Hyper threading

face=Tahoma>If the operating system
schedules multiple threads against a hyper-threaded CPU, the CLR automatically
takes advantage of this.  This is certainly the case for new versions of
the OS like Windows Server 2003.
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face=Tahoma>  style="FONT-SIZE: 12pt; FONT-FAMILY: 'Times New Roman'">

style="mso-bidi-font-family: Tahoma">Also, the
CLR did work to properly spin on a hyper threaded system.  If you are
writing your own spinlocks in managed code, be sure to use Thread.SpinWait so
that you get the same benefits.

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style="mso-bidi-font-family: Tahoma">We also tune
subsystems like the scalable server GC so that they make sensible decisions for
hyper threading.

Comments (5)

  1. Hi Chris,

    (Wow, i’m very impressed by dropping a comment on one of your posts)

    It’s almost a question, in fact. I was looking for infos about hyperthreading yesterday, and I found a page on Intel’s web site that says that both versions of XP support hyperthreading (with a compatible CPU, of course).


    So, does the CLR take advantage of an HT CPU on XP too?


  2. Chris Brumme says:

    Yes it does.

  3. Brian Grunkemeyer says:

    Chris, thanks for mentioning the SpinWait method. We’ve talked about this a few times in the past, but this never came up. I’ll use it in a few of my test cases. Perhaps I should mention this in my reliability document?

  4. The .NET 1.0 SDK documentation for Thread.SpinWait is not exactly illuminating:

    Thread.SpinWait Method [C#]: Causes a thread to wait the number of times defined by the iterations parameter.

    What exactly does Thread.SpinWait do?

  5. Chris Brumme says:

    Assume the usual caveats about how implementations are subject to change, etc.

    In a loop, we do a ‘rep nop’ instruction for the number of iterations you specify. This instruction is the approved way to create a yield from one logical CPU to another logical CPU of a hyper-threaded physical CPU.