Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

Rafael J. Wysocki
2007-07-12T12:40:30Z

On Thursday, 12 July 2007 19:09, Huang, Ying wrote:
> On Wed, 2007-07-11 at 22:48 -0700, Jeremy Fitzhardinge wrote:
> > >> The kexec jump is implemented in the framework of software suspend. In
> > >> fact, the kexec based hibernation can be seen as just implementing the
> > >> image writing and reading method of software suspend with a kexeced
> > >> Linux kernel.
> > >>
> >
> > I guess I'm (still) confused by the terminology here. Do you mean that
> > it fits into suspend-to-disk as a disk-writing mechanism, or in
> > suspend-to-ram as a way of going to sleep?
>
> It fits into suspend-to-disk as a disk-writing mechanism. But most
> tricks of suspend-to-disk will be no longer necessary in kexec based
> hibernation.
>
> > > I didn't understand the ACPI problem. Does this mean that CONFIG_ACPI must
> > > be disabled in the to-be-hibernated kernel, or in the little transient
> > > kexec kernel?
> > >
> >
> > I think the point is that if kernel A says "I'm suspending" and calls
> > the suspend method on all its devices, then kernel B finds that it has
> > no powered on devices to work with. But then couldn't it turn on the
> > ones it wants anyway? And don't you want to suspend them, to make sure
> > they're not still DMAing memory while B is trying to shuffle everything
> > off to disk?
>
> The devices should be put quiescent state to stop DMA like things. But
> they do not need to be put in low power state.

Exactly. Morover, I don't think it would be correct to put them into low power
states.

Greetings,
Rafael

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