linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200902202344.20040.rjw@sisk.pl>
Date:	Fri, 20 Feb 2009 23:44:18 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Arve Hjønnevåg <arve@...roid.com>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	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 20 February 2009, Oliver Neukum wrote:
> Am Freitag 20 Februar 2009 11:46:55 schrieb Rafael J. Wysocki:
> > On Thursday 19 February 2009, Oliver Neukum wrote:
> > > Am Donnerstag 19 Februar 2009 23:21:46 schrieb Rafael J. Wysocki:
> > > > > That's the whole point behind userspace wakelocks!  They provide a
> > > > > mechanism for userspace to tell the kernel when (as far as userspace
> > >
> > > is
> > >
> > > > > concerned) it is or is not okay to auto-sleep.
> > > >
> > > > Still, one can go further and observe that the user space can in fact
> > > > start automatic suspend by itself whenever it knows it's appropriate
> > > > ...
> > >
> > > User space initiating this is a race condition.
> >
> > Do you mean a race with the other user space processes or with the kernel?
> 
> With the set of runnable processes.There's always a window between
> evaluating the current set of runnable tasks and telling the kernel to sleep.
> IMO the most elegant solution would be a task attribute that would signal
> the kernel that a task should not count as keeping the system busy even
> if it is runnable and trigger the sleep in kernel space.

Please see my last reply to Arve (http://lkml.org/lkml/2009/2/20/182) and tell
me what you think.

Best,
Rafael
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