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    SubjectRe: [RFC][PATCH v5 00/14] sched: packing tasks
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    On 11 November 2013 17:38, Peter Zijlstra <peterz@infradead.org> wrote:
    > On Mon, Nov 11, 2013 at 11:33:45AM +0000, Catalin Marinas wrote:
    >> My understanding from the recent discussions is that the scheduler
    >> should decide directly on the C-state (or rather the deepest C-state
    >> possible since we don't want to duplicate the backend logic for
    >> synchronising CPUs going up or down). This means that the scheduler
    >> needs to know about C-state target residency, wake-up latency (I think
    >> we can leave coupled C-states to the backend, there is some complex
    >> synchronisation which I wouldn't duplicate).
    >>
    >> Alternatively (my preferred approach), we get the scheduler to predict
    >> and pass the expected residency and latency requirements down to a
    >> power driver and read back the actual C-states for making task
    >> placement decisions. Some of the menu governor prediction logic could
    >> be turned into a library and used by the scheduler. Basically what
    >> this tries to achieve is better scheduler awareness of the current
    >> C-states decided by a cpuidle/power driver based on the scheduler
    >> constraints.
    >
    > Ah yes.. so I _think_ the scheduler wants to eventually know about idle
    > topology constraints. But we can get there in a gradual fashion I hope.
    >
    > Like the package C states on x86 -- for those to be effective the
    > scheduler needs to pack tasks and keep entire packages idle for as long
    > as possible.

    That's the purpose of patches 12, 13 and 14. To get the current wakeup
    latency of a core and use it when selecting a core

    >
    >


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