linux-kernel - Re: [v4 PATCH 1/5]: cpuidle: Cleanup drivers/cpuidle/cpuidle.c

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Date:	Thu, 03 Sep 2009 11:40:38 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	arun@...ux.vnet.ibm.com
Cc:	Joel Schopp <jschopp@...tin.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [v4 PATCH 1/5]: cpuidle: Cleanup drivers/cpuidle/cpuidle.c

On Thu, 2009-09-03 at 10:12 +0530, Arun R Bharadwaj wrote:

> > OK, that's a start I guess. Best would be to replace all of pm_idle with
> > cpuidle, which is what should have been done from the very start.
> > 
> > If cpuidle cannot fully replace the pm_idle functionality, then it needs
> > to fix that. But having two layers of idle functions is just silly.
> > 
> > Looking at patch 2 and 3, you're making the same mistake on power, after
> > those patches there are multiple ways of registering idle functions, one
> > through some native interface and one through cpuidle, this strikes me
> > as undesirable.
> > 
> > If cpuidle is a good idle function manager, then it should be good
> > enough to be the sole one, if its not, then why bother with it at all.
> > 
> 
> Okay, I'm giving this approach a shot now. i.e. trying to make cpuidle
> as _the_ sole idle function manager. This would mean doing away with
> pm_idle and ppc_md.power_save. And, cpuidle_idle_call() which is the
> main idle loop of cpuidle, present in drivers/cpuidle/cpuidle.c will
> have to be called from arch specific code of cpu_idle()
> 
> Also this would mean enabling cpuidle for all platforms, even if the
> platform doesn't have multiple idle states. So suppose a platform doesnt
> have multiple states, it wouldn't want the bloated code of cpuidle
> governors, and would want just a simple cpuidle loop.

Do talk to the powerpc maintainers about this. But yes, something like
that should be doable.

AFAICT the whole governor thing is optional and cpuidle provides a
spinning idle loop by default, and platforms can always register a
simple alternative when they set up bits -- the only thing to be careful
about is not creating a chicken-egg problem where the platform setup
runs before cpuidle is able to register a new handler or something.

I'd be delighted to see the end of pm_idle on x86.

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