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Freedom1

macrumors member
Original poster
Jun 22, 2020
71
200
Mac expert sleuths needed. I have a 2017 27" iMac with 24g RAM and 2tb fusion drive. The latest OS is installed, which is 11.5.

About once or twice a year for three to four days, this machine slows down to the point it becomes unusable. Activity Monitor constantly shows high kernel_task activity. This is our main publishing platform for our business and we do daily design work on it. When this slow-down happens, here is our experience: Make a change, beach ball for 5 seconds. Make another change, beach ball for 6 seconds. Etc. This goes on for as long as we can stand to work, which isn't long. It's like trying to do design on a 2006 iMac, except that would probably be faster. It affects the whole system. Safari windows get beach ball, as does Saving, Opening, other programs, even Pages.

This is really a major problem during our production crunch times, which happen to be now. Argh!

One major clue is that the hard-drive runs constantly. I can hear and feel it in the machine. Normally, the fusion drive is not an issue for us, it's pretty fast at 7200 RPM, but I think that in these situations, the slowness of the mechanical part of the drive is making the kernel_task activity worse because it takes so long to complete — if indeed it is trying to "complete" something.

I have called Apple support numerous times, and they can only step me through the obvious: SMC and PRAM reset, make sure using latest OS, try Safe Mode, reinstall OS, remove start-up programs, etc. These are no help. My guess is that it is something to do either with iCloud or Photos ID. A week ago I upgraded to Apple One and I wonder if that caused an iCloud reset.

Anyway, this is clearly a deeper issue than the obvious, but I believe it is ultimately OS or software related. I am just looking for an answer as to WHAT is causing the kernel_task activity and HOW to end whatever it is. This requires a true, grassroots "Mac Genius," an experienced Mac person who has dealt with and solved this issue. We can't be the only ones. Thank you a million times in advance!!
 

AAPLGeek

macrumors 6502a
Nov 12, 2009
710
2,218
How is the internal fan behaving during the high kernel task activity?

If they're getting loud, it's likely that your iMac is experiencing thermal issues due to clogged bottom vents/internal fan.

 

Freedom1

macrumors member
Original poster
Jun 22, 2020
71
200
How is the internal fan behaving during the high kernel task activity?

If they're getting loud, it's likely that your iMac is experiencing thermal issues due to clogged bottom vents/internal fan.

Thank you so much for your reply. This is a great resource to have. I did check that and it does not seem to be the problem. I think it is something else related to some task being done by the OS that is not obvious. Any other thoughts?
 

wilberforce

macrumors 68030
Aug 15, 2020
2,923
3,199
SF Bay Area
High kernel_task activity is a classic symptom of a faulty temperature sensor/connection (or a truly high temperature). The computer thinks it is overheating, and kernel_task is used as a dummy process (among other things) that denies CPU resources to all other applications in order to cool the system down.
Suggest attempt to diagnose if a temperature sensor is faulty/high, e.g. by MacsFanControl or iStat Menus apps.

 
Last edited:

wilberforce

macrumors 68030
Aug 15, 2020
2,923
3,199
SF Bay Area
in what range should the temperature ideally be?
See attached screenshot for my typical idle temps for a 2020 27" iMac.
CPU/GPU limit is usually 100C.
I don't know specs for other components.
For a fusion drive you should also have a temp sensor on the hard drive.
Hope this helps

Screen Shot 2021-07-22 at 1.37.41 PM.png
 
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Nguyen Duc Hieu

macrumors 68040
Jul 5, 2020
3,001
995
Ho Chi Minh City, Vietnam
Thank you so much for your reply. This is a great resource to have. I did check that and it does not seem to be the problem. I think it is something else related to some task being done by the OS that is not obvious. Any other thoughts?

For a cheap test, you can clone your drive to an external SSD and boot from it to see if the issues still persist.
Or re-install OS + applications to an external SSD.

I doubt that the internal HDD is faulty, heating up and causing your issue.
A 4 year old HDD which has suffer heavy workload has high rates of failing, and you may just another unlucky owner of such HDD.
 
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