linux-kernel - Re: sched: deep power-saving states

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Date:	Wed, 22 Oct 2008 10:05:21 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: sched: deep power-saving states

Arjan van de Ven wrote:
> On Wed, 22 Oct 2008 09:42:52 -0400
> Gregory Haskins <gregory.haskins.ml@...il.com> wrote:
>
>   
>> What I was thinking is that a simple mechanism to quantify the
>> power-state penalty would be to add those states as priority levels in
>> the cpupri namespace.  E.g. We could substitute IDLE-RUNNING for IDLE,
>> and add IDLE-PS1, IDLE-PS2, .. IDLE-PSn, OTHER, RT1, .. RT99.  This
>> means the scheduler would favor waking an IDLE-RUNNING core over an
>> IDLE-PS1-PSn, etc.  The question in my mind is: can the power-states
>> be determined in a static fashion such that we know what value to
>> quantify the idle state before we enter it?  Or is it more dynamic
>> (e.g. the longer it is in an MWAIT, the deeper the sleep gets).
>>     
>
> it's a little dynamic, but just assuming the worst will be a very good
> approximation of reality. And we know what we're getting into in that
> sense.
>   

Ok, but if we just assume the worst case always, how do I differentiate
between, say, IDLE-RUNNING and IDLE-PSn?  If I assign them all to
IDLE-PSn apriori its no better than the basic single IDLE state we
support today.  Or am I misunderstanding you?

-Greg



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