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 16:11:56 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Oliver Neukum <oliver@...kum.org>,
	"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)

On Mon, Jun 08, 2009 at 05:06:03PM +0200, Ingo Molnar wrote:

> But if you think that tracking the usage state of the hardware is 
> 'complexity', then you very much dont know what you are talking 
> about. The main task of the kernel is to track hardware usage and to 
> abstract away the fact that the same hardware is used by multiple 
> tasks, and to do it safely. It's what the kernel does all day.

What I'm saying is that you don't *know* what the usage state of the 
hardware is, and in many cases you can't know. A given user may be happy 
to sacrifice their SATA hotplug support. Another with identical hardware 
may not. A given network application may be mission critical and 
intolerant of the network interface being shut down. The same 
application in a different context may not. We'd need to provide a 
bewildering array of interfaces to distinguish between these situations, 
and we'd be unable to turn on autosuspend until the entirity of 
userspace had been ported to them.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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