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

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Date:	Mon, 16 Jul 2007 21:18:32 -0700 (PDT)
From:	david@...g.hm
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	"Huang, Ying" <ying.huang@...el.com>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH 0/2] Kexec jump: The first step to kexec base hibernation

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
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