Subject: Re: [v7 PATCH 0/7]: cpuidle/x86/POWER: Cleanup idle power management code in x86, cleanup drivers/cpuidle/cpuidle.c and introduce cpuidle to POWER.

From: Vaidyanathan Srinivasan <[email-masked]>
Date: Wed, 7 Oct 2009 16:56:48 +0530

* Peter Zijlstra <[email-masked]> [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.

--Vaidy