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: <1254920711.26976.243.camel@twins>
Date:	Wed, 07 Oct 2009 15:05:11 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	svaidy@...ux.vnet.ibm.com
Cc:	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>,
	Balbir Singh <balbir@...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.

On Wed, 2009-10-07 at 16:56 +0530, Vaidyanathan Srinivasan wrote:
> * 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.  

>>From what I understood some broken ass bioses report different C state
availability on different CPUs in the same SMP system.

I'm suggesting to work around that by limiting all CPUs to the subset of
C states reported on all CPUs, instead of the current mess.

I haven't heard anybody tell me why that wouldn't be possible on x86

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