linux-kernel - Re: Hibernation considerations

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Message-Id: <200707172345.43574.rjw@sisk.pl>
Date:	Tue, 17 Jul 2007 23:45:42 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jeremy Maitin-Shepard <jbms@....edu>
Cc:	david@...g.hm, Alan Stern <stern@...land.harvard.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Huang\, Ying" <ying.huang@...el.com>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Al Boldi <a1426z@...ab.com>
Subject: Re: Hibernation considerations

On Tuesday, 17 July 2007 23:27, Jeremy Maitin-Shepard wrote:
> david@...g.hm writes:
> 
> [snip]
> 
> >> How do you guarantee that no tasks are scheduled when you get back to the
> >> hibernated kernel?
> 
> > just don't schedule any userspace tasks. all you need to do is to execute the
> > ACPI sleep functions. you normally do that after stopping userspace
> > anyway.
> 
> What does "stopping userspace" mean?  You already said it does not mean
> disabling interrupts.  But using the freezer is also not an option,
> since the avoidance of that is the main reason for the kexec approach in
> the first place.
> 
> [snip]
> 
> >> Well, not exactly.  If your battery runs out of power while you're suspended,
> >> but you have the image saved, it's still better to restore from the image,
> > even
> >> if something may not work correctly after the restore, than to risk a loss of
> >> data.
> 
> > if things don't work correctly you are still risking the loss of data, the user
> > just doesn't know it.
> 
> It should be possible on any system to do a hibernate followed by a
> shutdown (and then resume properly, without any problems).  Thus, for
> handling suspend to both, you resume as if the system had been shutdown,
> rather than resuming as if the system came from S4.

Exactly.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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