linux-kernel - Re: [linux-pm] Attempted summary of suspend-blockers LKML thread

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Message-ID: <20100805182111.GK2447@linux.vnet.ibm.com>
Date:	Thu, 5 Aug 2010 11:21:11 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	david@...g.hm, peterz@...radead.org, swetland@...gle.com,
	linux-kernel@...r.kernel.org, florian@...kler.org,
	linux-pm@...ts.linux-foundation.org, tglx@...utronix.de,
	alan@...rguk.ukuu.org.uk, Arjan van de Ven <arjan@...radead.org>
Subject: Re: [linux-pm] Attempted summary of suspend-blockers LKML thread

On Thu, Aug 05, 2010 at 05:09:17PM +0100, Mark Brown wrote:
> On Thu, Aug 05, 2010 at 08:12:11AM -0700, Paul E. McKenney wrote:
> > On Wed, Aug 04, 2010 at 10:18:40PM -0700, david@...g.hm wrote:
> 
> > > as for intramentation, the key tool to use to see why a system isn't
> > > going to sleep would be powertop, just like on other linux systems.
> 
> > Powertop is indeed an extremely valuable tool, but I am not certain
> > that it really provides the information that the Android guys need.
> > If I understand Arve's and Brian's posts, here is the scenario that they
> > are trying to detect:
> 
> > o	Some PM-driving application has a bug in which it fails to
> > 	release a wakelock, thus blocking suspend indefinitely.
> 
> > o	This PM-driving application, otherwise being a good citizen,
> > 	blocks.
> 
> > o	There are numerous power-oblivious apps running, consuming
> > 	significant CPU.
> 
> Or otherwise doing something power hungry.
> 
> > What the Android developers need to know is that the trusted application
> > is wrongly holding a wakelock.  Won't powertop instead tell them about
> > all the power-oblivious apps?
> 
> Right, and this isn't just information for developers - Android handsets
> expose this information to end users (so they can indentify any badly
> behaved applications they have installed or otherwise modify their
> handset usage if they are disappointed by their battery life).  That
> said, powertop and similar applications could always be extended to also
> include data from wakelocks.

Good point!!!  Of course, powertop would need to interact with Android's
user-level daemon for this to work, but perhaps this could be arranged.
(There is a user-level daemon in Android that acquires kernel-level
suspend blockers on behalf of applications, so a naive mod to powertop
would just finger the user-level daemon.)

							Thanx, Paul
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