Macbook pro fans spin up at 10% cpu

Discussion in 'MacBook Pro' started by whitedragon101, Dec 7, 2011.

  1. whitedragon101 macrumors 65816

    Sep 11, 2008
    I have always known flash video will spin the fans up on my macbook pro. Then Adobe said HD flash video will only use 10% of your CPU on the new Flash 10.0, great I thought. But the fans still spin up during most flash video. I look at the process monitor and there it is Safari (or chrome) flash process 95%. However, that is a 95% share of the CPU being used, not the total CPU. So looking at the bottom of the screen it says 90% idle.

    So HD (and SD) flash video is running using 10% CPU (or less) and yet the macbook pro still spins its fans up high.

    Why do the fans need to spin up for only 10% CPU use?
  2. GGJstudios, Dec 7, 2011
    Last edited: Dec 7, 2011

    GGJstudios macrumors Westmere


    May 16, 2008
    iStat Pro will give you accurate readings of your temps and fan speeds, among other things.

    Unless there is a rare defect in a Mac, most temps are well within the normal operating range, considering the workload being put on it. Websites with Flash content, games and other multimedia apps will put higher demand on the CPU/GPU, generating more heat. This is normal. If you're constantly putting high demands on your system, such as gaming or other multimedia tasks, expect temps to rise and fans to spin up accordingly. It's just your Mac doing its job to maintain temps within the normal range.

    Your fans are always on when your Mac is on, spinning at a minimum of 2000 rpm (for MBPs) or 1800 rpm (for MBAs, MBs and minis). They will spin faster as needed to keep temps at a safe level. If they're spinning up without increased heat, try resetting the SMC. PRAM/NVRAM has nothing to do with these issues, so resetting it will not help. Also, make sure you don't block the vents, which are located at the rear, near the hinge.

    Learn about the fans in your Mac
    Apple Portables: Operating temperature
  3. shardey macrumors 6502a


    Jan 28, 2010
    Flash video's will cause your GPU temps to increase, and depending on your model, the dedicated cards get quite a bit warmer, thus the reason for the fans.

    If you have a 13", the same will apply except your IGPU will get warmer as well.

    Post your temps when you notice the fans to increase as well as activity monitor.
  4. thundersteele macrumors 68030

    Oct 19, 2011
    The % are very confusing in activity monitor.

    The quad core CPU has hyperthreading, i.e. allows for a total of 8 threads on the CPU at the same time, two per core.

    Running flash puts one thread at close to 100%. Since this is only 1/8 of the CPU's potential, activity monitor shows the CPU as 10% load, 90% idle.

    However, actually the one thread fully exhausts one core, so we are closer to 25% of the CPUs capabilities. In addition, if only one core is under load, the CPU automatically overclocks it, to boost the performance of non-parallelised applications. I hope this is not confusing, but it should explain why the CPU gets hot even though it only shows 10%.

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