Return-Path: <linux-kernel-owner+w=401wt.eu-S1755692AbZFHNcb@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755692AbZFHNcb (ORCPT <rfc822;w@1wt.eu>);
	Mon, 8 Jun 2009 09:32:31 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754753AbZFHNcV
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Mon, 8 Jun 2009 09:32:21 -0400
Received: from cavan.codon.org.uk ([93.93.128.6]:33658 "EHLO
	vavatch.codon.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752754AbZFHNcU (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 8 Jun 2009 09:32:20 -0400
Date: Mon, 8 Jun 2009 14:32:15 +0100
From: Matthew Garrett <mjg59@srcf.ucam.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Alan Stern <stern@rowland.harvard.edu>,
       pm list <linux-pm@lists.linux-foundation.org>,
       ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Magnus Damm <magnus.damm@gmail.com>
Subject: Re: Run-time PM idea (was: Re: [linux-pm] [RFC][PATCH 0/2] PM:
	Rearrange core suspend code)
Message-ID: <20090608133215.GA15482@srcf.ucam.org>
References: <Pine.LNX.4.44L0.0906071651060.25203-100000@netrider.rowland.org> <200906072347.00580.rjw@sisk.pl> <20090608065419.GA13568@elte.hu> <200906081330.50045.rjw@sisk.pl> <20090608130509.GA3272@elte.hu> <20090608131159.GA15100@srcf.ucam.org> <20090608132235.GC13214@elte.hu>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20090608132235.GC13214@elte.hu>
User-Agent: Mutt/1.5.17+20080114 (2008-01-14)
X-SA-Exim-Connect-IP: <locally generated>
X-SA-Exim-Mail-From: mjg59@codon.org.uk
X-SA-Exim-Scanned: No (on vavatch.codon.org.uk); SAEximRunCond expanded to false
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1630
Lines: 35

On Mon, Jun 08, 2009 at 03:22:35PM +0200, Ingo Molnar wrote:
> 
> * Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> > 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?

How does the kernel know whether the user cares about SATA hotplug or 
not?

> 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 ;-)

It'll be up to the distributions to provide sane defaults and let them 
be reconfigured as necessary, depending on the information we have from 
the user and maybe platform-specific knowledge. But this is a difficult 
problem - we need to be smart about all the potential sources of 
information in order to pick an appropriate policy, and the kernel's not 
the right layer to do some of this information collection.

-- 
Matthew Garrett | mjg59@srcf.ucam.org
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/