linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200902202305.09992.oliver@neukum.org>
Date:	Fri, 20 Feb 2009 23:05:05 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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

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.

	Regards
		Oliver

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