linux-kernel - Re: Hibernation Redesign

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Date:	Thu, 12 Jul 2007 15:20:49 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Al Boldi <a1426z@...ab.com>
Cc:	Mark Lord <lkml@....ca>, Jeremy Maitin-Shepard <jbms@....edu>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Miklos Szeredi <miklos@...redi.hu>, jeremy@...p.org,
	pavel@....cz, nickpiggin@...oo.com.au,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: Hibernation Redesign

On Thursday, 12 July 2007 01:12, Al Boldi wrote:
> Rafael J. Wysocki wrote:
> > On Thursday, 12 July 2007 00:17, Al Boldi wrote:
> > > Mark Lord wrote:
> > > > Jeremy Maitin-Shepard wrote:
> > > > > I'll certainly admit the kexec idea is vaporware currently,
> > >
> > > Your idea is starting to become a reality with this thread:
> > > "[PATCH 0/2] Kexec jump: The first step to kexec base hibernation"
> > >
> > > > > but it does
> > > > > differ in a significant way from freezer-based approaches, such that
> > > > > I don't think it should be referred to as just another
> > > > > implementation of a freezer.  Specifically, it doesn't require that
> > > > > the "old kernel" be in a "consistent" state to a greater extent than
> > > > > suspend to ram; it is the case that all of the devices must be
> > > > > quiesced or shut down to some extent, but doing this without races
> > > > > and deadlocks (and without the freezer) is certainly very, very
> > > > > similar to what needs to be done for suspend to ram, which will need
> > > > > to be solved anyway.  Unlike the existing hibernate approaches,
> > > > > however, it will not be necessary to use any of the driver
> > > > > infrastructure once switched to the "save image" kernel, and thus it
> > > > > will not matter what locks are held, for instance.
> > > >
> > > > I really doubt that kexec(a special kernel) is going to solve anything
> > > > here. The new kernel will have to initialize, probe for devices, etc.
> > > > Which will take time.
> > > > Which will slow down hibernate to an unacceptable degree.
> > > > Right now, it (TuxOnIce) is *very* fast.
> > > > Adding 10 seconds or so for reprobing/resetting/reiniting devices
> > > > is not going to be useful.
> > > > And modifying all of the drivers to *not* do their usual probe
> > > > sequence sounds rather intrusive and is likely also a non-starter
> > > > here.
> > > >
> > > > Or is it?
> > >
> > > Well, it's definitely less intrusive than readying drivers for the
> > > freezer.
> >
> > There's nothing like this!
> 
> Are you sure?
> 
> # grep -i freeze drivers/*/* | wc -l
> 
> gives:  297
> 
> Maybe you can clarify?

Yes, I can.  For example, please have a look at 'struct ata_port_operations'. :-)

The only direct relationship between the freezer and drivers is that some of
them use kernel threads that call try_to_freeze() (and other freezer-related
functions).

Greetings,
Rafael


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