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100% CPU usage when using external screen AND plugged in?

1808 Views 8 Replies Latest reply: Jul 19, 2013 10:52 PM by Bob Kujda RSS
87racer Calculating status...
Currently Being Moderated
Aug 3, 2011 6:10 PM

So when I am using my mini-displayport and an external monitor on battery my (2010 Ultimate MBA running Lion) works perfectly but as soon as I plug it in the process kernel_task starts using 100% CPU and it becomes unusable.  If I unplug either the dp OR power it stops using 100% and goes back to working normally.  I have tried booting with them already plugged in, resuming with them plugged in, restarting with them [;ugged in and it all results in the same behavior.  BTW I did a clean install too.

MacBook Air, Mac OS X (10.7), 2010 Ultimate
  • josin88 Calculating status...

    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.

  • josin88 Level 1 Level 1 (0 points)

    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!

  • npunhani Calculating status...

    Same issue ...


    Apple should provide a hotfix. I'll try unplugging the power next time, I get this issue almost all the time.

  • npunhani Level 1 Level 1 (0 points)



    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.

  • yhom Calculating status...

    Same issue here, but as far as I observed, It did happen only since 1.8.1 :

  • Bob Kujda Level 1 Level 1 (20 points)

    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


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