CPU clock throttling during heavy usage (2011 i5/i7)?

Discussion in 'MacBook Air' started by bilinsky, Jul 27, 2011.

  1. bilinsky macrumors newbie

    Jul 27, 2011
    Hello, I went by the local apple store and did a few tests on the new 13" macbook air (i5 1.7 GHz). I was testing noise/performance during load and stressed all 4 threads maximum using glucas/cputest, whereafter I did a sequence of geekbench runs.

    The geekbench score was about 1000 points lower (~3300) directly after the stress test compared to the geekbench test (~4500) that was made some minutes after. This can be related to thermal processor throttling, which has been found in earlier macbook air models,

    If there is thermal throttling already after a few minutes of full load on the 1.7 GHz model, what about the i7 1.8 GHz?
  2. Xgm541 macrumors 65816

    May 3, 2011
    how long is a few minutes? You typically wont be using 100% cpu for extended periods of time. if a few minutes means 5, then I'd be worried. But if you mean 30, then it's fine.
  3. altecXP macrumors 65816

    Aug 3, 2009
    The intel CPU clocks itself based on heat, if its to hot the CPU will not clock itself up to full speed, it will only clock up to what is safe at the given temp. So after heavy use the Core i will not OC the full way to 2.9GHz it may only OC to 2.3GHz until temps drop back down.
  4. bilinsky thread starter macrumors newbie

    Jul 27, 2011
    Hello, with a few minutes I mean 2-3 minutes of full load. However, to really investigate if it really is thermal throttling more tests need to done, and the cpu frequency should be monitored as well, I don't know if MSR tools work for Lion (it doesn't work for 64 bit snow leopard either).

    I intend to use the computer for audio work with a lot of realtime processing, where more or less full load during hours is not uncommon. So for me it's not much use to equip a computer with a better processor if the design can't handle the thermal load. I think this is a general problem for laptops as they're often over spec'd in terms of cpu power compared to what the actual performance will be due to thermal load/design.
  5. fireslug macrumors newbie

    Aug 3, 2011
  6. Xgm541 macrumors 65816

    May 3, 2011
    My 1.4ghz c2d 11inch 2010 model doesnt throttle at all and it runs fairly cool at all times. I have a feeling that because c2d was in a mature stage in 2010, the design made it produce much less heat. Nonetheless, your throttled i5/i7 processors will still be faster than my c2d unthrottled. I wouldnt worry about it.
  7. nebulos macrumors 6502a


    Aug 27, 2010
    i'm looking at getting an Air on which i'll be doing music as well.

    i brought this same concern up in the geekbench scores thread; geekbench scores are super high on the new Airs, but because turbo boosting shuts down when different factors like heat are too high, these tests (which are over in a few seconds) don't necessarily show 'steady state' processing performance.

    i might be picking one up soon; if you give me an easily reproduce-able test, i might be able to run it.

    i don't know if i'll be doing anything super crazy music-wise, so i might be okay, but i'd like to know either way. and i'd like to know how to test the machine i buy, to see if it will work for me.

    the music community on here is also very underdeveloped; i'd be happy to contribute relevant info.
  8. nebulos macrumors 6502a


    Aug 27, 2010
    Anand explicitly argued in his review that he believes there is no CPU throttling in the new Airs.

    the issue here, i believe, is turbo boost.

    they're similar, but different. you can view the i7 as a 2.9GHz which throttles down, or as a 1.8GHz that boosts up.

    however, the issue in the past was Apple was throttling the CPUs themselves, and what Intel rated as a XGHz CPU was performing like a (X/2)GHz CPU (or whatever).

    anyways, hopefully someone that actually knows what they're talking about (not me) can step in and steer us in the right direction.
  9. KPOM macrumors G5

    Oct 23, 2010
    To the OP, I think the CPU will be fine for most tasks without significant throttling.

    As the ArsTechnica review points out, most of the time the CPU is in "Turbo Boost" mode, meaning that the "1.6GHz" CPU actually operates at 2.0GHz, the "1.7GHz" at 2.4GHz, and the "1.8GHz" at 2.6GHz (the dual-core boosted speeds).

    I encoded a DVD using Handbrake in Windows when I first got the new model and had CPU-z running. It ran for about 45 minutes, and about half the time it was running at 2.6GHz and the rest of the time at 1.8GHz (throttling back and forth throughout). At idle the processor runs at 800MHz. Encoding is very CPU intensive (it registered over 300% CPU utilization) and the processor got up to 95 degrees Celsius (maximum is 100), so if it was still able to spend half the time at 2.6GHz it seems to be pretty good to me.
  10. nebulos macrumors 6502a


    Aug 27, 2010
    okay, that satisfies me. thanks!
  11. jace88 macrumors regular


    Jan 3, 2011
    Sydney, Australia
    Does anyone know if the i5's can go the other way and underclock themselves not for performance/heat reasons but just to reduce battery consumption?
  12. KPOM macrumors G5

    Oct 23, 2010
    When idling, the processor slows to 800MHz to preserve energy.

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