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    SubjectRe: [RFC PATCH v1 0/3] Scaled statistics using APERF/MPERF in x86
    On Mon, 26 May 2008 22:54:43 +0530
    Balbir Singh <> wrote:

    > Arjan,
    > These problems exist anyway, irrespective of scaled accounting (I'd
    > say that they are exceptions)
    > 1. The management tool does have access to the current frequency and
    > maximum frequency, irrespective of scaled accounting. The decision
    > could still be taken on the data that is already available and
    > management tools can already use them

    it's sadly not as easy as you make it sound. From everything you wrote
    you're making the assumption "if we're not at maximum frequency, we
    have room to spare", which is very much not a correct assumption

    > 2. With IDA, we'd have to
    > document that APERF/MPERF can be greater than 100% if the system is
    > overclocked.
    > Scaled accounting only intends to provide data already available.
    > Interpretation is left to management tools and we'll document the
    > corner cases that you just mentioned.

    IDA is not overclocking, nor is it a corner case *at all*. It's the
    common case in fact on more modern systems. Having the kernel present
    "raw" data to applications that then have no idea how to really use it
    to be honest isn't very attractive to me as idea: you're presenting a
    very raw hardware interface that will keep changing over time in terms
    of how to interpret the data... the kernel needs to abstract such hard
    stuff from applications, not fully expose them to it. Especially since
    these things *ARE* tricky and *WILL* change. Future x86 hardware will
    have behavior that makes the "oh we'll document the corner cases"
    extremely unpractical. Heck, even todays hardware (but arguably not yet
    the server hardware) behaves like that. "Documenting the common case as
    corner case" is not the right thing to do when introducing some new
    behavior/interface. Sorry.

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