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    SubjectRe: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86
    * Arjan van de Ven <arjan@infradead.org> [2008-05-27 09:40:35]:

    > 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!

    You are right.... I kind of interchangeably used frequency and
    capacity assuming capacity is linearly proportional to frequency!

    In reality, I agree that capacity is not linearly proportional to
    frequency and it is dependent on cache usage etc.

    The differences apart, I am sure I have conveyed the relationship
    between scaled stats and CPU frequency. I used the term 'capacity' to
    generalise CPU performance, but I guess it may lead to a different
    discussion. I will stick to frequency. :)

    --Vaidy

    > > 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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