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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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