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Turbo Boost Issue

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  • Turbo Boost Issue

    Sorry if this has been discussed elsewhere.

    I suspect I'm not alone in taking a lot of interest in the new quad-core Sandy Bridge mobile processors, which promise desktop performance in a laptop. I notice that most of the CPU tests shown so far for the i7-2630QM and i7-2720QM have been classified as overclocked. These processors are not, in fact, overclockable in the sense that the turbo boost margins are factory-set. The processor is therefore working as its manufacturer intended. This makes me wonder whether turbo boost within factory limits should count as overclocking.

    I notice that some of the baselines show incorrect clock speeds (either none, or, in the case of one of the 2720QMs, 24GHz and the wrong number of cores). Referring to the 2720QM, I notice also that there are some examples recorded as running at base clock rate but still yielding similar performance to those recorded as overclocked. Could it be that the clock rate is measured only once, and it is a matter of luck whether the processor is running in turbo boost mode or not? How do you measure the clock speed during the performance test? How do anomalous clock speeds and core counts occur?

  • #2
    Calculating clock speed is an art not a science. Turbo boost makes it that much harder. PT tries to load the cpu enough to clock it up to get a accurate measurement but with the advent of turbo boost its a lot harder. Turbo boost is only enabled when some but not all cores are loaded. If the Core count is wrong PT may need a new build to fix the problem.

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    • #3
      We have a few changes coming in the next patch release. I just need to check if this will improve things.

      Years ago getting the CPU clock speed was relatively easy. But power control (under clocking) and Turbo mode (overclocking) have made it harder to work out what the nominal speed is. Added to this is the problem is that it is no longer feasible to purchase an example of each CPU, as there are too many variants on the market. There are also a bunch of useful MSR (Model-Specific Registers) that Intel doesn't document. So getting it right for all CPUs from all vendors is now fairly complex.


      • #4
        Yes, we plan a new build this week that we believe will resolve the CPU measurement issue on Sandy Bridge CPU's. Please note that the measured CPU does not impact the CPU test results as these are 2 seperate activities.

        There are however a small number of the 2720QM CPU's that show that Hyperthreading is Not Capable, and PT shows 8 cores instead of 4 cores with HT. If someone has this problem, please let us know as we would like to invesitigate this problem further.