Messages in this thread | | | Date | Tue, 17 Jul 2007 13:34:24 -0700 (PDT) | From | david@lang ... | Subject | Re: Hibernation considerations |
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On Tue, 17 Jul 2007, Rafael J. Wysocki wrote:
> On Tuesday, 17 July 2007 20:32, Alan Stern wrote: > >> I'm still not entirely clear on how "suspend-to-both" ought to be >> handled. Presumably it will start off as a normal hibernation. But >> instead of shutting down, wouldn't the kexec'd kernel return to the >> original kernel? > > No, I think the image-saving kernel should suspend. Then, on resume the > platform will go back to it and it will jump back to the hibernated kernel. > >> After all, the original kernel knows about all the devices and can put them >> into a low-power state, while the kexec'd kernel might not have sufficient >> information. > > That's correct, but ... > >> But what about the freezer? The original reason for using kexec was to >> avoid the need for the freezer. With no freezer, while the original >> kernel is busy powering down its devices, user tasks will be free to >> carry out I/O -- which will make the memory snapshot inconsistent with >> the on-disk data structures. > > ... we can't return to the hibernated kernel unless we are going to cancel the > hibernation.
this is where we disagree.
why not? if all that the hibernated kernel does is to suspend-to-ram and makes no changes to disks or TCP connections anything that it does do would be lost if power were to fail and you instead did a restore from disk.
there is only a problem if something takes place that would prevent the restore-from-disk from working. if this is done in a non-ACPI way that will work across a power cycle you don't have to worry about the hardware state not matching anyway.
> That's why I think that for the suspend-to-both the image-saving kernel will > need to support the same set of devices as the hibernated kernel.
suspend-to-both doesn't really make sense if the suspend-to-disk portion is useing the ACPI S4 mode.
if you don't run out of power you will restore-from-ram
if you do run out of power the restore-from-disk won't work either becouse devices are not in the right ACPI states.
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