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

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Message-ID: <20090608145102.GA17427@srcf.ucam.org>
Date:	Mon, 8 Jun 2009 15:51:02 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Ingo Molnar <mingo@...e.hu>
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)

On Mon, Jun 08, 2009 at 04:44:55PM +0200, Ingo Molnar wrote:
> 
> * Matthew Garrett <mjg59@...f.ucam.org> wrote:
> > No, we can't just close it - then we won't get notification that a 
> > key's been hit in order to unlock the screensaver. [...]
> 
> Looks like a broken notification model.

We've closed the input device. Where are we supposed to get the input 
event from?

> > [...] Yes, we can greatly expand the userland-visible interface to 
> > every piece of hardware in order to make this work, but that's a 
> > huge amount of effort to avoid a model where userspace sets some 
> > tunables appropriately.
> 
> What huge amount of effort? All you are doing is to track the "is 
> the device really used" state in user-space - and, if the current 
> desktop experience is any measure, highly imperfectly so.
> 
> What i'm suggesting is to track it properly in the kernel. It's not 
> like the kernel doesnt need to know whether a piece of hardware is 
> under use or not ...

So, for instance, we need to add interfaces like "I care about hotplug 
events on this SATA port" and "I'm listening for these keys so please 
don't suspend the device" and "The service bound to this port needs to 
maintain network connectivity and the one bound to this port doesn't, so 
only put the wireless card into deep powersave if the first exits", and 
then we need to wait for userspace to adopt these interfaces before we 
can enable any of the functionality because otherwise old userspace will 
be broken with new kernels.

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