linux-kernel - Re: [RFD] Automatic suspend

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Message-ID: <20090227100037.GB4582@elf.ucw.cz>
Date:	Fri, 27 Feb 2009 11:00:37 +0100
From:	Pavel Machek <pavel@....cz>
To:	Brian Swetland <swetland@...gle.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arjan van de Ven <arjan@...radead.org>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Alan Stern <stern@...land.harvard.edu>,
	Kyle Moffett <kyle@...fetthome.net>,
	Oliver Neukum <oliver@...kum.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arve Hj?nnev?g <arve@...roid.com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

Hi!

> > Arve said that the power state was equivalent in idle and suspend, but 
> > that they preferred suspend because it stopped any periodic timers. I'd 
> > be more interested in making sure that unnecessary timers aren't running 
> > than focusing on automatically entering system-wide suspend - Nokia have 
> > been managing this since 2005 with good results.
> 
> We'd totally agree that doing something about periodic timers would be a
> big win.  There's also the situation that the longest ARM linux can sit
> in idle right now is ~2s at a time (Arve can expand on the exact issue
> relating to a 32bit signed nanosecond value somewhere iirc), which we'd
> want to sort out as well.
> 
> Of course that still doesn't address userspace.  Aggressively going to
> suspend lets us compensate for userspace programs that do somewhat silly
> things (I agree that it would be best if they didn't but they do and
> getting *everyone* to write their userspace code to avoid spinning or
> avoid waking up on short-duration timers to poll is a losing battle).

Well, really? AFAICS, we can either

1) Android solution: let the polling code live, and modify everyone
that _really_ wants to run to use wakelocks.

2) Solution proposed here: fix the polling code.

IMNSHO 1) means modifying many applications, too... See android
marked, 50%+ apps request "keep system woke up" capability. Plus it
means modifying _good_ code, and leaving _bad_ code unfixed. So I'd
prefer 2). I believe ammount of work is pretty similar.

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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