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

[david@lang.hm]

On Mon, 16 Jul 2007, Rafael J. Wysocki wrote:

> 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.

is the only reason that device_shutdown() is not appropriate the amount of 
time it takes to shutdown some devices and then start them up again? (I'm 
specificly thinking of drive spin down/up as an example)

if so, it is probably worth implementing a demo with the long times 
involved to hash out any other problems, and then implemnt shortcuts to 
avoid the device_shutdown only where the time involved is excessive.

so, exactly where in the process above does the memory map need to be 
created? is this in the machine_shutdown step or would it need to be in 
the machine_kexec step?

David Lang
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