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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Pavel Machek <pavel@ucw.cz>
Subject: Re: [RFD] Automatic suspend
Date: Fri, 27 Feb 2009 15:22:39 +0100
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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>
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On Friday 27 February 2009, Pavel Machek wrote:
> 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...

Except that you have to check all of the wakelocks periodically in a loop =>
polling.  So?

Rafael