Re: Hibernation considerations

[david@lang.hm]

On Tue, 17 Jul 2007, Jeremy Maitin-Shepard wrote:

> david@lang.hm writes:
>
> [snip]
>
> > > How do you guarantee that no tasks are scheduled when you get back to the
> > > hibernated kernel?
>
> > just don't schedule any userspace tasks. all you need to do is to execute the
> > ACPI sleep functions. you normally do that after stopping userspace
> > anyway.
>
> What does "stopping userspace" mean?  You already said it does not mean
> disabling interrupts.  But using the freezer is also not an option,
> since the avoidance of that is the main reason for the kexec approach in
> the first place.

just don't schedule any non-kernel threads.

remember that the normal shutdown/suspend procedure is (from another 
related thread)

> >>sys_reboot(LINUX_REBOOT_CMD_KEXEC)
> >>     kernel_kexec
> >>         kernel_restart_prepare
> >>             device_shutdown
> >>         machine_shutdown
> >>         machine_kexec

I'm just saying that instead of going back to the normal operation of the 
kernel you just go directly to the new shutdown routine instead.

> [snip]
>
> > > Well, not exactly.  If your battery runs out of power while you're suspended,
> > > but you have the image saved, it's still better to restore from the image,
> > even
> > > if something may not work correctly after the restore, than to risk a loss of
> > > data.
>
> > if things don't work correctly you are still risking the loss of data, the user
> > just doesn't know it.
>
> It should be possible on any system to do a hibernate followed by a
> shutdown (and then resume properly, without any problems).  Thus, for
> handling suspend to both, you resume as if the system had been shutdown,
> rather than resuming as if the system came from S4.

I agree with this, but according to Rafael if the "hibernated" image is 
assuming that the devices were put into low-power mode by ACPI and you 
boot up instead the system doesn't work right.

David Lang
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