Re: [linux-pm] [RFC] why do we need run disk sync before entering S3

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> > > That really depends on the distrubution.  (open)SUSE always syncs before
> > > suspend/hibernation AFAICS, but I don't know about the other distros.
> > 
> > This doesn't address the real question: Should the system be allowed to 
> > go into S3 without doing a sync first?
> > 
> > Whether the sync is initiated by userspace or by the kernel doesn't 
> > make any difference.  Likewise, it doesn't matter if there are two 
> > syncs (because the second will be very fast, as Pavel said).
> > 
> > If you really wanted to speed up the suspend transition then you would
> > leave out the sync entirely.  But IMO this would be a mistake; the risk
> > of data loss is too great.  Which means the time overhead is necessary,
> > one way or another.  If userspace does a sync first then the suspend
> > transition will be faster, but this is just an accounting artifact (do
> > you count the time required for the sync toward the time required for
> > the suspend or not).
> 
> My point was in fact that if we left the syncing to the user space, then the
> user would be able to decide not to sync risking data loss.  At the moment the
> user has no choice. :-)

Well, if you can add the choice, without adding anything ugly and with
staying back-compatible, why not. (sync has to stay by default). I
believe ioctls() on /dev/snapshot may already enable you to do s2ram
without sync; if not they could be extended.

But remember there are even in-kernel s2ram triggers, for example on
zaurus when battery goes critical.

(And s2ram without sync _is_ "wrong": writeback timeouts are not
honored).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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