linux-kernel - Re: [RFD] Automatic suspend

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Message-ID: <20090227100941.GE4582@elf.ucw.cz>
Date:	Fri, 27 Feb 2009 11:09:41 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Arve Hj?nnev?g <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Oliver Neukum <oliver@...kum.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

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
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