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From: Oliver Neukum <oliver@neukum.org>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [RFD] Automatic suspend
Date: Fri, 20 Feb 2009 23:05:05 +0100
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Cc: Alan Stern <stern@rowland.harvard.edu>,
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       Nigel Cunningham <nigel@nigel.suspend2.net>,
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       mark gross <mgross@linux.intel.com>, Uli Luckas <u.luckas@road.de>,
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       Brian Swetland <swetland@google.com>, Len Brown <lenb@kernel.org>
References: <Pine.LNX.4.44L0.0902191659020.7953-100000@iolanthe.rowland.org> <200902192358.13068.oliver@neukum.org> <200902201146.59944.rjw@sisk.pl>
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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