Mac Pro, Hyperthreading

krispiekrispie
Posted:
in Current Mac Hardware edited January 2014
My Mac Pro says it has four processors.



My Linux machines with two dual-cores say they have eight, due to hyperthreading.



But then they're older Xeons, not the 51xx.



Do the Xeons in the Mac Pro machines support hyperthreading, but have Apple disabled it?



Or do they not support it??

Comments

  • Reply 1 of 8
    chuckerchucker Posts: 5,089member
    Intel Core, including Xeon 51xx (Woodcrest) doesn't support Hyperthreading at this point.
  • Reply 2 of 8
    backtomacbacktomac Posts: 4,579member
    Quote:
    Originally Posted by Chucker


    Intel Core, including Xeon 51xx (Woodcrest) doesn't support Hyperthreading at this point.



    Chucker,



    Do you think hyperthreading will make it to core 2. Seems like an easy way to increase performance without increasing power demand and heat output. Am I missing something?
  • Reply 3 of 8
    theapplegeniustheapplegenius Posts: 584member
    Quote:
    Originally Posted by backtomac


    Chucker,



    Do you think hyperthreading will make it to core 2. Seems like an easy way to increase performance without increasing power demand and heat output. Am I missing something?



    Intel says that HT won't make it into Core, but has a chance in Nehalem. We'll have to wait for that.
  • Reply 4 of 8
    xoolxool Posts: 2,460member
    Hyperthreading...
  • Reply 5 of 8
    backtomacbacktomac Posts: 4,579member
    Quote:
    Originally Posted by Xool


    Hyperthreading...



    Oops, did I say something wrong? What's the downside?
  • Reply 6 of 8
    lundylundy Posts: 4,466member
    All hyperthreading does is make the context switches faster. For any given nanosecond of time, the processor is still only executing code from a single thread. Making it appear to the OS as two separate processors is just smoke and mirrors.



    EDIT: well, strictly technically it is executing instructions from two threads simultaneously, in different units of the processor.



    But the gains from SMT depend heavily on the application, and also on the OS being savvy enough to know that the two "processors" are really on the same physical CPU.



    Depending on the application mix that is running, SMT can show a small improvement, no change, or even a slowdown.
  • Reply 7 of 8
    chuckerchucker Posts: 5,089member
    Quote:
    Originally Posted by backtomac


    Chucker,



    Do you think hyperthreading will make it to core 2.



    It won't, but perhaps to Core 3.



    Quote:

    Seems like an easy way to increase performance without increasing power demand and heat output. Am I missing something?



    Yes, as lundy explained, it can in some cases even cause slowdowns.
  • Reply 8 of 8
    krispiekrispie Posts: 260member
    Quote:
    Originally Posted by Chucker


    Intel Core, including Xeon 51xx (Woodcrest) doesn't support Hyperthreading at this point.



    Thanks for the info, Chucker.



    I'm not convinced that HT gives that much of a boost anyway.
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