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Hyper-Threading Speeds Linux

Posted by Hemos on from the making-things-faster dept.

developerWorks writes "The Intel Xeon processor introduces a new technology called Hyper-Threading (HT) that makes a single processor behave like two logical processors. The technology allows the processor to execute multiple threads simultaneously, which can yield significant performance improvement. But, exactly how much improvement can you expect to see? This article gives the results the investigation into the effects of Hyper-Threading (HT) on the Linux SMP kernel. It compares the performance of a Linux SMP kernel that was aware of Hyper-Threading to one that was not." Ah, the joys of high performance.

8 of 239 comments (clear)

  1. Fundamental mistake by cbcbcb · · Score: 5, Insightful
    >It compares the performance of a Linux SMP kernel that

    >was aware of Hyper-Threading to one that was not."

    But if you aren't going to use hyper threading you would use a UP (non-SMP) kernel, which would gain you considerable performance. The benefits are not so clear cut as many of the benchmarks show limited benefit from hyperthreading and would perform faster on a uniprocessor kernel.

  2. good stuff by The+Evil+Couch · · Score: 5, Insightful

    The results on Linux kernel 2.4.19 show Hyper-Threading technology could improve multithreaded applications by 30%. Current work on Linux kernel 2.5.32 may provide performance speed-up as much as 51%.

    while it may not be very useful for a single-user box(it actually looks like it would be a detriment), integrating it into client-server situations would give us some nice boosts in performance. web servers ought to see some real gains with this.

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    1. Re:good stuff by windex · · Score: 5, Insightful

      You aren't looking at this logically. It's not that "you need that much CPU for a webserver", is that "look at how many more customers you can squeeze in per server".

      This lowers cost for providers, and eventually lowers costs for consumers.

      Yee haw.

  3. Application dependant by PaschalNee · · Score: 5, Insightful

    The pretty detailed (for me anyway) article on Ars Technica concludes that performance on a HyperThreaded CPU will be very much dependant on the application mix. While research like this is useful it will probably always be a try and see scenario.

  4. Useful for development? by NixterAg · · Score: 5, Insightful

    Like most development shops, we do a great deal of development for multiprocessor machines so we write a lot of multithreaded code. Multithreaded code creates a whole host of new debugging pitfalls that don't show up if the developer is debugging on a single processor workstation. As John Robbins says in his terrific Debugging Applications book, if you are developing a multithreaded application, you better be certain you are doing your debugging in a multiprocessor environment.

    From a development standpoint, will a hyperthreaded chip provide an adequate environment in duplicating the behavior of a multi-processor PC well enough that shops can buy cheaper, one CPU machines for development and still be confident in their results? I'm guessing nothing will replace the real thing but I'd be interested in any commentary.

  5. It's just you by Royster · · Score: 5, Insightful

    WHat you've conveniently snipped out in your trollish post is all of the applications benchmarks showing improvements. If you're not going to run any application code, you might as well shut the machine off and save the marginal stress on the environment.

    Most of us have our computers do work and those applications, running on an OS which has *barely* slowed, will be able to do more work in the same amount of time under the HT-aware OS than under one which does not utilize the second, virtual processor.

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  6. Technical Summary by 0x69 · · Score: 5, Insightful

    If you're running code that's efficient on a P4 (few mis-predicted branches, low cache miss rate, good parallelism, etc.) then HT is pretty much useless.

    If you're running code that's inefficient on a P4 (which pays for its high GHz with long pipelines, large latencies, a slow decode stage, and several other drawbacks), then HT can usually paper over a fair percentage of these problems. But remember that HT requires OS support, may require application support, and "your mileage will vary".

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  7. Expensive HT or cheap real SMP? by ponos · · Score: 5, Insightful


    In Europe P4 3.0 with HT costs ~745 euro (+tax)
    An Asus A7M for dual Athlon costs ~260 euro (+tax)
    Two Athlon XP 2200+ cost ~340 euro (+tax).
    Alternatively you can get two Athlon MP 2000+ for
    roughly the same money (if you don't trust the
    XPs).

    Now, please explain to me why would someone
    with real SMP needs in mind (and NOT games)
    consider the P4 with HT.

    P.

    P.S. I understand that the prices in the US are
    different, but still, it is VERY expensive.