linux-kernel - Re: [v6 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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Date:	Fri, 25 Sep 2009 11:35:56 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	svaidy@...ux.vnet.ibm.com, arun@...ux.vnet.ibm.com,
	Len Brown <lenb@...nel.org>,
	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>,
	Shaohua Li <shaohua.li@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-acpi@...r.kernel.org
Subject: Re: [v6 PATCH 0/7]: cpuidle/x86/POWER: Cleanup idle power
 management code in x86, cleanup drivers/cpuidle/cpuidle.c and introduce
 cpuidle to POWER.

On Fri, 25 Sep 2009 10:54:24 +0200
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Fri, 2009-09-25 at 12:36 +0530, Vaidyanathan Srinivasan wrote:
> > * Arjan van de Ven <arjan@...radead.org> [2009-09-24 14:22:28]:
> > 
> > > On Thu, 24 Sep 2009 10:42:41 +0530
> > > Arun R Bharadwaj <arun@...ux.vnet.ibm.com> wrote:
> > > 
> > > > * Arun R Bharadwaj <arun@...ux.vnet.ibm.com> [2009-09-22
> > > > 16:55:27]:
> > > > 
> > > > Hi Len, (or other acpi folks),
> > > > 
> > > > I had a question regarding ACPI-cpuidle interaction in the
> > > > current implementation.
> > > > 
> > > > Currently, every cpu (i.e. acpi_processor) registers to cpuidle
> > > > as a cpuidle_device. So every cpu has to go through the process
> > > > of setting up the idle states and then registering as a cpuidle
> > > > device.
> > > > 
> > > > What exactly is the reason behind this?
> > > > 
> > > 
> > > technically a BIOS can opt to give you C states via ACPI on some
> > > cpus, but not on others.
> > > 
> > > in practice when this happens it tends to be a bug.. but it's
> > > technically a valid configuration
> > 
> > So we will need to keep the per-cpu registration as of now because
> > we may have such buggy BIOS in the field and we don't want the
> > cpuidle framework to malfunction there.
> 
> If the BIOS doesn't mention a certain C state on a cpu, and you try to
> set it anyway, does that go boom?
> 
> This whole per-cpu registration thing is horridly ugly, can't you
> have a per-cpu C state exception mask and leave it at that -- if its
> really needed?

the real solution is to make the acpi code always know about C1, even
if the bios doesn't.... That's one for Len :)

(C1 is just "hlt", what we do in the other idle loop ;-) 


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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