linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200902271522.41915.rjw@sisk.pl>
Date:	Fri, 27 Feb 2009 15:22:39 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
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

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
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