linux-kernel - Re: [RFD] Automatic suspend

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Date:	Fri, 27 Feb 2009 21:55:40 +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:
> On Fri 2009-02-27 15:22:39, Rafael J. Wysocki wrote:
> > 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?
> 
> No. I want to have single atomic_t for all the wakelocks... at least
> in non-debug version. Debug version will be slower. I believe you
> originally suggested that.

I did, but please don't call it "wakelocks".  It's confusing.

Thanks,
Rafael
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