linux-kernel - Re: Hibernation considerations

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Message-Id: <200707201259.44181.rjw@sisk.pl>
Date:	Fri, 20 Jul 2007 12:59:42 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Al Boldi <a1426z@...ab.com>
Cc:	Alan Stern <stern@...land.harvard.edu>, david@...g.hm,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Hibernation considerations

On Friday, 20 July 2007 06:40, Al Boldi wrote:
> Rafael J. Wysocki wrote:
> > On Wednesday, 18 July 2007 16:29, Alan Stern wrote:
> > >
> > > Never mind.  It seems clear that this approach will suffer the same
> > > drawback as the proposal for removing the freezer from the
> > > suspend-to-RAM pathway.  Namely, device drivers will have to be changed
> > > to prevent user I/O requests from proceeding while devices are supposed
> > > to be quiescent or in a low-power state.
> >
> > I agree.
> >
> > > If a driver fails to handle this properly, its device could be
> > > reactivated in order to service a user request before the memory
> > > snapshot is made.  This could easily ruin the snapshot.
> >
> > That's why I've been saying for quite some time that we first need to take
> > care of the drivers. :-)
> >
> > IMO we've reached the point at which, whatever we want to do next, the
> > drivers are in the way.
> 
> Correct, but only if we want ACPI support.

No, in general.

> Granted, we need a separation of  
> the hibernate/suspend PM functions, but in the absence of ACPI, all we need 
> right now are dump/restore routines for the crashkernel.

IMO you aren't right, but I guess there's no point in trying to convince you.

> Next, we should be looking into reducing the kexec'd kernel environment size, 
> which currently, at 16MB, is way too big, and even at 1MB would be 
> problematic for small systems.
> 
> So, ACPI should really be the least of our worries, and the reason why people 
> are fixating on ACPI is probably because they have nothing else to fixate 
> on.

Yeah, right.  Please read the $subject message again.  And sorry, but IMO your
previous replies to it haven't addressed any of the original points.

Greetings,
Rafael


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