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    SubjectRe: [v7 PATCH 0/7]: cpuidle/x86/POWER: Cleanup idle power management code in x86, cleanup drivers/cpuidle/cpuidle.c and introduce cpuidle to POWER.
    * Vaidy <svaidy@linux.vnet.ibm.com> [2009-10-07 16:56:48]:

    > * Peter Zijlstra <a.p.zijlstra@chello.nl> [2009-10-06 20:04:39]:
    >
    > > On Tue, 2009-10-06 at 22:05 +0530, Arun R Bharadwaj wrote:
    > >
    > > > Also, the per-cpu nature of registration/unregistration of cpuidle
    > > > has been maintained as ACPI needs this.
    > >
    > > Right, so can't we ditch that and have acpi default to the lowest common
    > > C-state and warn when various cpus report different C-states?
    >
    > Hi Peter,
    >
    > As Arjan mentioned previously, the per-cpu registration has to stay
    > for x86 for now due to legacy ACPI compatibility. Breaking that may
    > break lot of existing users and we do not have a clean fallback
    > method.
    >
    > As far as powerpc is concerned, we can work with a single global
    > registration. However we would like to have the same interface across
    > different archs.
    >
    > With the new re-factoring (v7), Arun has killed most of the list
    > traversal and linking between various cpu's cpuidle_driver structures.
    > Now we have a per-cpu stack of registered devices and we lookup the
    > structs using online cpumasks. The cpuidle_driver structure has list
    > of idle routing pointers (struct cpuidle_state) and rest of it is
    > statistics that needs to be maintained at a per-cpu level anyway. All
    > that is duplicated here is the array of idle routines (struct
    > cpuidle_state) on each cpu.
    >
    > The objective of the refactoring is to have a single common idle
    > routine management framework (remove pm_idle) and we have it done
    > through cpuidle registration framework. We can incrementally remove
    > the per-cpu registration later easily by splitting the cpuidle_driver
    > structure.
    >

    Yes, incremental refactoring makes the most sense from the do not
    break as you refactor point of view.

    --
    Balbir


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