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    SubjectRe: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86
    On Tue, 27 May 2008 19:34:40 +0530
    Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> wrote:
    >
    > What we are proposing is a scaled time value that is scaled to the
    > current CPU capacity. If the scaled utilisation is 50% when the CPU
    > is at 100% capacity, it is expected to remain at 50% even if the CPU's
    > capacity is dropped to 50%, while the traditional utilisation value
    > will be 100%.

    When you use the word "capacity" I cringe ;(

    >
    > The problem in the above two cases is that we had assumed that the
    > maximum CPU capacity is 100% at normal capacity (without IDA).
    >
    > If the CPU is at half the maximum frequency, then scaled stats should
    > show 50%.

    see frequency != capacity.
    It's about more than frequency. It's about how much cache you have
    available too. If you run single threaded on a dual core cpu, you have
    100% of the cache, but the cpu is 50% idle. But that doesn't mean that
    when you double the load, you actually get 2x the performance. So
    you're not at 50% of capacity!



    > The point I am trying to make is whether scaling should be done
    > relative to CPUs designed maximum capacity or maximum capacity under
    > current constraints is to be discussed.

    now you're back at "capacity".. we were at frequency before ;(


    >
    > Case A:
    > ------
    >
    > Scaled stats is stats relative to maximum designed capacity including
    > IDA

    you don't know what that is though.



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