Q: Kernel_task High CPU Usage

Please post the output from EtreCheck

<https://discussions.apple.com/docs/DOC-6174> or <http://etrecheck.com>

You have a very clean system.  That is good, but it also makes it harder to figure out exactly what is happening.

Experiment #1.  Quit Safari and see if the CPU usage goes back to normal.  It is possible there is some JavaScript running on one of the web pages you have open that is asking the system to do things on its behalf.  This is an easy experiment.

Experiment #2.  Rebuild your Spotlight index.

<Rebuild the Spotlight index on your Mac - Apple Support>

NOTE: Until the Spotlight index is completely rebuilt, it is going to chew up some CPU and I/O bandwidth.  So do not go looking right away after starting the rebuild.

There are several reports of this problem with Yosemite.

There are various "fixes" around the internet.

This provides a good summary of the problem and things to try:

http://www.cnet.com/news/kerneltask-process-taking-up-an-inordinate-amount-of-cp u/

If that doesn't help, there is everyone's favorite fix.

This proposed fix is kind of scary.

http://blog.viktorpetersson.com/post/100148585299/how-to-fix-kerneltask-cpu-usag e-on-yosemite

I'm guessing that maybe you are still within your 1 year warranty, so at the minimum you might want to make a Genius Bar appointment at your local Apple Store.  With your system in a totally clean state it would be ideal to avoid any finger pointing at 3rd party products.

Note:  I do not know why a high kernel task CPU usage would be caused by a hardware problem, but surprising things happen all the time.

Another experiment.  Boot into Safe mode

<http://support.apple.com/kb/ht1564>

This would load only Apple drivers, and some of them less optimized, to see if that changes anything.  I'm not expecting much, but again, it is an easy experiment.  You would not want to run full time in Safe mode, but as an experiment it is useful.

I think one of the rccharles links had resetting the SMC and PRAM.  If you did not do that yet, then also try those.

By any chance are you in the middle of FileVault encryption (or decryption) and that is what is occupying the kernel task?  Then again, a clean install should not have a lot on the system, so it should complete in a reasonable amount of time.  Also I would only expect FileVault encryption to occupy just 1 CPU or 100% not 500%.   You can check FileVault encryption status with the following Applications -> Utilities -> Terminal command

diskutil cs list | grep Conversion

Those all my ideas for this morning.

Note:  I do not know why a high kernel task CPU usage would be caused by a hardware problem, but surprising things happen all the time.

The author of internet article I found thought that  a hardware problem could invoke the high cpu.  Although, it was dealing with some external device.

R

Hi Elliott,

Did you send it off/fix it?

I had this issue on another model (2011) macbook running 10.11.06. Turned out to be dusty fans. CPU throttling due to overheating. I thought it was buggy OS after a recent upgrade and i saw all the threads on resets and moving files around but saw one guy saying it was a symptom of the system trying to slow heat production.

I checked the fans first before anything else and they were mildly caked, seems like in the three weeks since i last had it open after a logic board replacement,  it's picked up a year or two's worth of muck. removed them, paint brush, bit of blow dryer and reassembly and all is good again and much quieter. gone from 670%CPU back down to 5-3%

hope maybe this helps