Strange Temperature Behaviour (temp is not related to CPU load?)

Discussion in 'MacBook Air' started by lukekarts, Aug 11, 2011.

  1. lukekarts macrumors regular

    Mar 16, 2009
    2011 MBA, i5 256GB.

    Might be tricky to explain clearly, but I have installed SC2 and it runs absolutely fine, but I noticed strange temperature behaviour in iStatPro.

    Basically, as soon as I open Starcraft 2, to the main menu only, the i5 temperature shoots up to 94 degrees C within maybe 30 seconds; CPU load is pretty low at this point - say 15-18% - why is the i5 getting so hot?

    Temperature stays around 94 as the fans ramp up, regardless of whether CPU load is at 10 or 90%. It stays there until I exit the game.

    Now, normally it would make sense if the temperature was high under load - and outside of games, the MBA behaves pretty much as I'd expect, more CPU intensive processes generate heat, and web browsing etc doesn't. So why does the simple action of opening a game cause the i5 to lock in at full temp and full fan speed until I close it? Is this a hardware/software fault or am I missing something?
  2. Gav2k macrumors G3


    Jul 24, 2009
    Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8J2 Safari/6533.18.5)

    Gpu fella
  3. Hellhammer Moderator


    Staff Member

    Dec 10, 2008
    Is the CPU load the total load or the load for one core? The difference is, 15-18% total load can be 60-72% for one core if the process is single-threaded. 70% load might be enough to trigger the Turbo mode, which causes more heat. I made a quick picture to show the difference:


    The blue area can have CPU usage of up to 400% in your case because the usage is by each thread (you have two cores but due to Hyper-Threading, you have four threads). However, the total CPU usage (highlighted with red) cannot be higher than 100%.

    Also, the GPU is integrated into the same die as the CPU so while your CPU usage may be low, the GPU can be running that full speed.
  4. lukekarts thread starter macrumors regular

    Mar 16, 2009
    Thanks for the info. So do I just count the total % in activity monitor, to confirm if the usage is higher than the [red] total?

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