Message-Id: <201008022333.32623.rjw@sisk.pl>
Date:	Mon, 2 Aug 2010 23:33:32 +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 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).

> > > > on the suspend blockers for drivers; the linux device runtime PM is
> > > > effectively doing the same things; it allows drivers to suspend/resume
> > > > individually (with a very nice API/programming model I should say) based
> > > > on usage. And it works on a tree level, so that it's relatively easy
> > > > to do things like "I want to go to <this magic deep idle state>, but
> > > > only if <this set of devices is suspended already>". This is obviously
> > > > an important functionality for all low power devices, ARM or x86. 
> > > > Suspend blockers had this functionality as part of what it did (they do
> > > > more obviously) but I'd wager that the current Linux infrastructure is
> > > > outright nicer. 
> > > 
> > > This is what Rafael has been working on?
> > 
> > If you mean the runtime PM framework, then yes, I've been working on it.
> > 
> > > Of course, the Android guys also want to pay attention to which apps
> > > are running as well as to the state of devices on the system.
> > 
> > In fact the runtime PM framework is also important to Android, because it
> > can be used in there, for example, to implement the "early suspend" thing
> > I referred to in one of my previous messages in this thread.
> 
> Now we just need to convince the Android guys of that.  ;-)

I believe there's no need for that, as we were talking about that a few months
ago.

Thanks,
Rafael
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