OS X Temp monitoring accuracy?

Discussion in 'Overclocking' started by justr, Feb 13, 2011.

  1. justr

    justr

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    Feb 13, 2011 at 7:36 PM #1
    justr

    justr

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    I am not confident that i) I'm going about monitoring my temps in OS X properly, and ii) that monitoring temps in OS X is accurate even if it is done properly.

    Q 1: Am I monitoring properly in OS X? I installed, using Multibeast 3.1, fakeSMC and fakeSMC plugins. I also installed iStat Menus (3.01, I think). I see 4 cores, with 4 individual temps, and VCore.

    VCore matches what I get, roughly at various steppings when I compare to CPU-z in Win7, so I'm confident with that. In Win7 I measure temps with Real Temp, which shows distance from thermal max (so even if the absolute temps aren't right, I can get a sense of how close I am to hitting what Intel thinks are the highest temps before throttling the processor).

    Unfortunately, I don't have a way to compare, say, prime 95 load in Win7 to something similar in OS X-- I've found Prime 95 for OS X v. 25.11, but it seems old, and I don't know if I can use that to compare load temps to prime 95 in win7?

    Q 2: If I'm doing everything right-- fakeSMC + plugins from multibeast 3.1, followed by iStat Menu-- what are the opinions regarding the accuracy of the readings I'd get from iStat Menu?

    Part of the reason I ask this, is that I've hit 90 c in intel burn test before stopping, at some overclocked settings, and gotten BSODs, whereas with the same settings in OS X, runninge cinebench CPU benching or handbrake running at 90% total load, I don't go over 75 c in OS X and don't have stability issues in OS X so far.
     
  2. Burninator

    Burninator

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    Feb 13, 2011 at 8:32 PM #2
    Burninator

    Burninator

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    I'm pretty confident in the temperatures reported. It's just reading the values back from the sensors, the same as any Windows program would be. So the main difference will be how hot it runs doing different tasks on different OSes.
     
  3. justr

    justr

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    Feb 13, 2011 at 8:44 PM #3
    justr

    justr

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    But my understanding is that the sensors don't actually report a temperature-- that's the problem.

    The sensors in i7 chips report the distance (measured in degrees celsius) each core is from some theoretical maximum safe temperature. That maximum temperature is NOT published by Intel (though it is suspected to be around 100c, based on independent/external measurements by enthusiasts), and is determined for each core independently during testing prior to packaging. So each chip, and each core, can have a different max safe temperature. When those temps are hit, the chip automatically throttles itself to bring the temperatures into a safe range; if throttling doesn't do this quickly, the system shuts down.

    Because of this, absolute temperatures, as reported by software, can be wildly off-- the program guesses what the temperature is based on the measured distance to the max set by Intel. If you try, in Win7, for instance, both Real Temp and Speedfan, you'll often notice a discrepancy of 10c or more. And, if I'm right, Real Temp is the only program that i) uses a max theoretical safe temp based on external testing of when each model processor throttles, and ii) shows you the actual measurement of distance to that temperature so that at the very least, you know how close you are to the theoretical max safe temp even if the absolute max safe temp isn't necessarily accurate itself.

    I don't know what fakeSMC uses for max safe temp for an i7-9xx, because it only reports absolute temp (unless I just haven't found the distance to max reading).

    Anyone have any thoughts on this?
     
  4. justr

    justr

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    Feb 13, 2011 at 8:47 PM #4
    justr

    justr

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    It seems to me that without knowing the actual absolute safe temp, it's pointless for software to report absolute temps.

    We need software that will show us the RAW reading the sensor reports-- the distance (measured in degrees c) the core is from hitting its max safe temp.
     
  5. InActive8618

    InActive8618

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    Feb 13, 2011 at 9:38 PM #5
    InActive8618

    InActive8618

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    Ask this to the plugins developers, you won't get a satisfying answer here. As for the max temp you're talking about could it be the TjMax? Depending on the plugin you use it may be set manually in the info.plist, if you don't trust the auto detection. Here on my i7 860 IntelThermal reports:
    Code (Text):
    IntelThermal: CPU family 0x6, model 0x1e, stepping 0x5
    IntelThermal: Found 4 cores 8 threads
    IntelThermal: CPU#0 Tjmax 99
    IntelThermal: CPU#1 Tjmax 99
    IntelThermal: CPU#2 Tjmax 99
    IntelThermal: CPU#3 Tjmax 99
    RealTemp on windows reports the same Tjmax so I can trust that it's correct.
     

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