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

david
2007-07-17T04:36:13Z

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