linux-kernel - Re: [v8 PATCH 2/8]: cpuidle: implement a list based approach to register a set of idle routines.

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Date:	Thu, 08 Oct 2009 14:25:37 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	arun@...ux.vnet.ibm.com
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [v8 PATCH 2/8]: cpuidle: implement a list based approach to
 register a set of idle routines.

On Thu, 2009-10-08 at 17:31 +0530, Arun R Bharadwaj wrote:
> 
> > Uhm, no, it would mean ACPI putting its idle routines on the same level
> > as all others.
> > 
> 
> Putting them all on the same level would mean, we need an
> enable/disable routine to enable only the currently active routines.

What's this enable/disable stuff about?

> Also, the way governor works is that, it assumes that idle routines
> are indexed in the increasing order of power benefit that can be got
> out of the state. So this would get messed up.

Right, which is why I initially had a power-savings field in my
proposal, so it could weight the power savings vs the wakeup latency.

  http://lkml.org/lkml/2009/8/27/159

There it was said that was exactly what these governors were doing,
seems its not.

> > Sounds like something is wrong alright. If you can register an idle
> > routine you should be able to unregister it too.
> >
> 
> Yes, we can register and unregister in a clean way now.
> Consider this. We have a set of routines A, B, C currently registered.
> Now a module comes and registers D and E, and later on at some point
> of time wants to unregister. So how do you keep track of what all idle
> routines the module registered and unregister only those?
> Best way to do that is a stack, which is how I have currently
> implemented.

Right, so destroy that inner set thing, that way we only have one
left ;-)

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