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

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Message-Id: <201008030040.20704.rjw@sisk.pl>
Date:	Tue, 3 Aug 2010 00:40:20 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	arve@...roid.com, mjg59@...f.ucam.org, pavel@....cz,
	florian@...kler.org, stern@...land.harvard.edu,
	swetland@...gle.com, peterz@...radead.org, tglx@...utronix.de,
	alan@...rguk.ukuu.org.uk
Subject: Re: Attempted summary of suspend-blockers LKML thread

On Tuesday, August 03, 2010, Paul E. McKenney wrote:
> On Mon, Aug 02, 2010 at 11:33:32PM +0200, Rafael J. Wysocki wrote:
> > On Monday, August 02, 2010, Paul E. McKenney wrote:
> > > On Mon, Aug 02, 2010 at 03:52:20PM +0200, Rafael J. Wysocki wrote:
> > > > On Monday, August 02, 2010, Paul E. McKenney wrote:
> > > > > On Sun, Aug 01, 2010 at 03:47:08PM -0700, Arjan van de Ven wrote:
> > > > > > On Sun, 1 Aug 2010 12:12:28 -0700
> > > > > > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > > > ...
> > > > > > Another one: freezing whole cgroups..... we have that today. it
> > > > > > actually works quite well.... of course the hard part is the decision
> > > > > > what to put in which cgroup, and at what frequency and duration you let
> > > > > > cgroups run.
> > > > > 
> > > > > Indeed, the Android guys seemed to be quite excited by cgroup freezing
> > > > > until they thought about the application-classification problem.
> > > > > Seems like it should be easy for some types of applications, but I do
> > > > > admit that apps can have non-trivial and non-obvious dependencies.
> > > > 
> > > > This isn't more difficult than deciding which applications will be allowed to
> > > > use wakelocks (in the wakelocks world).  It actually seems to be pretty much
> > > > equivalent to me. :-)
> > > 
> > > If I understand correctly, the problem they were concerned about was
> > > instead "given that a certain set of apps are permitted to use wakelocks,
> > > which of the other apps can safely be frozen when the display blanks
> > > itself."
> > 
> > I _think_ the problem should be reformulated as "which of the other apps
> > can be safely frozen without causing the wakelocks-using ones to have
> > problems" instead (the particular scenario is that one of the wakelocks-using
> > apps may need one of the other apps to process something and therefore the
> > other app cannot be frozen; however, that may be resolved by thawing all of
> > the other apps in such situations IMO).
> 
> I agree that your statement is equivalent to mine.  From what I can see,
> the current Android code resolves this by not freezing any app while
> a wakelock is held.
> 
> Just out of curiosity, how are you detecting the situation in order to
> decide when to thaw the apps in the cgroup?

Well, in fact I would only be able to talk about that theoretically, as I'm
currently not involved in any project using cgroups for power management.
I have considered that, but I haven't tried to implement it.

Thanks,
Rafael
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