linux-kernel - Re: Power Management framework proposal

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Date:	Tue, 24 Jul 2007 13:14:29 -0700 (PDT)
From:	david@...g.hm
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Arjan van de Ven <arjan@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...ts.linux-foundation.org>
Subject: Re: Power Management framework proposal

On Tue, 24 Jul 2007, Benjamin Herrenschmidt wrote:

> On Sun, 2007-07-22 at 10:26 -0700, Arjan van de Ven wrote:
>> On Sat, 2007-07-21 at 23:49 -0700, david@...g.hm wrote:
>>
>>> this approach would allow the transition of ALL drivers to the new mode of
>>> operation in one fell swoop, and then adding additional power management
>>> features is just adding to the existing list rather then implementing new
>>> functions.
>>
>>
>> I have a concern with this approach though. It seems to assume that
>> there is one global thing somewhere that sets the system state; in my
>> experience that is the wrong approach; in fact there is a very definite
>> evidence that there are many decisions on power that are to be made
>> local at a high frequency. An example of this is the processor speed;
>> the ondemand governer does exactly this for the cpus that can switch
>> speeds fast; it's just impossible to beat such a local, fast decision
>> with anything on a global scale.
>>
>> On the other hand, some things (the high level goals and constraints)
>> are obviously global.
>
> I think we need a set of constraints that trickle down the power tree
> and limit what a given driver can do locally.

what sort of contraints are you thinking of?

David Lang
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