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

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Date:	Sun, 1 Aug 2010 18:16:57 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	linux-pm@...ts.linux-foundation.org,
	<linux-kernel@...r.kernel.org>, <arve@...roid.com>,
	<mjg59@...f.ucam.org>, <pavel@....cz>, <florian@...kler.org>,
	<rjw@...k.pl>, <swetland@...gle.com>, <peterz@...radead.org>,
	<tglx@...utronix.de>, <alan@...rguk.ukuu.org.uk>
Subject: Re: Attempted summary of suspend-blockers LKML thread

On Sun, 1 Aug 2010, Paul E. McKenney wrote:

> > I should have made a stronger point: "power-aware" is _not_ a good
> > term for these applications.  "power-enabled" would be better but
> > still not ideal.  Maybe "power-permitted"?  The definition is that
> > they are _permitted_ to do something (acquire suspend blockers), not
> > that they actually _do_ something.
> 
> How about "PM-driving applications", as Rafael suggested?

Perhaps.  But it's a little misleading, since what these applications
are permitted to do is to _prevent_ the system from going to low power.  
So in a real sense they don't drive PM -- they block it.  (Indeed,
that's what inspired the name "suspend blocker".)  Of course, the same 
objection applies to "power-permitted".

> > I was agreeing with the requirement but disagreeing with the reason
> > given for it.  Even when buffers are large enough that the danger of
> > overrunning them is infinitesimal, delays in input event delivery are
> > still undesirable.
> > 
> > Besides, the Android kernel doesn't vary its behavior based on whether
> > the recipient is power-permitted or power-naive; it _always_ delivers
> > input events in a timely fashion.
> 
> True, the difference between the two classes of applications is in
> whether or not the application is permitted to process the event.
> 
> I added "and to minimize response latencies" to the requirement.
> Does that capture it?

Yes.

> > > But leaving that aside, I thought that Arve and Brian explicitly
> > > stated this as a requirement on power-aware applications -- one of the
> > > responsibilities that came with the power to block suspend.
> > 
> > No.  There are _no_ requirements on power-permitted (or power-aware if
> > you prefer) applications, other than that the user decides to give it
> > the appropriate permission.
> > 
> > Internally, of course, Android may enforce this rule on their own
> > software.  But it has no force in regard to external applications.
> 
> So should this be moved to a new "ANDROID POLICY" section or some such?

Or DESIRED BEHAVIOR, or some such.

Alan Stern

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