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

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Date:	Thu, 5 Aug 2010 07:56:29 +0200
From:	Florian Mickler <florian@...kler.org>
To:	Florian Mickler <florian@...kler.org>
Cc:	paulmck@...ux.vnet.ibm.com, david@...g.hm,
	Arve Hjønnevåg 
	<arve@...roid.com>, Matthew Garrett <mjg59@...f.ucam.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	pavel@....cz, 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 Thu, 5 Aug 2010 07:33:59 +0200
Florian Mickler <florian@...kler.org> wrote:

> On Wed, 4 Aug 2010 16:10:03 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> 
> No no. In the David-Lang-CGroup-Scheme[1](tm?) suspend-from-idle
> is used. For idle decision a certain subset of tasks is ignored. 
> 
> Where suspend is prevented by the trusted
> process in android-world taking a wakelock, here it would just prevent
> the system from going idle by arming timers.
> 
> This would be pretty equivalent to the suspend-blocker scheme and not
> introduce new userspace api. But the downside is, as Arve pointed out,
> that now one can not get full-idle-power-leverage while suspend
> is blocked. 
> 
> [1] http://permalink.gmane.org/gmane.linux.kernel/1018452  and
> following 
> 
> 
> Cheers,
> Flo
> 

There are a few downsides that got mentioned already in reponse..  I got
a little lagged behind. 

There are upsides to this approach like not
having a special purpose userspace api, conceptually integrating
suspend into the idle mechanism .. 

Short summary of the cons that got mentioned:

  -  applications need to resort to polling to keep the system
	out of idle (->  system will never be fully idle)

  -  the race between deciding to suspend and becoming active
	again is not handled

  -  no special statistics available

  -  the timers of the ignored applications will behave unexpected
	(as the monotonic clock is not stopped)... while applications
	have already to cope with network-loss, other side effects of
	suspend without monotonic clock stopped are to be expected...


Cheers,
Flo
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