bengmugenr

Q: CPU usage more than 100% on iMac

Hi Folks

 

I got a bit confused about the percentage number of processor usage shown in  Activity Monitor, as its value could be higher than 100%. For example, in below screenshot, the CPU usage for Firefox is 109.7%. Actually the value was even higher, I just wasn't able to capture it when I was capturing the screen.

 

Screen shot 2014-06-09 at 12.35.42 AM.png

The OS is Snow Leopard, the computer is iMac Mid 2007 with Intel processor.

 

Any explanation about this please?

 

Thanks,

B

iMac, Mac OS X (10.6.8), Mid 2007

Posted on Jun 8, 2014 8:11 AM

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Q: CPU usage more than 100% on iMac

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  • by BobHarris,Helpful

    BobHarris BobHarris Jun 8, 2014 4:09 PM in response to bengmugenr
    Level 6 (19,272 points)
    Mac OS X
    Jun 8, 2014 4:09 PM in response to bengmugenr

    Multiple CPUs (cores) and an app having multiple execution threads, means each available CPU could be used in part or 100% for a sum in the Activity Monitor display greater than 100%.

     

    Firefox is is a multi-threaded app.

  • by bengmugenr,

    bengmugenr bengmugenr Jun 10, 2014 1:09 AM in response to BobHarris
    Level 1 (5 points)
    Jun 10, 2014 1:09 AM in response to BobHarris

    Thanks for your explanation.

     

    But it is interesting that I never observed the same on my Mac Pro mid 2012. Secondly, in my understanding, the %CPU should be an overall percentage of all processors or cores as commonly there is no point show a single CPU's performance and ignore the others.

     

    Am I correct?

  • by BobHarris,

    BobHarris BobHarris Jun 10, 2014 5:36 AM in response to bengmugenr
    Level 6 (19,272 points)
    Mac OS X
    Jun 10, 2014 5:36 AM in response to bengmugenr

    It all depends on what is reporting the CPU usage, and whether they want to count all cores and hyperthreading as fraction of 100% or if each thread of exection can consume 100% of a core or hyperthread.

     

    If you look at your own Activity Monitor screen shot you can see that mds is using 20.7%, so even if Firefox was listed as using "Just" 100%, the sum of Firefox and mds would be 120+% so you are still over 100%.  Thus Activity Monitor is allowing each core and hyperthread to have its own 100%.

     

    A different reporting service may count things differently.

     

    Anyway, depending on how many cores your Mac has AND whether the chip supports hyperthreading will determine Whether you have 200% (dual core no hyperthreading), 400% (quad core no hyperthreading), 800% (quad core with hyperthreading), 1600% (8 core with hyperthreading), etc...

  • by John Galt,

    John Galt John Galt Jun 10, 2014 5:53 AM in response to bengmugenr
    Level 8 (48,595 points)
    Mac OS X
    Jun 10, 2014 5:53 AM in response to bengmugenr