iMac Pro Where to find Turbo freq vs Cores for iMac Pro processors?

Discussion in 'iMac' started by propower, Jan 6, 2018.

  1. propower macrumors 6502a

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  2. Gav2k macrumors G3

    Gav2k

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  3. h9826790 macrumors G5

    h9826790

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  4. propower, Jan 6, 2018
    Last edited: Jan 6, 2018

    propower thread starter macrumors 6502a

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    Still no info here on Turbo Speed vs Cores used. The Max speed (always quoted everywhere) is always for just one core used. I have followed the link for Datasheet from the W-2155 page on ARK and it goes to a tableof XEON data sheets that does not include the W series as far as I can tell. I have seen people post these kinds of things - where do they find them?

    https://ark.intel.com/products/125042/Intel-Xeon--W-2155-Processor-13_75M-Cache-3_30-GHz
    View Datasheet goes here
    https://www.intel.com/content/www/us/en/processors/xeon/xeon-technical-resources.html
     
  5. bxs macrumors 6502a

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    I've been playing with the Intel Power Gadget trying to understand just what the Frequency display is referring to.

    I experimented on my 3.5 GHz MP6,1 6-core that has a max Turbo Boost of 3.9 GHz.

    Using Instruments (/Applications/Xcode.app/Contents/Applications/Instruments.app) to control the number of active cores and no Hyperthreading I can get Power Gadget to display various Frequencies while a single process runs using 100% CPU.

    6 cores - Varies between 3.60 to 3.68 GHz
    5 cores - Varies between 3.59 to 3.66 GHz
    4 cores - Steady at 3.7 GHz
    3 cores - Steady at 3.7 GHz
    2 cores - Steady at 3.7 GHz
    1 core - Steady at 3.9 GHz (max Turbo boost)
     
  6. propower thread starter macrumors 6502a

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    ^^^ This makes some sense to me and I would approximate that
    1 Core = max 3.9
    2-4 = 3.1
    5-6 = 3.6 something
     
  7. bxs macrumors 6502a

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    I played some more....

    Using Instruments (/Applications/Xcode.app/Contents/Applications/Instruments.app) to control the number of active cores and no Hyperthreading I can get Power Gadget to display various Frequencies while a various number of processes running using 100% CPU.

    With single process using 100% CPU

    6 cores - Varies between 3.65 to 3.68 GHz
    5 cores - Varies between 3.65 to 3.68 GHz
    4 cores - Steady at 3.70 GHz
    3 cores - Steady at 3.70 GHz
    2 cores - Steady at 3.70 GHz
    1 core - Steady at 3.90 GHz (and will sometimes will fall off to 3.70 GHz)

    With two processes using 100% CPU

    6 cores - Varies between 3.60 to 3.62 GHz with occasional spike to 3.40 GHz
    5 cores - Varies between 3.60 to 3.62 GHz with occasional spike to 3.40 GHz
    4 cores - Steady at 3.70 GHz
    3 cores - Steady at 3.70 GHz
    2 cores - Steady at 3.70 GHz
    1 core - Steady at 3.70 GHz

    With three processes using 100% CPU

    6 cores - Steady at 3.60 GHz
    5 cores - Steady at 3.60 GHz
    4 cores - Steady at 3.70 GHz
    3 cores - Steady at 3.70 GHz
    2 cores - Steady at 3.70 GHz
    1 core - Steady at 3.70 GHz

    With four processes using 100% CPU

    6 cores - Steady at 3.60 GHz
    5 cores - Steady at 3.60 GHz
    4 cores - Steady at 3.70 GHz
    3 cores - Steady at 3.70 GHz
    2 cores - Steady at 3.70 GHz
    1 core - Steady at 3.70 GHz

    With five processes using 100% CPU

    6 cores - Steady at 3.60 GHz
    5 cores - Steady at 3.60 GHz
    4 cores - Steady at 3.60 GHz
    3 cores - Steady at 3.70 GHz
    2 cores - Steady at 3.70 GHz
    1 core - Steady at 3.70 GHz

    With six processes using 100% CPU

    6 cores - Steady at 3.60 GHz
    5 cores - Steady at 3.60 GHz
    4 cores - Steady at 3.70 GHz
    3 cores - Steady at 3.70 GHz
    2 cores - Steady at 3.70 GHz
    1 core - Steady at 3.70 GHz
     
  8. propower thread starter macrumors 6502a

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    ^^^^^
    Cool - This looks pretty right to me (I had the same machine as well)
    now if only you had the iMac Pro too :)
     
  9. redshift27 macrumors newbie

    redshift27

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    8-core iMac Pro, using stockfish (chess engine) to selectively utilise 1-16 cores. Using a chess engine allows one to see how much output one is getting in terms of problem solving, as this does not necessarily scale linearly with the clock speed (or indeed the number of cores the engine is using).

    First of all, using only 10-20 second short tests where CPU temperature does not get a chance to rise above 80C. Using Instruments.app to alter processor cores, and Intel Power Gadget.app to measure CPU speeds and temps.

    (a) if on default out-of-the-box 16 active processor cores with hyperthreading on, then it makes no difference whether Stockfish runs on 1, 2, 3 ... all the way up to 16 cores, the clock speed is 3.90GHz in all instances.

    (b) If I ask Stockfish to use just 1 core ...
    (i) and turn down the CPU to 1 active core without hyperthreading, then the clock speed goes up to 4.2GHz.
    (ii) CPU is on 2 cores, still 4.2GHz
    (iii) CPU 3 cores, 4.0GHz
    (iii) CPU 4 cores, averaging 3.98GHz
    (iv) CPU 5 cores, 3.92GHz
    (v) CPU 6-8 cores, 3.90GHz

    Please note that Stockfish actually runs at least 10% FASTER as single core on 16-core CPU at 3.9GHz, than it does on 1-core CPU at 4.2GHz, presumably due to interruption by other processes. "Efficient" execution of single-core Stockfish, i.e. where delivers chess as fast as on an out-of-the-box iMP, is only reached when 4 or more CPU cores are active.

    Now at longer execution times on out-of-the-box iMP,
    (a) using 16 Stockfish cores, when CPU temp hits 91-93C (which is fairly soon, within a minute or two), then the CPU starts to throttle and speed jumps to and fro between 3.63 and 3.90GHz
    (b) using 8 Stockfish cores, even though CPU temp VERY gradually rises to 93C NO throttling occurs, and it continues to run at 3.90GHz. I watched this for about 15 minutes and it was flat-lining the curves at that point, steady state.

    Note that Stockfish runs FASTER at 8 cores than it does at 16 cores even before throttling sets in: hyperthreading 16 cores is less efficient than running 8 unhyperthreaded cores.
     
  10. bxs macrumors 6502a

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    #10
    redshift27: Thanks for that posting. Very interesting and helpful in understanding how the core frequency varies with workload.
     
  11. propower thread starter macrumors 6502a

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    #11
    Yes - excellent and insightful post! Many times in my Audio work (though in the last couple of years this is less of a factor) I have found a bit better low latency recording performance by turning HT off.
     
  12. sputnikBA macrumors 6502

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    #12
    Can anyone with a 10 core do a similar test?
     
  13. bxs macrumors 6502a

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    When I get mine I will be doing so. :)
     
  14. KalanHowse macrumors newbie

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    Apr 9, 2014
    #14
    Have you posted a test as of yet? I’m highly anticipating the results of short and long period instances that affect Turbo Boost frequencies! :)
     

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13 January 6, 2018