On Thu, 12 Jul 2007, Huang, Ying wrote:
On Wed, 2007-07-11 at 17:22 -0700, Andrew Morton wrote:
This sounds awesome. Am I correct in expecting that ultimately the
existing hibernation implementation just goes away and we reuse (and hence
strengthen) the existing kexec (and kdump?) infrastructure?
And that we get hibernation support almost for free on all kexec (and
relocatable-kernel?) capable architectures?
And that all the management of hibernation and resume happens in userspace?
Yes. Ultimately, most of the hibernation code such as process freezer,
memory shrinking, memory snapshot (atomic copy), image reading/writing
can go away, because kexec based hibernation doesn't depend on them.
Just the device/CPU state quiescent/save/restore is necessary to remain.
and the device/CPU quiesent/save/restore/sleep/wakeup functions are needed
for suspend-to-ram and low-power mode.
And, the management of hibernation and resume will happen in userspace.
I didn't understand the ACPI problem. Does this mean that CONFIG_ACPI must
be disabled in the to-be-hibernated kernel, or in the little transient
kexec kernel?
Under current implementation of device state quiescent/save/restore, the
CONFIG_ACPI must be turned off both in to-be-hibernated kernel and
transient kexec kernel.
But the hibernation people are going to separate the device suspend from
device hibernate. The device hibernate will put device in quiescent
state but not in low power state. When this is done, it is not necessary
to disable CONFIG_ACPI at all. It is just a workaround for current
implementation that disabling CONFIG_ACPI.
How close do you think all this is to being a viable thing?
The kexec jump is the first step, maybe the simplest step. There are
many other issues to be resolved, at least the following ones.
1. Separate device suspend from device hibernate.
you shouldn't need a device hibernate, hibernate will be a system
shutdown.
2. Do not reserve memory for kexec kernel. That is, backup needed memory
before kexec and restore them after kexec.
3. Support the in-place kexec? The relocatable kernel is not necessary
if this can be implemented.
4. Image writing/reading. (Only user space application is needed).
5. A smooth resume process. Maybe it is not needed to kexec a new kernel
for resume. For example, in the first stage of kernel boot, just first
16M (or a little more) RAM is used, if the resume image is found, the
saved kernel image is resumed; if the resume image is not found, turn on
the remaining RAM. This will depends on 3.
6. Reduce the boot-up time of kexec kernel. Maybe the kexec kernel can
be hibernate/resume by the normal kernel too. This way, a real
kexec/boot-up is only needed for the first time.
the hibernate kernel shouldn't need a lot of the features of the standard
kerneel (does it really need sound for example), and if tailored even
tighter could be configured to only have the drivers actually used for the
save and restore, makeing a _very_ minimal kernel (no USB, no network,
only simple video drivers, etc) greatly speeding up the boot
David Lang
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