Linux kernel boot process

[Sannu K]

On Sat, Aug 4, 2012 at 9:33 PM, Kristof Provost <kristof at sigsegv.be> wrote:
> On 2012-08-04 21:15:15 (+0530), Sannu K <sannumail4foss at gmail.com> wrote:
>> Is it possible to determine the reason for more time in hibernation
>> compared to windows (or profile the resume time)? If possible I could
>> do it in my machine and get some info which may be useful. Some one
>> may jump to solve this (or there may be some magic tweak to get a
>> better resume time) once it is profiled.
>>
> Possibly. I haven't looked at the details of the Linux hibernation
> subsystem. Take a look at Documentation/power/basic-pm-debugging.txt for
> a basic introduction.

Sure I will take a look.

>
>> >> Why should all the drivers be started again? Just we can load
>> >> the disk driver and some essential part of the kernel, disk driver (or
>> >> only few drivers necessary for reading the hibernate image) and use
>> >> the drivers stored in the disk (from hibernation image) for rest of
>> >> the devices.
>> > When resuming from hibernation all devices were powered down. The kernel
>> > needs to run through all of the initialisation code again. It needs to
>> > upload firmware, set configuration registers, ...
>>
>> That makes sense. Does that mean during hibernation the state of
>> drivers will not be preserved?
>
> That's correct.
>
>> Will the driver code be discarded
>> without saving in hibernation image (as we are starting the driver
>> again while resuming)?
>
> Again, I'm not an expert, but I see no reason to preserve the driver
> state (or perhaps even the rest of the kernel state). I believe the
> kernel doesn't even distinguish between a normal boot and a resume from
> hibernation until just before it starts userspace.

That's a new info I have got :)

>
> Regards,
> Kristof
>

Thanks,
Sannu K