linux-kernel - 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.

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Message-ID: <20091007114719.GH6818@balbir.in.ibm.com>
Date:	Wed, 7 Oct 2009 17:17:20 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arjan van de Ven <arjan@...radead.org>,
	arun@...ux.vnet.ibm.com, Joel Schopp <jschopp@...tin.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org
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.

* Vaidy <svaidy@...ux.vnet.ibm.com> [2009-10-07 16:56:48]:

> * Peter Zijlstra <a.p.zijlstra@...llo.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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