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Threading affects performance?

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4 thoughts on “Threading affects performance?
  • Tom J says:

    Threading affects performance ?
    Hey friends,

    How a Hyper threaded processor can affect the performance of the SQL Server ? It is a hot issue for Microsoft.

  • Joe Antarrior says:

    What is hyper threading? I have heard of it. Let me tell you what I know. Its a process by which with one microprocessor itself we can simulate two or more microprocessor i.e we can process two threads simultaneously.

    But I have also heard that this leaves a huge vulnerability in the system. It actually allows the threads of one virtual processor to interact with the other virtual processor thus causing systems to crash.

  • Tom J says:

    @Joe
    Yes, Joe you are quite right but plz mind to this also,

    Slava Oks, one of the SQL Server developers had a theory on why hyperthreading can be deterimental to performance. What item is part of his theory why hyperthreading can slowdown performance.

    So the answer is Lazywriter impacting L1 and L2 cache

    Explanation
    His theory was that the lazywriter would kick in and scan large blocks of memory. This results in lots of L1 and L2 cache reads. Since the hyperthreaded processors share L1 and L2 cache, this can quickly disrupt the caches and result in L1 and L2 misses for the worker threads. And potentially problems in acquiring spinlocks.

    Ref: To Hyper or Not to Hyper – http://blogs.msdn.com/slavao/archive/2005/11/12/492119.aspx

  • Joe Antarrior says:

    Interesting. This only talks about databases. Can any other applications be affected by hyperthreading?

    And one more doubt. Right now, who all are using hyperthreading? I mean the machines.

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