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

Rafael J. Wysocki
2007-07-16T15:32:55Z

On Monday, 16 July 2007 16:42, Huang, Ying wrote:
> On Mon, 2007-07-16 at 14:17 +0200, Rafael J. Wysocki wrote:
> > > is this a matter of running some test to find out, or is this a question
> > > for the kexec implemantors?
> >
> > Actually, I'd like someone to tell me. ;-)
> >
> > I've browsed the kexec code, but haven't found anything related to the devices
> > in it. Perhaps I didn't know where to look ...
>
> There are two stages for kexec. For "normal" kexec, first the
> sys_kexe_load is called to load the kernel image, then
> sys_reboot(LINUX_REBOOT_CMD_KEXEC) is called to boot the new kernel.

OK, thanks. This is the information that I was missing.

> The call chain is as follow:
>
> sys_reboot(LINUX_REBOOT_CMD_KEXEC)
> kernel_kexec
> kernel_restart_prepare
> device_shutdown
> machine_shutdown
> machine_kexec
>
> In device_shutdown, the dev->bus->shutdown or dev->driver->shutdown of
> every device is called to put device in quiescent state. In
> machine_kexec, the new kernel is booted.

Yes.

> So, for normal kexec, there is no code path for device state saving and
> restoring.

Exactly.

> State of device can be restore after shutdown? I don't think so.

No, it can't, but we need something like this for hibernation and
device_shutdown() is not appropriate for this purpose IMO.

> > I think that the right approach is to separate devices' suspend from the
> > devices' hibernation-related operations FIRST. Then, many different approaches
> > to hibernation will be much easier to implement than they are now.
> >
> > I've been saying this for weeks now, but no one seems to listen frankly I'm
> > tired of repeating it:
>
> I agree with you on this. :)

OK :-)

> > If we want to improve things, let's do that IN AN ORDERED WAY. If everyone
> > will come up with a new idea every two days, we won't be able to get anything
> > actually _done_.
>
> Yes, and I am very glad to collaborate with everybody who is interested
> in this subject. But I think we should try to verify our idea with code
> as early as possible. Now, I am trying to implement a prototype of
> kexec/kdump based image writing/reading mechanism to verify the
> feasibility. (I suppose you are working on separating device suspend and
> device hibernate).

Yes, I am.

> What do you think about the pattern of collaboration?

Sounds good.

> At last, thank you very much for your valuable reminding in the mail of
> "hibernation considerations".

You're welcome. :-)

Greetings,
Rafael

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