimes, even beyond that. I don't have any other third party apps installed that shows in Activity Monitor or Stats, so I was already down to the last resort: Backup, reformat, reinstall.
I'm still on Catalina, I've been holding off on Big Sur since I don't really need the nifty new features to get by.
I may also have a faulty GPU, as the display starts to get wonky on certain zoom settings whenever I use Adobe Illustrator, and switching to CPU display fixes that issue.
After reading through the comments and responses here, mostly about using right port for charging instead of the left ports, that heat from charging affects the other port and thus also heats up the port, and by extension, the GPU. After installing stats, I noticed that my MBPs CPU diode is at 90° even after a cold start, with the fans sometimes whirring at full speed, meaning it didn't wake up from sleep. I now shutdown after every session instead of putting the sleep to preserve the battery, and I religiously follow the 40-80% as much as I can, but with the slowdown issue during charging, I often leave it plugged-in when I'm in Zoom teaching sessions (with OBS), and unplug it after a while.
But, since I'm using an older MBP with both TB ports on the left next to the charging port, I'm out of other solutions except the last resort of backing it up, reformatting and reinstalling.
As a last ditch effort, something lit up (in my head), and I switched TB ports, using the one closer to the charging port. I know that counter-intuitive based on the comments, since the charger connection itself does heat up as well when connected.
The result? The kernel_task cpu overload disappeared. I launched Illustrator, Zoom, OBS, VLC, Viber, Slack, along with power hungry Firefox and Safari, observing the kernel_status in Activity Monitor, and the temperatures and fans in Stats, and the temperatures were a breezy 70° with the fans at roughly 3000rpm
I suppose the Thunderbolt port I have been using frequently has started to malfunction, causing the chassis to heat up, and since it's directly connected to the GPU, heats that up as well. So I guess in some cases, it has to do with faulty ports as well. That TB port has been well-used, more often than the other, so it has probably gone wonky for a while now when the slow down started.
Additional information: The charging port and the charging connector also heats up quite significantly during charging and can cause the TB ports to malfunction. Cleaning the ports and charging pins can help quite a lot, but if the pins have started to wear down, or don't pop-up anymore, this causes electricity to arc, heating the charging port a lot more. You will have to purchase a new charger.
kernel_task(PID 0) is the kernel (i.e., heart of the OS) itself and the very first process after the macOS/iOS/tvOS/watchOS boot process. Several core features are done in the kernel, temperature control being one of them, and it seems it’s exactly that that is behaving badly. This process obviously can’t be killed without bringing the whole system down so it’s especially bad when something in it misbehaves. Apple mentions its temperature control feature here: support.apple.com/en-us/HT207359kernel_taskwith very low CPU temperatures. High CPU temperature is fixed by throttling the CPU, not bykernel_task.