Re: Hibernation considerations

On Tuesday, 17 July 2007 23:27, david@xxxxxxx wrote:
On Tue, 17 Jul 2007, Jeremy Maitin-Shepard wrote:

david@xxxxxxx 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.

That's correct, some devices don't work right, but these are not disks. They
usually are devices closely related to the platform, like the embedded
controller.

Greetings,
Rafael


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