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Date: Fri, 27 Feb 2009 11:09:41 +0100
From: Pavel Machek <pavel@ucw.cz>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Arve Hj?nnev?g <arve@android.com>, Alan Stern <stern@rowland.harvard.edu>,
       "Woodruff, Richard" <r-woodruff2@ti.com>,
       Arjan van de Ven <arjan@infradead.org>,
       Kyle Moffett <kyle@moffetthome.net>, Oliver Neukum <oliver@neukum.org>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       pm list <linux-pm@lists.linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Nigel Cunningham <nigel@nigel.suspend2.net>,
       Matthew Garrett <mjg59@srcf.ucam.org>,
       mark gross <mgross@linux.intel.com>, Uli Luckas <u.luckas@road.de>,
       Igor Stoppa <igor.stoppa@nokia.com>,
       Brian Swetland <swetland@google.com>, Len Brown <lenb@kernel.org>
Subject: Re: [RFD] Automatic suspend
Message-ID: <20090227100941.GE4582@elf.ucw.cz>
References: <200902192215.18365.rjw@sisk.pl> <200902201657.01145.rjw@sisk.pl> <d6200be20902201503m59a13cddn59adfc47d0c2ed1e@mail.gmail.com> <200902210057.27781.rjw@sisk.pl>
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Hi!

> > > Then, the decision making logic will be able to use /sys/power/sleep whenever
> > > it wishes to and the kernel will be able to refuse to suspend if it's not
> > > desirable at the moment.
> > >
> > > It seems to be flexible enough to me.
> > 
> > This seems flexible enough to avoid race conditions, but it forces the
> > user space power manager to poll when the kernel refuse suspend.
> 
> And if the kernel is supposed to start automatic suspend, it has to monitor
> all of the wakelocks.  IMO, it's better to allow the power manager to poll the
> kernel if it refuses to suspend.

polling is evil -- it keeps CPU wake up => wastes power.

Wakelocks done right are single atomic_t... and if you set it to 0,
you just unblock "sleeper" thread or something. Zero polling and very
simple...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html