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    SubjectRe: PATCH] ftrace: Add a C/P state tracer to help power optimization
    On Mon, Oct 06, 2008 at 02:21:31PM -0700, Arjan van de Ven wrote:
    > > > the link between P states and frequency is... rather lose.
    > > > Especially with Turbo Mode it no longer is really relevant to list
    > > > frequencies.
    > >
    > > It would probably be less confusing for everyone if the higher level
    > > cpufreq layers reported the correct frequency for turbo mode too.
    > > I haven't checked how complicated this would be.
    >
    > it's impossible until after the fact; you don't know which frequencies
    > you got until you check back later.

    Well it could do that couldn't it? Ok not sure how big the cost
    would be.

    I can just imagine Turbo mode becoming a FAQ on this list and having
    better reporting upfront might mitigate this a bit.

    >
    >
    > > Ok.
    > >
    > > That means that when a CPU is idle forever there won't be any output?
    >
    > correct; it'll wait until it stops being idle before telling you how
    > long it was idle.
    >
    > if it really bothers you we could do a dummy broadcast ipi on shutting
    > down the tracer.. in practice it's not a problem.

    Or just mark entry/exit, but you just need a wakeup threshold to avoid
    the loop. A wakeup threshold seems like a good idea anyways though, just
    to get better efficiency on larger systems.

    > (we wake up all cpus all the time)

    I assume that will change in the future and might even not true
    anymore on some special stripped down configurations.

    -Andi

    --
    ak@linux.intel.com


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