linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Message-ID: <Pine.LNX.4.44L0.1005281029500.1939-100000@iolanthe.rowland.org>
Date:	Fri, 28 May 2010 10:35:47 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	Arve Hjønnevåg <arve@...roid.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	<felipe.balbi@...ia.com>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Fri, 28 May 2010, Alan Cox wrote:

> If I push the button we get an IRQ
> We come out of power save
> The app gets poked
> The app may be unimportant but the IRQ means we have a new timeout of
>     some form to run down to idle
> The app marks itself important
> The app stays awake for 60 seconds rsyncing your email
> The app marks itself unimportant
> Time elapses
> We return to suspend
> 
> 
> If you are absolutely utterly paranoid about it you need the button
> driver to mark the task it wakes back as important rather than rely on
> time for response like everyone else. That specific bit is uggglly but
> worst case its just a google private patch to a few drivers. I understand
> why Android wants it. The narrower the gap between 'we are doing nothing,
> sit in lowest CPU on state' and 'we are off' the better the battery life
> and the more hittable the condition.

That "private patch to a few drivers" is almost exactly what suspend
blockers are.  Given that much of this discussion has revolved around 
whether suspend blockers are accptable in the kernel, I don't think you 
should shrug them off quite so easily.

Also, you have forgotten about the case where there is no app waiting 
to get poked:

	The app is busy doing something else unimportant
	We do into power save
	Push a button, generate an IRQ
	Come out of power save
	No app to poke
	* System goes back to sleep and eventually wakes up again
	The app finishes what it was doing
	The app sees there is a keystroke and marks itself important
	...

The * step is where trouble can occur.

Alan Stern

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