linux-kernel - Re: Hibernation Redesign

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Message-Id: <200707112314.16500.rjw@sisk.pl>
Date:	Wed, 11 Jul 2007 23:14:15 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Mark Lord <lkml@....ca>
Cc:	Jeremy Maitin-Shepard <jbms@....edu>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Miklos Szeredi <miklos@...redi.hu>, a1426z@...ab.com,
	jeremy@...p.org, pavel@....cz, nickpiggin@...oo.com.au,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: Hibernation Redesign

On Wednesday, 11 July 2007 22:48, Mark Lord wrote:
> Jeremy Maitin-Shepard wrote:
> >>
> > I'll certainly admit the kexec idea is vaporware currently, 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, we're going to change what the drivers do during hibernation
for other reasons, so it may well be non-issue.  Still, we can only speculate
until it's done.

Which is why I think that the present discussion is premature.

Greetings,
Rafael


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