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

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Date:	Mon, 2 Aug 2010 07:00:27 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	"Ted Ts'o" <tytso@....edu>, 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, 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 Sun, Aug 01, 2010 at 09:05:48PM -0700, Arjan van de Ven wrote:
> On Sun, 1 Aug 2010 20:03:04 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > > on application programmers to do the right thing.  That's not to
> > > say that we shouldn't give up on trying to influence application
> > > programmers --- but relying on that as the only strategy seems to
> > > depart from the path of wisdom.
> > 
> > Unless someone can reliably automate whacking the moles, history is
> > not on the side of the mole-whackers.  I won't say that such
> > automation is impossible, but only because of all the "impossible"
> > things in my lifetime that have turned out to be possible.
> 
> we have a few things going for us here though
> 
> 1) It's easy to programatically detect the problems
>   1a) so programmers can detect issues before they ship software,
>   unlike the fsync() thing Ted mentions. History is showing this is at
>   least relatively successful in open source, but not with Adobe's
>   proprietary software such as Flash
> 2) Users can be made aware of what the bad guys are
> 3) The business models of many of the mobile apps gives programmers a
>    strong incentive to ship well behaving. The moment your first and
>    second review of your app read "this app was identified as reducing
>    battery life a lot"... your revenues will not go beyond the $1.98..
>    ... assuming these first two guys didn't refund their app.
> 
> Since we can detect who the bad guys are, we can also automatically
> quarantine them for the common cases..... which is good news.

Unless of course the app reducing battery life a lot does something
that users like better than the increment in battery life.

> I'm a little worried that this whole "I need to block suspend" is
> temporary. Yes today there is silicon from ARM and Intel where suspend
> is a heavy operation, yet at the same time it's not all THAT heavy
> anymore.... at least on the Intel side it's good enough to use pretty
> much all the time (when the screen is off for now, but that's a memory
> controller issue more than anything else). I'm pretty sure the ARM guys
> will not be far behind.

Heh!  One could make the "might be temporary" argument against any new
feature, including the ones that you are proposing.  For but one example,
I very well remember being told by many people in many communities that
SMP was temporary -- Moore's-Law increases in clock frequency would soon
mean that even the biggest systems would be uniprocessors.

If by "memory controller" you are referring to the need to save state
for cache SRAMs and perhaps also DRAM, then yes, I agree that some of
the most difficult low-power-state tradeoffs involve these devices.

							Thanx, Paul
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