Date: Wed, 22 Oct 2008 07:36:16 -0700
From: Arjan van de Ven <arjan@infradead.org>
To: Gregory Haskins <ghaskins@novell.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>,
       Peter Zijlstra <peterz@infradead.org>
Subject: Re: sched: deep power-saving states
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On Wed, 22 Oct 2008 10:26:49 -0400
Gregory Haskins <ghaskins@novell.com> wrote:
steps, so it'll be
> > faster) 
> 
> [Adding Peter Zijlstra to the thread]
> 
> Ah, yes of course!   That makes sense.  So I have to admit I am fairly
> ignorant of the ACPI C-state stuff, so I just read up on it.  In the
> context of what you said, it makes perfect sense to me now.
> 
> IIUC, the OS selects which C-state it will enter at idle points based
> on some internal criteria (TBD).  All we have to do is remap the
> cpupri "IDLE" state to something like IDLE-C1, IDLE-C2, ..., IDLE-Cn
> and have the cpupri map get updated coincident with the pm_idle()
> call.  Then the scheduler will naturally favor cores that are in
> lighter sleep over cores in deep sleep.
> 
> I am not sure if this is exactly what you were getting at during the
> conf, since it doesnt really consider deep-sleep latency times
> directly.  But I think this is a step in the right direction.

it for sure is a step in the right direction.
the actual exit costs are an optional parameter in this sense,
the steps between C states are non-linear (more like exponential)
so knowing the actual numbers could be used. but even if you don't
use it, it still makes sense and is a very good first order behavior.


-- 
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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