linux-kernel - Re: Run-time PM idea (was: Re: [linux-pm] [RFC][PATCH 0/2] PM: Rearrange core suspend code)

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Date:	Mon, 8 Jun 2009 15:22:35 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>
Subject: Re: Run-time PM idea (was: Re: [linux-pm] [RFC][PATCH 0/2] PM:
	Rearrange core suspend code)


* Matthew Garrett <mjg59@...f.ucam.org> wrote:

> On Mon, Jun 08, 2009 at 03:05:09PM +0200, Ingo Molnar wrote:
> > 
> > * Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > Well, we've been discussing it for quite a while and since more 
> > > and more people are interested, I'm giving it a high priority.
> > 
> > Cool. I think that if within a few years we could achieve that every 
> > default distro (both on desktops and on servers) triggers PM 
> > functionality runtime on common hardware, we'd both have lower power 
> > consumption in general, and we'd have more robust suspend-resume 
> > code as well.
> 
> The difficulty is in determining when it's viable to autosuspend a 
> given device. There's a limit to how much we can determine purely 
> from kernel state (for instance, we could suspend ahci when 
> there's no pending disk access, but we'd lose hotplug 
> notifications) so there's going to have to be some level of 
> userspace policy determination. Having the infrastructure in the 
> kernel is an important part of this, but there'll be some distance 
> to go after that.

What will the 'user space policy' bit do what the kernel cannot?

If you mean the user has to configure something manually - that wont 
really happen in practice. We are happy if they know where to put 
those USB sticks in ;-)

	Ingo
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