linux-kernel - Re: [PATCH 1/8] PM: Opportunistic suspend support.

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Date:	Thu, 27 May 2010 22:00:09 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Randy Dunlap <rdunlap@...otime.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Tejun Heo <tj@...nel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Nigel Cunningham <nigel@...onice.net>,
	Ming Lei <tom.leiming@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH 1/8] PM: Opportunistic suspend support.

On Thursday 27 May 2010, Dmitry Torokhov wrote:
> On Wed, May 26, 2010 at 05:52:40PM -0700, Arve Hjønnevåg wrote:
> > 2010/5/26 Alan Stern <stern@...land.harvard.edu>:
> > > On Wed, 26 May 2010, Arve Hjønnevåg wrote:
> > >
> > >> > I must be missing something.  In Arve's patch 1/8, if the system is in
> > >> > opportunistic suspend, and a wakeup event occurs but no suspend
> > >> > blockers get enabled by the handler, what causes the system to go back
> > >> > into suspend after the event is handled?  Isn't that a loop of some
> > >> > sort?
> > >> >
> > >>
> > >> Yes it is a loop. I think what you are missing is that it only loops
> > >> repeatedly if the driver that aborts suspend does not use a suspend
> > >> blocker.
> > >
> > > You mean "the driver that handles the wakeup event".  I was asking what
> > > happened if suspend succeeded and then a wakeup occurred.  But yes, if
> > > a suspend blocker is used then its release causes another suspend
> > > attempt, with no looping.
> > >
> > >> > And even if it isn't, so what?  What's wrong with looping behavior?
> > >>
> > >> It is a significant power drain.
> > >
> > > Not in the situation I was discussing.
> > >
> > 
> > If you meant it spend most of the time suspended, then I agree. It
> > only wastes power when a driver blocks suspend by returning an error
> > from its suspend hook and we are forced to loop doing no useful work.
> > 
> 
> If driver refuses to suspend that means there are events that need
> processing. I fail to see why it would be called "looping doing no
> useful work".

I guess Arve meant the case of events that didn't propagate to user space.

Rafael


> 
> 

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