Currently Being ModeratedAug 3, 2011 10:34 PM (in response to 87racer)
i am having a similar issue - I have a 2.13GHz 2009 MBA attached to an external monitor. Since upgrading to lion it has slowed right down with kernel_task using approximately 130% of the CPU according to Activity Monitor. When I unlpug the external monitor performance returns to normal. In both cases the MBA is on mains power - I have yet to test it on battery.
Currently Being ModeratedAug 10, 2011 2:14 PM (in response to 87racer)
Doing a clean install of lion from a flash drive fixed my issue. reinstalling lion over my lion install did not work. had to do a clean install.
Currently Being ModeratedAug 16, 2011 7:48 PM (in response to 87racer)
I also did a clean install, but that did not fix the problem. It seems kernel_task is likely being used by the Mac OS to throttle processor use to prevent overheating (which would explain why the problem is largely being reported by MBA users):
I set up an external fan to cool my MBA and the problem has disappeared (for now). It's a solution but not a great one!
Currently Being ModeratedAug 16, 2011 11:12 PM (in response to josin88)
A clean install means you create a new partition and in the lion install screen go to disk utility and unmount your old lion install or completely wipe your old lion partition. You cannot have any lion install mounted anywhere on your drive while installing lion. it pulls stuff from the other partition when installing.
also my problem is not caused by overheating. my problem results in overheating from kernel_task using 100% of the cpu. the cpu is never "throttled down" due to heat. If it gets hot it turns the fans on and if the fans cant keep it cool it will hit ~100°C and shutdown.
The closest answer I can come up with is that when you upgrade from snow leopard or lion the kernel or some of the kernel's dependencies gets corrupted causing it to enter an endless loop which can only be exited by unplugging either the mini-dp or power. This is likely code dealing with the ability to use a second display, keyboard, and mouse with the lid closed.
In any case try backing everything up(SuperDuper is awesome) to any external drive and completely wiping your drive to reinstall lion from a flash drive/dvd(apple has now posted a utility to create bootable rescue media or google it, there are plenty of guides or utilities.) Make sure to have your external backup unplguged when installing.
Currently Being ModeratedAug 22, 2011 2:39 AM (in response to 87racer)
Same issue ...
Apple should provide a hotfix. I'll try unplugging the power next time, I get this issue almost all the time.
Currently Being ModeratedAug 22, 2011 2:44 AM (in response to npunhani)
I DO NOT have any external devices plugged in. I get this issue while running multiple applications in full screen.
2.4 GHz MacBook Pro. i5 Processor. 4 Gb Ram.
Currently Being ModeratedSep 14, 2012 3:15 AM (in response to 87racer)
Same issue here, but as far as I observed, It did happen only since 1.8.1 :
Currently Being ModeratedJul 19, 2013 10:52 PM (in response to 87racer)
I have two external monitors connected to MacBook Pro - experiencing similar HIGH kernel task activty
In my case it appears to be a heat issue & high fan activity
Raised the MacBook Pro off the surface (placed small objects underneath & have a large room fan blowing over the MacBook
Solved my HIGH kernel task activity
Exterenl monitors or monitor + heat + fan = High Kernel task activity