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

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Message-Id: <200707161740.26703.rjw@sisk.pl>
Date:	Mon, 16 Jul 2007 17:40:25 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	david@...g.hm, Jeremy Maitin-Shepard <jbms@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

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
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